Polychlorobiphenyls inhibit skeletal muscle differentiation in culture

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent pollutants whose role in developmental toxicity is of great concern. The observation that the offspring of PCB-exposed mothers (both in humans and rodents) display reduced body mass prompted us to investigate the effects of commercial mixtures of PCB congeners (Aroclor 1232, 1254, and 1262) on differentiation of both a myogenic cell line and primary myogenic cell cultures. The fusion of L6 myoblasts into multinucleated myotubes and the increase of creatine kinase (CK) activity were dose-dependently inhibited by Aroclor 1254 at concentrations (0.1-4 microg/ml) that caused no effect on cell density. Ultrastructural analysis demonstrated that Aroclor 1254 also prevented the accumulation of contractile filaments while inducing hypertrophy of the smooth endoplasmic reticulum and appearance of membrane-filled autophagosomes. Half-maximal inhibition (IC50) of CK activity accumulation occurred at 0.01 microg/ml for Aroclor 1262, 2 microg/ml for Aroclor 1254, and 8 microg/ml for Aroclor 1232. Aroclor-dependent inhibition of myogenic differentiation was also shown by the reduced expression and nuclear accumulation of beta-galactosidase in primary cultures of fetal myoblasts from transgenic mice expressing this reporter gene under the control of the myosin light chain promoter. These data show that skeletal muscle differentiation is specifically impaired by PCBs and may explain the reported depression of body mass growth in PCB-exposed offspring at birth. Furthermore, myogenic cell cultures are highly sensitive to PCBs and allow the detection of biological effects of environmental levels of these pollutants.