Micro-Executor of Natural Products in Metabolic Diseases

Obesity, diabetes, and cardiovascular diseases are the major chronic metabolic diseases that threaten human health. In order to combat these epidemics, there remains a desperate need for effective, safe, and easily available therapeutic strategies. Recently, the development of natural product research has provided new methods and options for these diseases. Numerous studies have demonstrated that microRNAs (miRNAs) are key regulators of metabolic diseases, and natural products can improve lipid and glucose metabolism disorders and cardiovascular diseases by regulating the expression of miRNAs. In this review, we present the recent advances involving the associations between miRNAs and natural products and the current evidence showing the positive effects of miRNAs for natural product treatment in metabolic diseases. We also encourage further research to address the relationship between miRNAs and natural products under physiological and pathological conditions, thus leading to stronger support for drug development from natural products in the future.


Introduction
Metabolic diseases, which encompass a variety of risk factors highly associated with obesity, diabetes, and cardiovascular diseases, have come to be regarded as public health challenges [1][2][3][4].Due to their complex mechanisms of action, effective comprehensive treatments are still lacking.Even worse, the side effects of some curative drugs have been a major concern for their therapeutic usage [5][6][7].Therefore, it is imperative to provide an effective treatment approach to overcome the aforementioned diseases.
Natural products that are extracted from the source and from concentrated, fractionated, and purified yielding, which are generally defined as bioactive compounds [8,9], have the ability to modulate lipid metabolism, improve insulin signaling, and protect against cardiovascular damage [10,11].More importantly, natural products are widely distributed and readily available in nature [12].To date, extensive studies have shown that plentiful drugs are derived from structural modification based on natural products [13].MicroRNAs (miRNAs) and small noncoding RNAs are characterized by binding to the regulatory sites of 3 UTR of target mRNA, resulting in the inhibition of transcription or the promotion of degradation, accompanied by decreased protein synthesis [14,15].Natural products could also ameliorate metabolic diseases by targeting abundant miRNAs [16][17][18].Thus, the possibility for natural products to modify the abnormal patterns of these diseases is, at least in part, possible through a newly defined mechanism: the miRNAs cascade.
In this review, we summarize the positive effects of natural products on lipid and glucose metabolism disorders and cardiovascular diseases, explain the underlying molecular

