Search Results (59)

Diabetes mellitus severely impairs skeletal muscle regeneration after injury, limiting satellite cell activation and angiogenesis and disrupting barrier integrity while increasing fibrosis. Hypobaric hypoxia has been proposed to improve the regenerative microenvironment through hypoxia-responsive signaling, but its temporal effects and the coordination between vascular and myogenic programs in diabetic muscle remain unclear. To clarify these processes, adult male mice were divided into five groups: diabetes mellitus control (DM), cardiotoxin-injured (CTX) diabetes assessed on days 7 and 14 (CTX7, CTX14), and hypobaric-hypoxia-treated diabetic injury assessed on days 7 and 14 (H+CTX7, H+CTX14). Animals in the hypoxia groups were exposed to a hypobaric hypoxia chamber for 8 h per day for 14 days. Fibrosis, angiogenic and myogenic markers, and endothelial junctional genes were examined using histology, immunofluorescence, immunoblotting, and qRT-PCR (Quantitative Real-Time PCR). Hypobaric hypoxia on day 7 enhanced HIF-1α (hypoxia-inducible factor 1 alpha), VEGF (vascular endothelial growth factor), eNOS (endothelial nitric oxide synthas), Kdr (kinase insert domain receptor, VEGFR-2), and Angpt2 (angiopoietin-2) expression, accompanied by simultaneous endothelial sprouting and early myogenic stimulation compared to CTX7. Improvements were observed in Angpt1 (angiopoietin-1), Cdh5 (cadherin-5, VE-cadherin), Emcn (endomucin), the Angpt1/Angpt2 ratio, and CD31 density. Myogenin and MyHC (myosin heavy chain) were induced with a reduction in eMyHC (embryonic myosin heavy chain) in accordance with stabilization of endothelium and maturation of fibers, which occurred by day 14. A decrease in fibrosis and an increase in the myofiber cross-sectional area occurred. These findings suggest that hypobaric hypoxia modulates HIF-1α signaling, which in turn induces the VEGF-Kdr-eNOS pathway and the angiopoietin–Tie2–VE-cadherin pathway. Together, these pathways coordinate vascular remodeling and myogenic regeneration, ultimately improving the structural and functional recovery of diabetic muscle. Full article

Myopathy encompasses a group of diseases characterized by abnormalities in both muscle function and structure. However, the underlying regulatory mechanisms of newly formed myofiber development remain poorly defined. No promising therapeutic approach has been developed, but numerous medication options are available to alleviate symptoms. Our previous studies demonstrated that adenosine kinase (ADK) is critical in regulating adenosine metabolism, pathological angiogenesis, pathological vascular remodeling, and vascular inflammatory diseases. Adenosine dynamically distributes between extracellular and intracellular, and adenosine concentration regulates ADK expression. However, the mechanism by which adenosine triggers an ADK-dependent intracellular signaling pathway to regulate skeletal muscle regeneration is not well defined. This study aimed to evaluate whether the adenosine-induced intracellular signaling pathway is involved in regulating myopathy, and how it regulates the development of newly formed myofibers. In this study, an intramuscular injection of cardiotoxin was used to induce a skeletal muscle injury model; satellite cells and C2C12 cells were employed. Whether adenosine regulates satellite cell activity, new myofiber formation and differentiation, as well as fusion of myofibers, were determined by H&E staining, BrdU incorporation assay, and spheroid sprouting assay. Interaction between ADK and PFKFB3 was evaluated by IF staining, PPI network analysis, molecular docking simulation, and CO-immunoprecipitation assay. The results demonstrated that adenosine dynamically distributes between extracellular and intracellular through concentrative nucleoside transports or equilibrative nucleoside transporters, and it rapidly induces an ADK-dependent intracellular signaling pathway, which interacts with PFKFB3-mediated glycolytic metabolism to promote satellite cell activity, new myofiber formation, differentiation, and fusion, and eventually enhances skeletal muscle regeneration after injury stress. The remarkable endogenous regeneration capacity of skeletal muscle, which is regulated by adenosine-triggered intracellular signaling, presents a promising therapeutic strategy for treating muscle trauma and muscular dystrophies. Full article

