The obesity-induced inflammatory response inhibits insulin signaling in adipocytes and hepatocytes through a variety of signaling pathways, including inhibition of the expression of insulin receptor substrate 1 (IRS-1) and insulin receptor (IR) in insulin signaling pathways and inhibition of PPAR gamma function, and ultimately leads to insulin resistance (26, 27). Here, IRS1 is linked to obesity due to melanocortin 4 receptor deficiency.