Inflammatory Stress Exacerbated Mesangial Foam Cell Formation and Renal Injury via Disrupting Cellular Cholesterol Homeostasis

Remnant cholesterol, preinflammatory state and chronic kidney disease: association and mediation analyses

Blood lipid management is a key approach in the prevention of chronic kidney disease (CKD). Remnant cholesterol (RC) plays an important role in the development of multiple diseases via chronic inflammation. The aim of our study was to determine the relationship between RC and CKD and explore the role of inflammation in this relationship. The 7696 subjects from the Chinese Health and Nutrition Survey were divided into four subgroups according to the quartile of RC. The estimated glomerular filtration rate was calculated using the CKD Epidemiology Collaboration equation. Fasting RC was calculated as total cholesterol minus low-density lipoprotein cholesterol and high-density lipoprotein cholesterol. Logistic regression analysis was employed to evaluate the relationships between RC and CKD. Mediation analysis was undertaken to identify potential mediators of high-sensitivity C-reactive protein (hs-CRP) and white blood cells (WBCs). Of all participants, the mean age was 51 years, and the male accounted for 47.8%. The multivariable-adjusted odds ratios (95% CIs) for the highest versus lowest quartile of remnant cholesterol were 1.40 (1.10-1.78, p for trend = 0.006) for CKD. RC and preinflammatory markers have combined effect on CKD. The preinflammatory state, presented by increased hs-CRP or WBCs, partially mediated the association between RC and CKD with proportion of 10.14% (p = 0.002) and 11.65% (p = 0.012), respectively. In conclusion, this study suggested a positive relationship between RC and CKD, which was partially mediated by preinflammatory state. These findings highlight the importance of RC and inflammation in renal dysfunction.IMPACT STATEMENTWhat is already known on this subject?: Dyslipidemia plays an important role in the development of chronic kidney disease (CKD). Remnant cholesterol (RC), as a triglyceride-rich particle, can contribute to target organ damage, primarily through inflammatory pathways. However, the relationship between RC and CKD in the community-dwelling population, particularly the role of inflammation, is not yet fully understood.What do the results of this study add?: This study shows that RC was significantly associated with CKD. RC and preinflammatory status exhibit a combined effect on CKD. Preinflammatory state, presented by increased high-sensitivity C-reactive protein or white blood cells, partially mediated the association between RC and CKD.What are the implications of these findings for clinical practice and/or further research?: The study provides us with a better understanding of the role of RC and inflammation in kidney dysfunction and raises the awareness of RC in the management of CKD.

Air pollution combined with high-fat feeding aggravates metabolic and cardiovascular diseases: A dangerous, oxidative, and immune-inflammatory association

Obesity and particulate air pollutant (PM_2.5) are important risk factors for cardiometabolic diseases. PM_2.5 exacerbates insulin resistance and lipid ectopic deposition in obese animals. The inorganic fraction of PM_2.5, the Residual Oil Fly Ash (ROFA), is related to cardiovascular events, by enhancing the generation of reactive species, inflammatory cytokines, and leukocyte activation. However, the synergistic effects of ROFA and a high-fat diet (HFD) are still poorly described, and the studies were mainly conducted with males.

AIMS

To investigate if ROFA could potentiate the cardiometabolic effects of diet-induced obesity in female rats.

MATERIAL AND METHODS

Wistar female rats were divided into four groups: Control (n = 6), Polluted (n = 6), HFD (n = 6), and HFD + Polluted (n = 6). HFD and HFD + Polluted received a high-fat diet (HFD) (58.3 % as fats), whilst Control and Polluted groups received a standard diet (Nuvilab CR-1). In addition, Polluted and HFD + Polluted groups received intranasal instillation of ROFA (250 μg/50 μL), while Control and HFD groups received saline solution (50 μL) daily, five days per week. Both interventions occurred 24 weeks after the animals were euthanized.

KEY FINDINGS

HFD combined with ROFA exposure impaired lipid profile challenged systemic and cardiac antioxidant defense, and presented a synergistic effect in inducing an immune-inflammatory condition. We found that the lipid profile disturbance is associated with HFD-induced hepatic, but not cardiac, deposition of triglycerides in female animals.