Background: Virtual cells are embedded in widely used single-cell generative models. Nonetheless, the models’ implicit knowledge of perturbations remains unclear. Methods: We train variational autoencoders on three gene expression datasets spanning genetic, chemical, and temporal perturbations, and infer perturbations by differentiating decoder outputs with respect to latent variables. This yields vector fields of infinitesimal change in gene expression. Furthermore, we probe a publicly released scVI decoder trained on the $\mathrm{CELL}\times \mathrm{GENE}$ Discover Census ($\sim 5.7$ M mouse cells) and score genes by the alignment between local gradients and an empirical healthy-to-disease axis, followed by a novel large language model-based evaluation of pathways. Results: Gradient flows recover known transitions in Irf8 knockout microglia, cardiotoxin-treated muscle, and worm embryogenesis. In the pretrained Census model, gradients help identify pathways with stronger statistical support and higher type 2 diabetes relevance than an average expression baseline. Conclusions: Trained single-cell decoders already contain rich perturbation-relevant information that can be accessed by automatic differentiation, enabling in-silico perturbation simulations and principled ranking of genes along observed disease or treatment axes without bespoke architectures or perturbation labels. Full article

Myogenesis is a tightly regulated process essential for embryonic development, postnatal growth, and muscle regeneration. We recently identified that cytokinins (CTKs), a class of adenine-derived signaling molecules originally characterized in plants, are present in cultured skeletal muscle cells. The most abundant type of cytokinins detected within cultured muscle cells was isopentenyladenine (iP) in its nucleotide, riboside, and free base derivatives. The purpose of this study was to determine whether CTKs are also present in regenerating muscle tissue in vivo and to characterize the effects of iP and its riboside form, isopentenyladenosine (iPR), on muscle cell proliferation and differentiation. These effects were observed relative to adenine and adenosine, and to a second class of cytokinins with a large aromatic side chain, kinetin (the free base), and kinetin riboside. Cardiotoxin was used to induce muscle injury and repair processes in the gastrocnemius of 3- and 12-month-old mice. Samples were collected 3- and 7 days post-injury for ultra high-performance liquid chromatography tandem mass spectrometry with electrospray ionization (UHPLC-(ESI+)-HRMS/MS). Four CTKs (N⁶-benzyladenine (BA), dihydrozeatin-9-N-glucoside (DZ9G), isopentenyladenosine (iPR), and 2-methylthio-isopentenyladenosine (2-MeSiPR) were detected. 2-MeSiPR levels were significantly influenced by aging, as this CTK was increased in response to injury only in the younger mice. Treatment of C2C12 myoblasts with 10 µM of isopentenyladenosine (iPR) or kinetin riboside reduced cell proliferation, whereas iP (the free base) increased proliferation in a biphasic response. During differentiation, both iPR and kinetin riboside impaired myotube formation, while the free-base forms of iP and kinetin had no effect. Our data establishes that CTKs are present within muscle tissue and highly responsive to injury and aging. Furthermore, the biological activities of CTKs in muscle cells are influenced by structural modifications, including riboside conjugation and side chain composition. Understanding these differences provides insight into the distinct roles of CTKs in muscle cell metabolism and differentiation, offering potential implications for the use of exogenous CTKs in muscle biology and regenerative medicine. Full article

Double homeobox (DUX) genes are key embryonic regulators that are silenced after the early cleavage stages of embryogenesis. Aberrant expression of DUX4 in skeletal muscle is linked to facioscapulohumeral muscular dystrophy (FSHD). A recent study reported that Dux, the murine ortholog of DUX4, contributes to the dystrophic phenotype in mdx mice, a Duchenne muscular dystrophy (DMD) model, and that its deletion enhances muscle regeneration by reducing oxidative stress. However, convincing evidence of Dux expression in either intact or injured muscle of wild-type (WT) and mdx mice remains lacking, raising questions about its role in muscle homeostasis. To investigate this, we assessed Dux expression in WT and mdx mice and used Dux knockout (Dux^Δ/Δ) mice to evaluate its function during regeneration following cardiotoxin (CTX)-induced injury. Contrary to prior reports, Dux was not expressed in either WT or mdx mice. Moreover, Dux deletion did not enhance muscle regeneration or affect the expression of the oxidative stress regulator Nrf2 following CTX injury. Lastly, we confirmed that neither DUX4 nor its target genes were induced in muscle biopsies from DMD patients, excluding a role for DUX4 in DMD pathology. Collectively, our results demonstrate that Dux does not impact skeletal muscle regeneration or DUX4 contribution to the DMD dystrophic phenotype, directly challenging the conclusions of a previously published study. We comment on issues of editorial oversight that led to the publication of that study and highlight the deleterious impact of the growing wave of fraudulent publications. Full article

