Search Results (162)

Initially identified as a hormone linking obesity to insulin resistance, resistin is now recognized as a pleiotropic mediator whose cellular sources and biological functions differ substantially between humans and rodents. Beyond its established roles in metabolic dysfunction and inflammation, emerging evidence suggests that resistin may contribute to tissue remodeling and fibrosis in a context-dependent manner. This review critically synthesizes mechanistic, translational, and clinical evidence across the heart, liver, lung, and kidney. Reported interactions with candidate receptors or binding partners, including adenylyl cyclase-associated protein 1 (CAP1) and Toll-like receptor 4 (TLR4), link resistin-associated signaling to inflammatory, oxidative-stress, and profibrotic pathways that can influence fibroblast activation, hepatic stellate cell responses, extracellular matrix production, and structural tissue remodeling. However, the strength and nature of the available evidence differ markedly among organ systems. Direct profibrotic effects are most strongly supported in cardiac experimental models and selected hepatic systems, whereas pulmonary mechanistic evidence is derived largely from studies of other RELM/FIZZ family members, particularly RELMα/FIZZ1 and RELMβ/FIZZ2, rather than human resistin itself, and renal evidence remains predominantly associative. We, therefore, propose a mechanistic paradigm shift that expands, rather than replaces, the established inflammatory role of resistin. Within this framework, the “fibrotic switch” is presented as a unifying hypothesis whereby persistent resistin-associated signaling may couple chronic inflammatory and metabolic stress to progressive fibrogenic remodeling, requiring further organ-, species-, and cell-specific validation. Defining the relevant cellular sources, receptors, and causal pathways will be essential for evaluating resistin as a biomarker and potential therapeutic target in fibrotic disease. Full article

The automaticity of human-induced Pluripotent Stem Cell-derived cardiomyocytes (hiPSC-CMs) is governed by coupled Ca²⁺ and membrane clocks, coordinated through local Ca²⁺ releases (LCRs) and cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling. We investigated the role of PKA in hiPSC-CM energetics by measuring its dynamics in the cytosol and mitochondria, and its crosstalk with Ca²⁺. We tested three hypotheses: (i) Ca²⁺-activated PKA signaling regulates energy balance; (ii) adenylyl cyclase activity correlates with spontaneous beating; and (iii) PKA compartmentalization is Ca²⁺-dependent. We also compared hiPSC-CMs with rabbit sinoatrial node cells (SANCs). The key findings are: (i) PKA inhibition (H-89), Ca²⁺ chelation (BAPTA), or mitochondrial Ca²⁺ blockade (Ru360) led to energy imbalance; (ii) H-89 induced compartmentalized PKA activity in the cytosol, mitochondrial matrix, and outer mitochondrial membrane; (iii) Ca²⁺ chelation with BAPTA reduced PKA activity globally; and (iv) PKA dynamics and Ca²⁺-dependent regulation were similar in hiPSC-CMs and rabbit SANCs. In conclusion, intracellular Ca²⁺-mediated PKA compartmentalization is present in hiPSC-CMs and rabbit SANCs. Full article

Reliable reference genes are critical for ensuring the accuracy of RT-qPCR-based gene expression analysis, especially under environmental stress conditions. In this study, Leymus chinensis was used as the experimental material, and eight candidate reference genes—alpha-tubulin (TUA), beta-tubulin (TUB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), elongation factor 1-alpha (EF1α), 18S ribosomal RNA (18S rRNA), adenylyl cyclase-associated protein (CAP), adenine phosphoribosyl transferase (APRT), and actin (ACT)—were selected to evaluate their expression stability under cold, drought, heat, NaCl, high pH, wounding, abscisic acid (ABA) and jasmonic acid (JA) treatments. Primer specificity and amplification efficiency were first assessed, and the candidate genes were then comprehensively analyzed using geNorm, NormFinder, BestKeeper, and RefFinder. The results showed that the amplification efficiencies of all primers ranged from 95.0% to 107.2%, and the Ct values of the candidate genes ranged from 17.31 to 30.99. Comprehensive analysis using RefFinder showed that ACTIN was the most stable gene under ABA and NaCl treatments, EF1α under heat and wounding treatments, CAP under JA and high pH treatments, APRT under cold treatment, and TUB under drought treatment. geNorm analysis indicated that two reference genes were sufficient for accurate normalization under each treatment condition. The reliability of the screening results was further confirmed by expression-level validation of LcbZIP46, LcWRKY5, and LcFIN1. This study provides a stable reference gene system for RT-qPCR-based expression analysis in Leymus chinensis under environmental stress conditions. Full article

