Transcriptional Pathways Associated with Skeletal Muscle Changes after Spinal Cord Injury and Treadmill Locomotor Training

Abstract

The genetic and molecular events associated with changes in muscle mass and function after SCI and after the implementation of candidate therapeutic approaches are still not completely known. The overall objective of this study was to identify key molecular pathways activated with muscle remodeling after SCI and locomotor training. We implemented treadmill training in a well-characterized rat model of moderate SCI and performed genome wide expression profiling on soleus muscles at multiple time points: 3, 8, and 14 days after SCI. We found that the activity of the protein ubiquitination and mitochondrial function related pathways was altered with SCI and corrected with treadmill training. The BMP pathway was differentially activated with early treadmill training as shown by Ingenuity Pathway Analysis. The expression of several muscle mass regulators was modulated by treadmill training, including Fst, Jun, Bmpr2, Actr2b, and Smad3. In addition, key players in fatty acids metabolism (Lpl and Fabp3) responded to both SCI induced inactivity and reloading with training. The decrease in Smad3 and Fst early after the initiation of treadmill training was confirmed by RT-PCR. Our data suggest that TGFβ/Smad3 signaling may be mainly involved in the decrease in muscle mass observed with SCI, while the BMP pathway was activated with treadmill training.

Activity-Based Physical Rehabilitation with Adjuvant Testosterone to Promote Neuromuscular Recovery after Spinal Cord Injury

“…As evidence, after spinal transection, the incorporation of BWSTT completely preserved the muscle mass:body mass ratio [ 195 , 196 ] and prevented ~55% of soleus fCSA loss [ 196 ]. Similarly, in a moderate-contusion SCI model, BWSTT produced 23% higher soleus fCSA and 38% higher soleus peak tetanic force in comparison with untrained SCI animals [ 197 ], with analogous effects reported by others [ 49 , 197 , 198 , 199 , 200 ]. Similarly, several case-report and cohort-studies have reported muscle responses in individuals with motor-incomplete SCI.…”

“…The influence of these ubiquitin ligases on skeletal muscle atrophy has been demonstrated by the viral overexpression of MAFbx, which reduced the myotube diameter by ~85% in vitro, and by genetic elimination of MAFbx or MuRF1, which attenuated muscle atrophy in response to sciatic nerve transection [ 48 ]. Within several days of SCI, >50 protein ubiquination pathway genes are upregulated in sublesional muscle [ 49 ], an effect that likely influences the rapid muscle atrophy in response to injury. In particular, MAFbx and MuRF1 mRNA expressions are increased five- to >40-fold within two to eight days of injury [ 50 , 51 , 52 , 53 , 54 ], with protein expressions elevated >two-fold prior to the initiation of muscle atrophy [ 55 ].…”

“…In this regard, FOXO1 mRNA was 33% higher [ 54 ] and MAFbx and MuRF1 mRNA were >two-fold higher in rodents after spinal transection than in animals receiving sciatic nerve transection [ 53 ], potentially explaining the more rapid atrophy occurring after SCI than in other disuse conditions [ 53 , 56 ]. However, the increased expressions of these and other ubiquitin proteasome pathway genes do not persist after experimental SCI [ 49 ], with FOXO1, MAFbx, and MuRF1 gene expressions and pFOXO1 and pFOXO3 proteins reverting to the level of uninjured controls within two to 10 weeks of spinal cord transection [ 53 , 54 , 57 ]. Similarly, in humans with motor-complete SCI, MAFbx and MuRF1 expressions are high at one-month post-injury and decline by 50–75% at three- and 12-months, resulting from reductions in pFOXO1 and/or total FOXO3 proteins [ 58 ].…”

“…In comparison, ablation of PGC-1β in skeletal muscle myofibers in adulthood reduced mitochondrial CSA and mitochondrial respiration without altering fiber-type distribution, resulting in increased oxidative stress and impaired exercise performance [ 70 ]. Baligand et al used genome wide analysis and identified that genes associated with mitochondrial dysfunction and impaired oxidative phosphorylation were altered three to 14 days after SCI [ 49 ]. In particular, muscle PGC-1α mRNA expression was suppressed to a nearly undetectable level three days after spinal cord transection [ 54 ] and within two weeks, muscle PGC-1α protein was dramatically reduced, accompanying reductions in slow myosin heavy chain (MHC) protein expression [ 73 ] that is indicative of fewer oxidative fibers.…”

“…The structural improvements mentioned above appear to be influenced, in-part, by reduced catabolic signaling resulting from BWSTT. As evidence, in a rodent SCI model, three sessions of BWSTT suppressed >10 protein ubiquitination pathway genes, an effect accompanied by the full preservation of muscle mass [ 49 ]. Similarly, after spinal cord transection, five sessions of electrical stimulation of paralyzed muscle suppressed MAFbx and MuRF1 mRNA and myostatin mRNA in muscle [ 51 ].…”