Liping Xiong

Atg5-mediated autophagy deficiency in proximal tubules promotes cell cycle G2/M arrest and renal fibrosis

ABSTRACT Macroautophagy/autophagy protects against cellular stress. Renal sublethal injury-triggered tubular epithelial cell cycle arrest at G2/M is associated with interstitial fibrosis. However, the role of autophagy in renal fibrosis is elusive. Here, we hypothesized that autophagy activity in tubular epithelial cells is pivotal for inhibition of cell cycle G2/M arrest and subsequent fibrogenic response. In both renal epithelial cells stimulated by angiotensin II (AGT II) and the murine kidney after unilateral ureteral obstruction (UUO), we observed that occurrence of autophagy preceded increased production of COL1 (collagen, type I). Pharmacological enhancement of autophagy by rapamycin suppressed COL1 accumulation and renal fibrosis. In contrast, genetic ablation of autophagy by proximal tubular epithelial cell-specific deletion of Atg5, with reduction of the LC3-II protein level and degradation of SQSTM1/p62, showed marked cell cycle arrest at the G2/M phase, robust COL1 deposition, and severe interstitial fibrosis in a UUO model, as compared with wild-type mice. In vitro, AGT II exposure triggered autophagy preferentially in the G1/S phase, and increased COL1 expression in the G2/M phase in renal epithelial cells. Stimulation of Atg5-deficient primary proximal tubular cells with AGT II also resulted in elevated G2/M arrest and COL1 production. Pharmacological or genetic inhibition of autophagy increased AGT II-mediated G2/M arrest. Enhanced expression of ATG5, but not the autophagy-deficient ATG5 mutant K130R, rescued the G2/M arrest, suggesting the regulation of cell cycle progression by ATG5 is autophagy dependent. In conclusion, Atg5-mediated autophagy in proximal epithelial cells is a critical host-defense mechanism that prevents renal fibrosis by blocking G2/M arrest.

Serum Potassium Levels and Its Variability in Incident Peritoneal Dialysis Patients: Associations with Mortality

Background Abnormal serum potassium is associated with an increased risk of mortality in dialysis patients. However, the impacts of serum potassium levels on short- and long-term mortality and association of potassium variability with death in peritoneal dialysis (PD) patients are uncertain. Methods We examined mortality-predictability of serum potassium at baseline and its variability in PD patients treated in our center January 2006 through December 2010 with follow-up through December 2012. The hazard ratios (HRs) were used to assess the relationship between baseline potassium levels and short-term (≤1 year) as well as long-term (>1 year) survival. Variability of serum potassium was defined as the coefficient of variation of serum potassium (CVSP) during the first year of PD. Results A total of 886 incident PD patients were enrolled, with 248 patients (27.9%) presented hypokalemia (serum potassium <3.5 mEq/L). During a median follow-up of 31 months (range: 0.5–81.0 months), adjusted all-cause mortality hazard ratio (HR) and 95% confidence interval (CI) for baseline serum potassium of <3.0, 3.0 to <3.5, 3.5 to <4.0, 4.5 to <5.0, and ≥5.0 mEq/L, compared with 4.0 to <4.5 (reference), were 1.79 (1.02–3.14), 1.15 (0.72–1.86), 1.31 (0.82–2.08), 1.33 (0.71–2.48), 1.28 (0.53–3.10), respectively. The increased risk of lower potassium with mortality was evident during the first year of follow-up, but vanished thereafter. Adjusted all-cause mortality HR for CVSP increments of 7.5% to <12.0%; 12.0% to <16.7% and ≥16.7%, compared with <7.5% (reference), were 1.35 (0.67–2.71), 2.00 (1.05–3.83) and 2.18 (1.18–4.05), respectively. Similar association was found between serum potassium levels and its variability and cardiovascular mortality. Conclusions A lower serum potassium level was associated with all-cause and cardiovascular mortality during the first year of follow-up in incident PD patients. In addition, higher variability of serum potassium levels conferred an increased risk of death in this population.

The potential role of HMGB1 release in peritoneal dialysis-related peritonitis.

