Rongshan Li

MicroRNA-21 in the pathogenesis of acute kidney injury

Acute kidney injury (AKI), associated with significant morbidity and mortality, is widely known to involve epithelial apoptosis, excessive inflammation, and fibrosis in response to ischemia or reperfusion injury, which results in either chronic pathological changes or death. Therefore, it is imperative that investigations are conducted in order to find effective, early diagnoses, and therapeutic targets needed to help prevent and treat AKI. However, the mechanisms modulating the pathogenesis of AKI still remain largely undetermined. MicroRNAs (miRNAs), small non-coding RNA molecules, play an important role in several fundamental biological and pathological processes by a post transcriptional regulatory function of gene expression. MicroRNA-21 (miR-21) is a recently identified, typical miRNA that is functional as a regulator known to be involved in apoptosis as well as inflammatory and fibrotic signaling pathways in AKI. As a result, miR-21 is now considered a novel biomarker when diagnosing and treating AKI. This article reviews the correlative literature and research progress regarding the roles of miR-21 in AKI.

Intermedin protects against renal ischemia-reperfusion injury by inhibition of oxidative stress

Reactive oxygen species (ROS) play a critical role in renal ischemia-reperfusion injury (IRI). Intermedin (IMD) reportedly protected against myocardial IRI via its antioxidant effects; however, its protective role in renal IRI has not been investigated. We overexpressed IMD in rat kidneys and examined how the kidneys respond to renal IRI. Eukaryotic expression plasmid encoding the rat IMD gene or control empty vector was transfected into the left kidney using an ultrasound-microbubble-mediated delivery system. This method yielded high expression of IMD in kidney cells. Renal IRI was induced by clamping the left renal artery followed by reperfusion. In response to IRI, overexpression of IMD in the kidney significantly improved renal function and pathology compared with the kidney transfected with control plasmid. We investigated the mechanisms by which IMD protects against renal IRI. We examined renal superoxide dismutase (SOD) activity and malondialdehyde (MDA) content and found SOD activity was significantly increased, while MDA level was markedly decreased in kidneys transfected with IMD, suggesting ROS production and oxidative stress were reduced by IMD overexpression. We also measured myeloperoxidase (MPO) activity, tubular cell apoptosis, and the expression of intercellular adhesion molecule-1 (ICAM-1), P-selectin, and endothelin-1 (ET-1) in the kidney. Renal MPO activity and the expression of ICAM-1, P-selectin, and ET-1 stimulated by IRI were significantly inhibited by IMD overexpression. Moreover, IMD overexpression prevented kidney cells from apoptosis caused by IRI. Our results demonstrate that overexpression of IMD in the kidney protects against renal IRI, apparently by reducing oxidative stress, consequently suppressing inflammation and vasoconstrictor production and apoptosis.

Rapamycin ameliorates IgA nephropathy via cell cycle-dependent mechanisms

IgA nephropathy is the most frequent type of glomerulonephritis worldwide. The role of cell cycle regulation in the pathogenesis of IgA nephropathy has been studied. The present study was designed to explore whether rapamycin ameliorates IgA nephropathy via cell cycle-dependent mechanisms. After establishing an IgA nephropathy model, rats were randomly divided into four groups. Coomassie Brilliant Blue was used to measure the 24-h urinary protein levels. Renal function was determined using an autoanalyzer. Proliferation was assayed via Proliferating Cell Nuclear Antigen (PCNA) immunohistochemistry. Rat mesangial cells were cultured and divided into the six groups. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) and flow cytometry were used to detect cell proliferation and the cell cycle phase. Western blotting was performed to determine cyclin E, cyclin-dependent kinase 2, p27Kip1, p70S6K/p-p70S6K, and extracellular signal-regulated kinase 1/2/p- extracellular signal-regulated kinase 1/2 protein expression. A low dose of the mammalian target of rapamycin (mTOR) inhibitor rapamycin prevented an additional increase in proteinuria, protected kidney function, and reduced IgA deposition in a model of IgA nephropathy. Rapamycin inhibited mesangial cell proliferation and arrested the cell cycle in the G1 phase. Rapamycin did not affect the expression of cyclin E and cyclin-dependent kinase 2. However, rapamycin upregulated p27Kip1 at least in part via AKT (also known as protein kinase B)/mTOR. In conclusion, rapamycin can affect cell cycle regulation to inhibit mesangial cell proliferation, thereby reduce IgA deposition, and slow the progression of IgAN.

