Effects of mechanical trauma on the differentiation and ArfGAP3 expression of C2C12 myoblast and mouse levator ani muscle

ArfGAP3 Protects Mitochondrial Function and Promotes Autophagy Through Rab5a-Mediated Signals in Ageing Skeletal Muscle

BACKGROUND

Few researches have investigated the molecular mechanism responsible for the age-related loss of the pelvic floor muscle (PFM) mass and functionality-a pivotal contributor to pelvic organ prolapse and diminished physical well-being. ADP ribosylation factor GTPase activating protein 3 (ArfGAP3) is a member of ArfGAPs, which regulates the vesicular trafficking pathway and intracellular proteins transporting. However, its effects on skeletal muscle ageing remain largely unknown.

METHODS

Mouse models of natural ageing and D-gal (D-galactose)-induced ageing were subject to analyse the structure, function and pathological alterations of the PFM and the expression of ArfGAP3. Stable ArfGAP3 knockdown and overexpression C2C12 cell lines were established to investigate the anti-senescence effects of ArfGAP3 and the underlying mechanisms in ageing process, complemented by Rab5a genetic intervention and mRFP-GFP-LC3 adenoviral particles transfection. In vivo experiments entailed ArfGAP3 overexpression in mice alongside autophagy inhibitor treatment, with assessments encompassing tissue mass, bladder leak point pressure (BLPP), submicroscopic structure, antioxidative stress system and muscle regeneration.

RESULTS

Aged (24-month-old) mice exhibited significant physiological alterations in PFMs, including decreased muscle mass, diminished cross-sectional area (CSA), deteriorated supporting function (as evidenced by reduced BLPP), impaired autophagy and increased levels of oxidative stress (p < 0.001). Utilizing ageing C2C12 model, we observed a dose-dependent relationship between D-gal induction and cellular senescence, impaired differentiation and mitochondrial damage. Remarkably, the expression levels of ArfGAP3 were markedly downregulated in both in vitro and in vivo ageing models. Knockdown of ArfGAP3 exacerbated impaired differentiation potential and induced aberrant mitochondrial morphology and functional dysfunction in ageing C2C12 myoblasts, whereas ArfGAP3 overexpression largely mitigated these effects. Mechanistically, our findings revealed an interplay between ArfGAP3 and Rab5a, indicating their coordinated regulation. ArfGAP3-mediated activation of Rab5a-associated autophagy and IRS1-AKT-mTOR signalling pathways during cellular senescence and myogenesis was identified, leading to enhanced autophagic flux and improved resistance to oxidative stress. In vivo, ArfGAP3 overexpression ameliorated D-gal-induced loss of muscle mass and function, while promoting antioxidant responses and muscle regeneration in mice. However, these protective effects of ArfGAP3 overexpression were extinguished by autophagy inhibition.

CONCLUSIONS

Our study uncovers the significant role of ArfGAP3 in enhancing differentiation capacity and mitochondrial function through mediating Rab5a expression to activate IRS1-AKT-mTOR signalling pathways and promote autophagy during the ageing process. These findings underscore the potential of ArfGAP3 as a promising therapeutic target for ameliorating the decline in skeletal muscle function associated with ageing.

Tensile force impairs lip muscle regeneration under the regulation of interleukin-10

BACKGROUND

Orbicularis oris muscle, the crucial muscle in speaking, facial expression and aesthetics, is considered the driving force for optimal lip repair. Impaired muscle regeneration remains the main culprit for unsatisfactory surgical outcomes. However, there is a lack of study on how different surgical manipulations affect lip muscle regeneration, limiting efforts to seek effective interventions.

METHODS

In this study, we established a rat lip surgery model where the orbicularis oris muscle was injured by manipulations including dissection, transection and stretch. The effect of each technique on muscle regeneration was examined by histological analysis of myogenesis and fibrogenesis. The impact of tensile force was further investigated by the in vitro application of mechanical strain on cultured myoblasts. Transcriptome profiling of muscle satellite cells from different surgical groups was performed to figure out the key factors mediating muscle fibrosis, followed by therapeutic intervention to improve muscle regeneration after lip surgeries.

