Dimethylamine enhances platelet hyperactivity in chronic kidney disease model.

Chronic kidney disease (CKD) remains a major health threat worldwide which is associated with elevated blood level of dimethylamine (DMA) and unbalanced platelet functions. Dimethylamine, a simple aliphatic amine, is abundantly found in human urine as well as other body fluids like plasma. However, the relation between dimethylamine and platelet activation is unclear. This study aims to unravel the mechanism of DMA and platelet function in chronic kidney disease. Through in vitro platelet characterization assay and in vivo CKD mouse model, the level of DMA, platelet activity and renal function were assessed by established methods. PKCδ and its downstream kinase MEK1/2 were examined by immunoblotting analysis of human platelet extract. Rescue experiments with PKCδ inhibitor or choline deficient diet were also conducted. DMA level in plasma of mouse CKD model was elevated along with enhanced platelet activation and comprised renal function. DMA can activate platelet in vitro and in vivo. Inhibition of PKCδ could antagonize the effect of DMA on platelet activation. When choline as the dietary source of DMA was deprived from CKD mouse, the level DMA was reduced and platelet activation was attenuated. Our results demonstrate that dimethylamine could enhance platelet activation in CKD model, potentially through activation of PKCδ.

Effects of chronic alcohol exposure on ischemia-reperfusion-induced acute kidney injury in mice: the role of ß-arrestin 2 and glycogen synthase kinase 3.

Little is known about the effects of chronic alcohol intake on the outcome of acute kidney injury (AKI). Hence, we examined the effects of chronic alcohol intake on the development of renal fibrosis following AKI in an animal model of bilateral renal ischemia-reperfusion (IR) injury. We first found that chronic alcohol exposure exacerbated bilateral IR-induced renal fibrosis and renal function impairment. This phenomenon was associated with increased bilateral IR-induced extracellular matrix deposition and an increased myofibroblast population as well as increased bilateral IR-induced expression of fibrosis-related genes in the kidneys. To explore the mechanisms underlying this phenomenon, we showed that chronic alcohol exposure enhanced ß-arrestin 2 (Arrb2) expression and Akt and glycogen synthase kinase-3 (GSK3)ß activation in the kidneys. Importantly, pharmacological GSK3 inhibition alleviated bilateral IR-induced renal fibrosis and renal function impairment. Furthermore, we demonstrated that Arrb2-/- mice exhibited resistance to IR-induced renal fibrosis and renal function impairment following chronic alcohol exposure, and these effects were associated with attenuated GSK3ß activation in the kidneys. Taken together, our results suggest that chronic alcohol exposure may potentiate AKI via ß-arrestin 2/Akt/GSK3ß-mediated signaling in the kidney.

Loss of miR-125b contributes to upregulation of CYP24 in uraemic rats.

AIM: Abnormal upregulation of CYP24 contributes to vitamin D insufficiency and resistance to vitamin D therapy in chronic kidney disease (CKD), because human CYP24 is a key enzyme involved in the inactivation of 1a,25-dihydroxyvitamin D3 (1a,25(OH)2D3; calcitriol) and 1,25(OH)2D3. There are multiple mechanisms regulating CYP24 in a variety of types of tissues and diseases. An increasing body of evidence suggests that microRNA-125b (miR-125b) plays an important role in post-transcriptional regulation of CYP24 mRNA. METHODS: We sought to test hypothesis that abnormal elevation of CYP24 in CKD is a consequence of loss of miR-125b in CKD in a uraemia rat model. RESULTS: We found that expression of miR-125b was significantly inhibited in uraemic rats coupled with increased CYP24 at both protein and mRNA levels compared with normal controls. In NRK-52 kidney cells, we further found that miR-125b antagomirs increased CYP24 but miR-125b mimics decreased CYP24, and luciferase assay confirmed that CYP24 is a direct target of miR-125b. Vitamin D status exerted no significant effects on expression of both miR-125b and CYP24 in uraemic rats. CONCLUSION: These results suggest that modulation of miR-125b may be used for treatment of Vitamin D insufficiency in CKD.

Upregulation of nuclear factor-κB activity mediates CYP24 expression and reactive oxygen species production in indoxyl sulfate-induced chronic kidney disease.

AIM: Chronic kidney disease (CKD) is associated with an inflammation-mediated process, and the vitamin D (3) catabolizing enzyme, CYP24, is frequently overexpressed in CKD, where it may play a crucial role in kidney disease. METHODS: Herein, in this study, we investigated CYP24, reactive oxygen species (ROS), and inflammatory responses in an indoxyl sulfate (IS)-induced CKD model to elucidate the role of CYP24 in CKD. RESULTS: Our results showed that IS upregulates proinflammatory cytokine, CYP24 and nuclear factor-κB (NF-κB) expression in human renal proximal tubule epithelial cells. In addition, IS treatment increased ROS production and simultaneously upregulated CYP24 expression and NF-κB translocation. Moreover, the IS-induced upregulation of CYP24 expression was alleviated by an inhibitor of NF-κB, as well as a siRNA specific to NF-κB p65. Furthermore, the renal cortex of DN (Dahl salt-resistant normotensive) + IS, DH (Dahl salt-sensitive hypertensive), and DH + IS rats showed increased expression of NF-κB p65, CYP24, 8-hydroxydeoxyguanosine (8-OHdG), a marker of ROS and macrophage infiltration compared with DN rats. CONCLUSIONS: These results provide evidence that administration of IS in human renal tubular epithelial cells upregulates NF-κB, which leads to increase CYP24 expression and ROS production. They also suggest that suppressing NF-κB signalling is promising for the development into a strategy for CKD treatment.