Sebastian Frese

Accelerated aging phenotype in mice with conditional deficiency for mitochondrial superoxide dismutase in the connective tissue

The free radical theory of aging postulates that the production of mitochondrial reactive oxygen species is the major determinant of aging and lifespan. Its role in aging of the connective tissue has not yet been established, even though the incidence of aging‐related disorders in connective tissue‐rich organs is high, causing major disability in the elderly. We have now addressed this question experimentally by creating mice with conditional deficiency of the mitochondrial manganese superoxide dismutase in fibroblasts and other mesenchyme‐derived cells of connective tissues in all organs. Here, we have shown for the first time that the connective tissue‐specific lack of superoxide anion detoxification in the mitochondria results in reduced lifespan and premature onset of aging‐related phenotypes such as weight loss, skin atrophy, kyphosis (curvature of the spine), osteoporosis and muscle degeneration in mutant mice. Increase in p16INK4a, a robust in vivo marker for fibroblast aging, may contribute to the observed phenotype. This novel model is particularly suited to decipher the underlying mechanisms and to develop hopefully novel connective tissue‐specific anti‐aging strategies.

Long-Term Endurance Exercise in Humans Stimulates Cell Fusion of Myoblasts along with Fusogenic Endogenous Retroviral Genes In Vivo.

Myogenesis is defined as growth, differentiation and repair of muscles where cell fusion of myoblasts to multinucleated myofibers is one major characteristic. Other cell fusion events in humans are found with bone resorbing osteoclasts and placental syncytiotrophoblasts. No unifying gene regulation for natural cell fusions has been found. We analyzed skeletal muscle biopsies of competitive cyclists for muscle-specific attributes and expression of human endogenous retrovirus (ERV) envelope genes due to their involvement in cell fusion of osteoclasts and syncytiotrophoblasts. Comparing muscle biopsies from post- with the pre-competitive seasons a significant 2.25-fold increase of myonuclei/mm fiber, a 2.38-fold decrease of fiber area/nucleus and a 3.1-fold decrease of satellite cells (SCs) occurred. We propose that during the pre-competitive season SC proliferation occurred following with increased cell fusion during the competitive season. Expression of twenty-two envelope genes of muscle biopsies demonstrated a significant increase of putative muscle-cell fusogenic genes Syncytin-1 and Syncytin-3, but also for the non-fusogenic erv3. Immunohistochemistry analyses showed that Syncytin-1 mainly localized to the sarcolemma of myofibers positive for myosin heavy-chain isotypes. Cellular receptors SLC1A4 and SLC1A5 of Syncytin-1 showed significant decrease of expression in post-competitive muscles compared with the pre-competitive season, but only SLC1A4 protein expression localized throughout the myofiber. Erv3 protein was strongly expressed throughout the myofiber, whereas envK1-7 localized to SC nuclei and myonuclei. Syncytin-1 transcription factors, PPARγ and RXRα, showed no protein expression in the myofiber, whereas the pCREB-Ser133 activator of Syncytin-1 was enriched to SC nuclei and myonuclei. Syncytin-1, Syncytin-3, SLC1A4 and PAX7 gene regulations along with MyoD1 and myogenin were verified during proliferating or actively-fusing human primary myoblast cell cultures, resembling muscle biopsies of cyclists. Myoblast treatment with anti-Synycytin-1 abrogated cell fusion in vitro. Our findings support functional roles for ERV envelope proteins, especially Syncytin-1, contributing to cell fusion of myotubes.

Angiogenesis-related ultrastructural changes to capillaries in human skeletal muscle in response to endurance exercise

The ultrastructure of capillaries in skeletal muscle was morphometrically assessed in vastus lateralis muscle (VL) biopsies taken before and after exercise from 22 participants of two training studies. In study 1 (8 wk of ergometer training), light microscopy revealed capillary-fiber (C/F) ratio (+27%) and capillary density (+16%) to be higher (P ≤ 0.05) in postexercise biopsies than in preexercise biopsies from all 10 participants. In study 2 (6 mo of moderate running), C/F ratio and capillary density were increased (+23% and +20%; respectively, P ≤ 0.05) in VL biopsies from 6 angiogenesis responders (AR) after training, whereas 6 nonangiogenesis responders (NR) showed nonsignificant changes in these structural indicators (-4%/-4%, respectively). Forty capillary profiles per participant were evaluated by point and intersection counting on cross sections after transmission electron microscopy. In study 1, volume density (Vv) and mean arithmetic thickness (T) of endothelial cells (ECs; +19%/+17%, respectively) and pericytes (PCs; +20%/+21%, respectively) were higher (P ≤ 0.05), whereas Vv and T of the pericapillary basement membrane (BM) were -23%/-22% lower (P ≤ 0.05), respectively, in posttraining biopsies. In study 2, exercise-related differences between AR and NR-groups were found for Vv and T of PCs (AR, +26%/+22%, respectively, both P ≤ 0.05; NR, +1%/-3%, respectively, both P > 0.05) and BM (AR, -14%/-13%, respectively, both P ≤ 0.05; NR, -9%/-11%, respectively, P = 0.07/0.10). Vv and T of ECs were higher (AR, +16%/+18%, respectively; NR, +6%/+6%, respectively; all P ≤ 0.05) in both groups. The PC coverage was higher (+13%, P ≤ 0.05) in VL biopsies of individuals in the AR group but nonsignificantly altered (+3%, P > 0.05) in those of the NR group after training. Our study suggests that intensified PC mobilization and BM thinning are related to exercise-induced angiogenesis in human skeletal muscle, whereas training per se induces EC-thickening.

