Severin Ruoss

Quantitative changes in focal adhesion kinase and its inhibitor, FRNK, drive load-dependent expression of costamere components

Costameres are mechanosensory sites of focal adhesion in the sarcolemma that reinforce the muscle-fiber composite and provide an anchor for myofibrillogenesis. We hypothesized that elevated content of the integrin-associated regulator of costamere turnover in culture, focal adhesion kinase (FAK), drives changes in costamere component content in antigravity muscle in a load-dependent way in correspondence with altered muscle weight. The content of FAK in soleus muscle being phosphorylated at autoregulatory tyrosine 397 (FAK-pY397) was increased after 20 s of stretch. FAK-pY397 content remained elevated after 24 h of stretch-overload due to upregulated FAK content. Overexpression of FAK in soleus muscle fibers by means of gene electrotransfer increased the β1-integrin (+56%) and meta-vinculin (+88%) content. α7-Integrin (P = 0.46) and γ-vinculin (P = 0.18) content was not altered after FAK overexpression. Co-overexpression of the FAK inhibitor FAK-related nonkinase (FRNK) reduced FAK-pY397 content by 33% and increased the percentage of fast-type fibers that arose in connection with hybrid fibers with gene transfer. Transplantation experiments confirmed the association of FRNK expression with slow-to-fast fiber transformation. Seven days of unloading blunted the elevation of FAK-pY397, β1-integrin, and meta-vinculin content with FAK overexpression, and this was reversed by 1 day of reloading. The results highlight that the expression of components for costameric attachment sites of myofibrils is under load- and fiber type-related control via FAK and its inhibitor FRNK.

Regional regulation of focal adhesion kinase after concentric and eccentric loading is related to remodelling of human skeletal muscle

We assessed focal adhesion kinase (FAK) response to concentric (CON) vs eccentric (ECC) resistance training (RT) at two vastus lateralis (VL) sites, and the relationships between FAK, muscle protein synthesis (MPS) and morphological remodelling.

Lumbar multifidus muscle degenerates in individuals with chronic degenerative lumbar spine pathology

Histological and cell‐level changes in the lumbar musculature in individuals with chronic lumbar spine degenerative conditions are not well characterized. Although prior literature supports evidence of changes in fiber type and size, little information exists describing the tissue quality and biology of pathological features of muscle in this population. The purpose of this study was to quantify multifidus tissue composition and structure, inflammation, vascularity, and degeneration in individuals with chronic degenerative lumbar spine pathology. Human multifidus biopsies were acquired from 22 consecutive patients undergoing surgery for chronic degenerative lumbar spine pathology. Relative fractions of muscle, adipose, and extracellular matrix were quantified along with muscle fiber type and cross‐sectional area (CSA) and markers of inflammation, vascularity, satellite cell density, and muscle degeneration. On average, multifidus biopsies contained 48.5% muscle, 11.7% adipose tissue, and 26.1% collagen tissue. Elevated inflammatory cell counts (48.5 ± 30.0 macrophages/mm2) and decreased vascularity (275.6 ± 69.4 vessels/mm2) were also observed compared to normative values. Satellite cell densities were on average 13 ± 9 cells per every 100 muscle fibers. Large fiber CSA (3,996.0 ± 1,909.2 µm2) and a predominance of type I fibers (61.8 ± 18.0%) were observed in addition to evidence of pathological degeneration‐regeneration cycling (18.8 ± 9.4% centrally nucleated fibers, and 55.2 ± 24.2% of muscle regions containing degeneration). High levels of muscle degeneration, inflammation, and decreased vascularity were commonly seen in human multifidus biopsies of individuals with lumbar spine pathology in comparison to normative data. Evidence of active muscle degeneration suggests that changes in muscle tissue are more complex than simple atrophy.

