Smad3 deficiency promotes beta cell proliferation and function in db/db mice via restoring Pax6 expression.

Rationale: Transforming Growth Factor-beta (TGF-ß) /Smad3 signaling has been shown to play important roles in fibrotic and inflammatory diseases, but its role in beta cell function and type 2 diabetes is unknown. Methods: The role of Smad3 in beta cell function under type 2 diabetes condition was investigated by genetically deleting Smad3 from db/db mice. Phenotypic changes of pancreatic islets and beta cell function were compared between Smad3 knockout db/db (Smad3KO-db/db) mice and Smad3 wild-type db/db (Smad3WT-db/db) mice, and other littermate controls. Islet-specific RNA-sequencing was performed to identify Smad3-dependent differentially expressed genes associated with type 2 diabetes. In vitro beta cell proliferation assay and insulin secretion assay were carried out to validate the mechanism by which Smad3 regulates beta cell proliferation and function. Results: The results showed that Smad3 deficiency completely protected against diabetes-associated beta cell loss and dysfunction in db/db mice. By islet-specific RNA-sequencing, we identified 8160 Smad3-dependent differentially expressed genes associated with type 2 diabetes, where Smad3 deficiency markedly prevented the down-regulation of those genes. Mechanistically, Smad3 deficiency preserved the expression of beta cell development mediator Pax6 in islet, thereby enhancing beta cell proliferation and function in db/db mice in vivo and in Min6 cells in vitro. Conclusions: Taken together, we discovered a pathogenic role of Smad3 in beta cell loss and dysfunction via targeting the protective Pax6. Thus, Smad3 may represent as a novel therapeutic target for type 2 diabetes prevention and treatment.

Deletion of Smad3 prevents renal fibrosis and inflammation in type 2 diabetic nephropathy.

BACKGROUND: Transforming growth factor (TGF)-ß/Smad3 signaling is highly activated in kidneys of patients with type 2 diabetic nephropathy (T2DN), however, the precise role of Smad3 in the pathogenesis of diabetic nephropathy remains unclear. METHODS: Smad3 knockout (KO)-db/db mice were generated by intercrossing of male and female double-heterozygous Smad3+/- db/m mice. Renal functions including urinary albumin excretion and serum creatinine were determined. Renal histological injury including renal fibrosis and inflammation were examined by periodic acid Schiff (PAS), periodic acid-silver methenamine (PASM), and immunohistochemistry (IHC) staining. RESULTS: Smad3 knockout (KO)-db/db mice were protected from the development of diabetic kidney injury, characterized by the normal levels of urinary albumin excretion and serum creatinine without any evidence for renal fibrosis and inflammation. In contrast, Smad3 wild-type (WT) db/db and Smad3+/- db/db mice developed progressively decline in renal function over the 12 to 32-week time course, including increased microalbuminuria and elevated levels of serum creatinine. Pathologically, Smad3 WT db/db and Smad3+/- db/db mice exhibited a marked deposition of collagen-I (colI), collagen-IV(col-IV), and an increased infiltration of F4/80+ macrophages in kidney. Mechanistically, Smad3 deficiency decreased the lncRNA Erbb4-IR transcription, while increased miR-29b transcription and therefore protected the kidney from progressive renal injury in db/db mice. CONCLUSION: Results from this study imply that Smad3 may represent as a novel and effective therapeutic target for T2DN.

Urinary proteins induce lysosomal membrane permeabilization and lysosomal dysfunction in renal tubular epithelial cells.

Lysosomal membrane permeabilization (LMP) has been shown to cause the release of cathepsins and other hydrolases from the lysosomal lumen to the cytosol and initiate a cell death pathway. Whether proteinuria triggers LMP in renal tubular epithelial cells (TECs) to accelerate the progression of renal tubulointerstitial injury remains unclear. In the present study, we evaluated TEC injury as well as changes in lysosomal number, volume, activity, and membrane integrity after urinary protein overload in vivo and in vitro. Our results revealed that neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels were significantly increased in the urine of patients with minimal change nephrotic syndrome (MCNS) and the culture supernatant of HK-2 cells treated by urinary proteins extracted from MCNS patients. Urinary protein overload also induced apoptotic cell death in HK-2 cells. Importantly, we found that lysosomal volume and number were markedly increased in TECs of patients with MCNS and HK-2 cells overloaded with urinary proteins. However, lysosome function, as assessed by proteolytic degradation of DQ-ovalbumin and cathepsin-B and cathepsin-L activities, was decreased in HK-2 cells overloaded with urinary proteins. Furthermore, urinary protein overload led to a diffuse cytoplasmic immunostaining pattern of cathepsin-B and irregular immunostaining of lysosome-associated membrane protein-1, accompanying a reduction in intracellular acidic components, which could be improved by pretreatment with antioxidant. Taken together, our results indicate that overloading of urinary proteins caused LMP and lysosomal dysfunction at least partly via oxidative stress in TECs.

Continuation of immunosuppressive treatment may be necessary in IgA nephropathy patients with remission of proteinuria: Evaluation by repeat renal biopsy.

The present study aimed to evaluate the effects of an individualized, low-dose multi-drug immunosuppressive regimen for the treatment of immunoglobulin A nephropathy (IgAN). A preliminary investigation of the course of IgAN following immunosuppressive treatment was conducted based on repeat renal biopsies. Clinical and pathological data of 17 patients with IgAN who received repeat renal biopsies were analyzed retrospectively. In addition to basic treatment, 16 patients regularly received an individualized low-dose immunosuppressive regimen according to their clinical manifestations and pathological patterns following the first biopsy. Clinical parameters, including 24-h urinary protein excretion and levels of serum albumin, uric acid and total cholesterol were collected. Glomerular deposits of IgA and C3, as well as the activity and chronicity indexes of renal lesions were evaluated by semi-quantitative methods. The 24-h urinary protein excretion of the patients decreased significantly from the first biopsy (2.53±2.17 g/day) to the repeated biopsy (0.26±0.55 g/day) (P<0.001). Deposits of IgA and C3 in the glomerulus were persistent, but were reduced in quantity at the second biopsy. Although active renal lesions were observed in the majority of patients, the activity index decreased significantly from 3.18±1.33 prior to therapy to 2.47±0.80 following therapy (P<0.05), while the chronicity index did not change significantly (2.59±2.00 versus 2.76±1.89, respectively). The individualized, low-dose multi-drug immunosuppressive regimen used in the present study significantly minimized proteinuria, stabilized renal function and alleviated histological lesions in patients with IgAN without causing overt adverse effects during the short-term follow-up. In addition to proteinuria, renal pathological changes should be appraised when considering the withdrawal of immunosuppressants from IgAN treatment.