Skeletal muscle characteristics and mitochondrial function in Huntington's disease patients

Huntington’s disease (HD) is a hereditary neurodegenerative disorder characterized by hyperkinesia with choreatic movements, cachexia, and impaired cognitive function. HD is caused by the expansion of a CAG repeat in the gene encoding the protein huntingtin, which is also present in peripheral tissues including skeletal muscle. Despite considerable progress in the comprehension of the pathophysiology of HD, the role of huntingtin and according pathomechanisms in peripheral tissues still remain elusive. A possible cause for muscular dysfunction might be metabolic alterations. In particular, impaired mitochondrial function has been proposed to be a major pathogenic factor. Many HD patients suffer from cachexia, which has been related to alterations in energy metabolism and mitochondrial impairment. However, the underlying mechanisms for the muscle atrophy and mitochondrial disturbances are not known, whether they are primary or secondary to the disease. Unraveling these mechanisms may add to a better understanding of the HD pathogenesis and offer new potential therapeutic approaches. We investigated skeletal muscle morphology and mitochondrial function of 10 patients with genetically verified HD (6 men and 4 women, 54 6 7 years), and 11 ageand gender-matched healthy controls (7 men and 4 women, 56 6 14 years). Patients and healthy controls underwent a skeletal muscle biopsy obtained from the vastus lateralis muscle and mitochondrial respirometric measurements. The main finding was a difference in skeletal muscle fiber phenotype in HD patients when compared with healthy controls. Namely, HD patients had a significantly higher proportion of type I fibers than controls (67.1 6 9.2 vs 39.2 6 22.8%; P < .05). In contrast, there was no difference in cross-sectional area of any fiber type between patients and controls. In addition, mitochondrial respiratory capacity specific to complex I (63.9 6 13.1 vs 80.6 6 18.2 pmol O2 mg 21 s) and maximal oxidative phosphorylation capacity (88.9 6 18.7 vs 106.1 6 18.4 pmol O2 mg 21 s) were slightly lower in HD patients when compared with healthy controls (P < .05; Fig. 1A). However, when respiratory capacity was normalized to respiratory capacity of complex IV activity, no difference was observed, although respiratory capacity of complex IV FIG. 1. (A) Mass-specific mitochondrial respiratory capacity and (B) mitochondrial-specific respiratory capacity (normalized to COX) in patients with Huntington’s disease (white bars) and healthy controls (black bars). LN, leak respiration without adenylates; PETF, fatty acid oxidative capacity; PCI, respiratory capacity of complex I; P, oxidative phosphorylation capacity; LOmy, oligomycin-induced leak respiration; E, electron transport system capacity; PCII, respiratory capacity of complex II; ROX, residual oxygen consumption; COX, respiratory capacity of complex IV. Values are mean 6 standard deviation. *P < .050; nPatients 5 10, nControls 5 11.

Körperliches Training bei mitochondrialen Erkrankungen

ZusammenfassungKörperliches Training gilt bei mitochondrialen Myopathien als einer der vielversprechendsten therapeutischen Ansätze. Effektivität und Sicherheit sind bewiesen. Ausdauer- und Krafttraining haben unterschiedliche Wirkungen auf die Muskulatur von Patienten mit mitochondrialer Myopathie: Als therapeutischer Mechanismus des Krafttrainings gilt das so genannte „gene shifting“, die trainingsinduzierte Verschiebung des Anteils mutierter mitochondrialer DNS (mtDNS) zugunsten von Wildtyp-mtDNS durch Induktion muskulärer Satellitenzellen. Ausdauertraining regt die mitochondriale Biogenese an und hilft somit, den Circulus vitiosus aus verringertem Mitochondriengehalt, verringerter Kapazität der oxidativen Phosphorylierung, Belastungsintoleranz und daraus resultierender fortschreitender muskulärer Dekonditionierung zu durchbrechen. Die Effektivität und die Sicherheit medikamentöser Induktoren der mitochondrialen Biogenese – möglicherweise in Kombination mit Training – könnten Gegenstand künftiger Untersuchungen sein.AbstractExercise is a promising therapeutical option for the treatment of mitochondrial myopathies. Its efficacy and safety have been proven in various studies. In patients with mitochondrial myopathy, resistance training and aerobic exercise training lead to widely diversified effects: resistance training is thought to normalize the mitochondrial DNA (mtDNA) genotype in mature myofibers by enhancing the incorporation of satellite cells and thereby increasing the ratio of wild-type to mutant mtDNA (“gene shifting”). Aerobic exercise training induces mitochondrial biogenesis and helps breaking the vicious circle of low oxidative phosphorylation capacity, exercise intolerance, and progressive muscular deconditioning. Certain drugs act as inductors of mitochondrial biogenesis but their safety and efficacy in patients with mitochondrial myopathy have to be further investigated.