Bi Cheng Liu

Inflammatory Stress Exacerbates the Progression of Cardiac Fibrosis in High-Fat-Fed Apolipoprotein E Knockout Mice via Endothelial-Mesenchymal Transition

Background Chronic inflammation plays a crucial role in the progression of cardiac fibrosis. This study investigated whether inflammation exacerbated the progression of cardiac fibrosis in high-fat-fed apolipoprotein E knockout (ApoE KO) mice via endothelial-mesenchymal transition (EndMT). Methods Twenty-four male ApoE KO mice were divided into normal chow diet (Control), high-fat diet (HFD), or high-fat diet plus 10% casein injection (inflamed) groups for 8 weeks. The body weight of ApoE KO mice was measured at each week. The lipid profile and serum amyloid A (SAA) levels were examined using clinical biochemistry and enzyme-linked immunosorbent assays, respectively. Cardiac lipid and collagen accumulation was visualised with haematoxylin-eosin (HE) and Massons trichrome staining. EndMT-related molecule expression was examined by immunohistochemistry and Western blotting. Results SAA levels were increased in the inflamed group compared with the HFD and control groups, suggesting that inflammation was successfully induced. There were no differences in body weight among three groups at each week. Interestingly, inflammation significantly reduced serum total cholesterol, triglyceride, and low-density lipoprotein (LDL) levels compared with the HFD mice. However, both foam cell formation in cardiac blood vessels and cardiac collagen deposition were increased in the inflamed group, as demonstrated by HE and Masson trichrome staining. Furthermore, inflammation reduced protein expression of CD31 and increased protein expression of alpha-smooth muscle actin (α-SMA) and collagen I, which contribute to cardiac EndMT. Conclusions Inflammatory stress exacerbates the progression of cardiac fibrosis in high-fat-fed ApoE KO mice via EndMT, suggesting that hyperlipidaemia and inflammation act synergistically to redistribute plasma lipids to cardiac tissues and accelerate the progression of cardiac fibrosis.

Activation of mTOR modulates SREBP-2 to induce foam cell formation through increased retinoblastoma protein phosphorylation

AIMS Our previous studies demonstrated that inflammation contributes to atherosclerosis through disruption of the low density lipoprotein receptor (LDLr) pathway. However, this effect is overridden by rapamycin, which is an inhibitor of mammalian target of rapamycin (mTOR). This study investigated the role of the mTOR pathway in atherosclerosis in vivo and in vitro. METHODS AND RESULTS To induce inflammation, we used subcutaneous injection of 10% casein in apolipoprotein E knockout (ApoE KO) mice and lipopolysaccharide stimulation in rat vascular smooth muscle cells (VSMCs). Results showed that inflammation increased lipid accumulation in aortas of ApoE KO mice and in VSMCs, which were correlated with increased expressions of LDLr, sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP), and SREBP-2 as well as with enhanced translocation of SCAP/SREBP-2 complex from the endoplasmic reticulum (ER) to the Golgi. Furthermore, inflammation increased both the percentage of cells in the S phase of cell cycle and protein expressions of the phosphorylated forms of retinoblastoma tumour suppressor protein (Rb), mTOR, eukaryotic initiation factor 4E-binding protein 1 (4EBP1), and P70 S6 kinase. After treatment with rapamycin or mTOR siRNA, the activity of the mTOR pathway was blocked. Interestingly, the expression levels of LDLr, SCAP, and SREBP-2 and the translocation of SCAP/SREBP-2 complex from the ER to the Golgi in treated VSMCs were decreased even in the presence of inflammatory stress. CONCLUSION Our findings demonstrate for the first time that inflammation disrupts LDLr feedback regulation through the activation of the mTOR pathway. Increased mTORC1 activity was found to up-regulate SREBP-2-mediated cholesterol uptake through Rb phosphorylation.

Activation of mTORC1 disrupted LDL receptor pathway: A potential new mechanism for the progression of non-alcoholic fatty liver disease