Rapamycin Slows IgA Nephropathy Progression in the Rat

Background: IgA nephropathy (IgAN) is the most frequent glomerulonephritis worldwide. Different therapeutic approaches have been tested against IgAN. The present study was designed to explore the renoprotective potential of low-dose mammalian target of rapamycin (mTOR) inhibitor rapamycin in an IgAN rat model and the possible mechanism of action. Methods: After establishing an IgAN model, the rats were randomly divided into four groups: control, control with rapamycin treatment, IgAN model, and IgAN model with rapamycin treatment. Coomassie Brilliant Blue was utilized to measure 24-hour urinary protein levels. Hepatic and renal function was determined with an autoanalyzer. Proliferation was assayed via 5-bromo-2′-deoxyuridine incorporation. Real-time PCR and immunohistochemistry were utilized to detect the expression of α-SMA, collagen I, collagen III, TGF-β1 and platelet-derived growth factor. Western blotting and immunohistochemistry were performed to determine p-S6 protein levels. Results: Low-dose mTOR inhibitor rapamycin prevented an additional increase in proteinuria and protected kidney function in a model of IgAN. Rapamycin directly or indirectly interfered with multiple key pathways in the progression of IgAN to end-stage renal disease: (1) reduced the deposition of IgA and inhibited cell proliferation; (2) decreased the expression of fibrosis markers α-SMA and type III collagen, and (3) downregulated the expression of the profibrotic growth factors platelet-derived growth factor and TGF-β1. The expression of p-S6 was significantly elevated in IgAN rats. Conclusions: The mTOR pathway was activated in IgAN rats and the early application of low-dose mTOR inhibitor rapamycin may slow the renal injury of IgAN in rats.

A novel mechanism of NALP3 inducing ischemia reperfusion injury by activating MAPK pathway in acute renal failure.

Acute renal failure (ARF) is a rapid loss of kidney function. The reasons and mechanism by which this occurs has not been clarified so far thus creating obstacles to management of this disease. Presently, the experimental research using the accepted renal ischemia reperfusion injury (I/R injury) model represented for ARF focuses on several possible relevant factors such as reactive oxygen species, no-reflow phenomenon, apoptosis and extensive inflammatory response. The latter is much talked about currently. Some intracellular danger sensing proteins, such as the nucleotide binding domain leucine rich repeats-containing family proteins known as NLRs, adjust the inflammatory response through the formation of a multi-protein complex known as an inflammasome. The most classic family member of this complex is NALP3 confirmed to serve as a contributor to I/R injury. However, how it contributes to the pathology remains obscure. The extensive inflammatory response is considered to be modulated by the mitogen-activated protein kinases (MAPK) signaling pathway. NOD2, another family member of NLR, which shares similar structure with NALP3, indicated that it induced the activation of MAPK in response to a pathogen, thus we assumed that NALP3 performed the harmful process of I/R injury, resulting probably from the activation of the MAPK signaling pathway. If this hypothesis proves to be correct, it might benefit the management of ARF.

ROCK1 reduces mitochondrial content and irisin production in muscle suppressing adipocyte browning and impairing insulin sensitivity.

Irisin reportedly promotes the conversion of preadipocytes into “brown-like” adipocytes within subcutaneous white adipose tissue (WAT) via a mechanism that stimulates UCP-1 expression. An increase in plasma irisin has been associated with improved obesity and insulin resistance in mice with type 2 diabetes. But whether a low level of irisin stimulates the development of obesity has not been determined. In studying mice with muscle-specific constitutive ROCK1 activation (mCaROCK1), we found that irisin production was down-regulated and the mice developed obesity and insulin resistance. Therefore, we studied the effects of irisin deficiency on energy metabolism in mCaROCK1 mice. Constitutively activation of ROCK1 in muscle suppressed irisin expression in muscle resulting in a low level of irisin in circulation. Irisin deficiency reduced heat production and decreased the expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) and subcutaneous WAT. Moreover, mCaROCK1 mice also displayed impaired glucose tolerance. Notably, irisin replenishment in mCaROCK1 mice partially reversed insulin resistance and obesity and these changes were associated with increased expression of UCP1 and Pref-1 in subcutaneous WAT. These results demonstrate that irisin mediates muscle-adipose tissue communication and regulates energy and glucose homeostasis. Irisin administration can correct obesity and insulin resistance in mice.

Intermedin ameliorates IgA nephropathy by inhibition of oxidative stress and inflammation

IgA nephropathy (IgAN) is the most frequent form of glomerulonephritis worldwide. The role of oxidative stress and inflammation in the pathogenesis of IgAN has been reported. Intermedin (IMD) is a newly discovered peptide that is closely related to adrenomedullin. We have recently reported that IMD can significantly reduce renal ischemia/reperfusion injury by diminishing oxidative stress and suppressing inflammation. The present study was designed to explore whether IMD ameliorates IgAN via oxidative stress- and inflammation-dependent mechanisms. Our results showed that IMD administration resulted in the prevention of albuminuria and ameliorated renal pathomorphological changes. These findings were associated with (1) decreased renal TGF-β1 and collagen IV expression, (2) an increased SOD level and reduced MDA level, (3) the inhibition of the renal activation of NF-κB p65 and (4) the downregulation of the expression of inflammatory factors (TNF-α, MCP-1 and MMP-9) in the kidney. These results indicate that IMD in the kidney protects against IgAN by reducing oxidative stress and suppressing inflammation.