RESULTS

Evaluation of lip muscle regeneration till 56 days after injury revealed that the stretch group resulted in the most severe muscle fibrosis (n = 6, fibrotic area 48.9% in the stretch group, P < 0.001, and 25.1% in the dissection group, P < 0.001). There was the lowest number of Pax7-positive nuclei at Days 3 and 7 in the stretch group (n = 6, P < 0.001, P < 0.001), indicating impaired satellite cell expansion. Myogenesis was impaired in both the transection and stretch groups, as evidenced by the delayed peak of centrally nucleated myofibers and embryonic MyHC. Meanwhile, the stretch group had the highest percentage of Pdgfra+ fibro-adipogenic progenitors infiltrated area at Days 3, 7 and 14 (n = 6, P = 0.003, P = 0.006, P = 0.037). Cultured rat lip muscle myoblasts exhibited impaired myotube formation and fusion capacity when exposed to a high magnitude (ε = 2688 μ strain) of mechanical strain (n = 3, P = 0.014, P = 0.023). RNA-seq analysis of satellite cells isolated from different surgical groups demonstrated that interleukin-10 was the key regulator in muscle fibrosis. Administration of recombinant human Wnt7a, which can inhibit the expression of interleukin-10 in cultured satellite cells (n = 3, P = 0.041), exerted an ameliorating effect on orbicularis oris muscle fibrosis after stretching injury in surgical lip repair.

CONCLUSIONS

Tensile force proved to be the most detrimental manoeuvre for post-operative lip muscle regeneration, despite its critical role in correcting lip and nose deformities. Adjunctive biotherapies to regulate the interleukin-10-mediated inflammatory process could facilitate lip muscle regeneration under conditions of high surgical tensile force.

Genetics of Female Pelvic Organ Prolapse: Up to Date

Pelvic organ prolapse (POP) is a benign disease characterized by the descent of pelvic organs due to weakened pelvic floor muscles and fascial tissues. Primarily affecting elderly women, POP can lead to various urinary and gastrointestinal tract symptoms, significantly impacting their quality of life. The pathogenesis of POP predominantly involves nerve-muscle damage and disorders in the extracellular matrix metabolism within the pelvic floor. Recent studies have indicated that genetic factors may play a crucial role in this condition. Focusing on linkage analyses, single-nucleotide polymorphisms, genome-wide association studies, and whole exome sequencing studies, this review consolidates current research on the genetic predisposition to POP. Advances in epigenetics are also summarized and highlighted, aiming to provide theoretical recommendations for risk assessments, diagnoses, and the personalized treatment for patients with POP.

Ferrostatin-1 alleviates the damage of C2C12 myoblast and mouse pelvic floor muscle induced by mechanical trauma

Ferroptosis is a special form of regulated cell death, which is reported to play an important role in a variety of traumatic diseases by promoting lipid peroxidation and devastating cell membrane structure. Pelvic floor dysfunction (PFD) is a kind of disease affecting the quality and health of many women's lives, which is closely related to the injury of the pelvic floor muscle. Clinical findings have discovered that there is anomalous oxidative damage to the pelvic floor muscle in women with PFD caused by mechanical trauma, but the specific mechanism is still unclear. In this study, we explored the role of ferroptosis-associated oxidative mechanisms in mechanical stretching-induced pelvic floor muscle injury, and whether obesity predisposed pelvic floor muscle to ferroptosis from mechanical injury. Our results, in vitro, showed that mechanical stretch could induce oxidative damage to myoblasts and trigger ferroptosis. In addition, glutathione peroxidase 4 (GPX4) down-regulation and 15-lipoxygenase 1(15LOX-1) up-regulation exhibited the same variational characteristics as ferroptosis, which was much more pronounced in palmitic acid (PA)-treated myoblasts. Furthermore, ferroptosis induced by mechanical stretch could be rescued by ferroptosis inhibitor (ferrostatin-1). More importantly, in vivo, we found that the mitochondria of pelvic floor muscle shrank, which were consistent with the mitochondrial morphology of ferroptosis, and GPX4 and 15LOX-1 showed the same change observed in cells. In conclusion, our data suggest ferroptosis is involved in the injury of the pelvic floor muscle caused by mechanical stretching, and provide a novel insight for PFD therapy.