Our previous studies demonstrated that inflammation exacerbates the progression of non-alcoholic fatty liver disease (NAFLD) by disrupting cholesterol homeostasis. This study aimed to investigate the role of mammalian target of rapamycin complex 1 (mTORC1) in NAFLD under conditions of inflammation. Chronic inflammation was induced by using subcutaneous injections of 10% casein in apolipoprotein E knockout (ApoE KO) mice in vivo and interleukin-1β stimulation of the HepG2 hepatoblastoma cell line in vitro. Results demonstrated that inflammation increased lipid accumulation in HepG2 cells and in livers of apolipoprotein E knockout mice. These effects were correlated with an increase in low density lipoprotein receptor (LDLR) gene transcription, which was mediated through the up-regulation of sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP), SREBP-2, and through enhanced translocation of the SCAP/SREBP-2 complex from endoplasmic reticulum (ER) to Golgi. In addition, our data indicated that inflammation down-regulated the expression of proprotein convertase subtilisin kexin 9 (PCSK9) and prevented the degradation of LDLR protein via posttranscriptional mechanisms. Further analysis showed that inflammation increased the protein phosphorylation of mTOR, eukaryotic initiation factor 4E-binding protein 1, and p70 S6 kinase. Interestingly, blocking mTORC1 activity inhibited the translocation of SCAP/SREBP-2 complex from the ER to the Golgi and decreased the expression of LDLR, SCAP, and SREBP-2. These effects were accompanied by an increase in the expression of PCSK9 and accelerated LDLR degradation. Our findings demonstrated that increased mTORC1 activity exacerbated the progression of NAFLD by disrupting LDLR expression via transcriptional and posttranscriptional mechanisms.

Inflammation disrupts the LDL receptor pathway and accelerates the progression of vascular calcification in ESRD patients.

Background Chronic inflammation plays a crucial role in the progression of vascular calcification (VC). This study was designed to investigate whether the low-density lipoprotein receptor (LDLr) pathway is involved in the progression of VC in patients with end-stage renal disease (ESRD) during inflammation. Methods and Results Twenty-eight ESRD patients were divided into control and inflamed groups according to plasma C-reactive protein (CRP) level. Surgically removed tissues from the radial arteries of patients receiving arteriovenostomy were used in the experiments. The expression of tumour necrosis factor-α (TNF-α) and monocyte chemotactic protein-1 (MCP-1) of the radial artery were increased in the inflamed group. Hematoxylin-eosin and alizarin red S staining revealed parallel increases in foam cell formation and calcium deposit formation in continuous cross-sections of radial arteries in the inflamed group compared to the control, which were closely correlated with increased LDLr, sterol regulatory element binding protein-2 (SREBP-2), bone morphogenetic proteins-2 (BMP-2), and collagen I protein expression, as shown by immunohistochemical and immunofluorescent staining. Confocal microscopy confirmed that inflammation enhanced the translocation of the SREBP cleavage-activating protein (SCAP)/SREBP-2 complex from the endoplasmic reticulum to the Golgi, thereby activating LDLr gene transcription. Inflammation increased alkaline phosphatase protein expression and reduced α-smooth muscle actin protein expression, contributing to the conversion of the vascular smooth muscle cells in calcified vessels from the fibroblastic to the osteogenic phenotype; osteogenic cells are the main cellular components involved in VC. Further analysis showed that the inflammation-induced disruption of the LDLr pathway was significantly associated with enhanced BMP-2 and collagen I expression. Conclusions Inflammation accelerated the progression of VC in ESRD patients by disrupting the LDLr pathway, which may represent a novel mechanism involved in the progression of both VC and atherosclerosis.

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.

Dysregulation of low-density lipoprotein receptor contributes to podocyte injuries in diabetic nephropathy

Dyslipidemia plays crucial roles in the progression of diabetic nephropathy (DN). This study investigated the effects of high glucose on lipid accumulation in podocytes and explored its underlying mechanisms. Male db/m and db/db mice were fed a normal chow diet for 8 wk. Immortalised mouse podocytes were treated with or without high glucose for 24 h. The changes to the morphology and ultramicrostructures of the kidneys in mice were examined using pathological staining and electron microscopy. Intracellular lipid accumulation was evaluated by Oil Red O staining and a free cholesterol quantitative assay. The expressions of the molecules involved in low-density lipoprotein receptor (LDLr) pathway and podocyte injury were examined using immunofluorescent staining, real-time PCR, and Western blot. There were increased levels of plasma lipid, serum creatinine, and proteinuria in db/db mice compared with db/m mice. Moreover, there was significant mesangial matrix expansion, basement membrane thickening, podocyte foot process effacement, and phenotypic alteration in the db/db group. Additionally, lipid accumulation in the kidneys of db/db mice was increased due to increased protein expressions of LDLr, sterol regulatory element-binding protein (SREBP) cleavage-activating protein, and SREBP-2. These effects were further confirmed by in vitro studies. Interestingly, the treatment with LDLr siRNA inhibited lipid accumulation in podocytes and decreased the protein expression of molecules associated with phenotypic alteration in podocytes. High glucose disrupted LDLr feedback regulation in podocytes, which may cause intracellular lipid accumulation and alteration of podocyte phenotype, thereby accelerating DN progression.

Lipid disorder and intrahepatic renin-angiotensin system activation synergistically contribute to non-alcoholic fatty liver disease.

This study aimed to investigate the possible synergistic effects of lipid disorder with renin–angiotensin system (RAS) activation in non‐alcoholic fatty liver disease (NAFLD).