Two different renin isoforms are expressed in extrarenal tissues. The classical renin-a has been associated with detrimental effects, whereas renin-b exerts protective effects during glucose starvation. Glucose starvation selectively increased renin-b mRNA levels. 8Br-cAMP increased renin-a mRNA levels independently of glucose as well as of renin-b in glucose-starved cells. Adenylyl cyclase (AC) stimulation by forskolin increased expression of both renin transcripts, while AC inhibition by SQ22536 produced the opposite effect. PKA inhibition by KT5720 reduced the mRNA levels of both renin transcripts glucose-independently. Forskolin reversed the effect of KT5720 on renin mRNA levels. A23187-mediated increase in [Ca²⁺]i increased renin-b mRNA levels in glucose-starved cells. Ca²⁺ chelator BAPTA decreased renin-a mRNA expression in control cells and renin-b levels glucose-independently. Forskolin reversed the BAPTA-mediated decreases in renin-a but not renin-b expression. While the regulation of renin transcript levels by cAMP and PKA resembled known regulation in the kidney, the effect of intracellular free Ca²⁺ levels were opposite. This supports the existence of a separate renin system in cardiac cells. Full article

Cyclic adenosine monophosphate (cAMP) is a ubiquitous second messenger downstream of G protein-coupled receptors (GPCRs) and a central regulator of cellular signaling. Genetically encoded exchange proteins directly activated by cAMP (Epac)-based Förster resonance energy transfer (FRET) biosensors enable real-time monitoring of cAMP dynamics in living cells, but commonly used cyan/yellow FRET pairs require short-wavelength excitation, limiting compatibility with multiplex imaging and blue-light optogenetic tools such as bacterial photoactivated adenylyl cyclases (bPACs). Here, we engineered and systematically characterized four red-shifted Epac-based single-chain FRET cAMP sensors combining yellow or orange FRET donors with red fluorescent FRET acceptors. Using ratiometric live-cell imaging, we quantified stimulus-evoked FRET responses and identified Epac_red4 as the best-performing variant, showing an approximately 55% decrease in normalized FRET after forskolin stimulation. Epac_red4 also reliably detected G_i/o-mediated decreases in cAMP following μ-opioid receptor activation. Brief 405 nm light pulses induced graded and reversible cAMP elevations using the low dark-activity variant bPAC-F198Y. Furthermore, Epac_red4 enabled analysis of cAMP recovery kinetics during phosphodiesterase inhibition and multiplex imaging of cAMP and intracellular Ca²⁺ using Fura-2 with minimal spectral and pH-related interference under physiological imaging conditions. Together, Epac_red4 represents a robust red-shifted cAMP sensor for optogenetic and multiplex signaling studies. Full article

Methamphetamine (METH) induces neurotoxicity via excessive and incomplete autophagy, although the underlying mechanisms remain unclear. This study investigated cannabidiol (CBD)’s protective effect and the role of the 5-Hydroxytryptamine 1A receptor (5-HT1A)/adenylyl cyclase (AC)/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element-binding protein (CREB) pathway in primary hippocampal neurons. METH (2 mM, 24 h) reduced neuronal viability, downregulated 5-HT1A, activated the AC/cAMP/PKA/CREB pathway, and simultaneously upregulated autophagy-related proteins (Beclin-1, Microtubule-associated protein 1 light chain 3 [LC3], and Sequestosome 1 [p62]) and overall autophagic flux, indicating impaired lysosomal degradation during autophagy. CBD (1–10 μM) reversed METH-induced autophagy, restored viability, and normalized pathway protein expression. 5-HT1A agonist eptapirone synergized with CBD to inhibit autophagy, while the antagonist WAY-100635 abolished CBD’s effects. These findings demonstrate that CBD, acting as an allosteric modulator of 5-HT1A, alleviates METH-induced neuroautophagy by restoring 5-HT1A activity and suppressing excessive AC/cAMP/PKA/CREB activation, highlighting its potential as a therapeutic agent for METH-related neurotoxicity. Full article

