Chun-Liang Lin

MicroRNA-29a Promotion of Nephrin Acetylation Ameliorates Hyperglycemia-Induced Podocyte Dysfunction

Podocyte dysfunction is a detrimental feature in diabetic nephropathy, with loss of nephrin integrity contributing to diabetic podocytopathy. MicroRNAs (miRs) reportedly modulate the hyperglycemia-induced perturbation of renal tissue homeostasis. This study investigated whether regulation of histone deacetylase (HDAC) actions and nephrin acetylation by miR-29 contributes to podocyte homeostasis and renal function in diabetic kidneys. Hyperglycemia accelerated podocyte injury and reduced nephrin, acetylated nephrin, and miR-29a levels in primary renal glomeruli from streptozotocin-induced diabetic mice. Diabetic miR-29a transgenic mice had better nephrin levels, podocyte viability, and renal function and less glomerular fibrosis and inflammation reaction compared with diabetic wild-type mice. Overexpression of miR-29a attenuated the promotion of HDAC4 signaling, nephrin ubiquitination, and urinary nephrin excretion associated with diabetes and restored nephrin acetylation. Knockdown of miR-29a by antisense oligonucleotides promoted HDAC4 action, nephrin loss, podocyte apoptosis, and proteinuria in nondiabetic mice. In vitro, interruption of HDAC4 signaling alleviated the high glucose-induced apoptosis and inhibition of nephrin acetylation in podocyte cultures. Furthermore, HDAC4 interference increased the acetylation status of histone H3 at lysine 9 (H3K9Ac), the enrichment of H3K9Ac in miR-29a proximal promoter, and miR-29a transcription in high glucose-stressed podocytes. In conclusion, hyperglycemia impairs miR-29a signaling to intensify HDAC4 actions that contribute to podocyte protein deacetylation and degradation as well as renal dysfunction. HDAC4, via epigenetic H3K9 hypoacetylation, reduces miR-29a transcription. The renoprotective effects of miR-29a in diabetes-induced loss of podocyte integrity and renal homeostasis highlights the importance of post-translational acetylation reactions in podocyte microenvironments. Increasing miR-29a action may protect against diabetic podocytopathy.

Dickkopf-1 Promotes Hyperglycemia–Induced Accumulation of Mesangial Matrix and Renal Dysfunction

Wnt/beta-catenin signaling mediates renal fibrosis in several model systems including diabetic nephropathy. Dickkopf-1 (DKK-1) is an endogenous inhibitor of Wnt/beta-catenin signaling, but whether DKK-1 modulates diabetic nephropathy is unknown. Here, we studied whether DKK-1 participates in high glucose (HG)-induced expression of profibrotic factors and renal damage. In vitro, HG increased expression of DKK1, receptor Kremen-2, TGF-beta1, and fibronectin in mesangial cells. Loss and gain of DKK1 function modulated HG-mediated c-Jun, TGF-beta1, and fibronectin expression. DKK1 mediated HG-induced phosphorylation of Ser45-beta-catenin and reduction of nuclear beta-catenin levels, but not phosphorylation of ERK kinase. Wnt3a protein and the beta-catenin (Delta45) mutation increased nuclear beta-catenin but abrogated HG-induced DKK1 and fibronectin expression. Exogenous DKK1 antisense oligonucleotide attenuated the increase in both serum DKK1 and urinary protein excretion in streptozotocin-induced diabetic rats. Knocking down DKK1 inhibited mesangial expression of TGF-beta1 and fibronectin and reduced both the glomerular volume and deposition of mesangial matrix in diabetic kidneys. Taken together, DKK1 mediates HG-induced destabilization of beta-catenin and matrix accumulation in mesangial cells. Knocking down DKK1 prevents diabetes-induced renal dysfunction and microstructure deterioration, suggesting that inhibition of DKK1offers therapeutic potential for diabetic nephropathy.

Sustained Wnt/β-catenin signaling rescues high glucose induction of transforming growth factor-β1-mediated renal fibrosis.

