The impact of severe LDL receptor mutations on SREBP-pathway regulation in homozygous familial hypercholesterolemia (FH)

High fat diet-induced hyperlipidemia and tissue steatosis in rabbits through modulating ileal microbiota

High-fat diet (HFD) and overnutrition are important starting factors that may alter intestinal microbiota, lipid metabolism, and systemic inflammation. However, there were few studies on how intestinal microbiota contributes to tissue steatosis and hyperlipidemia. Here, we investigated the effect of lipid metabolism disorder-induced inflammation via toll-like receptor 2 (TLR-2), toll-like receptor 4 (TLR-4), and nuclear factor-κB (NF-κB) pathways at the intestinal level in response to HFD. Twenty 80-day-old male New Zealand White rabbits were randomly divided into the normal diet group (NDG) and the high-fat diet group (HDG) for 80 days. Growth performance, blood biochemical parameters, lipid metabolism, inflammation, degree of tissue steatosis, and intestinal microbial composition were measured. HFD increased the relative abundance of Christensenellaceae_R_7_group, Marvinbryantia, Akkermansia etc., with a reduced relative abundance of Enterorhabdus and Lactobacillus. Moreover, HFD caused steatosis in the liver and abdominal fat and abnormal expression of some genes related to lipid metabolism and tight junction proteins. The TLR-2, TLR-4, NF-κB, TNF-α, and IL-6 were confirmed by overexpression with downregulation of IL-10. Serum biochemical indices (TG, TCHO, LDL-C, and HDL-C) were also increased, indicating evidence for the development of the hyperlipidemia model. Correlation analysis showed that this microbial dysbiosis was correlated with lipid metabolism and inflammation, which were associated with the intestinal tract's barrier function and hyperlipidemia. These results provide an insight into the relationship between HFD, the intestinal microbiota, intestinal barrier, tissue inflammation, lipid metabolism, and hyperlipidemia. KEY POINTS: • High-fat diet leads to ileal microbiota disorders • Ileal microbiota mediates local and systemic lipid metabolism disorders and inflammation • There is a specific link between ileal microbiota, histopathology, and hyperlipidemia.

Familial hypercholesterolemia and COVID-19: A menacing but treatable vasculopathic condition

SARS-CoV-2 infection continues to cause increased morbidity and mortality, and due to the slow pace of vaccination COVID-19 will probably remain a global burden to health systems for a long time. Unfortunately, the necessary prevention and treatment strategies of COVID-19 have led to restriction measures that are hampering the routine care of common chronic metabolic conditions like hypercholesterolemia. It is of particular concern that during the acute phase of COVID-19, the control of pre-existing metabolic diseases tends to get worse which again increases the risk for complications and a poor outcome in these patients. A significant contributor to these complications is endothelial dysfunction which is associated with COVID-19. This Commentary will discuss the impact of COVID-19 on endothelial function particularly in patients with familial hypercholesterolemia (FH), a metabolic inherited disease known to in itself adversely affect endothelial function. There should be no hesitation to continue with statin therapy in severe hypercholesterolemic patients with COVID-19. We argue that in FH patients with COVID-19 the clinicians need even consider intensifying statin therapy as well as the addition of other lipid-lowering agents, such as proprotein convertase subtilisin/kexin type 9(PCSK9) inhibitors. In contrast to statins, the PCSK9 inhibitors lower lipoprotein(a) [Lp(a)] level, and, accordingly, these latter drugs need to be considered particularly in FH patients with an elevated level of Lp(a). This call applies to the in-hospital stay and also beyond. When considering that the vasculopathic effects of COVID-19 may persist, a long-term follow-up of individualized therapies in FH patients is warranted.

Recent developments in the regulation of cholesterol transport by natural molecules

The dysregulation of cholesterol metabolism is a high-risk factor for non-alcoholic fatty liver disease (NAFLD), dyslipidemia, and atherosclerosis (AS). Cholesterol transport maintains whole-body cholesterol homeostasis. Low-density apolipoprotein receptor (LDLR) mediates cholesterol uptake in cells and plays an important role in the primary route of circulatory cholesterol clearance in liver cells. Caveolins 1 is an integral membrane protein and shuttle between the cytoplasm and cell membrane. Caveolins 1 not only plays a role in promoting cholesterol absorption in cells but also in the transport of cellular cholesterol efflux by interacting with the ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type I (SR-BI). These proteins, which are associated with reverse cholesterol transport (RCT), are potential therapeutic targets for NAFLD and AS. Many studies have indicated that natural products have lipid-lowering effects. Moreover, natural molecules, derived from natural products, have the potential to be developed into novel drugs. However, the mechanisms underlying the regulation of cholesterol transport by natural molecules have not yet been adequately investigated. In this review, we briefly describe the process of cholesterol transport and summarize the mechanisms by which molecules regulate cholesterol transport. This article provides an overview of recent studies and focuses on the potential therapeutic effects of natural molecules; however, further high-quality studies are needed to firmly establish the clinical efficacies of natural molecules.