Effects of Natural Products on Lipid Metabolism Disorders
Lipid metabolism is a crucial and complex biochemical reaction in the body, and diseases caused by lipid metabolism disorders are common in modern society, such as obesity and hyperlipidemia [19].Lipids are known to be important substances in energy storage and energy supply.Hence, the proper amount of adipose tissue is necessary for the human body.In general, however, patients have difficulty sticking to a long-term diet and physical activity regimen to combat these metabolic disorders.Therefore, food components that ameliorate the risk factors associated with these diseases can facilitate dietary-based therapies [16].Dietary natural products have long been of great interest for improving lipid metabolism by modulating miRNA expression.
Specifically, miR-122 and miR-33 are two of the best-studied miRNAs involved in the regulation of lipid metabolism [53].As is shown in Tables 1 and 2, numerous pieces of evidence have revealed that grape seed proanthocyanidin extract treatments reduced fatty acid synthesis and de novo lipogenesis, increased liver cholesterol efflux to high-density lipoprotein (HDL) formation by decreasing the expression of miR-122 and miR-33, which could regulate several genes that control fatty acid and transcriptional regulatory factors, such as fatty acid synthase (FAS) and peroxisome proliferator-activated receptor beta/delta (PPARβ/δ), as well as genes that regulate fatty acid β-oxidation, such as ATP-binding cassette transporter A1 (ABCA1) and carnitine palmitoyltransferase 1a (CPT1a), respectively [16,[25][26][27]29,54].Further detection revealed that the levels of total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) were reduced while the level of high-density lipoproteins cholesterol (HDL-C) was enhanced in a dose-dependent manner [16,[25][26][27].Averrhoa carambola-free phenolic extract, citrus peel flavonoids, lychee pulp phenolics, mulberry fruit extract, and portulaca oleracea extract treatments could also improve lipid metabolism in in vitro and in vivo studies; the underlying mechanism was miR-33 or miR-122-mediated changes in the signaling pathways [20,22,33,34,37,38].However, the opposite expression of miR-122 was reflected in a natural product experiment using coffee polyphenols, which could enhance energy metabolism and reduce lipogenesis by targeting sterol regulatory element binding protein (SREBP) 1c mediated by miR-122 [23].Accountably, SREBP1c, one of the three isoforms of SREBPs, comes into play in fatty acid synthesis and metabolism [55,56].It potentially illustrates the point that the same type of miRNAs can act on a variety of target genes with different expressions.Similarly, the same target gene may also be regulated by multiple miRNAs.Recent studies have shown that miR-103 and miR-107 reduced obesogenic diet-induced hepatic steatosis via decreasing the protein expression of SREBP1 in resveratrol-treated rats [49], and pseudoprotodioscin promoted cholesterol effluxion through targeting SREBP1c and SREBP2 mediated by miR-33a/b in an in vitro experiment [48].In addition, distinctively, the overexpression of hepatic miR-98 induced by oleanolic acid, an active component of the traditional Chinese herb olea europaea, increased the degradation of peroxisome proliferator-activated receptor gamma coactivator-1beta (PGC1β), known as a transcriptional co-activator of SREBP-1 and the master regulator of hepatic lipogenesis [46,57].
Intuitively, both FAS and SREBP1 are involved in the process of fatty acid synthesis, and the connection between them is found in the following experiments.SP1 transcription factor (SP1), an important member of the ubiquitously expressed SP/KLF transcription factor family, acts together with SREBP1 to synergistically activate the promoter of the FAS gene and is involved in de novo lipogenesis [58].Hence, resveratrol reduced the expression of SP1 through upregulating miR-539, along with decreasing the expression of the SREBP1 protein and FAS gene in vivo and in vitro [50].Nevertheless, the correlation between them still needs to be systematically and intensively investigated beyond all doubt.
Lipid metabolism is a complex process, and natural products can regulate lipogenesis and lipodieresis in a variety of ways.Zerumbone is a cyclic sesquiterpene isolated from the wild ginger Zingiber zerumbet smith.It has been proved that zerumbone could improve lipid metabolism disorder by reducing lipogenesis and increasing fatty acid oxidation [52].For one thing, zerumbone acted as a miR-146b inhibitor and downregulated miR-146b, leading to the activation of sirtuin type 1 (Sirt1), which induced the de-acetylation of forkhead box O1 (FOXO1) and peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC1α); for another, zerumbone induced the phosphorylation of AMP-activated protein kinase (AMPK), which could limit fatty acid efflux from adipocytes and favor fatty acid oxidation, as well as decrease de novo fatty acid synthesis through the phosphorylationmediated inhibition of acetyl-CoA carboxylase (ACC) [59][60][61] and also activated Sirt1 indirectly [52].With these similar natural product experiments, miR-27a/b, miR-96, miR-34a, miR-194, and miR-355 also participated in the process of lipid metabolism by targeting Sirt1 or FOXO1, which could both increase energy expenditure and the clearance of lipid accumulation [21,28,30,31,35,36].And ginger extract could enhance AMPK activity and ameliorate obesity and inflammation by regulating miRNAs expressions in high-fat diet (HFD)-fed rats [24].
Based on the present studies, regulating miRNAs is potentially becoming a dominant feature in terms of natural products regulating lipid metabolism (Figure 1).On the one hand, it can inhibit fatty synthesis by reducing fatty acid synthesis and increasing fatty acids mobilization.On the other hand, it can also accelerate lipodieresis by enhancing the oxidation and phosphorylation of fatty acids.
metabolism by targeting Sirt1 or FOXO1, which could both increase energy expenditure and the clearance of lipid accumulation [21,28,30,31,35,36].And ginger extract could enhance AMPK activity and ameliorate obesity and inflammation by regulating miRNAs expressions in high-fat diet (HFD)-fed rats [24].
Based on the present studies, regulating miRNAs is potentially becoming a dominant feature in terms of natural products regulating lipid metabolism (Figure 1).On the one hand, it can inhibit fatty synthesis by reducing fatty acid synthesis and increasing fatty acids mobilization.On the other hand, it can also accelerate lipodieresis by enhancing the oxidation and phosphorylation of fatty acids.