Introduction:Although diabetic nephropathy is attributable to transforming growth factor-&bgr;1 (TGF-&bgr;1) overproduction in glomer-ular mesangial cells, the biological role of Wnt/&bgr;-catenin signaling in controlling high glucose-induced TGF-&bgr;1 has not yet been elucidated. Methods:This study found that sustained Wnt/&bgr;-catenin signaling was required to protect glomerular mesangial cells from high glucose induction of TGF-&bgr;1-mediated fibrosis using in vitro and in vivo diabetic models. Results:High glucose down-regulated the Wnt signaling associated with increased TGF-&bgr;1 and fibronectin messenger RNA expression in glomerular mesangial cells. Restoring Wnt4, Wnt5a and cytosolic &bgr;-catenin levels by transfecting Wnt4, Wnt5a and stable &bgr;-catenin alleviated the stimulatory effect of high glucose on c-Jun mediated TGF-&bgr;1 fibrosis. Transfection of kinase-active glycogen synthase kinase-3&bgr; (GSK-3&bgr;) also abrogated high glucose promotion of nuclear c-Jun levels, TGF-&bgr;1 and fibronectin messenger RNA expression in mesangial cells. Pharmacological modulation of GSK-3&bgr;&bgr; and &bgr;&bgr;-catenin signaling by recombinant Wnt5a or GSK-3&bgr; inhibitor (BIO or LiCl) suppressed high glucose promotion of TGF-&bgr;1-mediated fibrosis. Exogenous BIO and SB216763 alleviated TGF-&bgr;1-mediated fibrogenic expression in the kidneys of diabetic rats. Immunohistochemistry showed that GSK-3&bgr; inhibitor significantly reversed the diabetic attenuation of TGF-&bgr;1 and c-Jun coinciding with fibronectin immunoreactivity within glomeruli. Immunofluorescence demonstrated that cells within the glomeruli restored &bgr;-catenin expression after BIO and SB216763 treatment in cells within diabetic glomeruli colocalized with fragmented nuclei by 4′,6-diamidino-2-phenylindole staining. Conclusions:Sustained Wnt signaling reduced c-Jun-dependent TGF-&bgr;1-mediated fibronectin accumulation in mesangial cells. These findings suggest that modulation of Wnt signaling is a viable alternative strategy to rescue the TGF-&bgr;1-mediated fibrotic signaling pathway in diabetic renal injury.

Superoxide Destabilization of β-Catenin Augments Apoptosis of High-Glucose-Stressed Mesangial Cells

Intense mesangial cell apoptosis contributes to the pathogenesis of diabetic nephropathy. Although reactive oxygen radicals and Wnt signaling components are potent regulators that modulate renal tissue remodeling and morphogenesis, cross-talk between oxidative stress and Wnt/beta-catenin signaling in controlling high-glucose-impaired mesangial cell survival and renal function have not been tested. In this study, high glucose induced Ras and Rac1 activation, superoxide burst, and Wnt5a/beta-catenin destabilization and subsequently promoted caspase-3 and poly (ADP-ribose) polymerase cleavage and apoptosis in mesangial cell cultures. The pharmacological and genetic suppression of superoxide synthesis by superoxide dismutase and diphenyloniodium, dominant-negative Ras (S17N), and dominant-negative Rac1 (T17N) abrogated high-glucose-induced glycogen synthase kinase (GSK-3beta) activation and caspase-3 and poly (ADP-ribose) polymerase degradation. Inactivation of Ras and Racl also reversed Wnt/beta-catenin expression and survival of mesangial cells. Stabilization of beta-catenin by the transfection of stable beta-catenin (Delta45) and kinase-inactive GSK-3beta attenuated high-glucose-mediated mesangial cell apoptosis. Exogenous superoxide dismutase administration attenuated urinary protein secretion in diabetic rats and abrogated diabetes-mediated reactive oxygen radical synthesis in renal glomeruli. Immunohistological observation revealed that superoxide dismutase treatment abrogated diabetes-induced caspase-3 cleavage and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) and increased Wnt5a/beta-catenin expression in renal glomeruli. Taken together, high glucose induced oxidative stress and apoptosis in mesangial cells. The Ras and Rac1 regulation of superoxide appeared to raise apoptotic activity by activating GSK-3beta and inhibiting Wnt5a/beta-catenin signaling. Controlling oxidative stress and Wnt/beta-catenin signaling has potential for protecting renal tissue against the deleterious effect of high glucose.