Genomic and lipidomic actions of nandrolone on detached rotator cuff muscle in sheep

Reversal of fatty infiltration of pennate rotator cuff muscle after tendon release is hitherto impossible. The administration of nandrolone starting at the time of tendon release prevents the increase in fat content, but does not revert established fatty infiltration. We hypothesised that tendon release and myotendinous retraction cause alterations in lipid related gene expression leading to fatty muscle infiltration, which can be suppressed by nandrolone through its genomic actions if applied immediately after tendon release. The effects of infraspinatus tendon release and subsequent tendon repair at 16 weeks were studied in six Swiss Alpine sheep. In the interventional groups, 150mg nandrolone was administered weekly after tendon release until sacrifice (N22W, n=6) or starting at the time of repair (N6W, n=6). Infraspinatus volume, composition, expressed transcripts, lipids, and selected proteins were analyzed at baseline, 16 and 22 weeks. Tendon release reduced infraspinatus volume by 22% and increased fat content from 11% to 38%. These changes were not affected by repair. Fatty infiltration was associated with up-regulation of 227 lipid species, and increased levels of the adipocyte differentiation marker PPARG2 (peroxisome proliferator-activated receptor gamma 2). Nandrolone abrogated lipid accumulation, halved the loss in fiber area percentage, and up-regulated androgen receptor levels and transcript expression in the N22W but not the N6W group. The results document that nandrolone mitigates muscle-to-fat transformation after tendon release via a general down-regulation of lipid accumulation concomitantly with up-regulated expression of its nuclear receptor and downstream transcripts in skeletal muscle. Reduced responsiveness of retracted muscle to nandrolone as observed in the N6W group is reflected by a down-regulated transcript response.

Costamere protein expression and tissue composition of rotator cuff muscle after tendon release in sheep

Previous studies suggested that degradation of contractile tissue requires cleavage of the costamere, a structural protein complex that holds sarcomeres in place. This study examined if costamere turnover is affected by a rotator cuff tear in a previously established ovine model. We found the activity of focal adhesion kinase (FAK), a main regulator of costamere turnover, was unchanged at 2 weeks but decreased by 27% 16 weeks after surgical release of the infraspinatus tendon. This was accompanied by cleavage of the costamere protein talin into a 190 kDa fragment while full length talin remained unchanged. At 2 weeks after tendon release, muscle volume decreased by 17 cm3 from an initial 185 cm3, the fatty tissue volume was halved, and the contractile tissue volume remained unchanged. After 16 weeks, the muscle volume decreased by 36 cm3, contractile tissue was quantitatively lost, and the fat content increased by 184%. Nandrolone administration mitigated the loss of contractile tissue by 26% and prevented fat accumulation, alterations in FAK activity, and talin cleavage. Taken together, these findings imply that muscle remodeling after tendon release occurs in two stages. The early decrease of muscle volume is associated with reduction of fat; while, the second stage is characterized by substantial loss of contractile tissue accompanied by massive fat accumulation. Regulation of costamere turnover is associated with the loss of contractile tissue and seems to be impacted by nandrolone treatment. Clinically, the costamere may represent a potential intervention target to mitigate muscle loss after a rotator cuff tear.

Sarcolab pilot study into skeletal muscle’s adaptation to long-term spaceflight

Spaceflight causes muscle wasting. The Sarcolab pilot study investigated two astronauts with regards to plantar flexor muscle size, architecture, and function, and to the underlying molecular adaptations in order to further the understanding of muscular responses to spaceflight and exercise countermeasures. Two crew members (A and B) spent 6 months in space. Crew member A trained less vigorously than B. Postflight, A showed substantial decrements in plantar flexor volume, muscle architecture, in strength and in fiber contractility, which was strongly mitigated in B. The difference between these crew members closely reflected FAK-Y397 abundance, a molecular marker of muscle’s loading history. Moreover, crew member A showed downregulation of contractile proteins and enzymes of anaerobic metabolism, as well as of systemic markers of energy and protein metabolism. However, both crew members exhibited decrements in muscular aerobic metabolism and phosphate high energy transfer. We conclude that countermeasures can be effective, particularly when resistive forces are of sufficient magnitude. However, to fully prevent space-related muscular deterioration, intersubject variability must be understood, and intensive exercise countermeasures programs seem mandatory. Finally, proteomic and metabolomic analyses suggest that exercise benefits in space may go beyond mere maintenance of muscle mass, but rather extend to the level of organismic metabolism.Muscles: Onboard exercise limits muscle loss in spacePhysical activity with resistive forces helps preserve muscle volume, architecture and strength in space. A team led by Jörn Rittweger from the German Aerospace Center in Cologne studied two crew members who spent six months on board the International Space Station. During the Sarcolab pilot study, one of these astronauts performed less exercise than the other. After returning to Earth, the one who trained less showed more substantial deterioration of the plantar flexor muscle in the foot—a difference detectable also at the molecular level, with lower levels of proteins involved in anaerobic and aerobic muscle metabolism. The findings highlight the need to vigorously exercise in space to limit muscle weakness. Doing so does not seem to fully prevent space-related problems, though, as evidenced by signs of muscle wasting even in the astronaut who trained regularly.