High mobility group box 1 (HMGB1), a DNA-binding nuclear protein, has been implicated as an endogenous danger signal in the pathogenesis of infection diseases. However, the potential role and source of HMGB1 in the peritoneal dialysis (PD) effluence of patients with peritonitis are unknown. First, to evaluate HMDB1 levels in peritoneal dialysis effluence (PDE), a total of 61 PD patients were enrolled in this study, including 42 patients with peritonitis and 19 without peritonitis. Demographic characteristics, symptoms, physical examination findings and laboratory parameters were recorded. HMGB1 levels in PDE were determined by Western blot and ELISA. The concentrations of TNF-α and IL-6 in PDE were quantified by ELISA. By animal model, inhibition of HMGB1 with glycyrrhizin was performed to determine the effects of HMGB1 in LPS-induced mice peritonitis. In vitro, a human peritoneal mesothelial cell line (HMrSV5) was stimulated with lipopolysaccharide (LPS), HMGB1 extracellular content in the culture media and intracellular distribution in various cellular fractions were analyzed by Western blot or immunofluorescence. The results showed that the levels of HMGB1 in PDE were higher in patients with peritonitis than those in controls, and gradually declined during the period of effective antibiotic treatments. Furthermore, the levels of HMGB1 in PDE were positively correlated with white blood cells (WBCs) count, TNF-α and IL-6 levels. However, pretreatment with glycyrrhizin attenuated LPS-induced acute peritoneal inflammation and dysfunction in mice. In cultured HMrSV5 cells, LPS actively induced HMGB1 nuclear-cytoplasmic translocation and release in a time and dose-dependent fashion. Moreover, cytosolic HMGB1 was located in lysosomes and secreted via a lysosome-mediated secretory pathway following LPS stimulation. Our study demonstrates that elevated HMGB1 levels in PDE during PD-related peritonitis, at least partially, from peritoneal mesothelial cells, which may be involved in the process of PD-related peritonitis and play a critical role in acute peritoneal dysfunction.

Higher serum triglyceride to high-density lipoprotein cholesterol ratio was associated with increased cardiovascular mortality in female patients on peritoneal dialysis

BACKGROUND AND AIMS High serum triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) ratio has been found to be an independent predictor for cardiovascular events in the general population. We aimed to evaluate whether a high TG/HDL-C ratio was associated with an increased risk of mortality in patients on continuous ambulatory peritoneal dialysis (CAPD). METHODS AND RESULTS In this single-center retrospective cohort study, 1170 incident patients on peritoneal dialysis (PD) from 1 January 2007 to 31 December 2011 were recruited and followed up until 31 December 31 2013. The mean age was 47.4 ± 15.2 years, and 24.7% were diabetic. During a median of the 34.5-month follow-up period, 213 (18.2%) deaths occurred, 121 of which (56.8%) were caused by cardiovascular disease (CVD). The serum median TG/HDL-C ratio at baseline was 2.57 (range: 0.06-39.39). On multivariate Cox regression analysis, the highest quartile of the TG/HDL-C ratio (≥4.19) was associated with increased risk of all-cause mortality (hazard ratio (HR) 1.98, 95% confidence interval (CI), 1.17-3.36; P = 0.011) and CVD mortality (HR 2.28, 95% CI, 1.16-4.47; P = 0.017). For female patients, each one-unit higher baseline TG/HDL-C was associated with 13% (95% CI 1.06-1.22; P = 0.001) increased risk of CVD mortality, whereas such an association was not observed for male patients, (HR 1.00, 95% CI 0.92-1.08; P = 0.977). CONCLUSIONS A higher serum TG/HDL-C ratio was associated with an increased risk of all-cause and CVD mortality in PD patients. Moreover, the increased risk of CVD mortality was significantly higher in female than male PD patients.