Curcumin Rescues Diabetic Renal Fibrosis by Targeting Superoxide-Mediated Wnt Signaling Pathways

ABSTRACT The purposes of this study were to investigate whether curcumin can weaken diabetic nephropathy by modulating both oxidative stress and renal injury from Wnt signaling mediation. Wnt5a/&bgr;‐catenin depression and induction of superoxide synthesis are associated with high glucose (HG) induced transforming growth factor (TGF)‐&bgr;1 and fibronectin expression in mesangial cells. Curcumin resumes HG depression of Wnt/&bgr;‐catenin signaling and alleviates HG induction of superoxide, TGF‐&bgr;1 and fibronectin expression in renal mesangial cell. Exogenous curcumin alleviated urinary total proteinuria and serum superoxide level in diabetic rats. Based on laser‐captured microdissection for quantitative real‐time polymerase chain reaction, it was found that diabetes significantly increased TGF‐&bgr;1 and fibronectin expression in line with depressed Wnt5a expression. Curcumin treatment reduced the TGF‐&bgr;1 and fibronectin activation and the inhibiting effect of diabetes on Wnt5a/&bgr;‐catenin expression in renal glomeruli. Immunohistochemistry showed that curcumin treatment significantly reduced 8‐hydroxy‐2′‐deoxyguanosine, TGF‐&bgr;1 and fibronectin, and was in line with the restoration of the suppressed Wnt5a expression immunoreactivities in glomeruli of diabetic rats. Curcumin alleviated extracellular matrix accumulation in diabetic nephropathy by not only preventing the diabetes‐mediated superoxide synthesis but also resuming downregulation of Wnt/&bgr;‐catenin signaling. These findings suggest that regulation of Wnt activity by curcumin is a feasible alternative strategy to rescue diabetic renal injury.

Hyperuricemia Is an Independent Risk Factor for New Onset Micro-Albuminuria in a Middle-Aged and Elderly Population: A Prospective Cohort Study in Taiwan

Background Hyperuricemia is now regarded as a risk factor for cardiovascular disease. Micro-albuminuria is associated with increased risk for cardiovascular disease and chronic kidney disease. We hypothesized that elevated serum uric acid (UA) is associated with development of micro-albuminuria in the general population. Methodology/Principal Findings We conducted a community-based prospective cohort study. A total of 1862 subjects from southern Taiwan, all older than 40 years, were screened and 993 of these participants without micro-albuminuria were followed for 4 years. Urinary albumin-to-creatinine ratio was measured two times per year. A multiple linear regression model indicated that serum UA was independently associated with ln(ACR) after adjustment for 8 factors (age, sex, and 6 metabolic metrics) (β = 0.194, p<0.01). Logistic regression analysis indicated that each 1 mg/dL increase of UA was associated with a 1.42-fold increased risk of micro-albuminuria after adjustment for the same 8 factors (OR = 1.42, 95% CI: 1.27–1.59, p<0.01). A Cox regression model using subjects with serum UA less than 5 mg/dL as reference group indicated higher hazard ratios (HRs) only found in subjects with serum UA more than 7 mg/dL (HR = 3.54, 95% CI: 2.11–5.93, p<0.01) and not in subjects with serum UA of 5 to 7 mg/dL (HR = 1.30, 95% CI: 0.82–2.07, p = 0.15). Conclusion Hyperuricemia is significantly associated with micro-albuminuria in middle-aged and elderly males and females from a general population in Taiwan. Elevated serum UA is an independent predictor for development of micro-albuminuria in this population.

Cannabinoid receptor 1 disturbance of PPARγ2 augments hyperglycemia induction of mesangial inflammation and fibrosis in renal glomeruli.

