High expression of 5-HT and its end product metabolite (5-hydroxyindoleacetic acid) in the serum is strongly associated with the pathogenesis of renal dysfunction in DM [49], whereas 5-HTR antagonists exert renoprotective effects in DKD [50], suggesting that EMPA plays a renoprotective role by regulating the metabolism of gut bacteria. This evidence concerns the gene HTR5A and diabetic kidney disease.