Diabetic nephropathy (DN) is one of the leading causes of chronic kidney disease (CKD), during which hyperglycemia is composed of the major force for the deterioration to end-stage renal disease (ESRD). However, the underlying mechanism triggering the effect of hyperglycemia on DN is not very clear and the clinically available drug for hyperglycemia-induced DN is in need of urgent development. Here, we found that high glucose (HG) increased the activity of cyclin-dependent kinase 5 (CDK5) dependent on P35/25 and which upregulated the oxidative stress and apoptosis of mouse podocytes (MPC-5). TFP5, a 25-amino acid peptide inhibiting CDK5 activity, decreased the secretion of inflammation cytokines in serum and kidney, and effectively protected the kidney function in db/db mouse from hyperglycemia-induced kidney injuries. In addition, TFP5 treatment decreased HG-induced oxidative stress and cell apoptosis in MPC-5 cells and kidney tissue of db/db mouse. The principal component analysis (PCA) of RNA-seq data showed that MPC-5 cell cultured under HG, was well discriminated from that under low glucose (LG) conditions, indicating the profound influence of HG on the properties of podocytes. Furthermore, we found that HG significantly decreased the level of NGF and Sirt1, both of which correlated with CDK5 activity. Furthermore, knockdown of NGF was correlated with the decreased expression of Sirt1 while NGF overexpression leads to upregulated Sirt1 and decreased oxidative stress and apoptosis in MPC-5 cells, indicating the positive regulation between NGF and Sirt1 in podocytes. Finally, we found that K252a, an inhibitor of NGF treatment could undermine the protective role of TFP5 on hyperglycemia-induced DN in db/db mouse model. In conclusion, the CDK5-NGF/Sirt1 regulating axis may be the novel pathway to prevent DN progression and TFP5 may be a promising compound to improved hyperglycemia induced DN.

Islet β‐cell damage and dysfunction represent the pathophysiological basis of diabetes. Excessive activation of cyclin‐dependent kinase 5 (CDK5) is involved in the pathogenesis of type 2 diabetes mellitus (T2DM), although the exact mechanism remains unclear. Therefore, this study investigated the role of a CDK5 inhibitor (TFP5) in islet β‐cell damage under diabetic conditions by regulating the expression of CDK5 in vitro and in vivo. CDK5 was upregulated under high glucose conditions in vivo and in vitro, which resulted in inflammation, oxidative stress, and apoptosis of islet β‐cells, thereby decreasing insulin secretion. However, TFP5 treatment inhibited the overexpression of CDK5; reduced the inflammatory response, oxidative stress, and apoptosis of islet β cells; and restored insulin secretion. In conclusion, CDK5 is involved in islet β‐cell damage under high glucose conditions, and TFP5 may represent a promising candidate for the development of treatments for T2DM.

Type 2 diabetes mellitus (T2DM) is worldwide epidemic, which challenges the health of the public. The pathological hyperactivity of cyclin-dependent kinase 5 (Cdk5) contributes to the pathogenesis of T2DM. P5, a peptide derived from the Cdk5 activator p35, shows excellent performance as a Cdk5 activity inhibitor. However, its inhibitory effect and functional regulation on Cdk5 activity needs to be confirmed. In this study, we conjugated P5 with a fluorescein isothiocyanate (FITC) tag at the N-terminus and a TAT protein transduction domain, an 11-amino acid peptide, at the C-terminus to synthesize TFP5, which was used to inhibits Cdk5 activity. We then evaluated the efficiency of TFP5 in treating T2DM. We demonstrated that TFP5 effectively penetrated pancreatic β-cells, inhibited the pathological hyperactivity of Cdk5, enhanced insulin secretion, and protected penetrated pancreatic β-cells (MIN6 cells) from apoptosis in pancreatic tissues of db/db mice (type II diabetes mice). Furthermore, we found that TFP5 reduced inflammation in pancreatic islets by reducing the expression of inflammatory cytokines, including TGF-β1, TNF-α, and IL-1β. These data indicates that the TFP5 peptide is a promising candidate for T2DM treatment.

Type 2 diabetes mellitus (T2DM) is among the most important public health challenges. The pathological hyperactivity of multifunctional cyclin-dependent kinase 5 (Cdk5) contributes to the pathogenesis of T2DM. P5, a peptide derived from the Cdk5 activator p35, shows potential as a Cdk5 activity inhibitor. However, its inhibitory effect and functional regulation of Cdk5 activity need to be confirmed. In this study, we conjugated P5 with a Fluorescein Isothiocyanate (FITC) tag at the N-terminus and a TAT protein transduction domain containing an 11 amino acid peptide at the C-terminus to synthesize TFP5, which we used to inhibit Cdk5 activity. We then evaluated the efficiency of TFP5 in treating T2DM. We demonstrated that TFP5 effectively penetrated pancreatic β-cells, inhibited the pathological hyperactivity of Cdk5, enhanced insulin secretion, and protected MIN6 cells from apoptosis in pancreatic tissues of db/db mice (Type II diabetes mice). Furthermore, we found that TFP5 reduced inflammation in pancreatic islets by reducing the expression of inflammatory cytokines (including TGF-β, TNF-α, and IL-1β). These data indicate that the TFP5 peptide is a promising candidate for T2DM treatment.