Inhibitory Effects on Adipocyte Differentiation and Accumulation
From the perspective of the cellular level, however, the growth of adipose tissue is the result of an increase in the number of adipocytes and the volume of individual cells [51].The former contributes to promoting pre-adipocyte differentiation into mature adipocytes, whereas the latter is due to lipid accumulation.Here, we summarized the functional role of natural products in this regard, as well as their potential mechanisms of action (Figure 1 and Tables 1 and 2).
Adipocyte differentiation is a highly precisely regulated cellular process.Ahead of terminal differentiation, the mitotic clonal expansion (MCE) of stimulated pre-adipocytes is an essential procedure in adipocyte differentiation.Moreover, the transcriptional activation of adipocyte-specific functional genes is closely related to their differentiation [62].3T3-L1 pre-adipocytes have long been considered as the "gold standard" for investigating pre-adipocyte differentiation in vitro [63,64].There has been evidence that the MCE

Inhibitory Effects on Adipocyte Differentiation and Accumulation
From the perspective of the cellular level, however, the growth of adipose tissue is the result of an increase in the number of adipocytes and the volume of individual cells [51].The former contributes to promoting pre-adipocyte differentiation into mature adipocytes, whereas the latter is due to lipid accumulation.Here, we summarized the functional role of natural products in this regard, as well as their potential mechanisms of action (Figure 1 and Tables 1 and 2).
Adipocyte differentiation is a highly precisely regulated cellular process.Ahead of terminal differentiation, the mitotic clonal expansion (MCE) of stimulated pre-adipocytes is an essential procedure in adipocyte differentiation.Moreover, the transcriptional activation of adipocyte-specific functional genes is closely related to their differentiation [62].3T3-L1 pre-adipocytes have long been considered as the "gold standard" for investigating preadipocyte differentiation in vitro [63,64].There has been evidence that the MCE process could be delayed by persimmon tannin by enhancing the expression of miR-27 in 3T3-L1 pre-adipocytes [47].Furthermore, multiple transcriptional factors, including peroxisome proliferator-activated receptor-gamma (PPARγ) and CCAAT/enhancer-binding protein alpha (C/EBPα) were also attenuated by miR-27, resulting in a decrease in adipocytespecific genes, such as adipocyte fatty acid binding protein (aP2) and lipoprotein lipase (LPL).Similarly, the MCE process was blocked by miR-27a/b in the study of a-type ECG and EGCG dimers [40].As we all know, lipids are important structural components in cell membranes [65].Notably, with different molecular structures, a-type ECG and EGCG dimers strongly disturbed the structures of cell membranes by decreasing fluidity and hydrophobicity and increasing the permeability of the membrane of 3T3-L1 pre-adipocyte cells, thus displaying significant inhibition on differentiation [40].EGCG also suppressed 3T3-L1 cell growth via miR-143/MAPK7 pathways [43].Nonivamide-induced reduction in lipid accumulation was mediated by transient receptor potential cation channel subfamily V member 1 (TRPV1) activation [45].Although miRNAs are involved in the adipocyte differentiation process, whether they affect membrane structure remains to be intensively studied in natural product therapy.
The activation of C/EBPα and PPARγ is not only necessary for adipocyte differentiation in the early stage but is also crucial for terminal adipocyte differentiation [66].The evidence suggests that grape seed procyanidin B2 could inhibit pre-adipocyte differentiation and reduce intracellular lipid accumulation by modulating the miR-483/PPARγ axis [42].Resveratrol reduced the expression of CEBP/α by boosting miR-155, resulting in decreasing lipogenesis [51].Consistent with these, as shown in Table 2, similar results were also obtained in the research of lycopene by regulating the expression of miR-21 [44].What is noteworthy is that accompanied with the involvement of multiple miRNAs, Rosmarinus officinalis extract significantly reduced triglyceride incorporation during pre-adipocyte maturation in a dose-dependent manner and decreased the expression of cell cycle genes, such as cyclin-dependent kinase 4, cyclin D1, and cyclin-dependent kinase inhibitor 1A [39].The final and most studied phase of adipocyte differentiation involves terminal differentiation and the induction of a signaling cascade to promote the expression of the genes necessary for adipocyte function [67,68].The canonical Wnt signaling cascade is an effective approach to suppress adipogenesis [69][70][71].Recently, investigators found that curcumin repressed 3T3-L1 pre-adipocyte cell adipogenic differentiation by inhibiting the expression of miR-17 and stimulating transcription factor 7-like 2 (TCF7L2), which is the Wnt signaling pathway effector and a direct downstream target of miR-17 [41].And guarana extract also exerted an anti-adipogenic effect by regulating the Wnt signaling pathway, mediated by miRNAs [32].In summary, natural products may inhibit adipocyte differentiation and accumulation by regulating miRNAs, which play a crucial role in the process of lipogenesis.
[86] miR-150↓ 50 or 100 mg/kg/d for 12 weeks Gavage HFD-fed mice PDX1 • Alleviated pancreatic impairments; • Improved the dysfunction of β pancreatic cells.• Increased glucose and insulin tolerance; • Relieved the disorder of lipid metabolism and oxidative stress; • Improved endothelium-dependent vasorelaxation. [90] The up arrow means an increase, and the down arrow means a decrease.• Reduced blood glucose; • Increased glucose and insulin tolerance; • Relieved the disorder of lipid metabolism and oxidative stress; • Improved endothelium-dependent vasorelaxation. [90] The up arrow means an increase, and the down arrow means a decrease.• Reduced blood glucose; • Increased glucose and insulin tolerance; • Relieved the disorder of lipid metabolism and oxidative stress; • Improved endothelium-dependent vasorelaxation. [90] The up arrow means an increase, and the down arrow means a decrease.• Reduced blood glucose; • Increased glucose and insulin tolerance; • Relieved the disorder of lipid metabolism and oxidative stress; • Improved endothelium-dependent vasorelaxation. [90] The up arrow means an increase, and the down arrow means a decrease.• Reduced blood glucose; • Increased glucose and insulin tolerance; • Relieved the disorder of lipid metabolism and oxidative stress; • Improved endothelium-dependent vasorelaxation. [90] The up arrow means an increase, and the down arrow means a decrease.

