Verena Peters

Aim Although of potential biomedical relevance, dipeptide metabolism has hardly been studied. We found the dipeptidase carnosinase‐2 (CN2) to be abundant in human proximal tubules, which regulate water and solute homeostasis. We therefore hypothesized, that CN2 has a key metabolic role, impacting proximal tubular transport function. Methods A knockout of the CN2 gene ( CNDP2 ‐KO) was generated in human proximal tubule cells and characterized by metabolomics, RNA‐seq analysis, paracellular permeability analysis and ion transport. Results CNDP2 ‐KO in human proximal tubule cells resulted in the accumulation of cellular dipeptides, reduction of amino acids and imbalance of related metabolic pathways, and of energy supply. RNA‐seq analyses indicated altered protein metabolism and ion transport. Detailed functional studies demonstrated lower CNDP2 ‐KO cell viability and proliferation, and altered ion and macromolecule transport via trans‐ and paracellular pathways. Regulatory and transport protein abundance was disturbed, either as a consequence of the metabolic imbalance or the resulting functional disequilibrium. Conclusion CN2 function has a major impact on intracellular amino acid and dipeptide metabolism and is essential for key metabolic and regulatory functions of proximal tubular cells. These findings deserve in vivo analysis of the relevance of CN2 for nephron function and regulation of body homeostasis.

Carnosine and anserine supplementation markedLy reduce diabetic nephropathy in rodents. The mode of nephroprotective action of both dipeptides in diabetes, via local protection or improved systemic glucose homeostasis, is uncertain. Global carnosinase-1 knockout mice (Cndp1-KO) and wild-type littermates (WT) on a normal diet (ND) and high fat diet (HFD) (n = 10/group), with streptozocin (STZ)-induced type-1 diabetes (n = 21–23/group), were studied for 32 weeks. Independent of diet, Cndp1-KO mice had 2- to 10-fold higher kidney anserine and carnosine concentrations than WT mice, but otherwise a similar kidney metabolome; heart, liver, muscle and serum anserine and carnosine concentrations were not different. Diabetic Cndp1-KO mice did not differ from diabetic WT mice in energy intake, body weight gain, blood glucose, HbA1c, insulin and glucose tolerance with both diets, whereas the diabetes-related increase in kidney advanced glycation end-product and 4-hydroxynonenal concentrations was prevented in the KO mice. Tubular protein accumulation was lower in diabetic ND and HFD Cndp1-KO mice, interstitial inflammation and fibrosis were lower in diabetic HFD Cndp1-KO mice compared to diabetic WT mice. Fatalities occurred later in diabetic ND Cndp1-KO mice versus WT littermates. Independent of systemic glucose homeostasis, increased kidney anserine and carnosine concentrations reduce local glycation and oxidative stress in type-1 diabetic mice, and mitigate interstitial nephropathy in type-1 diabetic mice on HFD.