SIGNIFICANCE

Our results support the hypothesis that ROFA exposure combined with bad feeding can exacerbate metabolic and cardiovascular diseases.

Progress of research on dyslipidemia accompanied by nephrotic syndrome

Nephrotic syndrome is a relatively common clinical disease. Associated dyslipidemia is a risk factor for the occurrence and development of cardiovascular and renal diseases that might gradually develop into atherosclerosis, glomerulosclerosis or tubulointerstitial injury. It also confers an elevated risk of complications such as thromboembolism. If not properly controlled over the long term, dyslipidemia will become a key factor in a poor prognosis. Furthermore, dyslipidemia correlates with an increase in hepatic compensatory synthetic lipoprotein levels and a decrease in lipoprotein clearance, which can be sourced to the downregulation of hepatic and lipoprotein lipase activities in endothelial cells, muscle, and adipose tissue, and clinically characterized as hypertriglyceridemia or hypercholesterolemia. However, further investigations into the mechanism(s) of dyslipidemia are needed, with the resultant detailed perspectives and analyses substantially aiding the further development of treatment guidelines. Currently, statins represent the most popular type of pharmaceutical intervention because they lower hepatic cholesterol production and promote the absorption of low-density lipoprotein-cholesterol from the bloodstream, followed by second-line and other potential therapies to regulate the expression of specific receptors.

Inflammation Induces Lipid Deposition in Kidneys by Downregulating Renal PCSK9 in Mice with Adriamycin-Induced Nephropathy

BACKGROUND Previous studies of human and animal models indicate that inflammation alters lipid metabolism. The pro-protein convertase subtilisin kexin type 9 (PCSK9) plays an important role in lipid metabolism. MATERIAL AND METHODS We examined the effect of inflammation on PCSK9 expression and lipid deposition in the kidneys of mice with Adriamycin-induced nephropathy. RESULTS The results indicated an increased expression of inflammatory cytokines and lipid deposition over 12 weeks. During this time, the expression of PCSK9 and its transcriptional activator (hepatocyte nuclear factor 1alpha, HNF1alpha) decreased, and the expression of the low-density lipoprotein receptor (LDLR) and its transcriptional activator (sterol regulatory element binding protein-2, SREBP-2) increased. Exogenous inflammation appeared to further aggravate this process. CONCLUSIONS Our mouse model of nephropathy suggests that a key step in the inflammation-induced deposition of lipids in the kidneys is the downregulation renal PCSK9 expression.

Leukocyte cell-derived chemotaxin 2 inhibits development of atherosclerosis in mice

Leukocyte cell-derived chemotaxin 2 (LECT2), a multifunctional hepatokine, is involved in many pathological conditions. However, its role in atherosclerosis remains undefined. In this study, we administered vehicle or LECT2 to male Apoe^-/- mice fed a Western diet for 15 weeks. Atherosclerotic lesions were visualized and quantified with Oil-red O and hematoxylin staining. The mRNA expression levels of MCP-1, MMP-1, IL-8, IL-1β, and TNF-α were analyzed by quantitative real-time polymerase chain reaction. Serum TNF-α, IL-1β, IL-8, MCP-1, and MMP-1 concentrations were measured by enzyme-linked immunosorbent assay. CD68, CD31, and α-SMA, markers of macrophages, endothelial cells, and smooth muscle cells, respectively, were detected by immunostaining. Results showed that LECT2 reduced total cholesterol and low-density lipoprotein concentrations in serum and inhibited the development of atherosclerotic lesions, accompanied by reductions in inflammatory cytokines and lower MCP-1, MMP-1, TNF-α, IL-8, and IL-1β mRNA abundance. Furthermore, LECT2 decreased CD68, but increased α-SMA in atherosclerotic lesions, suggesting an increase in smooth muscle cells and reduction in macrophages. In summary, LECT2 inhibited the development of atherosclerosis in mice, accompanied by reduced serum total cholesterol concentration and lower inflammatory responses.