Background: Three aconitine poisoning events occurred in two Canadian provinces in 2022: one in British Columbia (BC) and two in Ontario (ON). Aconitine is a potent alkaloid found in several species of the plant Aconitum, containing cardiotoxins and neurotoxins. It is used in traditional Chinese medicine (TCM) for pain management, and in powdered form, Aconitum is similar in appearance to sand ginger (Kaempferia galanga), which can lead to poisonings from misidentification and mislabeling. Methods: Aconitine poisoning is rare in Canada; here, we compare communications, collaborations, laboratory testing options and actions during investigations. Results: Fourteen cases occurred from the consumption of sand ginger: in BC (n = 2), purchased at an Asian health food store; in ON (n = 11), Kaempferia galanga powder (KGP) spices were used to prepare meals at a restaurant, and in one ON case, KGP was purchased. Traceback found product imported from China contained aconitine levels ranging from 1304 to 5500 ppm. Later investigations revealed mislabeling of Aconitum as KGP from the same imported lot (January 2020). Plant DNA testing found no KGP in any spice packets, including lots not linked to illness, suggestive of adulteration. Conclusion: Method development for aconitine in BC led to an improved response time for testing in ON. BC and ON updated outbreak response protocols and communications. Full article

Skin aging is accelerated by inflammation processes generated by oxidative stress and external factors such as UV radiation. Plants belonging to the genus Kalanchoe that are rich sources of antioxidants could potentially strengthen the skin barrier if used as ingredients in cosmetic formulations. However, their use is limited due to the contents of bufadienolides, known cardiotoxins. This study aimed to establish a semi-quantitative profile of bufadienolides in the juices of K. blossfeldiana, K. daigremontiana, and K. pinnata using UHPLC combined with charged aerosol detection (CAD) and high-resolution mass spectrometry (HR-MS). Additionally, the study determined the ability of bufadienolides to penetrate the skin barrier using the Bronaugh Diffusion Cell Apparatus and Strat-M membrane. The study also assessed the ferric and molybdenum-reducing powers, as well as the radical scavenging capabilities of these plants juices using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) methods. The in vitro antihyaluronidase and antityrosinase activities and sun protection factor (SPF) were evaluated spectrophotometrically, indicating moderate capability to inhibit the skin enzymes, but low SPF protection for all analyzed juices. The semi-qualitative analysis demonstrated the presence of bufadienolides occurring in two juices from K. daigremontiana and K. pinnata, with the highest contents of 1,3,5-bersaldegenin-orthoacetate, bryophyllin-A/bryotoxin-C, bersaldegenin-acetate/bryophyllin-C, and diagremontianin. After passing through the skin model, no bufadienolide compounds were present in the subcutaneous filtrate. Antiradical and reduction assays revealed the antioxidant potential of K. blossfeldiana and K. pinnata. These results indicate that Kalanchoe juices have antiaging potential and appear safe for dermal applications. Full article

Collagen I is the most abundant type of intramuscular collagen. Lysyl oxidase promotes collagen cross-link formation, which helps stabilize the extracellular matrix. Furthermore, matrix metalloproteinases, responsible for collagen degradation, maintain typical muscle structure and function through remodeling. Although it is well known that aging leads to delayed recovery of muscle fibers, the impact of aging on the remodeling of intramuscular collagen is not well understood. In this study, we investigated the impact of aging on collagen remodeling during muscle injury recovery using young and old mouse models. Muscle injury was induced in the right tibialis anterior (TA) muscle of male C57BL/6J mice [aged 21 weeks (young) and 92 weeks (old)] using intramuscular cardiotoxin injection, with the left TA serving as a sham with saline injection. Following a one-week recovery period, aging was found to delay the recovery of the fiber cross-sectional area. The intensity and area of immunoreactivity for collagen I were significantly increased in old mice compared to young mice post-injury. Additionally, Lox expression and the number of LOX (+) cells in the extracellular matrix significantly increased in old mice compared to young mice post-injury. Furthermore, Mmp9 and MMP9 expression levels after muscle injury were higher in old mice than in young mice. These results suggest that muscle injury in old mice can lead to increased collagen I accumulation, enhanced collagen cross-link formation, and elevated MMP9 expression compared to young mice. Full article

