Line Jensen

Aging affects the transcriptional regulation of human skeletal muscle disuse atrophy.

Important insights concerning the molecular basis of skeletal muscle disuse-atrophy and aging related muscle loss have been obtained in cell culture and animal models, but these regulatory signaling pathways have not previously been studied in aging human muscle. In the present study, muscle atrophy was induced by immobilization in healthy old and young individuals to study the time-course and transcriptional factors underlying human skeletal muscle atrophy. The results reveal that irrespectively of age, mRNA expression levels of MuRF-1 and Atrogin-1 increased in the very initial phase (2–4 days) of human disuse-muscle atrophy along with a marked reduction in PGC-1α and PGC-1β (1–4 days) and a ∼10% decrease in myofiber size (4 days). Further, an age-specific decrease in Akt and S6 phosphorylation was observed in young muscle within the first days (1–4 days) of immobilization. In contrast, Akt phosphorylation was unchanged in old muscle after 2 days and increased after 4 days of immobilization. Further, an age-specific down-regulation of MuRF-1 and Atrogin-1 expression levels was observed following 2 weeks of immobilization, along with a slowing atrophy response in aged skeletal muscle. Neither the immediate loss of muscle mass, nor the subsequent age-differentiated signaling responses could be explained by changes in inflammatory mediators, apoptosis markers or autophagy indicators. Collectively, these findings indicate that the time-course and regulation of human skeletal muscle atrophy is age dependent, leading to an attenuated loss in aging skeletal muscle when exposed to longer periods of immobility-induced disuse.

Ageing is associated with diminished muscle re-growth and myogenic precursor cell expansion early after immobility-induced atrophy in human skeletal muscle

•  Elderly individuals require a prolonged recovery phase in order to return to initial muscle mass levels following short‐term immobilisation. •  The cellular mechanisms responsible for the attenuated re‐growth and associated molecular signalling processes in ageing human skeletal muscle are not fully understood. •  The main study finding was the observation of a less marked muscle mass recovery after immobilisation in elderly compared to young individuals that was paralleled by an elevation in myogenic precursor cell content in young individuals only, whereas the elderly failed to demonstrate any change in myogenic precursor cells. •  No age‐related differences were observed in the expression of major myogenic regulating factors known to promote skeletal muscle hypertrophy or satellite cell proliferation (IGF‐1Ea, MGF, MyoD1, myogenin, HGF gene products). •  In contrast, the expression of myostatin demonstrated a more pronounced up‐regulation following immobilisation along with an attenuated down‐regulation in response to reloading in older compared to young individuals, which may have contributed to the present lack of satellite cell proliferation in ageing muscle.

Carbohydrate restricted recovery from long term endurance exercise does not affect gene responses involved in mitochondrial biogenesis in highly trained athletes

The aim was to determine if the metabolic adaptations, particularly PGC‐1α and downstream metabolic genes were affected by restricting CHO following an endurance exercise bout in trained endurance athletes. A second aim was to compare baseline expression level of these genes to untrained. Elite endurance athletes (VO2max 66 ± 2 mL·kg−1·min−1, n = 15) completed 4 h cycling at ~56% VO2max. During the first 4 h recovery subjects were provided with either CHO or only H2O and thereafter both groups received CHO. Muscle biopsies were collected before, after, and 4 and 24 h after exercise. Also, resting biopsies were collected from untrained subjects (n = 8). Exercise decreased glycogen by 67.7 ± 4.0% (from 699 ± 26.1 to 239 ± 29.5 mmol·kg−1·dw−1) with no difference between groups. Whereas 4 h of recovery with CHO partly replenished glycogen, the H2O group remained at post exercise level; nevertheless, the gene expression was not different between groups. Glycogen and most gene expression levels returned to baseline by 24 h in both CHO and H2O. Baseline mRNA expression of NRF‐1, COX‐IV, GLUT4 and PPAR‐α gene targets were higher in trained compared to untrained. Additionally, the proportion of type I muscle fibers positively correlated with baseline mRNA for PGC‐1α, TFAM, NRF‐1, COX‐IV, PPAR‐α, and GLUT4 for both trained and untrained. CHO restriction during recovery from glycogen depleting exercise does not improve the mRNA response of markers of mitochondrial biogenesis. Further, baseline gene expression of key metabolic pathways is higher in trained than untrained.