Intensive fibrosis in the glomerular microenvironment is a prominent feature of diabetic nephropathy. Cannabinoid receptor 1 (CB1R) reportedly mediates diabetes-induced renal injury. However, studies on the molecular events underlying CB1R promotion of renal dysfunction are limited. This study is undertaken to investigate whether CB1R signaling via Ras or PPARγ pathway regulates mesangial fibrosis in diabetic kidneys. In streptozotocin-induced diabetic rats, hyperglycemia induced glomerular hypertrophy and fibrosis in association with increased IL-1β, fibronectin, and CB1R expressions and reduced PPARγ2 signaling. CB1R transgenic mice gained kidney weight, and renal glomeruli strongly displayed IL-1β and fibrotic matrices. Disruption of CB1R by antisense oligonucleotides or inverse agonist AM251 restored PPARγ2 signaling and reduced the promotional effects of hyperglycemia on the expression of fibrogenic transcription factor c-Jun, inflammation regulator SOCS3, proinflammatory cytokines, and accumulation of fibrotic matrix. PPARγ agonist rosiglitazone reduced the hyperglycemia-mediated enhancement of CB1R signaling, inflammation, and glomerular fibrosis in diabetic animals. In vitro, CB1R antagonism restored PPARγ2 action and reduced the promotional effects of high glucose on Ras, ERK, c-Jun, SOCS3 signaling, IL-1β, and fibronectin expression in renal mesangial cells. Activation of PPARγ2 reduced the high glucose-induced CB1R expression in mesangial cells. Taken together, CB1R signaling contributes to the hyperglycemia disturbance of PPARγ2 signaling and increases inflammatory cytokine secretion and fibrotic matrix deposition in renal glomeruli. CB1R mediates the hyperglycemia-induced inflammation and fibrosis in mesangial cells by regulating Ras, ERK, and PPARγ2 signaling. CB1R blockade has a therapeutic potential to reduce the deleterious actions of hyperglycemia on renal glomerular integrity.Key messageHyperglycemia increases glomerular fibrosis, inflammation, and CB1R signaling.CB1R signaling promotes fibrosis and inflammation of renal tissue.Loss of CB1R function alleviates diabetes-mediated renal deterioration.PPARγ agonist decreases CB1R expression in diabetic renal glomeruli.Ras and ERK mediated CB1R promotion of fibrosis matrix deposition in mesangial cells.

Induction of Proteinuria by Cannabinoid Receptors 1 Signaling Activation in CB1 Transgenic Mice

Abstract:Proteinuria is not only a sign of kidney damage but is also involved in the progression of renal disease as an independent pathologic factor. Although patients with mutated type 1 cannabinoid receptors (CB1) polymorphism are associated with renal microvascular damage, the biologic role of CB1 signaling in proteinuria remains uncharacterized till now. Herein, we investigate whether CB1 participates in glomerular proteinuria in CB1 transgenic mice and treatment with CB1 agonist WIN55212-2 rat, neither of which are diabetic models. The CB1 transgenic mice and rats treated with CB1 agonist WIN55212-2 had higher kidney weight and urinary protein concentrations but not blood glucose levels compared with the wild-type group. A combination of laser-capture microsdissection, quantitative reverse transcription–polymerase chain reaction, immunoblotting and immunohistochemical validation revealed that CB1 transgenic mice and rats treated with CB1 agonist WIN55212-2 had higher vascular endothelial growth factor (VEGF) expression in renal glomeruli than that of the wild-type group. Geneticorpharmacological activation of CB1 by transgenic CB1 mice or treatment with WIN55212-2 reduced nephrin expression in the renal glomeruli compared with that of the wild-type group in the glomerular mesanglium. Taken together, CB1 transgenic mice and rats treated with CB1 agonist WIN55212-2 induced proteinuria with upregulation of CB1 resulting in impaired nephrin expression, by inducing excess VEGF reaction in the renal glomeruli. Genetic and pharmacological manipulation of CB1 signaling revealed VEGF-dependent nephrin depression of glomerulopathy. Controlling CB1 activity can be used an alternative strategy for sustaining renal function in the presence of CB1 activation.

