PPARA and obesity due to melanocortin 4 receptor deficiency: Toxicology studies in animal models, cell models, and key molecular initiating events such as PPARα and sterol regulatory element-binding protein (SREBP/SREBF) activation provide mechanisms for PFAS-mediated metabolic diseases such as fatty liver disease, obesity, increased cholesterol and LDL, and diabetes [6,52,60,68,145,156,157].