Loss of podocytes by apoptosis characterizes the early stages of diabetic nephropathy. To examine its mechanism we studied glomeruli and podocytes isolated from db/db mice with early diabetic nephropathy and albuminuria. Phosphorylation of AKT (protein kinase B, a key survival protein) was found to be lower in the glomeruli of 12 week old db/db compared to db/+ mice. In vitro, insulin phosphorylated AKT solely in podocytes from db/+ mice. Serum deprivation and exposure to tumor necrosis factor-alpha significantly compromised cell viability in podocytes from db/db but not from db/+ mice, and this was associated with a significant decrease in AKT phosphorylation. Inhibition of AKT was necessary to achieve the same degree of cell death in db/+ podocytes. Our study shows that podocyte inability to respond to insulin and susceptibility to cell death may partially account for the decreased podocyte number seen in early diabetic nephropathy.

SummaryBackground and objectives Previous studies reporting an association between high BP and high sodium and low potassium intake or urinary sodium/potassium ratio (U[Na + ]/[K + ]) primarily included white men and did not control for cardiovascular risk factors.Design, setting, participants, & measurements This cross-sectional study investigated the association of U[Na + ]/ [K + ] with BP in 3303 participants using robust linear regression.Results Mean age was 43610 years, 56% of participants were women, and 52% were African American. BP was higher in African Americans than in non-African Americans, 131/81620/11 versus 120/76616/9 mmHg (P,0.001). Mean U[Na + ]/[K + ] was 4.463.0 in African Americans and 4.162.5 in non-African Americans (P=0.002), with medians (interquartile ranges) of 3.7 (3.2) and 3.6 (2.8). Systolic BP increased by 1.6 mmHg (95% confidence interval, 1.0, 2.2) and diastolic BP by 1.0 mmHg (95% confidence interval, 0.6, 1.4) for each 3-unit increase in U[Na + ]/[K + ] (P,0.001 for both). This association remained significant after adjusting for diabetes mellitus, smoking, body mass index, total cholesterol, GFR, and urine albumin/creatinine ratio. There was no interaction between African-American race and U[Na + ]/[K + ], but for any given value of U[Na + ]/[K + ], both systolic BP and diastolic BP were higher in African Americans than in non-African Americans. The diastolic BP increase was higher in men than in women per 3-unit increase in U[Na + ]/[K + ] (1.6 versus 0.9 mmHg, interaction P=0.03).Conclusions Dietary Na + excess and K + deficiency may play an important role in the pathogenesis of hypertension independent of cardiovascular risk factors. This association may be more pronounced in men than in women.

C-jun N-terminal kinase (JNK) regulates both the development of insulin resistance and inflammation. Podocytes of the widely used db/db mouse model of diabetic nephropathy lose their ability to respond to insulin as albuminuria develops, in comparison to control db/+ mice. Here we tested whether JNK inhibition or its gene deletion would prevent albuminuria in experimental diabetes. Phosphorylated/total JNK was significantly increased in vivo in glomeruli of db/db compared to db/+ mice. Treatment of podocytes isolated from these two strains of mice with tumor necrosis factor-alpha caused greater phosphorylation of JNK in those obtained from diabetic animals. When db/db mice were treated with a cell-permeable TAT-JNK inhibitor peptide, their insulin sensitivity and glycemia significantly improved compared to controls. We induced diabetes in JNK1 knockout mice with streptozotocin and found that they had significantly better insulin sensitivity compared to diabetic wild-type or JNK2 knockout mice. Albuminuria was, however, worse in all mice treated with the JNK inhibitor and in diabetic JNK2 knockout mice compared to controls. Nephrin expression was also reduced in JNK inhibitor-treated mice compared to controls. A similar degree of mesangial expansion was found in all diabetic mice. Our study shows that targeting JNK to improve systemic insulin sensitivity does not necessarily prevent diabetic nephropathy.

Diabetic nephropathy (DN) is the leading cause of end stage renal disease (ESRD). Although the pathogenesis of DN is multifactorial, local inflammatory stress may result from both the metabolic and hemodynamic derangements observed in DN. Inflammatory markers such as Interleukin-18 and Tumor Necrosis Factor (TNF)-alpha are increased in the serum of patients with diabetes and DN. This occurs at a very early stage of disease, and correlates with the degree of albuminuria. Recent data suggest that standard pharmacologic interventions for DN, such as angiotensin converting enzyme inhibitors, angiotensin receptor blockers and aldosterone antagonists, may have anti-inflammatory properties that are independent of their hemodynamic effect. Although inflammation is traditionally thought of as a process resulting in macrophage infiltration, current scientific progress has lead to the novel idea that even cells distant from the blood stream, such as podocytes, can produce cytokines and can express molecules that are part of the co-stimulatory pathway. A strong translational research effort is currently aimed at defining the role of such molecules in cells other than lymphocytes and macrophages. Experimental animal models have recently provided evidence that some acute phase markers of inflammation such as intracellular cell adhesion molecule-1 (ICAM-1), TNF-alpha and Monocytes Chemoattractant Protein-1 (MCP-1) may have a causative role in the development of DN. Here, we review the current evidence supporting the role of inflammation in the early phases of clinical and experimental DN. A complete understanding of inflammatory pathways activated in DN may lead to the discovery of earlier and more reliable markers of DN than albuminuria and the identification of novel therapeutic targets.

Aims/hypothesis Inhibition of c-jun N-terminal kinase (JNK) favours pancreatic islet function and survival. Since two JNK isoforms are present in the pancreas (JNK1 and JNK2), we addressed their specific roles in experimental islet transplantation. Methods C57BL/6J (wild-type [WT]), Jnk1 (also known as Mapk8)−/− and Jnk2 (also known as Mapk9) −/− mice were used as donor/recipients in a syngeneic islet transplantation model. Islet cell composition, function, viability, production of cytokines and of vascular endothelial growth factor (VEGF) were also studied in vitro.Results Jnk1 −/− islets secreted more insulin in response to glucose and were more resistant to cytokine-induced cell death compared with WT and Jnk2 −/− islets (p<0.01).Cytokines reduced VEGF production in WT and Jnk2 recipients had diabetes reversal (0% vs 71% in WT, p=0.0003). Co-culture of WT islets with macrophages from each strain revealed a discordant cytokine production. Conclusions/interpretation We have shown a deleterious effect of JNK2 deficiency on islet graft outcome, most likely related to JNK1 activation, suggesting that specific JNK1 blockade may be superior to general JNK inhibition, particularly when administered to transplant recipients.