Hypoglycemic Action
At the heart of glucose metabolism is maintaining an equilibrium of glucose concentrations in the blood.So, blood glucose concentration is used as an important indicator of glucose metabolism in the body [91].Insulin, secreted by β-cells in the pancreas, is the hormone currently known to lower blood glucose in the body.However, it has been now well established from a variety of studies that natural products can reduce blood glucose by acting on insulin (Tables 3 and 4), while the potential mechanisms of action are diverse (Figure 2).

Hypoglycemic Action
At the heart of glucose metabolism is maintaining an equilibrium of glucose concentrations in the blood.So, blood glucose concentration is used as an important indicator of glucose metabolism in the body [91].Insulin, secreted by β-cells in the pancreas, is the hormone currently known to lower blood glucose in the body.However, it has been now well established from a variety of studies that natural products can reduce blood glucose by acting on insulin (Tables 3 and 4), while the potential mechanisms of action are diverse (Figure 2).Protein tyrosine phosphatase 1B (PTP1B) is a major negative regulator of the insulin signaling pathway in metabolism and dephosphorylates insulin receptor (IR) and insulin receptor substrate 1 (IRS1) at tyrosine residues to inhibit the activation of downstream Akt and ERK1/2 signaling cascades [92,93].Curcumin, however, could induce miR-206 expression, which, in turn, decreased fructose-induced PTP1B overexpression to improve glucose intolerance and insulin sensitivity in fructose-fed rats [83].Interestingly, the same results were also found in a study on licorice flavonoid, which reversed the decrease of miR-122 induced by the overexpression of PTP1B and abrogated the hepatic insulin resistance induced by an HFD diet [80].Gypenoside A attenuated the dysfunction of Protein tyrosine phosphatase 1B (PTP1B) is a major negative regulator of the insulin signaling pathway in metabolism and dephosphorylates insulin receptor (IR) and insulin receptor substrate 1 (IRS1) at tyrosine residues to inhibit the activation of downstream Akt and ERK1/2 signaling cascades [92,93].Curcumin, however, could induce miR-206 expression, which, in turn, decreased fructose-induced PTP1B overexpression to improve glucose intolerance and insulin sensitivity in fructose-fed rats [83].Interestingly, the same results were also found in a study on licorice flavonoid, which reversed the decrease of miR-122 induced by the overexpression of PTP1B and abrogated the hepatic insulin resistance induced by an HFD diet [80].Gypenoside A attenuated the dysfunction of pancreatic β cells by activating pancreatic duodenal homeobox-1 (PDX1) signal transduction via the inhibition of miR-150 in HFD-fed mice [86].Vaccarin, an active flavonoid glycoside extracted from vaccariae semen, reduced blood glucose, increased glucose and insulin tolerance, and relieved glucose metabolism disturbances in STZ/HFD-induced type 2 diabetes mellitus (T2DM) mice by regulating miR-34a expression [90].Coreopsis tinctoria nutt extract treatment also showed the effect of lowering fasting blood by inhibiting the expression of miR-192 and miR-200b [78].From the above, insulin plays an important role in blood glucose stability, and importantly, both low-insulin secretion and insulin resistance can lead to blood glucose disorders.This can, however, be reversed, at least in part, by natural products through miRNA cascades.
In addition, by using hierarchical clustering analysis, the miRNA expression patterns, as well as miRNA microarray analysis, are shown in Table 3.It was macroscopically discovered that various miRNAs participated in the hypoglycemic process in Alpinia oxyphylla extract treatment [76]; however, the underlying mechanism of action is not yet clear.