Indoxyl sulfate—a bacterially derived metabolite—has been identified as a toxin that is elevated in children with autism spectrum disorder (ASD). As a neurotoxin, uremic toxin, nephrotoxin, cardiotoxin, osteotoxin, and myotoxin, indoxyl sulfate has been associated with several other conditions, including chronic kidney disease, acute kidney injury, Parkinson’s disease, cognitive disorders, and mood disorders such as anxiety and depression. Indoxyl sulfate is derived from bacterial modification of host tryptophan, and elevated levels of indoxyl sulfate are associated with decreased levels of important neurotransmitters including serotonin, dopamine, and norepinephrine. This article will review what is currently known about indoxyl sulfate in relation to ASD and its comorbidities. A systematic review identified six studies of levels of indoxyl sulfate in children with ASD. All six studies found that indoxyl sulfate was significantly elevated in the urine of children with ASD compared to typically developing children. Through this review, indoxyl sulfate was identified as a toxic microbially derived metabolite that is significantly increased in a subset of children with ASD and may contribute to both core and co-morbid ASD symptoms. Full article

Background/Objectives:Porphyromonas gingivalis infection has been associated with various systemic diseases and may cause delayed healing of muscle injury. However, the relationship between muscle injury healing and P. gingivalis infection remains unclear. Our hypothesis was that P. gingivalis infection delays the healing of muscle injuries. Methods: Fifty-six 8-week-old male Wistar rats were randomly divided into two groups: sonicated P. gingivalis was intraperitoneally administered in one group (PG group), whereas saline was administered in the other group (CO group). Skeletal muscle injury was induced via cardiotoxin injections in all animals. The cross-sectional area of regenerating muscle cells was evaluated by haematoxylin–eosin staining, and the degree of muscle fibrosis was evaluated by Masson’s trichrome staining. The expression of paired box protein (Pax7) and myoblast determination protein (MyoD) and the identified stages of myocyte regeneration were analysed by immunohistochemical staining. Motion analysis was performed during walking. Results: The cross-sectional area of muscle cells was significantly smaller in the PG group on days 7 and 14 post-injury than in the CO group. The Pax7+/MyoD− ratio was significantly lower in the PG group on day 1 post-injury than in the CO group. Motion analysis of treadmill walking showed that the PG group had a lower minimum calcaneal height on days 3 and 7 post-injury than the CO group. Conclusions: This study suggests that administration of sonicated P. gingivalis in rats can delay the healing process of muscle injury. Further research is needed to understand this mechanism of delay of P. gingivalis. Full article

Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is a critical enzyme that regulates nitric oxide (NO) signaling through the degradation of asymmetric dimethylarginine (ADMA). Previous studies have revealed a link between the beneficial effects of aerobic exercise and the upregulation of DDAH1 in bones and hearts. We previously reported that skeletal muscle DDAH1 plays a protective role in cardiotoxin (CTX)-induced skeletal muscle injury and regeneration. To determine the effects of aerobic exercise on CTX-induced skeletal muscle injury and the role of DDAH1 in this process, wild-type (WT) mice and skeletal muscle-specific Ddah1-knockout (Ddah1^MKO) mice were subjected to swimming training for 8 weeks and then injected with CTX. In WT mice, swimming training for 8 weeks significantly promoted skeletal muscle regeneration and attenuated inflammation, oxidative stress, and apoptosis in the gastrocnemius (GA) muscle after CTX injection. These phenomena were associated with increases in the protein expression of PAX7, myogenin, MEF2A, eNOS, SOD2, and peroxiredoxin 5 and decreases in iNOS expression in GA muscles. Swimming training also decreased serum ADMA levels and increased serum nitrate/nitrite (NOx) levels and skeletal muscle DDAH1 expression. Interestingly, swimming training in Ddah1^MKO mice had no obvious effect on CTX-induced skeletal muscle injury or regeneration and did not repress the CTX-induced inflammatory response, superoxide generation, or apoptosis. In summary, our data suggest that DDAH1 is important for the protective effect of aerobic exercise on skeletal muscle injury and regeneration. Full article