Association of Pulmonary Hypertension with Mortality in Incident Peritoneal Dialysis Patients

♦ Background: The prognostic value of pulmonary hypertension at the start of peritoneal dialysis (PD) in patient survival is unclear. ♦ Methods: We conducted a retrospective study of incident patients who initiated PD therapy from January 2007 to December 2011, and followed up through June 2013. Pulmonary hypertension was defined as an estimated systolic pulmonary artery pressure (PAP) of ≥ 35 mm Hg using echocardiography. Clinical parameters and laboratory findings were compared between patients with and without pulmonary hypertension and a logistic regression model was elaborated. Patient outcomes (all-cause and cardiovascular mortality) were recorded during follow-up. Survival curves were constructed by the Kaplan-Meier method, and the influences of pulmonary hypertension on outcomes were analyzed by Cox regression models. ♦ Results: Pulmonary hypertension was prevalent in 99 (16.0%) of the 618 patients studied. The independent risk factors for pulmonary hypertension were female (odds ratio [OR] = 2.12; 95% confidence interval [CI]: 1.29 – 3.46), left atrial diameter (OR = 1.15; 95% CI: 1.10 – 1.20), left ventricular ejection fraction (OR = 0.97; 95% CI: 0.95 – 0.99), and serum sodium (OR = 0.94; 95% CI: 0.89 – 0.99). Over a median follow-up of 29.4 months, 93 patients (15.0%) died, 59.1% of them due to cardiovascular disease. Kaplan-Meier survival analysis showed that patients with pulmonary hypertension had worse overall rates of survival and cardiovascular death-free survival than those without pulmonary hypertension. After multivariate adjustment, pulmonary hypertension was independently associated with increased risk for both all-cause and cardiovascular mortality, with hazard ratios (HRs) of 2.10 (95% CI: 1.35 – 3.27) and 2.60 (95% CI: 1.48 – 4.56), respectively. ♦ Conclusions: The prevalence of pulmonary hypertension at the start of PD was common and associated with increased risk of both all-cause and cardiovascular mortality in incident PD patients.

Heat shock protein 72 suppresses apoptosis by increasing the stability of X-linked inhibitor of apoptosis protein in renal ischemia/reperfusion injury

X-linked inhibitor of apoptosis protein (XIAP) negatively regulates apoptotic pathways at a post-mitochondrial level. XIAP functions by directly binding and inhibiting activation of specific caspases. Upon apoptotic stimuli, mitochondrial second mitochondria-derived activator of caspases (Smac)/direct IAP-binding protein with low PI (DIABLO) is released into the cytosol, which results in displacement of XIAP from caspases. Heat shock protein 72 (HSP72), an anti-apoptotic protein, prevents mitochondrial injury resulting from acute renal ischemia/reperfusion (I/R), its role in Smac/DIABLO and XIAP signaling remains to be elucidated. In the present study, the hypothesis that HSP72 prevents XIAP degradation in vivo and in vitro was assessed. To this purpose, a rat model of I/R injury was used to investigate the renoprotective role of HSP72 by treatment with geranylgeranylacetone (GGA), a specific inducer of HSP72. The mechanism of the cytoprotective properties of HSP72 was also investigated in vitro using adenovirus-mediated overexpression of HSP72 in adenosine triphosphate (ATP)-depleted human kidney 2 (HK-2) cells. Pre-conditioning rats with GGA attenuated renal tubular cell damage, reduced cell apoptosis, preserved XIAP protein content and improved renal function following I/R injury. An in vitro study was performed in which cells were transiently exposed to 5 mM sodium cyanide in a glucose-free medium in order to induce apoptosis. Compared with the control, overexpression of HSP72 inhibited Smac/DIABLO release from the mitochondria and increased levels of XIAP and pro-caspase 3 in ATP-depleted HK-2 cells. In addition, HSP72 interacted with Smac/DIABLO. The present data demonstrates that HSP72 preserves renal function in I/R injury through its anti-apoptotic effects, which act by suppressing mitochondrial Smac/DIABLO release and preserving XIAP protein content.

