Reinnervation-induced alterations in rat skeletal muscle

Automated muscle fiber type population analysis with ImageJ of whole rat muscles using rapid myosin heavy chain immunohistochemistry

INTRODUCTION

Skeletal muscle consists of different fiber types which adapt to exercise, aging, disease, or trauma. Here we present a protocol for fast staining, automatic acquisition, and quantification of fiber populations with ImageJ.

METHODS

Biceps and lumbrical muscles were harvested from Sprague-Dawley rats. Quadruple immunohistochemical staining was performed on single sections using antibodies against myosin heavy chains and secondary fluorescent antibodies. Slides were scanned automatically with a slide scanner. Manual and automatic analyses were performed and compared statistically.

RESULTS

The protocol provided rapid and reliable staining for automated image acquisition. Analyses between manual and automatic data indicated Pearson correlation coefficients for biceps of 0.645-0.841 and 0.564-0.673 for lumbrical muscles. Relative fiber populations were accurate to a degree of ± 4%.

CONCLUSIONS

This protocol provides a reliable tool for quantification of muscle fiber populations. Using freely available software, it decreases the required time to analyze whole muscle sections. Muscle Nerve 54: 292-299, 2016.

Microarray Analysis Gene Expression Profiles in Laryngeal Muscle After Recurrent Laryngeal Nerve Injury

OBJECTIVES

The pathophysiology of recurrent laryngeal nerve (RLN) transection injury is rare in that it is characteristically followed by a high degree of spontaneous reinnervation, with reinnervation of the laryngeal adductor complex (AC) preceding that of the abducting posterior cricoarytenoid (PCA) muscle. Here, we aim to elucidate the differentially expressed myogenic factors following RLN injury that may be at least partially responsible for the spontaneous reinnervation.

METHODS

F344 male rats underwent RLN injury (n = 12) or sham surgery (n = 12). One week after RLN injury, larynges were harvested following euthanasia. The mRNA was extracted from PCA and AC muscles bilaterally, and microarray analysis was performed using a full rat genome array.

RESULTS

Microarray analysis of denervated AC and PCA muscles demonstrated dramatic differences in gene expression profiles, with 205 individual probes that were differentially expressed between the denervated AC and PCA muscles and only 14 genes with similar expression patterns.

CONCLUSIONS

The differential expression patterns of the AC and PCA suggest different mechanisms of reinnervation. The PCA showed the gene patterns of Wallerian degeneration, while the AC expressed the gene patterns of reinnervation by adjacent axonal sprouting. This finding may reveal important therapeutic targets applicable to RLN and other peripheral nerve injuries.

Cellular players in skeletal muscle regeneration

Skeletal muscle, a tissue endowed with remarkable endogenous regeneration potential, is still under focused experimental investigation mainly due to treatment potential for muscle trauma and muscular dystrophies. Resident satellite cells with stem cell features were enthusiastically described quite a long time ago, but activation of these cells is not yet controlled by any medical interventions. However, after thorough reports of their existence, survival, activation, and differentiation there are still many questions to be answered regarding the intimate mechanism of tissue regeneration. This review delivers an up-to-date inventory of the main known key players in skeletal muscle repair, revealed by various models of tissue injuries in mechanical trauma, toxic lesions, and muscular dystrophy. A better understanding of the spatial and temporal relationships between various cell populations, with different physical or paracrine interactions and phenotype changes induced by local or systemic signalling, might lead to a more efficient approach for future therapies.

Molecular mechanism of active zone organization at vertebrate neuromuscular junctions

Organization of presynaptic active zones is essential for development, plasticity, and pathology of the nervous system. Recent studies indicate a trans-synaptic molecular mechanism that organizes the active zones by connecting the pre- and the postsynaptic specialization. The presynaptic component of this trans-synaptic mechanism is comprised of cytosolic active zone proteins bound to the cytosolic domains of voltage-dependent calcium channels (P/Q-, N-, and L-type) on the presynaptic membrane. The postsynaptic component of this mechanism is the synapse organizer (laminin β2) that is expressed by the postsynaptic cell and accumulates specifically on top of the postsynaptic specialization. The pre- and the postsynaptic components interact directly between the extracellular domains of calcium channels and laminin β2 to anchor the presynaptic protein complex in front of the postsynaptic specialization. Hence, the presynaptic calcium channel functions as a scaffolding protein for active zone organization and as an ion-conducting channel for synaptic transmission. In contrast to the requirement of calcium influx for synaptic transmission, the formation of the active zone does not require the calcium influx through the calcium channels. Importantly, the active zones of adult synapses are not stable structures and require maintenance for their integrity. Furthermore, aging or diseases of the central and peripheral nervous system impair the active zones. This review will focus on the molecular mechanisms that organize the presynaptic active zones and summarize recent findings at the neuromuscular junctions and other synapses.

