CLDN1 and obesity due to melanocortin 4 receptor deficiency: Improvement in gut barrier function and increased IL-22 levels was associated with increases in tight junction gene expression, including claudin 1 and ZO1, and upregulated expression of antimicrobial peptide Reg3g and mucus secretion gene Muc2, all of which are known to be downregulated during obesity [4, 26].