Restraining Effects on Oxidative Stress
Insulin signaling has been one of the most important and highly studied metabolic hormones for glucose metabolism homeostasis.ROS are usually produced in the process of biological oxidation and energy conversion in mitochondria; however, the enhancement of ROS induced by a hyperglycemic environment disrupts the balance between ROS and the antioxidant system, resulting in oxidative stress, which subsequently induces insulin resistance and pancreatic β cell dysfunction via their ability to activate stress-sensitive signaling pathways [94].Therefore, oxidative stress has been defined as a disturbance in the dynamic balance between ROS generation and antioxidant capacity [95], and ROS generation is also regarded as a marker of oxidative stress, which can lead to pancreatic β cell dysfunction and peripheral insulin resistance, hence, resulting in glucose metabolic disorders [95,96].A growing number of studies have shown that natural products can inhibit oxidative stress by monitoring various miRNAs (Tables 3 and 4).
Insulin resistance in the brain is a specific form of T2DM; however, Nigella sativa oil has a possible benefit as a disease-modifying agent for insulin resistance in the brain by suppressing oxidative stress and enhancing the brain insulin signaling pathway; multiple miRNAs are involved in this process, especially miR-34a and miR-26b [81].This also supports the view that insulin resistance partly originates from oxidative stress [97].In addition, in experiments on blueberry anthocyanin extract, Crataegus persica extract, polydatin, and sodium tanshinone IIA sulfonate treatments all decreased the ROS level and alleviated the oxidative stress induced by different high-concentration glucose environments [77,79,88,89].Pieces of evidence have been accumulating regarding Sirt1 playing an important role in the cellular redox balance and resistance to oxidative stress [98,99].Furthermore, Sirt1 can regulate nuclear factor erythroid 2-related factor 2 (Nrf2) to regulate the transcription of pro-and anti-oxidant enzymes, subsequently affecting the cellular redox state [100].Dioscin, a natural steroid saponin isolated from various herbs [101], significantly decreased the formation of ROS and suppressed oxidative stress by regulating the miR-34a/Sirt1/Nrf2-mediated pathway in vivo and in vitro [84].These results were consistent with the data obtained from a study on genistein which could raise anti-oxidative ability through the upregulation of Sirt1 via inhibiting miR-34a in in vitro experiments [85].Additionally, astragaloside IV also increased cellular antioxidant capacity and alleviated high-glucose-induced cell damage, the potential mechanism of which probably owes credit to the enhanced Sirt1/Nrf2 activity induced by miR-138 [82].Oridonin, a diterpenoid isolated from Rabdosia rubescens, attenuated hydrogen peroxide-induced oxidative stress by altering miRNAs expression; statistically, six miRNAs were upregulated, and 15 miRNAs were downregulated by using microarray analysis [87].
In general, as a negative effect produced by excess ROS in the body, oxidative stress is an important common pathogenesis of pancreatic β cell injury, which, in turn, affects insulin secretion.As antioxidants, natural products are effective at removing excess free radicals from the body and regulating oxidative stress (Figure 2).From the perspective of drug development, the study of oxidative stress can help to shed further light on the pathogenesis of abnormal glucose metabolism and provide a theoretical basis for the prevention and treatment of glucose metabolism disorders and their complications.

