Characterization of diabetic nephropathy in CaM kinase IIα (Thr286Asp) transgenic mice

miR-182-5p Inhibition Ameliorates Ischemic Acute Kidney Injury

Acute kidney injury (AKI) remains a major clinical event with high mortality rates. We previously identified renal miR-182 as the main driver of post-transplantation AKI. Therefore, we tested the causal inference of miR-182 by inhibiting its renal expression in vivo. In 45 rats AKI was induced by right nephrectomy and contralateral clamping of the renal pedicle for 40 minutes. Systemically administered antisense oligonucleotide (ASO) inhibited miR-182 in the kidneys up to 96 hours. The maximum creatinine elevation was on day 2 after injury (mg/dL; median and interquartile range): ASO 2.5mg/kg: 1.9 (1.3; 3.2), ASO 25mg/kg: 2.8 (0.7; 5.0), mismatch oligonucleotide (MM) 25mg/kg: 5.7 (5,0; 5.8), saline: 4.4 (3.5; 5.8) (P = 0.016, analysis of variance). Blinded semiquantitative histologic evaluation of renal biopsies showed better preserved morphology in both ASO groups than saline- and MM-treated kidneys (median and interquartile range of overall injury scores): ASO both concentrations 1 (1, 1), saline 3 (3, 3) and MM 3 (3, 3) (P< 0.001, analysis of variance). ASO facilitated cell proliferation, metabolism, and angiogenesis on a genome-wide level. ASO when applied in normothermic kidney machine perfusion reduced renal miR-182 expression by more than two magnitudes. In summary, we showed that in vivo inhibition of miR-182 by ASO improved kidney function and morphology after AKI. This technique may be applicable to reduce the high rate of AKI in the human renal transplantation setting.

CaMKII as a pathological mediator of ER stress, oxidative stress, and mitochondrial dysfunction in a murine model of nephronophthisis

Polycystic kidney diseases (PKDs) are genetic diseases characterized by renal cyst formation with increased cell proliferation, apoptosis, and transition to a secretory phenotype at the expense of terminal differentiation. Despite recent progress in understanding PKD pathogenesis and the emergence of potential therapies, the key molecular mechanisms promoting cystogenesis are not well understood. Here, we demonstrate that mechanisms including endoplasmic reticulum stress, oxidative damage, and compromised mitochondrial function all contribute to nephronophthisis-associated PKD. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is emerging as a critical mediator of these cellular processes. Therefore, we reasoned that pharmacological targeting of CaMKII may translate into effective inhibition of PKD in jck mice. Our data demonstrate that CaMKII is activated within cystic kidney epithelia in jck mice. Blockade of CaMKII with a selective inhibitor results in effective inhibition of PKD in jck mice. Mechanistic experiments in vitro and in vivo demonstrated that CaMKII inhibition relieves endoplasmic reticulum stress and oxidative damage and improves mitochondrial integrity and membrane potential. Taken together, our data support CaMKII inhibition as a new and effective therapeutic avenue for the treatment of cystic diseases.

Osteopontin plays a critical role in interstitial fibrosis but not glomerular sclerosis in diabetic nephropathy

BACKGROUND/AIMS

Osteopontin (OPN) has been implicated in the pathology of several renal conditions. The aim of this study was to clarify the roles of OPN in diabetic nephropathy.

METHODS

Diabetes mellitus (DM) was induced in wild-type (WT) and OPN knockout (KO) mice by injecting streptozotocin. The mice were killed 20 weeks after induction of DM and their kidneys removed.

RESULTS

Renal mRNA expression of OPN was increased in WT-DM mice compared to WT-sham mice. Immunohistochemistry showed high levels of OPN expression in the proximal tubules of WT-DM mice. Kidney weight and urinary albumin excretion increased to similar levels in the WT-DM and KO-DM mice. Interstitial fibrosis was increased in WT-DM mice compared to KO-DM mice. However, there were no differences in the degree of mesangial expansion or glomerular hypertrophy between the two groups. F4/80-positive cells (macrophages) and FSP-1-positive cells (fibroblasts) showed significantly higher infiltration in WT-DM mice than in KO-DM mice. Renal mRNA expression of NADPH oxidase subunits and urinary 8-isoprostane excretion were also increased in WT-DM mice.

CONCLUSIONS

These results indicated that OPN is a key molecule that induces interstitial fibrosis in the diabetic kidney, but does not induce glomerular sclerosis.

Deletion of platelet-derived growth factor receptor-β improves diabetic nephropathy in Ca²⁺/calmodulin-dependent protein kinase IIα (Thr286Asp) transgenic mice

AIMS/HYPOTHESIS

The activation of platelet-derived growth factor receptor-β (PDGFR-β) signalling is increased in the glomeruli and tubules of diabetic animals. In this study, we examined the role of PDGFR-β signalling during the development of diabetic nephropathy.

METHODS

We recently generated pancreatic beta cell-specific Ca(2+)/calmodulin-dependent protein kinase IIα (Thr286Asp) transgenic mice (CaMKIIα mice), which show very high plasma glucose levels up to 55.5 mmol/l and exhibit the features of diabetic nephropathy. These mice were crossed with conditional knockout mice in which Pdgfr-β (also known as Pdgfrb) was deleted postnatally. The effect of the deletion of the Pdgfr-β gene on diabetic nephropathy in CaMKIIα mice was evaluated at 10 and 16 weeks of age.

RESULTS

The plasma glucose concentrations and HbA(1c) levels were elevated in the CaMKIIα mice from 4 weeks of age. Variables indicative of diabetic nephropathy, such as an increased urinary albumin/creatinine ratio, kidney weight/body weight ratio and mesangial area/glomerular area ratio, were observed at 16 weeks of age. The postnatal deletion of the Pdgfr-β gene significantly decreased the urinary albumin/creatinine ratio and mesangial area/glomerular area ratio without affecting the plasma glucose concentration. Furthermore, the increased oxidative stress in the kidneys of the CaMKIIα mice as shown by the increased urinary 8-hydroxydeoxyguanosine (8-OHdG) excretion and the increased expression of NAD(P)H oxidase 4 (NOX4), glutathione peroxidase 1 (GPX1) and manganese superoxide dismutase (MnSOD) was decreased by Pdgfr-β gene deletion.

CONCLUSIONS/INTERPRETATION

The activation of PDGFR-β signalling contributes to the progress of diabetic nephropathy, with an increase in oxidative stress and mesangial expansion in CaMKIIα mice.