Association of baseline, longitudinal serum high-sensitive C-reactive protein and its change with mortality in peritoneal dialysis patients

BackgroundThe prognostic values of baseline, longitudinal high-sensitivity C-reactive protein (hs-CRP) and its change over time on mortality in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) remain uncertain.MethodsWe retrospectively studied 1228 consecutive CAPD patients from 2007 to 2012, and followed up through December 2014. Cox regression models were performed to assess the association of hs-CRP on outcomes using serum hs-CRP levels as: (1) stratified by tertile of baseline or longitudinal hs-CRP levels; (2) baseline or longitudinal hs-CRP levels as continuous variables; and (3) categorized by tertile of slopes of hs-CRP change per year for each subject.ResultsHigher baseline hs-CRP levels were not associated with clinical outcomes after adjustment for potential confounders. However, patients with the upper tertile of longitudinal hs-CRP had a nearly twice-fold increased risk of both all-cause and cardiovascular mortality [adjusted hazard ratio (HR) 1.77; (95% CI 1.16–2.70) and 2.08 (1.17–3.71), respectively], as compared with those with lower tertile. Results were similar when baseline or longitudinal hs-CRP was assessed as continuous variable. Additionally, the risk of all-cause and cardiovascular mortality in patients with increased trend in serum hs-CRP levels over time (tertile 3) was significantly higher [adjusted HR 2.48 (1.58–3.87) and 1.99 (1.11–3.56), respectively] when compared to those with relatively stable hs-CRP levels during follow-up period. These associations persisted after excluding subjects with less than 1-year follow up.ConclusionsHigher longitudinal serum hs-CRP levels and its elevated trend over time, but not baseline levels were predictive of worse prognosis among CAPD patients.

Faster Transport Status and Mortality in Anuric Patients Undergoing Continuous Ambulatory Peritoneal Dialysis

Background: There are limited data regarding the relationship between transport status and mortality in anuric continuous ambulatory peritoneal dialysis (CAPD) patients. Methods: According to the dialysate to plasma creatinine ratio (D/P Cr), 292 anuric CAPD patients were stratified to faster (D/P Cr ≥0.65) and slower transport groups (D/P Cr <0.65). The Cox proportional hazards models were used to evaluate the association of transport status with mortality. Results: During a median follow-up of 22.1 months, 24% patients died, 61.4% of them due to cardiovascular disease (CVD). Anuric patients with faster transport were associated with an increased risk of all-cause mortality (HR (95% CI) = 2.16 (1.09-4.26)), but not cardiovascular mortality, after adjustment for confounders. Faster transporters with pre-existing CVD had a greater risk for death compared to those without any history of CVD. Conclusion: Faster transporters were independently associated with high all-cause mortality in anuric CAPD patients. This association was strengthened in patients with pre-existing CVD.

High Peritoneal Transport Status Was Not Associated with Mortality in Peritoneal Dialysis Patients with Diabetes

Background Continuous ambulatory peritoneal dialysis (CAPD) patients with diabetes are at increased risk of mortality and high peritoneal transporters appear to contribute to poor survival. However, little is known about the combined impacts of high peritoneal transporters and diabetes on mortality. Methods This was a prospective observational cohort study. 776 incident CAPD patients were enrolled. Unadjusted and adjusted Cox proportional regression models were used to evaluate the association and interaction of peritoneal transport and diabetic status with mortality Results In the entire cohort, high peritoneal transport status was associated with an increased risk of all-cause mortality in unadjusted model [hazard ratio (HR) 2.35, 95% confidence interval (CI) 1.30 to 4.25, P = 0.01], but this association was not significant in multivariable model. There was an interaction between peritoneal membrane transport status and diabetes (P = 0.028). Subgroup analyses showed that compared to low and low average transporters, high transporters was associated with a higher risk of all-cause mortality (adjusted HR 1.78, 95% CI 1.07 to 4.70, P = 0.04) in CAPD patients without diabetes, but not in those with diabetes (adjusted HR 0.79, 95%CI 0.33 to 1.89, P = 0.59). Results were similar when transport status was assessed as a continuous variable. Conclusions The association between high peritoneal transport and all-cause mortality was likely to vary with diabetes status. High peritoneal transport was associated with an elevated risk of death among CAPD patients without diabetes, but not in those with diabetes.

Association of left ventricular systolic dysfunction with mortality in incident peritoneal dialysis patients

Cardiovascular disease is associated with morbidity and mortality in peritoneal dialysis patients but the relationship between left ventricular ejection fraction (LVEF) and outcomes is unclear. This study aimed to explore the association between LVEF and mortality in incident continuous ambulatory peritoneal dialysis (CAPD) patients.