AQP3 and obesity due to melanocortin 4 receptor deficiency: Because hyperglycemia is induced by obesity-associated insulin resistance, we investigated whether high glucose concentrations influence the expression of cell cycle regulatory molecules, keratins, desmosomal molecules, and AQP3. The mRNA levels of cyclin D1 (CCND1), CCND2, and cyclin-dependent kinase 2 (CDK2) were unchanged by glucose treatment, whereas those of CDK inhibitor 1A (CDKN1A) and CDKN1C increased in a glucose concentration-dependent manner, suggesting that upregulation of these genes resulted directly from the increased glucose concentration (Fig 5).