Activation of the CXCL16/CXCR6 Pathway by Inflammation Contributes to Atherosclerosis in Patients with End-stage Renal Disease

Background: Chronic inflammation plays a critical role in the progression of atherosclerosis (AS). This study aimed to determine the effects of the CXC chemokine ligand 16 (CXCL16)/CXC chemokine receptor 6 (CXCR6) pathway on cholesterol accumulation in the radial arteries of end-stage renal disease (ESRD) patients with concomitant microinflammation and to further investigate the potential effects of the purinergic receptor P2X ligand-gated ion channel 7 (P2X7R). Methods: Forty-three ESRD patients were divided into the control group (n=17) and the inflamed group (n=26) based on plasma C-reactive protein (CRP) levels. Biochemical indexes and lipid profiles of the patients were determined. Surgically removed tissues from the radial arteries of patients receiving arteriovenostomy were used for preliminary evaluation of AS. Haematoxylin-eosin (HE) and Filipin staining were performed to assess foam cell formation. CXCL16/CXCR6 pathway-related protein expression, P2X7R protein expression and the expression of monocyte chemotactic protein-1 (MCP-1), tumour necrosis factor-α (TNF-α), and CD68 were detected by immunohistochemical and immunofluorescence staining. Results: Inflammation increased both MCP-1 and TNF-α expression and macrophage infiltration in radial arteries. Additionally, foam cell formation significantly increased in the radial arteries of the inflamed group compared to that of the controls. Further analysis showed that protein expression of CXCL16, CXCR6, disintegrin and metalloproteinase-10 (ADAM10) in the radial arteries of the inflamed group was significantly increased. Furthermore, CXCL16 expression was positively correlated with P2X7R expression in the radial arteries of ESRD patients. Conclusions: Inflammation contributed to foam cell formation in the radial arteries of ESRD patients via activation of the CXCL16/CXCR6 pathway, which may be regulated by P2X7R.

Inflammatory stress exacerbates lipid accumulation and podocyte injuries in diabetic nephropathy

AimsDiabetic nephropathy (DN) is a chronic inflammatory disease that is accompanied by different degrees of lipid disorders. The present study was conducted to determine whether inflammatory stress exacerbates lipid accumulation in podocytes and to investigate its underlying mechanisms in DN using in vitro and in vivo studies.MethodsWe used IL-1β stimulation in podocytes in vitro and casein injections in db/db mice in vivo to induce inflammatory stress. The plasma levels of serum inflammatory cytokines were determined using an enzyme-linked immunosorbent assay. The renal pathology was evaluated using pathological staining and electron microscopy. Intracellular lipid accumulation was evaluated by Oil Red O staining and a cholesterol quantitative assay. The gene and protein expression levels of extracellular matrix proteins, biomarkers of podocyte injury, and molecules involved in the LDLr pathway were evaluated using immunofluorescence staining, real-time PCR, and western blot analysis.ResultsIncreased plasma levels of inflammatory cytokines in the casein-injected db/db mice indicated a successful induction of the inflamed DN model. The kidney morphological changes, podocyte injury, and epithelial mesenchymal transition (EMT) were more significant in casein-injected db/db mice. Moreover, inflammation increased the lipid droplet accumulation in the kidneys of db/db mice, which resulted from the increased protein expression levels of LDLr, sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP), and SREBP-2 in the kidneys of db/db mice. The in vitro studies further demonstrated that inflammation increased the lipid accumulation in the podocytes and induced podocyte EMT, which were correlated with inflammation-mediated increases in the expression levels of LDLr, SCAP, and SREBP-2, and increased translocation of the SCAP/SREBP-2 complex from the endoplasmic reticulum to the Golgi in the podocytes.ConclusionInflammation induced lipid accumulation and the EMT of podocytes through the dysregulation of the LDLr pathway, which contributed to podocyte injury and accelerated the progression of DN.

The Emerging Roles of Microparticles in Diabetic Nephropathy

Microparticles (MPs) are a type of extracellular vesicles (EVs) shed from the outward budding of plasma membranes during cell apoptosis and/or activation. These microsized particles then release specific contents (e.g., lipids, proteins, microRNAs) which are active participants in a wide range of both physiological and pathological processes at the molecular level, e.g., coagulation and angiogenesis, inflammation, immune responses. Research limitations, such as confusing nomenclature and overlapping classification, have impeded our comprehension of these tiny molecules. Diabetic nephropathy (DN) is currently the greatest contributor to end-stage renal diseases (ESRD) worldwide, and its public health impact will continue to grow due to the persistent increase in the prevalence of diabetes mellitus (DM). MPs have recently been considered as potentially involved in DN onset and progression, and this review juxtaposes some of the research updates about the possible mechanisms from several relevant aspects and insights into the therapeutic perspectives of MPs in clinical management and pharmacological treatment of DN patients.