Primary human muscle precursor cells obtained from young and old donors produce similar proliferative, differentiation and senescent profiles in culture.

The myogenic behaviour of primary human muscle precursor cells (MPCs) obtained from young (aged 20-25 years) and elderly people (aged 67-82 years) was studied in culture. Cells were compared in terms of proliferation, DNA damage, time course and extent of myogenic marker expression during differentiation, fusion, size of the formed myotubes, secretion of the myogenic regulatory cytokine TGF-ß1 and sensitivity to TGF-ß1 treatment. No differences were observed between cells obtained from the young and elderly people. The cell populations were expanded in culture until replicative senescence. Cultures that maintained their initial proportion of myogenic cells (desmin positive) with passaging (n = 5) were studied and compared with cells from the same individuals in the non-senescent state. The senescent cells exhibited a greater number of cells with DNA damage (γ-H2AX positive), showed impaired expression of markers of differentiation, fused less well, formed smaller myotubes and secreted more TGF-ß. The data strongly suggest that MPCs from young and elderly people have similar myogenic behaviour.

p38 mitogen-activated protein kinase is not activated in the quadriceps of patients with stable chronic obstructive pulmonary disease.

Quadriceps weakness is associated with a poor prognosis in COPD. Several data suggest that immobility and muscle wasting may be related through up-regulation of the p38 Mitogen associated protein kinase (MAPK) signalling pathway. We therefore hypothesised that this might occur in the quadriceps of COPD patients. We studied 105 stable COPD outpatients (mean FEV(1) 43.9% predicted) and 27 age and gender matched controls. We measured fat-free mass, quadriceps strength and daily physical activity using triaxial accelerometry. A quadriceps biopsy was obtained in which components of the p38-MAPK signalling pathway were examined. Patients had reduced fat-free mass index (16.1 (2.2) kg/m(2) vs 17.2 (2.2) kg/m(2), p = 0.02) and exhibited quadriceps weakness (mean (SD) maximal voluntary contraction force 72.1% (18.7) predicted and 82.3% (7.1) predicted for patients and controls respectively, p = 0.01). Physical activity was significantly reduced in the patient group; in particular mean (SD) locomotion time was 101 (48) minutes/12 hours in controls and 48 (31) minutes in patients (p < 0.0001). However, in biopsies obtained from these patients, no differences were observed for total or phosphorylated HSP27 or p38 MAPK protein or p38 MAPK mRNA (MAPK14); of the downstream products both GADD45ß and c-jun mRNA were reduced in COPD patients while c-myc was not different from controls. No parameter correlated with physiological data within the patient group. We conclude that, despite the presence of reduced fat-free mass, quadriceps weakness and inactivity, p38 MAPK signalling was not up-regulated in skeletal muscle of stable out-patients with COPD.

Sera from young and older humans equally sustain proliferation and differentiation of human myoblasts.

Using a human primary muscle cell culture model the behaviour of myoblasts (satellite cells) cultured in human serum obtained from either young or elderly individuals was studied. Serum was obtained from a total of 13 young (7 males and 6 females aged, 23-36 years) and 9 elderly (4 males and 5 females aged 69-84 years) subjects and used in a number of experiments. Myoblasts were extracted from human muscle biopsy samples taken from the vastus lateralis. In the first experiment myoblasts were isolated immediately after extraction from the biopsy in media containing human sera to examine its effects on the onset and progression of Ki67 and desmin expression. No effect of the age of the serum was observed at 3, 5 or 7 days of culture. In addition, cells were studied that had been expanded initially in optimum myoblast growth medium (GM, containing foetal calf serum and additional growth factors) prior to culture in medium containing 15% human serum. The proportion of proliferating muscle cells coexpressing desmin and Ki67 antigens after 46 h was again similar in the young and old serum conditions. Culturing these myoblasts in media containing 2% human serum to study their fusion and differentiation also resulted in no difference between young and old serum conditions in terms of the percentage of nuclei inside myosin heavy chain positive myotubes. Despite the variability of different samples of myoblasts, the age of the serum donor has no effect on the expression of any measured index.