Surface electromyographic activity of five residual limb muscles recorded during isometric contraction in transfemoral amputees with osseointegrated prostheses

BACKGROUND

Femoral osseointegrated implants represent a new development in amputee rehabilitation, eliminating socket pressure discomfort, improving hip range of movement and facilitating prosthetic limb attachment. A clinical aspect that has not previously been reported on is the function of muscles in the residuum with implications concerning energy expenditure, hip-hiking and viability of the electrogram as a myoprocessor. Typically, amputees fitted with osseointegrated fixation have shorter residuums and weaker attachment of cleaved muscles. Function of muscle can be assessed by surface electromyography through changes in amplitude and median frequency of the signal.

METHODS

Five male transfemoral amputees with osseointegrated fixations participated together with a control group comprised of ten adult males. Electrodes recorded surface electromyographic activity of five residual limb muscles or left lower limb muscles of control subjects. Isometric contractions were performed against resistance. The increase in mean rectified amplitude from resting to maximally contracting was calculated and median frequencies estimated.

FINDINGS

The amputees were unable to maintain a maximum voluntary contraction of constant amplitude. Amplitude increase was lowest for rectus femoris and adductor magnus. The median frequency of adductor magnus was significantly greater (P=0.02) for the amputees than intact subjects and there was a significant difference (P<0.01) between gluteus maximus and adductor magnus for amputee subjects.

INTERPRETATION

High electromyographic amplitude variability suggests that using residuum muscles singly as a myoprocessor might be challenging. Adductor magnus displayed a different sEMG profile compared to intact subjects indicating decreased function and neuromuscular changes. Further work into optimal muscle anchorage is required to ensure maximal mechanical performance.

Calcium channels link the muscle-derived synapse organizer laminin β2 to Bassoon and CAST/Erc2 to organize presynaptic active zones

Synapse formation requires the organization of presynaptic active zones, the synaptic vesicle release sites, in precise apposition to postsynaptic neurotransmitter receptor clusters; however, the molecular mechanisms responsible for these processes remain unclear. Here, we show that P/Q-type and N-type voltage-dependent calcium channels (VDCCs) play essential roles as scaffolding proteins in the organization of presynaptic active zones. The neuromuscular junction of double knock-out mice for P/Q- and N-type VDCCs displayed a normal size but had significantly reduced numbers of active zones and docked vesicles and featured an attenuation of the active-zone proteins Bassoon, Piccolo, and CAST/Erc2. Consistent with this phenotype, direct interactions of the VDCC β1b or β4 subunits and the active zone-specific proteins Bassoon or CAST/Erc2 were confirmed by immunoprecipitation. A decrease in the number of active zones caused by a loss of presynaptic VDCCs resembled the pathological conditions observed in the autoimmune neuromuscular disorder Lambert-Eaton myasthenic syndrome. At the synaptic cleft of double knock-out mice, we also observed a decrease of the synaptic organizer laminin β2 protein, an extracellular ligand of P/Q- and N-type VDCCs. However, the transcription level of laminin β2 did not decrease in double knock-out mice, suggesting that the synaptic accumulation of laminin β2 protein required its interaction with presynaptic VDCCs. These results suggest that presynaptic VDCCs link the target-derived synapse organizer laminin β2 to active-zone proteins and function as scaffolding proteins to anchor active-zone proteins to the presynaptic membrane.

Modulation of satellite cells in rat facial muscle following denervation and delayed reinnervation

CONCLUSION

Long-term denervation-induced satellite cells (SCs) deficiency impairs facial muscle regenerative capacity. Delayed reinnervation can reactivate residual SCs to engage in muscle regeneration. However, the underlying mechanism remains to be elucidated.

OBJECTIVE

To evaluate the effects of denervation and delayed reinnervation on SCs in facial muscle.

