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, the impact of Cr(VI) exposure on musculoskeletal system is largely unknown. The 3-month toxicity study by National Toxicology Program (NTP) reported a dose-related increase of serum creatine kinase (CK) activities in rodents exposed to Cr(VI) via drinking water compared to the control

group, indicating muscle injury. Consistently, a significant increase of serum CK activity was 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 preliminary 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. Furthermore, whole transcriptome profiling using RNA- sequencing identified many molecules and pathways that mediate Cr(VI) inhibition of myogenic differentiation. 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 Cr(VI) exposure as a risk factor for muscle impairment, and provide additional insights on prevention and therapeutic approaches

for muscle-related disease.