Effects of Natural Products on Cardiovascular Diseases
Cardiovascular disease is one of the major causes of death worldwide, with morbidity and mortality rising year by year [102].Cardiovascular disease, also known as circulatory disease, is a series of diseases that involve the circulatory systems [103].Moreover, abnormal lipid metabolism and glucose metabolism are important factors in the process of cardiovascular disease [104].The changes experienced by using natural products in recent years are still unprecedented.Existing natural product studies have shown therapeutic effects on myocardial cell injury and protective effects on vascular endothelial cells via miRNA-mediated signaling pathways (Tables 5 and 6).

Therapeutic Effects on Myocardial Cell Injury
Cardiomyocyte injury is closely related to the development of cardiovascular diseases, such as myocardial failure, myocardial ischemia, cardiac fibrosis, and myocardial infarction [105][106][107][108]. Increasing evidence suggests that natural products protect cardiomyocytes from various injuries by managing the expression of miRNAs.
Tanshinone IIA, the active ingredient isolated from the rhizome of the Chinese herb Salvia miltiorrhiza (also known as "Danshen" in Chinese), is an effective cardioprotective agent.Latterly, it was indicated that tanshinone IIA could protect cardiomyocytes from ischemic and hypoxic damage, which was based on downregulating the expression of miR-1 and upregulating the expression of miR-133 by activating the P38 MAPK and ERK1/2 signal pathway, respectively [109,110].It could also modulate the overexpressed miR-1 by regulating serum response factor (SRF) [111], a transcriptional regulator of muscle-specific and growth-regulated genes, which may lower the risk of sudden cardiac death [112].As we mentioned in the context of glucose metabolism disorders, ROS accumulation is not only an indicator of oxidative stress injury but also a marker of cardiomyocyte damage.The interventional treatment of gypenoside A, resveratrol, and portulaca oleracea extract significantly reduced ROS production and attenuated myocardial injuries; meanwhile, it exerted cardio-protective effects via miRNA-mediated signaling pathways [113][114][115], whereas dioscin inhibited myocardial oxidative insult and alleviated doxorubicin-induced cardiotoxicity via the miR-140/Sirt2/Nrf2 signaling pathway [116].
There is evidence that apoptosis is involved in the development of myocardial infarction and heart failure [117].A test study indicated that resina draconis treatment inhibited the endoplasmic reticulum-induced apoptosis of myocardial cells via regulating the miR-423/ERK signaling pathway in a tree shrew myocardial IR model [118], whereas salvianolate treatment blocked apoptosis during myocardial infarction by downregulating miR-122 [119].As a heart-healthy compound, it was uncovered for the first time that resveratrol (100 mg/kg/day) treatment could suppress the apoptosis of myocardium in cold-treated mice by inhibiting miR-328 expression [120].Furthermore, curcumin could also protect cardiomyocytes against hypoxia-induced apoptosis by modulating specific protein 1, which participated in co-ordinating the transactivation of survivin, a crucial gene in regulating cell apoptosis [121], which is regulated by miR-7a/b [122].Some other natural products or their extracts, such as puerarin, ginsenoside Rb1, theaflavin, astragalus root dry extract, and Crataegus persica extract, also contributed to the protection of various types of myocardial injury and exhibited cardio-protective effects by controlling miRNA cascades, respectively [79,[123][124][125][126].
Myocardial fibrosis, a common cardiac response in a variety of forms of damage, is characterized by excessive collagen deposition and extra-cellular matrix accumulation [127].However, celastrol, a quinone methide triterpene isolated from the root extracts of Tripterygium wilfordii (Thunder god vine) [128], could reverse these undesirable phenom-ena induced by downregulating miR-21 expression and inhibiting MAPK/ERK signaling in transverse aortic constriction mice [129].Similarly, Luteolin-7-diglucuronide, a naturally occurring flavonoid glycoside found in the leaves of Basil or Verbena officinalis, also attenuated isoproterenol-induced myocardial fibrosis both at the histo-pathological and molecular levels, accompanied by regulating the expression of miRNAs, including miR-29c, miR-39c, miR-133b, and miR-21 via the TGF-β signaling pathway [130].Astragaloside IV inhibited cardiac fibrosis by targeting the miR-135a-TRPM7-TGF-β/Smads signaling pathway [131].Identical results were also detected in the study of panax notoginseng saponins [18].Myocardial damage and the consequent fibrotic alterations impair the normal heart architecture and cause cardiac dysfunction (Figure 3).Fortunately, these studies provide new insight into the molecular mechanisms of natural products in the studies of cardiovascular diseases.
Tripterygium wilfordii (Thunder god vine) [128], could reverse these undesirable phenomena induced by downregulating miR-21 expression and inhibiting MAPK/ERK signaling in transverse aortic constriction mice [129].Similarly, Luteolin-7-diglucuronide, a naturally occurring flavonoid glycoside found in the leaves of Basil or Verbena officinalis, also attenuated isoproterenol-induced myocardial fibrosis both at the histo-pathological and molecular levels, accompanied by regulating the expression of miRNAs, including miR-29c, miR-39c, miR-133b, and miR-21 via the TGF-β signaling pathway [130].Astragaloside IV inhibited cardiac fibrosis by targeting the miR-135a-TRPM7-TGF-β/Smads signaling pathway [131].Identical results were also detected in the study of panax notoginseng saponins [18].Myocardial damage and the consequent fibrotic alterations impair the normal heart architecture and cause cardiac dysfunction (Figure 3).Fortunately, these studies provide new insight into the molecular mechanisms of natural products in the studies of cardiovascular diseases.• Protected from LPS-induced neuroinflammation and memory decline through antioxidant and anti-inflammatory effects. [115] Resina draconis miR-423↑ 0.25, 0.5 and 1.0 mg/mL