MG132 protects against renal dysfunction by regulating Akt-mediated inflammation in diabetic nephropathy

Diabetic nephropathy (DN), the leading cause of end-stage renal disease (ESRD). To date, mounting evidence has shown that inflammation may contribute to the pathogenesis of DN. Recent reports have shown that proteasome inhibitors display cytoprotection by reducing the phosphorylation of Akt, a serine/threonine kinase, plays a critical role in cellular survival and metabolism and can crosstalk with inflammation. Therefore, we hypothesized that MG132, specific proteasome inhibitor, could provide renoprotection by suppressing Akt-mediated inflammation in DN. In vivo, male Sprague-Dawley rats were divided into normal control group (NC), diabetic nephropathy group (DN), DN model plus MG132 treatment group (MG132), and DN model plus deguelin treatment group (Deguelin)(deguelin, a specific inhibitor of Akt). In vitro, a human glomerular mesangial cell lines (HMCs) was exposed to 5.5 mmol/L glucose (CON), 30 mmol/L glucose (HG), 30 mmol/L glucose with 0.5 umol/L MG132 (MG132) and 30 mmol/L glucose with 5 umol/L deguelin (Deguelin). Compared with NC, DN showed a significant increase in the urinary protein excretion rate and inflammatory cytokines, as well as p-Akt. Compared with CON, HMCs co-cultured with HG was notably proliferated, which is in accord with α-smooth muscle actin (α-SMA) expression. These alterations were inhibited by administration of MG132 or deguelin. In conclusion, MG132 significantly inhibits the development of DN by regulating Akt phosphorylation-mediated inflammatory activation.

Combination of Chymostatin and Aliskiren attenuates ER stress induced by lipid overload in kidney tubular cells

Background

Lipotoxicity plays an important role in the pathogenesis of kidney injury. Our previous study demonstrated that activation of local renin-angiotensin system (RAS) was involved in saturated free fatty acids palmitic acid (PA)-induced tubular cell injuries. The current study aims to investigate whether suppression of RAS by combination of direct renin inhibitor aliskiren and noncanonical RAS pathway chymase inhibitor chymostatin attenuates PA or cholesterol induced-endoplasmic reticulum stress (ER stress) and apopotosis in cultured human proximal tubular HK2 cells.

Methods

HK2 cells were treated with saturated fatty acid PA (0.6 mM) for 24 h or cholesterol (10 μg/ml) for 6d with or without chymostatin and/or aliskiren. Expressions of the ER stress associated proteins and apoptosis markers were detected by western blotting. The mRNA levels of RAS components were measured by real-time qPCR.

Results

Combination treatment of chymostatin and aliskiren markedly suppressed PA or cholesterol-induced ER stress, as reflected by increased BiP, IRE1α, phosphorylated-eIF2α and ATF4 as well as proapoptotic transcription factor CHOP. The ratio of Bax/Bcl-2 and cleaved caspase-3, two markers of apoptosis were upregulated by PA or cholesterol treatment. PA treatment was also associated with increased levels of angiotensinogen and angiotensin type 1 receptor (AT1R) mRNA expression. Combination treatment of chymostatin and aliskiren markedly suppressed PA or cholesterol-induced ER stress and apoptosis. The protective effect of two inhibitors was also observed in primary cultured cortical tubular cells treated with PA. In contrast, chymostatin and/or aliskiren failed to prevent ER stress induced by tunicamycin.

Conclusions

These results suggested that combination treatment of chymostatin and aliskiren attenuates lipid-induced renal tubular cell injury, likely through suppressing activation of intracellular RAS.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0818-1) contains supplementary material, which is available to authorized users.

Dysfunction of cholesterol sensor SCAP promotes inflammation activation in THP-1 macrophages