Skeletal Muscle Remodelling as a Function of Disease Progression in Amyotrophic Lateral Sclerosis

Muscle weakness is considered the pivotal sign of amyotrophic lateral sclerosis (ALS). Knowledge about the skeletal muscle degeneration/regeneration process and the myogenic potential is limited in ALS patients. Therefore, we investigate these processes in a time course perspective by analysing skeletal muscle biopsies from ALS patients collected before and after a 12-week period of normal daily activities and compare these with healthy age-matched control tissue. We do this by evaluating mRNA and protein (immunohistochemical) markers of regeneration, neurodegeneration, myogenesis, cell cycle regulation, and inflammation. Our results show morphological changes indicative of active denervation and reinnervation and an increase in small atrophic fibres. We demonstrate differences between ALS and controls in pathways controlling skeletal muscle homeostasis, cytoskeletal and regenerative markers, neurodegenerative factors, myogenic factors, cell cycle determinants, and inflammatory markers. Our results on Pax7 and MyoD protein expression suggest that proliferation and differentiation of skeletal muscle stem cells are affected in ALS patients, and the myogenic processes cannot overcome the denervation-induced wasting.

“The preadipocyte factor” DLK1 marks adult mouse adipose tissue residing vascular cells that lack in vitro adipogenic differentiation potential

Delta‐like 1 (Dlk1) is expressed in 3T3‐L1 preadipocytes and has frequently been referred to as “the” preadipocyte marker, yet the phenotype of DLK1+ cells in adipose tissue remains undetermined. Herein, we demonstrate that DLK1+ cells encompass around 1–2% of the adult mouse adipose stromal vascular fraction (SVF). Unexpectedly, the DLK1+SVF population was enriched for cells expressing genes generally ascribed to the vascular lineage and did not possess any adipogenic differentiation potential in vitro. Instead, DLK1+ cells comprised an immediate ability for cobblestone formation, generation of tube‐like structures on matrigel, and uptake of Acetylated Low Density‐Lipoprotein, all characteristics of endothelial cells. We therefore suggest that DLK1+SVF cells are of a vascular origin and not them‐selves committed preadipocytes as assumed hitherto.

High Expression of KCa3.1 in Patients with Clear Cell Renal Carcinoma Predicts High Metastatic Risk and Poor Survival

Background Ca2+-activated K+ channels have been implicated in cancer cell growth, metastasis, and tumor angiogenesis. Here we hypothesized that high mRNA and protein expression of the intermediate-conductance Ca2+-activated K+ channel, KCa3.1, is a molecular marker of clear cell Renal Cell Carcinoma (ccRCC) and metastatic potential and survival. Methodology/Principal Findings We analyzed channel expression by qRT-PCR, immunohistochemistry, and patch-clamp in ccRCC and benign oncocytoma specimens, in primary ccRCC and oncocytoma cell lines, as well as in two ccRCC cell lines (Caki-1 and Caki-2). CcRCC specimens contained 12-fold higher mRNA levels of KCa3.1 than oncocytoma specimens. The large-conductance channel, KCa1.1, was 3-fold more highly expressed in ccRCC than in oncocytoma. KCa3.1 mRNA expression in ccRCC was 2-fold higher than in the healthy cortex of the same kidney. Disease specific survival trended towards reduction in the subgroup of high-KCa3.1-expressing tumors (p<0.08 vs. low-KCa3.1-expressing tumors). Progression-free survival (time to metastasis/recurrence) was reduced significantly in the subgroup of high-KCa3.1-expressing tumors (p<0.02, vs. low-KCa3.1-expressing tumors). Immunohistochemistry revealed high protein expression of KCa3.1 in tumor vessels of ccRCC and oncocytoma and in a subset of ccRCC cells. Oncocytoma cells were devoid of KCa3.1 protein. In a primary ccRCC cell line and Caki-1/2-ccRCC cells, we found KCa3.1-protein as well as TRAM-34-sensitive KCa3.1-currents in a subset of cells. Furthermore, Caki-1/2-ccRCC cells displayed functional Paxilline-sensitive KCa1.1 currents. Neither KCa3.1 nor KCa1.1 were found in a primary oncocytoma cell line. Yet KCa-blockers, like TRAM-34 (KCa3.1) and Paxilline (KCa1.1), had no appreciable effects on Caki-1 proliferation in-vitro. Conclusions/Significance Our study demonstrated expression of KCa3.1 in ccRCC but not in benign oncocytoma. Moreover, high KCa3.1-mRNA expression levels were indicative of low disease specific survival of ccRCC patients, short progression-free survival, and a high metastatic potential. Therefore, KCa3.1 is of prognostic value in ccRCC.

