Cr(VI) exposure and skeletal muscle differentiation and regeneration

SUMMARY Hexavalent chromium, Cr(VI), is widely used in industrial processes such as stainless steel production, electroplating, textile manufacturing, wood preservation, and leather tanning. Occupational or environmental exposures to Cr(VI) have been associated with a variety of adverse respiratory, cardiovascular, gastrointestinal, hematological, and hepatic effects. However, very little is known about the impact of Cr(VI) on skeletal muscles, the largest organ in the human body comprising about 40% of body mass. The 3-month toxicity study by National Toxicology Program (NTP) reported a dose-related increase of serum creatine kinase (CK) activities in both male and female rats exposed to Cr(VI) via drinking water compared to the control group, indicating muscle injury. Consistently, a significant increase of serum CK activity has been reported in chrome plating workers compared to the control subjects. Despite a clear sign of muscle injury has been reported in both human and animal study, the impact of Cr(VI) exposure on muscle injury and regeneration is completely unknown. Our recent study reveals that acute exposure of mouse C2C12 myoblast cells to Cr(VI) inhibits myogenic differentiation in a dose- dependent manner. Additionally, Cr(VI) inhibition of myogenesis is further confirmed in freshly isolated mouse primary myoblasts ex vivo. Moreover, the expression of key myogenic regulatory factors (MRFs) was significantly altered in Cr(VI)-treated cells. Taking together, our results demonstrate an inhibitory effect of Cr(VI) in myogenic differentiation in vitro and ex vivo. Given that in vitro myogenic differentiation largely recapitulates in vivo myogenesis during early embryo development and adult muscle regeneration, we hypothesize that Cr(VI) adversely affects skeletal muscle development and regeneration in vivo. In this proposal, we aim to address whether Cr(VI) lead to defective myogenesis and impaired muscle regeneration with the following specific aims. First, we will examine the effects of acute or chronic Cr(VI) exposure on adult muscle injury and regeneration in vivo. Second, we will explore the impact of Cr(VI) on skeletal muscle development by assessing primary and secondary myogenesis in mouse embryos prenatally exposed to Cr(VI). Lastly, to elucidate the mechanism underlying Cr(VI) inhibition of myogenic differentiation, we will analyze the role of MyoD and Myf5 in Cr(VI)- induced defective myogenic differentiation, and explore whether special AT-rich sequence-binding protein 2 (Satb2), a known Cr(VI) target gene in lung carcinogenesis, acts as an important target or a functional mediator of Cr(VI) in myogenic differentiation. The success of the proposed research will generate valuable evidence to support the adverse impact of Cr(VI) on skeletal muscle development and regeneration, and promote more epidemiological research on Cr(VI) exposure as a significant risk factor for skeletal muscle health.