Glucagon-like peptide (GLP)-1 receptor (GLP1R) agonists exert a multitude of beneficial cardiovascular effects beyond control of blood glucose levels and obesity reduction. GLP-1R is a G protein-coupled receptor (GPCR), coupling to adenylyl cyclase (AC)-stimulatory Gs proteins to raise cyclic 3′-5′-adenosine monophosphate (cAMP) levels in cells. cAMP exerts various effects mainly via protein kinase A (PKA) and Exchange protein directly activated by cAMP (Epac). Cardiac GLP-1R has been reported to induce atrial natriuretic peptide (ANP) secretion via Epac2, while ANP is known to inhibit aldosterone secretion from adrenocortical zona glomerulosa (AZG) cells. Herein, we tested the effects of the GLP-1R agonist liraglutide on ANP secretion in H9c2 cardiomyocytes and on angiotensin II (AngII)-induced aldosterone secretion. We also examined whether phosphodiesterase (PDE)-4 inhibition with roflumilast could potentiate liraglutide’s effects. We found that liraglutide stimulated ANP secretion from H9c2 cardiomyocytes, an effect potentiated by roflumilast but blocked by AC inhibition. Epac inhibition with ESI-09 also significantly reduced liraglutide-dependent ANP secretion in H9c2 cardiomyocytes. Moreover, application of medium from liraglutide-treated H9c2 cardiomyocytes, but not from control cardiomyocytes, led to suppression of AngII-dependent aldosterone secretion from H295R cells. This effect was blocked by cyclic guanosine monophosphate (cGMP)-dependent protein kinase inhibition (an effector of ANP) in H295R cells, while direct application of liraglutide to these cells failed to suppress AngII-induced aldosterone secretion. Again, aldosterone suppression was more potent when medium from liraglutide plus roflumilast-treated cardiomyocytes was applied to H295R cells. Taken together, these results suggest that roflumilast enhances the adrenocortical aldosterone suppression induced by GLP-1R agonists via cardiac GLP-1R/cAMP/Epac-dependent ANP secretion. Given the cardio-toxic effects of elevated aldosterone levels in the context of various heart diseases, such as post-myocardial infarction heart failure, combination of a GLP-1R agonist drug with a PDE4 inhibitor drug may be more advantageous than either agent alone in treatment of certain cardiovascular diseases. Full article

Air pollution is a growing hazard to global health. Epidemiological studies have reported a potential role of air pollutant exposure in the development or aggravation of neurodegenerative diseases. However, the underlying mechanisms are ill-defined. Ferroptosis is an iron- and reactive oxygen species (ROS)-dependent form of cell death that drives neuronal loss in neurodegenerative diseases. Our previous studies reported the involvement of adenosine 3′,5′-cyclic monophosphate (cAMP) and EPAC (exchange protein directly activated by cAMP) in ferroptotic cell death. Here, we investigated the effects of diesel exhaust particles (DEP) in mouse hippocampal (HT22) neuronal cells. Our data showed that toxicity induced by RSL3 (50–75 nM), a ferroptosis inducer, was significantly increased by the addition of DEP (100 μg/mL). Pharmacological inhibition of EPAC1 (CE3F4 30 μM or AM-001 30 μM) and soluble adenylyl cyclase (sAC; TDI-10229 1 μM or TDI-11861 0.1 μM) prevented enhanced ferroptotic HT22 cell death caused by DEP, while pharmacological modulation of EPAC2, protein kinase A (PKA), phosphodiesterases (PDEs), or transmembrane AC did not. DEP in combination with RSL3 exposure increased intracellular calcium levels and induced lysosomal de-acidification. Furthermore, inhibition of EPAC1 prevented mitochondrial ROS (MitoSOX) and lipid peroxidation (BODIPY C11 and MDA levels) after DEP and RSL3 co-exposure. Collectively, EPAC1 may serve as a novel target for the treatment or prevention of neurodegenerative diseases accelerated by air pollution. Full article