ArfGAP3 regulates vesicle transport and glucose uptake in myoblasts

Skeletal muscle injuries are common, and damaged myofibers are repaired through proliferation and differentiation of muscle satellite cells. GLUT4 is enriched in GLUT4 storage vesicles (GSVs) and plays a crucial role in the maintenance of muscle function. ArfGAP3 regulates the vesicle transport especially for COPI coat assembly, but its effects on GSVs and the repair process after skeletal muscle injury remains unclear. In this study, datasets related to skeletal muscle injury and myoblast differentiation GSE469, GSE5413, GSE45577 and GSE108040 were retrieved through the GEO database and the expression of heptameric coat protein complex I (COPI) and Golgi vesicle transport-related genes in various datasets, as well as the expression correlation between ArfGAP2, ArfGAP3 and COPI-related genes COPA, COPB1, COPB2, COPE, COPZ1, COPZ2 were analyzed. The results suggested that ArfGAP3 was expressed in the process of repair after skeletal muscle injury and myoblast differentiation and that ArfGAP3 was positively correlated with COPI-related genes. In vitro experimental results showed that ArfGAP3 was colocalized with COPA, COPB, COPG protein, and GLUT4 in C2C12 myoblasts. After the downregulation of ArfGAP3 expression, intracellular vesicle transport, and glucose uptake were blocked, the proliferation of myoblasts under low glucose culture conditions was impaired, the proportion of apoptosis increased, and myotube differentiation was impaired. In summary, ArfGAP3 regulates COPI-associated vesicle and GSVs transport and affects the proliferation and differentiation ability of myoblasts by influencing glucose uptake, thereby modulating the repair process after skeletal muscle injury.

Restoration of NAD+ homeostasis protects C2C12 myoblasts and mouse levator ani muscle from mechanical stress-induced damage

Excessive mechanical traction damages the levator ani muscle (LAM), increasing the incidence of pelvic floor dysfunction (PFD). In this study, we explored the effects of oxidized nicotinamide adenine dinucleotide (NAD⁺) on the damage to both muscle cells and LAM tissue induced by mechanical stress (MS) at the cellular and animal levels. The cell damage model was established using a four-point bending system. The LAM damage model was established using vaginal distention and traction. Exogenous addition of PJ34, an inhibitor of poly (ADP-ribose) polymerase-1 (PARP-1), and the nicotinamide mononucleotide (NMN) precursor of NAD⁺ increased NAD⁺ levels. ATP content and mitochondrial membrane potential were measured to assess mitochondrial function. NAD⁺ levels, cell viability, and PARP-1 activity were detected using commercial kits. DNA damage in cells was detected with immunofluorescence staining, and LAM damage was detected with tissue TUNEL staining. PARP-1 activity and DNA damage of LAM were detected by immunohistochemistry. A small amount of DNA damage and PARP-1 activation did not affect NAD⁺ levels, while excessive DNA damage and PARP-1 activation led to an imbalance of NAD⁺ homeostasis. Furthermore, increasing NAD⁺ levels in vivo and in vitro could rescue mitochondrial dysfunction and damage to both muscle cells and LAM tissue induced by MS. In conclusion, MS can induce damage to both C2C12 cells and LAM tissue. Restoring NAD⁺ homeostasis can rescue this damage by improving mitochondrial function.

CACNA1H downregulation induces skeletal muscle atrophy involving endoplasmic reticulum stress activation and autophagy flux blockade

Multiple vaginal delivery (MVD) is an important factor for pelvic floor muscle (PFM) function decline and pelvic floor dysfunction (PFD). PFD is common in middle-aged and elderly women, but its pathogenesis is not clear. In this study, we found that the expression of CACNA1H was lower in the PFM of old mice after MVD compared with old or adult mice. In in-vitro studies, we found that treatment with the T-type Ca²⁺ channel (T-channel) inhibitor NNC-55 or downregulation of the CACNA1H gene by siRNA intervention promoted myotube atrophy and apoptosis. Mechanistically, we revealed that NNC-55 increased the expression of GRP78 and DDIT3 in myotubes, indicating endoplasmic reticulum stress (ERS) activation, and that the IRE1 and PERK pathways might be involved in this effect. NNC-55 induced the formation of autophagosomes but inhibited autophagy flux. Moreover, rapamycin, an autophagy activator, did not rescue myotube atrophy or apoptosis induced by NNC-55, and the autophagy inhibitors 3-MA and HCQ accelerated this damage. Further studies showed that the ERS inhibitors 4-PBA and TUDAC relieved NNC-55-induced damage and autophagy flux blockade. Finally, we found multisite muscle atrophy and decreased muscle function in Cacna1h^−/− (TH-null) mice, as well as increased autophagy inhibition and apoptotic signals in the PFM of old WT mice after MVD and TH-null mice. Taken together, our results suggest that MVD-associated PFD is partially attributed to CACNA1H downregulation-induced PFM atrophy and that ERS is a potential therapeutic target for this disease.