Neuronal nitric oxide synthase is dislocated in type I fibers of myalgic muscle but can recover with physical exercise training

Trapezius myalgia is the most common type of chronic neck pain. While physical exercise reduces pain and improves muscle function, the underlying mechanisms remain unclear. Nitric oxide (NO) signaling is important in modulating cellular function, and a dysfunctional neuronal NO synthase (nNOS) may contribute to an ineffective muscle function. This study investigated nNOS expression and localization in chronically painful muscle. Forty-one women clinically diagnosed with trapezius myalgia (MYA) and 18 healthy controls (CON) were included in the case-control study. Subsequently, MYA were randomly assigned to either 10 weeks of specific strength training (SST, n = 18), general fitness training (GFT, n = 15), or health information (REF, n = 8). Distribution of fiber type, cross-sectional area, and sarcolemmal nNOS expression did not differ between MYA and CON. However, MYA showed increased sarcoplasmic nNOS localization (18.8 ± 12 versus 12.8 ± 8%, P = 0.049) compared with CON. SST resulted in a decrease of sarcoplasm-localized nNOS following training (before 18.1 ± 12 versus after 12.0 ± 12%; P = 0,027). We demonstrate that myalgic muscle displays altered nNOS localization and that 10 weeks of strength training normalize these disruptions, which supports previous findings of impaired muscle oxygenation during work tasks and reduced pain following exercise.

Aging is associated with diminished muscle re-growth and myogenic precursor cell expansion in the early recovery phase after immobility-induced atrophy in human skeletal muscle

•  Elderly individuals require a prolonged recovery phase in order to return to initial muscle mass levels following short‐term immobilisation. •  The cellular mechanisms responsible for the attenuated re‐growth and associated molecular signalling processes in ageing human skeletal muscle are not fully understood. •  The main study finding was the observation of a less marked muscle mass recovery after immobilisation in elderly compared to young individuals that was paralleled by an elevation in myogenic precursor cell content in young individuals only, whereas the elderly failed to demonstrate any change in myogenic precursor cells. •  No age‐related differences were observed in the expression of major myogenic regulating factors known to promote skeletal muscle hypertrophy or satellite cell proliferation (IGF‐1Ea, MGF, MyoD1, myogenin, HGF gene products). •  In contrast, the expression of myostatin demonstrated a more pronounced up‐regulation following immobilisation along with an attenuated down‐regulation in response to reloading in older compared to young individuals, which may have contributed to the present lack of satellite cell proliferation in ageing muscle.

Molecular regulation of human muscle atrophy with 4 days immobilization – effects of aging

Abstracts of the 6th Cachexia Conference, Milan, Italy, December 8–10, 2011s of the 6th Cachexia Conference, Milan, Italy, December 8–10, 2011

Influence of Resistance Training on Neuromuscular Function and Physical Capacity in ALS Patients

Objectives The present study aimed to explore the effect of resistance training in patients with amyotrophic lateral sclerosis (ALS), a disease characterized by progressive motor neuron loss and muscle weakness. Materials and Methods Following a 12-week “lead-in” control period, a population of ALS patients from Funen, Denmark, completed a 12-week resistance training program consisting of 2-3 sessions/week. Neuromuscular function (strength and power) and voluntary muscle activation (superimposed twitch technique) were evaluated before and after both control and training periods. Physical capacity tests (chair rise and timed up and go), the revised ALS functional rating scale (ALSFRS-R) scores, and muscle cross sectional area (histology) were also assessed. Results Of twelve ALS patients assessed for eligibility, six were included and five completed the study. Training did not significantly affect the ALSFRS-R score, and loss of neuromuscular function (strength and power) increased following the training period. However, an improved functionality (chair rise) and an increase in greatly hypertrophied type II fibres combined with an increase in atrophied fibres following the training period compared to the control period were observed. Conclusion In this small study, the present form of resistance training was unable to attenuate progressive loss of neuromuscular function in ALS, despite some changes in physical capacity and morphology.