Intramuscular injection
Ischemia-reperfusion tree shrew ERK • Reduced the infarct size, enhanced the superoxide dismutase expression, and downregulated the malondialdehyde concentration; • Suppressed the ischemia-reperfusion-induced apoptosis.

Cav3
• Improved the myofibrillar alignment and sarcomere development; • Promoted the development of t-tubules; • Upregulated the t-tubules biogenesis-related genes.• Improved the myofibrillar alignment and sarcomere development; • Promoted the development of t-tubules; • Upregulated the t-tubules biogenesis-related genes.• Cardio-protective effect; • Attenuated I/R-induced injures; • Activated AMPK signaling.

Cav3
• Improved the myofibrillar alignment and sarcomere development; • Promoted the development of t-tubules; • Upregulated the t-tubules biogenesis-related genes.• Protective effect on cardiomyocytes.

Protective Effects on Vascular Endothelial Cells
Vascular endothelial cells form the interface between blood and tissues and are involved in physiological and pathological processes, including cardiovascular diseases [139,140].Massive cardiovascular diseases lead to various degrees of vascular endothelial injury, which, in turn, exacerbates cardiovascular diseases.Vascular endothelial dysfunction is closely related to the development of cardiovascular diseases [141].Vascular endothelial cells are not only the target organs of cardiovascular diseases but also the new target organs of many drugs [142,143].Therefore, improving vascular endothelial function has been an important aspect of anti-cardiovascular drug development in recent years.Obviously, as shown in Tables 5 and 6, natural products that regulate the expressions of miRNAs may be a better choice.
Polyphenolics from açaí and red muscadine grape ameliorated human umbilical vascular endothelial cell (HUVEC) injury by inhibiting the gene expression of adhesion molecules, including vascular cell adhesionmolecule-1 (VCAM-1), which is targeted by miR-126 [132].Ginsenoside-Rg1, which is derived from Ginseng, was considered an agent that promotes angiogenesis because the decreased expression of miR-23a negatively regulates the angiogenic activities of HUVEC in vitro [136].Sodium tanshinone IIA sulfonate treatment improved angiogenesis by regulating the miR-133a/GCH-1 signaling pathway in experimental peripheral arterial disease (PAD) in diabetes [89].
In addition, vascular endothelial cell injury is the initial stage of atherosclerosis [144].According to the research, xiaoxianggou, the dried root and stem of Ficus pandurata hance var.angustifolia Cheng, Ficus panduram hane var.hoiophylla Migo, and Ficus erecta thunb.var.bcecheyana King, could reduce the area of atherosclerotic plaque by elevating miR-203 expression and reducing the expression of E26 oncogene homolog 2 (Ets2) [133], which could promote further lesion destabilization by directly affecting endothelial cell function, promoting vessel leakage and expansive neovascular growth from the adventitia into the intimal area [145].Intimal hyperplasia has long been a major problem plaguing vascular surgery.The proliferation of vascular smooth muscle cells (VSMCs) is an important factor that causes intimal thickening [146].Nevertheless, resveratrol improved atherosclerosis by reducing higher collagen deposition and promoting elastin integrity and VSMC survival mediated by reducing the expression of miR-29b in the Fbn1 C1039G/+ Marfan mouse model [137].There were similar results in the study on emodin; interestingly, miR-126 participated in this process by mediating the Wnt4/Dvl-1/β-catenin signaling pathway in balloon-injured carotid artery rats [135].Berberine improved vascular dementia in diabetes, which is possibly related to the suppression of miR-133a ectopic expression in endothelial cells [134].A key regulatory role for Krüppel-like factor 4 (KLF4) in vascular function has been shown in vitro and in vivo, and KLF4 deficiency is associated with atherothrombosis [147][148][149][150]. Tanshinone IIA harmonized the crosstalk of autophagy and polarization in macrophages via activating KLF4 mediated by miR-375 to attenuate atherosclerosis [138].These studies set out our vision of the protective effect of natural products on vascular endothelial cells by the regulation of multiple miRNAs (Figure 3), and provide molecular evidence for further studies on natural products as novel anti-cardiovascular therapies.