Glucagon-like-peptide-1 receptor (GLP-1R) agonists are under development as new drugs to treat type 2 diabetes, liver disease, obesity and cardiovascular diseases. Some of these drugs are solely agonists of the GLP-1R. It turned out that their benefit could be improved when they also stimulated the glucagon receptor (GCGR) and/or the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR). Stimulation of GLP-1R in cell cultures but also in neonatal atrial and/or ventricular cardiomyocytes and adult atrial cardiomyocytes raised the activity of adenylyl cyclase and thus augmented the 3’,5’cyclic adenosine monophosphate (cAMP) levels. We discuss here the acute contractile effects of such agonists on isolated human atrial and ventricular cardiac preparations from failing and non-failing hearts. We address the receptors involved, GLP-1R expression in various cardiac regions of the human heart, single and multiple receptor agonists and the post-receptor signal transduction system of the GLP-1R in the human heart. Some of the new drugs addressed are still in the early phases of clinical development. We critically discuss the experimental and clinical data available and we also define research needs for experimental and clinical studies. Full article

This experiment investigated the effects of dietary Artemisia ordosica Krasch. (AOK) supplementation on the n3-polyunsaturated fatty acid (n3-PUFA) profile of subcutaneous adipose tissue (SADT) in Arbas cashmere goats and explored the underlying transcriptional mechanisms. Forty healthy, weaned kids (120 ± 10 days of age; similar body weight) were randomly allocated to two groups (n = 20): a control group (CON, basal diet) and an AOK group (AOK, basal diet with 3% of the roughage replaced by AOK). The feeding trial spanned 104 days, consisting of a 14-day adaptation period and 90 days of data acquisition. Compared with the CON group, AOK significantly reduced the content of saturated fatty acids (SFAs) and n6-polyunsaturated fatty acids (n6-PUFAs)/n3-PUFAs (n6/n3). In contrast, the levels of n3-PUFAs in the SADT of cashmere goats increased markedly (p < 0.05). Compared with the CON group, AOK exhibited significantly higher activities of hormone-sensitive lipase (HSL) (p = 0.027), adenylyl cyclase 2 (ADCY2) (p = 0.010), adenylyl cyclase 5 (ADCY5) (p = 0.046), cluster of differentiation 36 (CD36) (p = 0.013), solute carrier family 27 member 4 (SLC27A4) (p = 0.021), and fatty acid binding protein 4 (FABP4) (p = 0.040), along with significantly lower activities of fatty acid synthase (FAS) (p = 0.002), lipoprotein lipase (LPL) (p = 0.048), and stearoyl-coa desaturase (SCD) (p = 0.026) in SADT. Compared with the CON group, the activities of superoxide dismutase (SOD) (p = 0.032), catalase (CAT) (p = 0.010), glutathione peroxidase (GSH-PX) (p = 0.029), and total antioxidant capacity (T-AOC) (p = 0.002) were significantly increased in the AOK group. Transcriptomic profiling revealed that AOK supplementation downregulated mRNA levels of ADCY2, ADCY5, LPL, FAS, SCD, stearoyl-CoA desaturase 1 (SCD1), stearoyl-CoA desaturase 2 (SCD2), glycogen synthase 1 (GYS1), acyl-CoA oxidase 1 (ACOX1), acetyl-CoA carboxylase (ACC), diacylglycerol acyltransferase 1 (DGAT1), fatty acid desaturase 1 (FADS1), solute carrier family 27 member 2 (SLC27A2), erythroblastic leukemia viral oncogene homolog 4 (ERBB4), and carnitine palmitoyltransferase 1B (CPT1B) (p < 0.05). It also markedly induced acyl-CoA synthetase long-chain family member 4 (ACSL4) (p < 0.01) in SADT. Genes significantly enriched in the adenosine-monophosphate-activated protein kinase (AMPK) signaling pathway included LPL, SCD1, CPT1B, and GYS1 (p = 0.010). Genes significantly enriched in the phosphatidylinositol 3-kinase-akt (PI3K-Akt) signaling pathway included GYS1 and ERBB4 (p = 0.015). CPT1B, ADCY2, and GYS1 were identified as the genes significantly enriched in the insulin resistance signaling pathway (p = 0.048). LPL was the only gene significantly enriched in the cholesterol metabolism pathway (p = 0.049). Genes showing a tendency toward significant enrichment in the peroxisome-proliferator-activated receptor (PPAR) signaling pathway included ACSL4, CPT1B, SCD1, and LPL (p = 0.051). These interconnected cascades improve insulin sensitivity, stimulate triglyceride (TG) hydrolysis, and modulate n3-PUFA levels. Supplementation with AOK enhances n3-PUFA content by accelerating TG breakdown while simultaneously restraining FA oxidation in SADT. Consequently, AOK supplementation can be effectively used to enhance the nutritional value of cashmere goat meat through improved n3-PUFA deposition in SADT. Full article