Impact of Gout on Left Atrial Function: A Prospective Speckle-Tracking Echocardiographic Study

The purpose of our study was to evaluate the left ventricular (LV) and left atrial (LA) function in patients with gout. A total of 173 patients underwent a comprehensive Doppler-echocardiography examination. Participants were divided into four groups–Stage 0: control (n = 35), Stage I: asymptomatic hyperuricemia (n = 30), Stage II: gouty arthritis without tophi (n = 58), and Stage III: tophaceous gout (n = 50). Serum uric acid levels were not significantly different between stage I, II and III. Stage III patients demonstrated a higher ratio of the transmitral and myocardial peak early diastolic velocities (E/Em) (10.50±3.18 vs. 8.58±2.07; P = 0.008), and larger maximal LA volume index (LAVi) (29.60±9.89 vs. 20.07±4.76 ml/m2; P<0.001) compared with controls. Stage III patients had decreased LV global longitudinal systolic strain (LVε) compared with controls (−20.2±3.06 vs. −21.79±2.27; P = 0.002). Stage III patients also had decreased peak atrial longitudinal strain rate during ventricular systole (ALSRsyst), peak atrial longitudinal strain rate during ventricular early diastole (ALSRearly), and peak atrial longitudinal strain rate during ventricular late diastole (ALSRlate) compared with controls (1.73±0.48 vs. 2.05±0.55 1/s, −1.44±0.53 vs. −2.07±0.84 1/s, −2.07±0.7 vs. −2.66±0.91 1/s, respectively; all P<0.005). Multiple regression analysis revealed severity of gout had an independent negative impact on LA pump function (ALSRlate). In conclusion, gout caused LV diastolic dysfunction, LV subclinical systolic dysfunction and LA reservoir, conduit, and booster pump dysfunction.

Association of Adiponectin with High-Sensitivity C-Reactive Protein and Clinical Outcomes in Peritoneal Dialysis Patients: A 3.5-Year Follow-Up Study.

Introduction Adiponectin (ADPN), one of most abundant fat-derived biologically active substances, plays an important role in anti-atherosclerotic process. There are conflicting results about the impact of ADPN on cardiovascular (CV) outcomes and mortality, particularly in patients undergoing peritoneal dialysis (PD). Moreover, the relationship between ADPN and inflammatory mediators has been seldom explored in this population. Therefore, we examined the relationship between ADPN and longitudinal high-sensitivity C-reactive protein (hs-CRP) changes and investigated whether ADPN or hs-CRP levels could predict CV outcomes and mortality in prevalent PD patients after comprehensive adjustment of possible confounders. Methods In this prospective cohort study, 78 PD patients were enrolled and followed from February 2009 to August 2012. During follow-up, CV events and all-cause mortality were recorded. Results The mean baseline ADPN value was 29.46±18.01 μg/ml and duration of PD treatment was 37.76±36.96 months. In multiple linear regression analysis, plasma ADPN levels positively correlated with high-density lipoprotein and negatively associated with hs-CRP, body mass index, D4/D0 glucose, triglyceride, and duration of PD treatment. After stratified by genders, the inverse association between baseline ADPN and hs-CRP was more significant in the female group. The hs-CRP levels were followed up annually and remained significantly lower in the high ADPN group in the first 2 years. Patients were then stratified into two groups according to the median ADPN value (23.8 μg/ml). The results of Kaplan-Meier survival analysis demonstrated less CV events and better survival in high ADPN group. On multivariate Cox regression analysis, only ADPN level (HR: 0.93, 95% CI: 0.88–0.98, p = 0.02), age and history of CV diseases were independent risk factors for future CV events. Furthermore, hs-CRP (HR: 1.11, 95% CI:1.001–1.22, p = 0.04) was identified as independent predictor of all-cause mortality. Conclusions Serum hs-CRP levels were consistently lower in the high ADPN group during 2-year follow-up. We also demonstrated the importance of ADPN and hs-CRP in predicting CV events and all-cause mortality in PD population during 3.5-year follow-up.