Conclusions
In all the studies reviewed here, while natural products have provided new insights into the treatment of metabolic diseases by regulating miRNA cascades and have revealed anti-obesity, anti-diabetes, and anti-cardiovascular disease functions, as well as demonstrating a rich source of therapeutic agents, there are still some pressing issues that need to be addressed.Primarily, the mechanisms of metabolic diseases and the correlations between them are complex and still require systematic and in-depth studies beyond all doubt.Moreover, the plentiful miRNAs existing in our bodies often act together with their cluster members or other miRNAs [151]; hence, the complicated regulatory network of miRNAs can also not be ignored in natural product treatments.In addition, with a view of providing better clues for drug development, there are many natural products that have not muscle cells; Wnt1, wingless-type MMTV integration site family member 1; Wnt10b, wingless-type MMTV integration site family member 10b; Wnt3a, wingless-type MMTV integration site family member 3a; Wnt4, wingless-type MMTV integration site family member 4; ZEB2, zinc finger E-Box binding homeobox 2.

Figure 1 .
Figure 1.Schematic illustration of the main mechanisms by which natural products improve lipid metabolism disorders mediated by miRNAs.The red arrow means an increase, and the green arrow means a decrease.

Figure 1 .
Figure 1.Schematic illustration of the main mechanisms by which natural products improve lipid metabolism disorders mediated by miRNAs.The red arrow means an increase, and the green arrow means a decrease.

Figure 2 .
Figure 2. Schematic illustration of the main mechanisms by which natural products improve glucose metabolism disorders mediated by miRNAs.The red arrow means an increase, and the green arrow means a decrease.

Figure 2 .
Figure 2. Schematic illustration of the main mechanisms by which natural products improve glucose metabolism disorders mediated by miRNAs.The red arrow means an increase, and the green arrow means a decrease.

Figure 3 .
Figure 3. Schematic illustration of the main mechanisms by which natural products improve cardiovascular diseases mediated by miRNAs.The red arrow means an increase, and the green arrow means a decrease.

Figure 3 .
Figure 3. Schematic illustration of the main mechanisms by which natural products improve cardiovascular diseases mediated by miRNAs.The red arrow means an increase, and the green arrow means a decrease.

Table 1 .
The effects of natural products (extracts) on lipid metabolism disorders.

Table 2 .
The effects of natural products (compounds) on lipid metabolism disorders.
• Inhibited pre-adipocyte differentiation;• Reduced intracellular lipid accumulation; • Blocked MCE process;• Decreased the fluidity and hydrophobicity and increased the permeability of membrane.

Table 3 .
The effects of natural products (extracts) on glucose metabolism disorders.

Table 4 .
The effects of natural products (compounds) on glucose metabolism disorders.

Table 5 .
The effects of natural products (extracts) on cardiovascular diseases.
• Increased MET protein expression in a time-dependent manner;• Induced angiogenesis by the inverse regulation of MET tyrosine kinase receptor expression.•IncreasedMET protein expression in a time-dependent manner;• Induced angiogenesis by the inverse regulation of MET tyrosine kinase receptor expression.•IncreasedMET protein expression in a time-dependent manner;• Induced angiogenesis by the inverse regulation of MET tyrosine kinase receptor expression.•IncreasedMET protein expression in a time-dependent manner;• Induced angiogenesis by the inverse regulation of MET tyrosine kinase receptor expression.