Crosstalk occurs between dyslipidemia and chronic inflammation, which are both precipitants of atherosclerosis. Sterol regulatory element binding proteins cleavage-activating protein (SCAP) plays a key role in regulating cholesterol homeostasis. The present study investigated the effects of SCAP dysfunction on the expression of inflammatory cytokines and lipid metabolism in THP-1 macrophages. Intracellular cholesterol content was assessed by Oil Red O staining and quantitative assays. The expression of SCAP, HMGCR, pro-IL-1β and N-SREBP2, p65(N) in the nucleus were examined by real-time quantitative RT-PCR and Western blotting. The level of secretary proteins IL-1β, TNF-α and MCP-1 in the supernatants were determined by ELISA. The translocation of SCAP from the endoplasmic reticulum (ER) to the Golgi was detected by confocal microscopy. Our results demonstrated that over-expression of SCAP significantly increased the expression of HMGCR, pro-IL-1β in the cytoplasm, and mature IL-1β, TNF-α, MCP-1 in the supernatants, while knocking down SCAP dramatically decreased the expression of these molecules. Betulin effectively suppressed the accumulation of intracellular cholesterol in the SCAP over-expressed THP-1 macrophages, but did not affect the expression of inflammatory cytokines, indicating that the pro-inflammatory effect of SCAP was independent of its routine role in regulating cholesterol homeostasis. Furthermore, we investigated the molecular mechanisms mediating the crosstalk between dyslipidemia and inflammatory responses. Knocking down SCAP attenuated LPS-induced IκB phosphorylation and reduced the nuclear level of p65, while over-expression of SCAP increased the nuclear level of p65. Knocking down p65 abolished the proinflammatory effect represented by elevated expression of the inflammatory mediators in the SCAP over-expressed THP-1 macrophages, suggesting that SCAP dysfunction stimulated inflammatory responses via activating the NF-κB signaling pathway. In conclusion, the cholesterol sensor SCAP plays a role in regulating the expression of inflammatory factors such as IL-1β, TNF-α, and MCP-1 in THP-1 macrophages. SCAP mediates the inflammatory response via activating the NF-κB pathway. This new function of SCAP is independent of its role in lipid metabolism.

Inflammasomes in the Kidney

Inflammasomes influence a diverse range of kidney disease, including acute and chronic kidney diseases, and those mediated by innate and adaptive immunity. Both IL-18 and in particular IL-1β are validated therapeutic targets in several kidney diseases. In addition to leukocyte-derived inflammasomes, renal tissue cells express functional inflammasome components. Furthermore, a range of endogenous substances that directly activate inflammasomes also mediate kidney injury. Many of the functional studies have focussed on the NLRP3 inflammasome, and there is also evidence for the involvement of other inflammasomes in some conditions. While, at least in some disease, the mechanistic details of the involvement of the inflammasome remain to be elucidated, therapies focussed on inflammasomes and their products have potential in treating kidney disease in the future.

Dyslipidaemia in nephrotic syndrome: mechanisms and treatment

Nephrotic syndrome is a highly prevalent disease that is associated with high morbidity despite notable advances in its treatment. Many of the complications of nephrotic syndrome, including the increased risk of atherosclerosis and thromboembolism, can be linked to dysregulated lipid metabolism and dyslipidaemia. These abnormalities include elevated plasma levels of cholesterol, triglycerides and the apolipoprotein B-containing lipoproteins VLDL and IDL; decreased lipoprotein lipase activity in the endothelium, muscle and adipose tissues; decreased hepatic lipase activity; and increased levels of the enzyme PCSK9. In addition, there is an increase in the plasma levels of immature HDL particles and reduced cholesterol efflux. Studies from the past few years have markedly improved our understanding of the molecular pathogenesis of nephrotic syndrome-associated dyslipidaemia, and also heightened our awareness of the associated exacerbated risks of cardiovascular complications, progressive kidney disease and thromboembolism. Despite the absence of clear guidelines regarding treatment, various strategies are being increasingly utilized, including statins, bile acid sequestrants, fibrates, nicotinic acid and ezetimibe, as well as lipid apheresis, which seem to also induce partial or complete clinical remission of nephrotic syndrome in a substantial percentage of patients. Future potential treatments will likely also include inhibition of PCSK9 using recently-developed anti-PCSK9 monoclonal antibodies and small inhibitory RNAs, as well as targeting newly identified molecular regulators of lipid metabolism that are dysregulated in nephrotic syndrome.