Cytotoxins (CTs) are three-finger membrane-active toxins present mainly in cobra venom. Our analysis of the available CT amino acid sequences, literature data on their membrane activity, and conformational equilibria in aqueous solution and detergent micelles allowed us to identify specific amino acid residues which interfere with CT incorporation into membranes. They include Pro9, Ser28, and Asn/Asp45 within the N-terminal, central, and C-terminal loops, respectively. There is a hierarchy in the effect of these residues on membrane activity: Pro9 > Ser28 > Asn/Asp45. Taking into account all the possible combinations of special residues, we propose to divide CTs into eight groups. Group 1 includes toxins containing all of the above residues. Their representatives demonstrated the lowest membrane activity. Group 8 combines CTs that lack these residues. For the toxins from this group, the greatest membrane activity was observed. We predict that when solely membrane activity determines the cytotoxic effects, the activity of CTs from a group with a higher number should exceed that of CTs from a group with a lower number. This classification is supported by the available data on the cytotoxicity and membranotropic properties of CTs. We hypothesize that the special amino acid residues within the loops of the CT molecule may indicate their involvement in the interaction with non-lipid targets. Full article

Skeletal muscle atrophy (SMA) is caused by a rise in muscle breakdown and a decline in protein synthesis, with a consequent loss of mass and function. This study characterized the effect of an amino acid mixture (AA) in models of SMA, focusing on mitochondria. C57/Bl6 mice underwent immobilization of one hindlimb (I) or cardiotoxin-induced muscle injury (C) and were compared with controls (CTRL). Mice were then administered AA in drinking water for 10 days and compared to a placebo group. With respect to CTRL, I and C reduced running time and distance, along with grip strength; however, the reduction was prevented by AA. Tibialis anterior (TA) muscles were used for histology and mitochondria isolation. I and C resulted in TA atrophy, characterized by a reduction in both wet weight and TA/body weight ratio and smaller myofibers than those of CTRL. Interestingly, these alterations were lightly observed in mice treated with AA. The mitochondrial yield from the TA of I and C mice was lower than that of CTRL but not in AA-treated mice. AA also preserved mitochondrial bioenergetics in TA muscle from I and C mice. To conclude, this study demonstrates that AA prevents loss of muscle mass and function in SMA by protecting mitochondria. Full article

Skeletal muscle is a complex tissue comprising multinucleated and post-mitotic cells (i.e., myofibers). Given this, skeletal muscle must maintain a fine balance between growth and degradative signals. A major system regulating the remodeling of skeletal muscle is autophagy, where cellular quality control is mediated by the degradation of damaged cellular components. The accumulation of damaged cellular material can result in elevated apoptotic signaling, which is particularly relevant in skeletal muscle given its post-mitotic nature. Luckily, skeletal muscle possesses the unique ability to regenerate in response to injury. It is unknown whether a relationship between autophagy and apoptotic signaling exists in injured skeletal muscle and how autophagy deficiency influences myofiber apoptosis and regeneration. In the present study, we demonstrate that an initial inducible muscle-specific autophagy deficiency does not alter apoptotic signaling following cardiotoxin injury. This finding is presumably due to the re-establishment of ATG7 levels following injury, which may be attributed to the contribution of a functional Atg7 gene from satellite cells. Furthermore, the re-expression of ATG7 resulted in virtually identical regenerative potential. Overall, our data demonstrate that catastrophic injury may “reset” muscle gene expression via the incorporation of nuclei from satellite cells. Full article

Nitric oxide (NO) is an important biological signaling molecule affecting muscle regeneration. The activity of NO synthase (NOS) is regulated by dimethylarginine dimethylaminohydrolase 1 (DDAH1) through degradation of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA). To investigate the role of DDAH1 in muscle injury and regeneration, muscle-specific Ddah1-knockout mice (Ddah1^MKO) and their littermates (Ddah1^f/f) were used to examine the progress of cardiotoxin (CTX)-induced muscle injury and subsequent muscle regeneration. After CTX injection, Ddah1^MKO mice developed more severe muscle injury than Ddah1^f/f mice. Muscle regeneration was also delayed in Ddah1^MKO mice on Day 5 after CTX injection. These phenomena were associated with higher serum ADMA and LDH levels as well as a great induction of inflammatory response, oxidative stress and cell apoptosis in the gastrocnemius (GA) muscle of Ddah1^MKO mice. In the GA muscle of CTX-treated mice, Ddah1 deficiency decreased the protein expression of M-cadherin, myogenin, Bcl-2, peroxiredoxin 3 (PRDX3) and PRDX5, and increased the protein expression of MyoD, TNFα, Il-6, iNOS and Bax. In summary, our data suggest that DDAH1 exerts a protective role in muscle injury and regeneration. Full article