S100A9 and obesity due to melanocortin 4 receptor deficiency: To understand the epidermal overexpression of S100A9 in obesity, we stimulated keratinocytes with obesity-associated mediators including metabolic factors such as SFA (BSA-complexed palmitic acid (PA)), insulin, high glucose (25 mM), with inflammatory factors (TNFα, IL-1β) that are increased due to the low grade inflammatory state in obesity, or with S100A9 to control for auto/paracrine effects.