Pertussis toxin (PTx) is a major virulence factor of Bordetella pertussis and an AB5-type exotoxin that disrupts host signaling. Its enzymatic A subunit ADP-ribosylates the α-subunit of inhibitory G proteins (Gα_i), preventing them from mediating receptor-induced inhibition of adenylyl cyclase (AC). This leads to unrestrained cAMP accumulation in host cells, a canonical mechanism underlying many pertussis disease manifestations. PTx works in concert with the bacterium’s adenylate cyclase toxin (ACT) to subvert immune defenses and establish infection. Interestingly, PTx exerts both cAMP-dependent and cAMP-independent effects. In addition to the well-known cAMP-mediated pathway, PTx’s B oligomer can engage host cell surface receptors to trigger signaling cascades independent of the A subunit’s catalytic activity. Such B oligomer-mediated pathways modulate cellular responses in the absence of ADP-ribosylation. This review provides a comprehensive analysis of PTx’s dual functionality, distinguishing its G_i protein-dependent elevation of cAMP from the noncanonical activities of the B oligomer. It also highlights how disruption of constitutive G_i signaling and the interplay between PTx and ACT shape host–pathogen interaction in pertussis pathogenesis. Full article

The second messenger cyclic AMP (cAMP) is very likely involved in phototactic as well as gravitactic behavior of the unicellular flagellate Euglena gracilis. A slight but significant increase in cAMP was observed when cells encountered sub-threshold acceleration (0.16 × g) force after microgravity [µg]. No differences in cAMP levels were found between cells on a clinostat and 1x-controls. This observation is consistent with the ones of earlier studies. Illumination of cells resulted in a significant increase in cellular cAMP levels. After RNAi-mediated knockdown or CRISPR-Cas9 knockout of the photoactivated adenylyl cyclases PACα and/or PACβ in the photoreceptor, light-induced changes in cAMP levels were no longer observed. In parallel, phototactic behavior was abolished, supporting the essential role of photoactivated adenylyl cyclases in phototaxis. Cells spin around their length axis during locomotion (1–2 Hz). In order to generate a signal in the light direction, the cells should be capable of synthesizing and degrading cAMP within 0.5–1 s. The rapid fixation of cells upon transition from dark to light or light to dark revealed that detectable changes in cAMP-levels (increase or decrease) occur within a 100–200 ms time window, which is sufficiently fast to account for the proposed theoretical kinetics of cAMP oscillations. Full article

Galanin is a highly conserved neuropeptide widely expressed in the central nervous system (CNS), where it regulates neurotransmission, neuroplasticity, and neuroendocrine functions. Its effects are mediated through three G protein-coupled galanin receptor subtypes, GalR1, GalR2, and GalR3, each exhibiting distinct tissue distributions, ligand affinities, and intracellular signaling mechanisms. Endogenous ligands, including galanin, galanin-like peptide (GALP), and spexin, interact with these receptors to trigger receptor-specific pathways, such as adenylyl cyclase (AC) inhibition (GalR1/GalR3) and phospholipase C-mediated calcium signaling (GalR2), enabling modulation of neuronal excitability, neurotransmitter release, and cell survival. Exogenous ligands, including peptide analogs and non-peptide agonists, have further elucidated receptor function and highlighted opportunities for pharmacological intervention. Preclinical evidence demonstrates that targeting galanin receptors (GalRs) can influence mood, cognition, pain perception, epilepsy, metabolic regulation, and neuroprotection, suggesting therapeutic potential across diverse CNS disorders. By integrating knowledge of ligand–receptor interactions and downstream signaling, this review highlights the central role of GalRs in CNS physiology and their emerging relevance as targets for clinical applications. Full article