The Akt/mTOR/p70S6K pathway is activated in IgA nephropathy and rapamycin may represent a viable treatment option☆

IgA nephropathy (IgAN) is one of the most frequent forms of glomerulonephritis, and 20 to 40% of patients progress to end-stage renal disease (ESRD) within 20 years of disease onset. However, little is known about the molecular pathways involved in the altered physiology of mesangial cells during IgAN progression. This study was designed to explore the role of mTOR signaling and the potential of targeted rapamycin therapy in a rat model of IgAN. After establishing an IgA nephropathy model, the rats were randomly divided into four groups: control, control+rapamycin, IgAN and IgA+rapamycin. Western blotting and immunohistochemistry were performed to determine phospho-Akt, p70S6K and S6 protein levels. Coomassie Brilliant Blue was utilized to measure 24-h urinary protein levels. The biochemical parameters of the rats were analyzed with an autoanalyzer. To evaluate IgA deposition in the glomeruli, FITC-conjugated goat anti-rat IgA antibody was used for direct immunofluorescence. Cellular proliferation and the mesangial matrix in glomeruli were assayed via histological and morphometric procedures. Our results showed that p70S6K, S6 and Akt phosphorylation were significantly upregulated in IgAN rats, and rapamycin effectively inhibited p70S6K and S6 phosphorylation. A low dose of the mTOR inhibitor rapamycin reduced proteinuria, inhibited IgA deposition, and protected kidney function in an IgAN rat model. Low-dose rapamycin treatment corresponded to significantly lower cellular proliferation rates and a decreased mesangial matrix in the glomeruli. In conclusion, the Akt/mTOR/p70S6K pathway was activated in IgAN, and our findings suggested that rapamycin may represent a viable option for the treatment of IgAN.

Intermedin/adrenomedullin 2 protects against tubular cell hypoxia‐reoxygenation injury in vitro by promoting cell proliferation and upregulating cyclin D1 expression

Intermedin/adrenomedullin 2 (IMD/ADM2) is a newly discovered peptide closely related to adrenomedullin. We recently reported that IMD/ADM2 gene transfer could significantly reduce renal ischaemia/reperfusion injury. In this study, we evaluated the effect of IMD/ADM2 on cell proliferation and regeneration in a cultured rat renal tubular epithelial cell line (NRK‐52E) of hypoxia‐reoxygenation (H/R) injury.

Mitogen-activated protein kinase mediates mevalonate-stimulated human mesangial cell proliferation

The metabolic products of intracellular mevalonate (MVA) are important for the growth of eukaryotic cells. These products include cholesterol and several non-sterol isoprenoids. It has been reported that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors ameliorate glomerular injury in several experimental models of progressive glomerular disease by inhibiting the production of MVA and its metabolites. However, the mechanisms by which MVA stimulates the growth of human mesangial cells (HMCs) remain to be elucidated. To investigate the role of MVA in HMC proliferation, apoptosis, cell cycle and accumulation of extracellular matrix (ECM), the effects of MVA on HMCs at different durations and at various doses were evaluated. To examine the mechanisms of the effects of MVA on HMCs, the cells were treated with MVA, with or without PD98059, an extracellular signal-regulated kinase (ERK) inhibitor, SP600125, c-Jun NH2-teminal kinase (JNK) inhibitor, or SB203580, a P38 mitogen-activated protein kinase (MAPK) inhibitor. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reduction assay was used to measure the proliferation of the HMCs, a flow cytometric assay was used to assess the proliferative index, and an ELISA was performed to determine the expression of transforming growth factor-β1 (TGF-β1), Type IV and Type I collagen (Col-IV and Col-I). The expression of B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), phosphorylated (p)-ERK1/2, p-JNK and p-p38 were also examined using western blot analysis. MVA significantly stimulated HMC proliferation and markedly increased the secretion of TGF-β1 and expression levels of Col-IV and Col-I. In addition, treatment with MVA significantly upregulated the expression of Bcl-2 and suppressed the expression of Bax in the HMCs. These responses were partially inhibited by the addition of inhibitors of ERK or JNK, however, they were not inhibited by the p38 MAPK inhibitor. These results demonstrated that MVA promoted HMC proliferation and ECM protein expression, which were associated with an increase in the expression of TGF-β1 and the inhibition of apoptosis. These effects were mediated, at least in part, by the JNK and ERK pathways.