Morphological and molecular comparisons between tibialis anterior muscle and levator veli palatini muscle: A preliminary study on their augmentation potential

A novel method for visualizing in-vivo rates of protein degradation provides insight into how TRIM28 regulates muscle size

Skeletal muscle size is controlled by the balance between protein synthesis and protein degradation. Given the essential role of skeletal muscle in maintaining a high quality of life, understanding the mechanisms that modulate this balance are of critical importance. Previously, we demonstrated that muscle-specific knockout of TRIM28 reduces muscle size and function and in the current study, we discovered that this effect is associated with an increase in protein degradation and a dramatic reduction in the expression of Mettl21c. Importantly, we also determined that overexpression of Mettl21c is sufficient to induce hypertrophy in both control and TRIM28 knockout muscles. Moreover, we developed a simple pulse-chase biorthogonal non-canonical amino acid tagging technique that enabled us to visualize the in vivo rate of protein degradation, and with this technique were able to conclude that the hypertrophic effect of Mettl21c is due, at least in part, to an inhibition of protein degradation.

Effects of Low-Intensity and Long-Term Aerobic Exercise on the Psoas Muscle of mdx Mice: An Experimental Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a muscle disease characterized by the absence of the protein dystrophin, which causes a loss of sarcolemma integrity, determining recurrent muscle injuries, decrease in muscle function, and progressive degeneration. Currently, there is a need for therapeutic treatments to improve the quality of life of DMD patients. Here, we investigated the effects of a low-intensity aerobic training (37 sessions) on satellite cells, peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1α protein (PGC-1α), and different types of fibers of the psoas muscle from mdx mice (DMD experimental model). Wildtype and mdx mice were randomly divided into sedentary and trained groups (n = 24). Trained animals were subjected to 37 sessions of low-intensity running on a motorized treadmill. Subsequently, the psoas muscle was excised and analyzed by immunofluorescence for dystrophin, satellite cells, myosin heavy chain (MHC), and PGC-1α content. The minimal Feret’s diameters of the fibers were measured, and light microscopy was applied to observe general morphological features of the muscles. The training (37 sessions) improved morphological features in muscles from mdx mice and caused an increase in the number of quiescent/activated satellite cells. It also increased the content of PGC-1α in the mdx group. We concluded that low-intensity aerobic exercise (37 sessions) was able to reverse deleterious changes determined by DMD.

Wnt7a promotes muscle regeneration in branchiomeric orbicularis oris muscle

BACKGROUND

The orbicularis oris muscle exhibits a deficiency in cleft lip patients. Compared with the somite-derived limb muscles, the regeneration performance of the branchiomeric orofacial muscle has seldom been investigated.

OBJECTIVE

This study aims to explore the possibility of augmenting the orbicularis oris muscle through the stimulus of Wnt7a.

METHODS

Adult rat orbicularis oris muscle and tibialis anterior muscle were injected with recombinant human Wnt7a protein. The muscles were harvested at different time points after Wnt7a delivery. Muscle regeneration-related activity, including cell proliferation, stem cell proportion, myofiber plasticity, and total fiber number, was examined.

RESULTS

Adult rat orbicularis oris muscle and tibialis anterior muscle exhibit similar regeneration-related activities after Wnt7a administration. Recombinant human Wnt7a administration resulted in enhanced cell proliferation, stem cell expansion, and fiber type remodelling in rat orbicularis oris muscle. In addition, newly formed myofibers were detected, contributing to an increased total fiber number.

CONCLUSION

Wnt7a induces vigorous regeneration in rat orbicularis oris muscle. This study helps lay a foundation for developing biotherapies to combat orofacial muscle deficiency.

Phosphatase orphan 1 inhibits myoblast proliferation and promotes myogenic differentiation

Myogenesis includes sequential stages of progenitor cell proliferation, myogenic commitment and differentiation, myocyte fusion, and myotube maturation. Different stages of myogenesis are orchestrated and regulated by myogenic regulatory factors and various downstream cellular signaling. Here we identify phosphatase orphan 1 (Phospho1) as a new player in myogenesis. During activation, proliferation, and differentiation of quiescent satellite cells, the expression of Phospho1 gradually increases. Overexpression of Phospho1 inhibits myoblast proliferation but promotes their differentiation and fusion. Conversely, knockdown of Phospho1 accelerates myoblast proliferation but impairs myotube formation. Moreover, knockdown of Phospho1 decreases the OXPHO protein levels and mitochondria density, whereas overexpression of Phospho1 upregulates OXPHO protein levels and promotes mitochondrial oxygen consumption. Finally, we show that Phospho1 expression is controlled by myogenin, which binds to the promoter of Phospho1 to regulate its transcription. These results indicate a key role of Phospho1 in regulating myogenic differentiation and mitochondrial function.