Background/Objectives: Cells derived from direct chemical reprogramming into osteoblasts represent a promising source for bone regeneration, but the efficiency needs improvement. Here, we systematically evaluated whether the natural compound psoralen (Psr) could enhance this process and explored its therapeutic potential and mechanism of action. Methods: Mouse embryonic fibroblasts (MEFs) were treated with a cocktail of forskolin and phenamil (FP), supplemented with Psr. In vitro differentiation was assessed by alkaline phosphatase and Alizarin Red S staining, reverse transcription quantitative PCR, immunofluorescence and Western blot. The bone-regenerative potential of the derived chemically induced osteoblast-like cells (ciOBs) was evaluated in critical-sized calvarial defects, femoral cortical defects and a subcutaneous ectopic implantation model, using micro-computed tomography and histology. Mechanistic insights of Psr were gained by analyzing the adenylyl cyclase 9 (ADCY9)/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element-binding protein (CREB) axis using inhibitor SQ22536. Results: Psr acted synergistically with the FP cocktail to drive efficient osteogenic reprogramming of MEFs. At an optimal concentration of 25 μM, Psr enabled the most robust induction of early osteogenic markers and generation of mature, mineralizing ciOBs in vitro. In vivo, FP + Psr-induced ciOBs repaired critical-sized calvarial and femoral cortical defects and generated substantial, vascularized bone tissue in ectopic sites. Mechanistically, Psr co-treatment potently activated the ADCY9/cAMP/PKA/CREB pathway, and pharmacological inhibition of this pathway completely abolished the pro-osteogenic effects of Psr. Conclusions: Psr acts as a potent synergistic enhancer of direct chemical reprogramming, generating functional osteoblast-like cells with robust bone-regenerative capacity via activation of the ADCY9/cAMP/PKA/CREB pathway. Full article

Fibrosis manifests as an excessive accumulation of fibrillar collagen in tissues where secreted collagen exceeds degradation. Myofibroblasts are important contributors to the excessive collagen seen in fibrotic lesions. Accordingly, targeting signaling pathways that enhance collagen degradation and subdue myofibroblast differentiation has the potential to optimize collagen remodeling and improve organ fibrosis. One of the most promising molecular targets for therapeutic development is the G protein-coupled receptor (GPCR) family, which is diverse, cell-type-specific, multi-pass transmembrane receptors that participate in the regulation of extracellular matrix remodeling. GPCRs are categorized into multiple subclasses, some of which activate signaling cascades that can augment or reduce pro-fibrotic processes, depending on which Gα class is activated. Specifically, activation of Gαs GPCR stimulates production of the second messenger, cyclic adenosine monophosphate (cAMP), which generally inhibits pro-fibrotic mediators. A related, second approach for control of fibrosis is the blockade of a specific mechanosensitive, Ca²⁺-permeable channel that is implicated in fibrosis and contributes to myofibroblast differentiation, the transient receptor potential vanilloid type 4 (TRPV4). In health, TRPV4 activation regulates collagen remodeling, but when dysregulated, it promotes pro-fibrotic gene expression through mechanosensitive transcription factors. In this review, we focus on the functions of the Gαs GPCR pathway and TRPV4 activation through the interplay of the second messengers cAMP and Ca²⁺ ions. Ca²⁺ influx modulates cAMP levels by regulating phosphodiesterases and adenylyl cyclases. We consider evidence that Gαs GPCR and TRPV4 signaling pathways interact antagonistically to either promote collagen degradation or to increase the formation of myofibroblasts through signaling that involves cAMP and Ca²⁺ conductance. Coordinated activation of the Gαs GPCR pathway and inhibition of TRPV4 could provide a novel, bimodal approach to control tissue fibrosis. Full article