Inflammatory stress promotes the development of obesity-related chronic kidney disease via CD36 in mice

Ectopic fat located in the kidney has emerged as a novel cause of obesity-related chronic kidney disease (CKD). In this study, we aimed to investigate whether inflammatory stress promotes ectopic lipid deposition in the kidney and causes renal injury in obese mice and whether the pathological process is mediated by the fatty acid translocase, CD36. High-fat diet (HFD) feeding alone resulted in obesity, hyperlipidemia, and slight renal lipid accumulation in mice, which nevertheless had normal kidney function. HFD-fed mice with chronic inflammation had severe renal steatosis and obvious glomerular and tubular damage, which was accompanied by increased CD36 expression. Interestingly, CD36 deficiency in HFD-fed mice eliminated renal lipid accumulation and pathological changes induced by chronic inflammation. In both human mesangial cells (HMCs) and human kidney 2 (HK2) cells, inflammatory stress increased the efficiency of CD36 protein incorporation into membrane lipid rafts, promoting FFA uptake and intracellular lipid accumulation. Silencing of CD36 in vitro markedly attenuated FFA uptake, lipid accumulation, and cellular stress induced by inflammatory stress. We conclude that inflammatory stress aggravates renal injury by activation of the CD36 pathway, suggesting that this mechanism may operate in obese individuals with chronic inflammation, making them prone to CKD.

Dysregulation of the Low-Density Lipoprotein Receptor Pathway Is Involved in Lipid Disorder-Mediated Organ Injury

The low-density lipoprotein receptor (LDLR) pathway is a negative feedback system that plays important roles in the regulation of plasma and intracellular cholesterol homeostasis. To maintain a cholesterol homeostasis, LDLR expression is tightly regulated by sterol regulatory element-binding protein-2 (SREBP-2) and SREBP cleavage-activating protein (SCAP) in transcriptional level and by proprotein convertase subtilisin/kexin type 9 (PCSK9) in posttranscriptional level. The dysregulation of LDLR expression results in abnormal lipid accumulation in cells and tissues, such as vascular smooth muscle cells, hepatic cells, renal mesangial cells, renal tubular cells and podocytes. It has been demonstrated that inflammation, renin-angiotensin system (RAS) activation, and hyperglycemia induce the disruption of LDLR pathway, which might contribute to lipid disorder-mediated organ injury (atherosclerosis, non-alcoholic fatty liver disease, kidney fibrosis, etc). The mammalian target of rapamycin (mTOR) pathway is a critical mediator in the disruption of LDLR pathway caused by pathogenic factors. The mTOR complex1 activation upregulates LDLR expression at the transcriptional and posttranscriptional levels, consequently resulting in lipid deposition. This paper mainly reviews the mechanisms for the dysregulation of LDLR pathway and its roles in lipid disorder-mediated organ injury under various pathogenic conditions. Understanding these mechanisms leading to the abnormality of LDLR expression contributes to find potential new drug targets in lipid disorder-mediated diseases.

Liver ergothioneine accumulation in a guinea pig model of non-alcoholic fatty liver disease. A possible mechanism of defence?

L-ergothioneine (ET), a putative antioxidant compound acquired by animals through dietary sources, has been suggested to accumulate in certain cells and tissues in the body that are predisposed to high oxidative stress. In the present study, we identified an elevation of ET in the liver of a guinea pig model of non-alcoholic fatty liver disease (NAFLD), elucidated a possible mechanism for the increased uptake and investigated the possible role for this accumulation. This increase in liver ET levels correlated with cholesterol accumulation and disease severity. We identified an increase in the transcriptional factor, RUNX1, which has been shown to upregulate the expression of the ET-specific transporter OCTN1, and could consequently lead to the observable elevation in ET. An increase was also seen in heat shock protein 70 (HSP70) which seemingly corresponds to ET elevation. No significant increase was observed in oxidative damage markers, F2-isoprostanes, and protein carbonyls, which could possibly be attributed to the increase in liver ET through direct antioxidant action, induction of HSP70, or by chelation of Fe(2+), preventing redox chemistry. The data suggest a novel mechanism by which the guinea pig fatty liver accumulates ET via upregulation of its transporter, as a possible stress response by the damaged liver to further suppress oxidative damage and delay tissue injury. Similar events may happen in other animal models of disease, and researchers should be aware of the possibility.