METHODS

This was a prospective, randomized, controlled study in the rat facial nerve ligation and delayed decompression model. Animals were divided into denervation, 8-week-delay, and 16-week-delay reinnervation groups. Sham-operated animals served as a control group. Specific markers were used to investigate the differences in SC status, including quiescent (Pax7) and activated (myoD and myogenin) SCs and regenerative myofibers (embryonic myosin heavy chain, eMyHC). Quantitative assessment was performed by real-time PCR and Western blotting.

RESULTS

Activated SCs were detected 2-4 weeks after denervation and maintained for 4-8 weeks, accompanied by regenerating myofibers, whereas no SCs were detected beyond 20 weeks post-denervation. The myoD and myogenin up-regulation peaked 6-8 weeks after denervation and declined gradually to normal baseline 12 weeks after denervation. The 8-week-delay reinnervation group showed more activated SCs and regenerating myofibers than the 16-week-delay group, as well as greater up-regulation of myoD and myogenin (p < 0.05), suggesting reactivation of SCs for repair of adjacent fibers.

Oxygenomics in environmental stress

Environmental stressors such as chemicals and physical agents induce various oxidative stresses and affect human health. To elucidate their underlying mechanisms, etiology and risk, analyses of gene expression signatures in environmental stress-induced human diseases, including neuronal disorders, cancer and diabetes, are crucially important. Recent studies have clarified oxidative stress-induced signaling pathways in human and experimental animals. These pathways are classifiable into several categories: reactive oxygen species (ROS) metabolism and antioxidant defenses, p53 pathway signaling, nitric oxide (NO) signaling pathway, hypoxia signaling, transforming growth factor (TGF)-beta bone morphogenetic protein (BMP) signaling, tumor necrosis factor (TNF) ligand-receptor signaling, and mitochondrial function. This review describes the gene expression signatures through which environmental stressors induce oxidative stress and regulate signal transduction pathways in rodent and human tissues.

Transcriptional profiling of skeletal muscle reveals factors that are necessary to maintain satellite cell integrity during ageing

Skeletal muscle ageing is characterized by faulty degenerative/regenerative processes that promote the decline of its mass, strength, and endurance. In this study, we used a transcriptional profiling method to better understand the molecular pathways and factors that contribute to these processes. To more appropriately contrast the differences in regenerative capacity of old muscle, we compared it with young muscle, where robust growth and efficient myogenic differentiation is ongoing. Notably, in old mice, we found a severe deficit in satellite cells activation. We performed expression analyses on RNA from the gastrocnemius muscle of young (3-week-old) and old (24-month-old) mice. The differential expression highlighted genes that are involved in the efficient functioning of satellite cells. Indeed, the greatest number of up-regulated genes in young mice encoded components of the extracellular matrix required for the maintenance of the satellite cell niche. Moreover, other genes included Wnt inhibitors (Wif1 and Sfrp2) and Notch activator (Dner), which are putatively involved in the interconnected signalling networks that control satellite cell function. The widespread expression differences for inhibitors of TGFbeta signalling further emphasize the shortcomings in satellite cell performance. Therefore, we draw attention to the breakdown of features required to maintain satellite cell integrity during the ageing process.

Regeneration of reinnervated rat soleus muscle is accompanied by fiber transition toward a faster phenotype

The functional recovery of skeletal muscles after peripheral nerve transection and microsurgical repair is generally incomplete. Several reinnervation abnormalities have been described even after nerve reconstruction surgery. Less is known, however, about the regenerative capacity of reinnervated muscles. Previously, we detected remarkable morphological and motor endplate alterations after inducing muscle necrosis and subsequent regeneration in the reinnervated rat soleus muscle. In the present study, we comparatively analyzed the morphometric properties of different fiber populations, as well as the expression pattern of myosin heavy chain isoforms at both immunohistochemical and mRNA levels in reinnervated versus reinnervated-regenerated muscles. A dramatic slow-to-fast fiber type transition was found in reinnervated soleus, and a further change toward the fast phenotype was observed in reinnervated-regenerated muscles. These findings suggest that the (fast) pattern of reinnervation plays a dominant role in the specification of fiber phenotype during regeneration, which can contribute to the long-lasting functional impairment of the reinnervated muscle. Moreover, because the fast II fibers (and selectively, a certain population of the fast IIB fibers) showed better recovery than did the slow type I fibers, the faster phenotype of the reinnervated-regenerated muscle seems to be actively maintained by selective yet undefined cues.