Withaferin A ameliorates ovarian cancer-induced cachexia and proinflammatory signaling

BACKGROUND

Ovarian cancer is the fifth leading cause of cancer-related deaths amongst women in the United States. Cachexia is the primary cause of death in approximately 30% of cancer patients, and is often evidenced in ovarian cancer patients. We tested the steroidal lactone Withaferin A to examine if it could ameliorate ovarian cancer-induced cachexia.

METHODS

Six-week-old severely immunodeficient female mice were xenografted with the ovarian cancer cell line A2780 followed by treatment with Withaferin A or vehicle. Changes in functional grip strength were assessed on a weekly basis. Postmortem, H&E staining was performed on skeletal muscle sections and immunofluorescent immunohistochemistry was performed on skeletal muscle and tumor sections. The levels of NF-κB-related proinflammatory cytokines were assessed in the xenografted tumors and in resident host skeletal muscle.

RESULTS

Xenografting of the A2780 cell line resulted in a significant rate of mortality, which was attenuated by a therapeutic dosage of Withaferin A. Mice that received vehicle treatment following xenografting exhibited functional muscle decline over the course of the study. The therapeutic dosage Withaferin A treatment attenuated this reduction in grip strength, whereas the supratherapeutic dosage of Withaferin A was found to be toxic/lethal and demonstrated a further decline in functional muscle strength and an increased rate of mortality on par with vehicle treatment. At a histological level, the vehicle treated tumor-bearing mice exhibited a profound reduction in myofibrillar cross-sectional area compared to the vehicle treated tumor-free control group. The atrophic changes induced by the xenografted tumor were significantly ameliorated by treatment with Withaferin A. The combination of functional muscle weakening and induction of myofibrillar atrophy corroborate a cachectic phenotype, which was functionally rescued by Withaferin A. Further, treatment completely abolished the slow-to-fast myofiber type conversion observed in the settings of cancer-induced cachexia. In both host resident skeletal muscle and the xenografted tumors, we report an increase in NF-κB-related proinflammatory cytokines that was reversed by Withaferin A treatment. Finally, we demonstrated that Withaferin A significantly downregulates cytosolic and nuclear levels of phospho-p65, the active canonical NF-κB transcription factor, in xenografted tumors.

CONCLUSIONS

Cumulatively, our results demonstrate a previously overlooked role of Withaferin A in a xenograft model of ovarian cancer. We propose mechanisms by which Withaferin A reduces NF-κB-dependent pro-inflammatory cytokine production leading to an attenuation of the cachectic phenotype in an i.p. xenograft model of ovarian cancer.

Orofacial Muscles: Embryonic Development and Regeneration after Injury

Orofacial congenital defects such as cleft lip and/or palate are associated with impaired muscle regeneration and fibrosis after surgery. Also, other orofacial reconstructions or trauma may end up in defective muscle regeneration and fibrosis. The aim of this review is to discuss current knowledge on the development and regeneration of orofacial muscles in comparison to trunk and limb muscles. The orofacial muscles include the tongue muscles and the branchiomeric muscles in the lower face. Their main functions are chewing, swallowing, and speech. All orofacial muscles originate from the mesoderm of the pharyngeal arches under the control of cranial neural crest cells. Research in vertebrate models indicates that the molecular regulation of orofacial muscle development is different from that of trunk and limb muscles. In addition, the regenerative ability of orofacial muscles is lower, and they develop more fibrosis than other skeletal muscles. Therefore, specific approaches need to be developed to stimulate orofacial muscle regeneration. Regeneration may be stimulated by growth factors such fibroblast growth factors and hepatocyte growth factor, while fibrosis may be reduced by targeting the transforming growth factor β1 (TGFβ1)/myofibroblast axis. New approaches that combine these 2 aspects will improve the surgical treatment of orofacial muscle defects.

Wnt7a induces satellite cell expansion, myofiber hyperplasia and hypertrophy in rat craniofacial muscle

Craniofacial muscles drive critical functions in the head, including speech, feeding and expression. Compared with their counterparts in trunk and limbs, craniofacial muscles are of distinct embryonic origins, which might consequently lead to different growth patterns and regenerative potential. In this study, rat levator veli palatini muscle and masseter muscle were compared with tibialis anterior muscle in their response to exogenous Wnt7a stimulus, which has been proved effective in promoting muscle regeneration in the limbs. Histological, cellular and molecular analyses were performed both under basal condition and after a single dose injection of recombinant human Wnt7a. Under basal condition, levator veli palatini muscle demonstrated considerably more satellite cells than the others. After Wnt7a administration, regeneration-related activities, including satellite cell expansion, myofiber hyperplasia and hypertrophy were generally observed in all three muscles, but with obvious differences in the extent. The composition of fast/slow myofibers underwent substantial alterations, and the pattern varied among the three muscles. Location-specific alterations in the expression level of core components in planar cell polarity pathway, Akt/mTOR pathway and myostatin pathway were also observed. In conclusion, both craniofacial and limb muscles could be effectively expanded by exogenous Wnt7a stimulus, but muscle-to-muscle variations in response patterns existed.