Author Correction: Sarcolab pilot study into skeletal muscle’s adaptation to longterm spaceflight

The original version of this Article contained an error in the spelling of the author Claudio Franceschi, which was incorrectly given as Claudio Francheschi. This has now been corrected in both the PDF and HTML versions of the Article.

Neurectomy preserves fast fibers when combined with tenotomy of infraspinatus muscle via upregulation of myogenesis: Protein expression with denervation and tenotomy

Introduction: We evaluated the contribution of denervation‐related molecular processes to rotator cuff muscle degeneration after tendon release. Methods: We assessed the levels of myogenic (myogenin and myogenic differentiation factor [myoD]) and proadipogenic (peroxisome proliferator‐activated receptor γ) transcription factors; the denervation‐associated proteins tenascin‐C, laminin‐2, and calcium/calmodulin‐dependent kinase II (CaMKII); and cellular alterations in sheep after infraspinatus tenotomy (TEN), suprascapular neurectomy (NEU), or both (TEN‐NEU). Results: Extracellular ground substance increased at the expense of contractile tissue 16 weeks after surgery, correlating with CaMKII isoform levels. Sheep undergoing NEU and TEN‐NEU had exaggerated infraspinatus atrophy and increased fast fibers compared with TEN sheep. The βMCaMKII isoform levels increased with TEN, and myoD levels tripled after denervation and were associated with slow fibers. Discussion: In sheep, denervation did not affect muscle‐to‐fat conversion after TEN of the infraspinatus. Furthermore, concurrent NEU mitigated the loss of fast fibers after TEN by inducing a fast‐contractile phenotype. Muscle Nerve 59:100–107, 2019

Knee extensors muscle plasticity over a 5-years rehabilitation process after open knee surgery

We investigated molecular and cellular parameters which set metabolic and mechanical functioning of knee extensor muscles in the operated and contralateral control leg of 9 patients with a chronically insufficient anterior cruciate ligament (ACL; 26.6 ± 8.3 years, 8 males, 1 female) after open reconstructive surgery (week 0), after ambulant physiotherapy under cast immobilization (week 9), succeeding rehabilitation training (up to week 26), and subsequent voluntary physical activity (week 260). Clinical indices of knee function in the operated leg were improved at 52 weeks and remained at a comparable level at week 260. CSA of the quadriceps (-18%), MCSA of muscle fibers (-24%), and capillary-to-fiber ratio (-24%) in m. vastus lateralis from the ACL insufficient leg were lower at week 0 than reference values in the contralateral leg at week 260. Slow type fiber percentage (-35%) and mitochondrial volume density (-39%) were reduced in m. vastus lateralis from the operated leg at weeks 9 and 26. Composition alterations in the operated leg exceeded those in the contralateral leg and, with the exception of the volume density of subsarcolemmal mitochondria, returned to the reference levels at week 260. Leg-specific deterioration of metabolic characteristics in the vasti from the operated leg was reflected by the down-regulation of mitochondrial respiration complex I-III markers (-41–57%) at week 9. After rehabilitation training at week 26, the specific Y397 phosphorylation of focal adhesion kinase (FAK), which is a proxy for mechano-regulation, was elevated by 71% in the operated leg but not in the contralateral leg, which had performed strengthening type exercise during ambulant physiotherapy. Total FAK protein and Y397 phosphorylation levels were lowered in both legs at week 26 resulting in positive correlations with mitochondrial volume densities and mitochondrial protein levels. The findings emphasize that a loss of mechanical and metabolic characteristics in knee extensor muscle remains detectable years after untreated ACL rupture, which may be aggravated in the post-operative phase by the deterioration of slow-oxidative characteristics after reconstruction due to insufficient load-bearing muscle activity. The reestablishment of muscle composition subsequent to years of voluntary physical activity reinforces that slow-to-fast fiber transformation is reversible in humans.