Circulating miR-200c is up-regulated in paediatric patients with familial hypercholesterolaemia and correlates with miR-33a/b levels: implication of a ZEB1-dependent mechanism

Hypercholesterolaemia provokes reactive oxygen species (ROS) increase and is a major risk factor for cardiovascular disease (CVD) development. We previously showed that circulating miR-33a/b expression levels were up-regulated in children with familial hypercholesterolaemia (FH). miR-33a/b control cholesterol homoeostasis and recently miR-33b has been demonstrated to directly target the transcription factor zinc finger E-box-binding homeobox 1 (ZEB1). The latter acts in a negative feedback loop with the miR-200 family. Our previous studies showed that the ROS-dependent miR-200c up-regulation induces endothelial dysfunction and provokes a ZEB1-dependent apoptosis and senescence. In the present study, we aimed to verify whether circulating miR-200c was induced in FH children, and whether a correlation existed with miR-33a/b. Total RNA was extracted from plasma of 28 FH children and 25 age-matched healthy subjects (HS) and miR-200c levels were measured. We found that miR-200c was up-regulated in FH compared with HS (4.00 ± 0.48-fold increase, P<0.05) and exhibited a positive correlation with miR-33a/b. miR-200c did not correlate with plasma lipids, but correlated with C-reactive protein (CRP) plasma levels and glycaemia (GLI). Ordinary least squares (OLS) regression analysis revealed that miR-200c was significantly affected by GLI and by miR-33a (P<0.01; P<0.001 respectively). Moreover, we found that miR-33 overexpression, in different cell lines, decreased ZEB1 expression and up-regulated both the intracellular and the extracellular miR-200c expression levels. In conclusion, circulating miR-200c is up-regulated in FH, probably due to oxidative stress and inflammation and via a miR-33a/b-ZEB1-dependent mechanism. The present study could provide the first evidence to point to the use of miR-33a/b and miR-200c, as early biomarkers of CVD, in paediatric FH.

Circulating miR-200c is up-regulated in paediatric patients with familial hypercholesterolaemia and correlates with miR-33a/b levels: implication of a ZEB1-dependent mechanism

Hypercholesterolaemia provokes reactive oxygen species (ROS) increase and is a major risk factor for cardiovascular disease (CVD) development. We previously showed that circulating miR-33a/b expression levels were up-regulated in children with familial hypercholesterolaemia (FH). miR-33a/b control cholesterol homoeostasis and recently miR-33b has been demonstrated to directly target the transcription factor zinc finger E-box-binding homeobox 1 (ZEB1). The latter acts in a negative feedback loop with the miR-200 family. Our previous studies showed that the ROS-dependent miR-200c up-regulation induces endothelial dysfunction and provokes a ZEB1-dependent apoptosis and senescence. In the present study, we aimed to verify whether circulating miR-200c was induced in FH children, and whether a correlation existed with miR-33a/b. Total RNA was extracted from plasma of 28 FH children and 25 age-matched healthy subjects (HS) and miR-200c levels were measured. We found that miR-200c was up-regulated in FH compared with HS (4.00 ± 0.48-fold increase, P<0.05) and exhibited a positive correlation with miR-33a/b. miR-200c did not correlate with plasma lipids, but correlated with C-reactive protein (CRP) plasma levels and glycaemia (GLI). Ordinary least squares (OLS) regression analysis revealed that miR-200c was significantly affected by GLI and by miR-33a (P<0.01; P<0.001 respectively). Moreover, we found that miR-33 overexpression, in different cell lines, decreased ZEB1 expression and up-regulated both the intracellular and the extracellular miR-200c expression levels. In conclusion, circulating miR-200c is up-regulated in FH, probably due to oxidative stress and inflammation and via a miR-33a/b-ZEB1-dependent mechanism. The present study could provide the first evidence to point to the use of miR-33a/b and miR-200c, as early biomarkers of CVD, in paediatric FH.

Association between familial hypobetalipoproteinemia and the risk of diabetes. Is this the other side of the cholesterol-diabetes connection? A systematic review of literature

Statin therapy is beneficial in reducing LDL cholesterol (LDL-C) levels and cardiovascular events, but it is associated with the risk of incident diabetes mellitus (DM). Familial hypercholesterolemia (FH) is characterized by genetically determined high levels of plasma LDL-C and a low prevalence of DM. LDL-C levels seem then inversely correlated with prevalence of DM. Familial hypobetalipoproteinemia (FHBL) represents the genetic mirror of FH in terms of LDL-C levels, very low in subjects carrying mutations of APOB, PCSK9 (FHBL1) or ANGPTL3 (FHBL2). This review explores the hypothesis that FHBL might represent also the genetic mirror of FH in terms of prevalence of DM and that it is expected to be increased in FHBL in comparison with the general population. A systematic review of published literature on FHBL was made by searching PubMed (1980-2016) for articles presenting clinical data on FHBL probands and relatives. The standardized prevalence rates of DM in FHBL1 were similar to those of the reference population, with a prevalence rate of 8.2 and 9.2%, respectively, while FHBL2 showed a 4.9% prevalence of DM. In conclusion, low LDL-C levels of FHBL do not seem connected to DM as it happens in subjects undergoing statin therapy and the diabetogenic effect of statins has to be explained by mechanisms that do not rely exclusively on the reduced levels of LDL-C. The review also summarizes the published data on the effects of FHBL on insulin sensitivity and the relationships between FH, statin therapy, FHBL1 and intracellular cholesterol metabolism, evaluating possible diabetogenic pathways.

Clinical Significance of Determining Plasma MicroRNA33b in Type 2 Diabetic Patients with Dyslipidemia

Aim: Sterol regulatory element-binding protein (SREBP)-1c is the dominant liver insulin-stimulated isoform and strongly correlates with diabetic dyslipidemia characterized by hyperinsulinemia [i.e., high-density lipoprotein cholesterol (HDL-C) levels and hypertriglyceridemia]. MicroRNA (miRNA) 33b is harbored in the intron of SREBP-1c and represses ATP-binding cassette, sub-family A, and member 1 (ABCA1) expression, essential for HDL formation. We measured plasma miRNA33b levels as possible biomarkers for diabetic dyslipidemia in patients with type 2 diabetes mellitus (T2DM) showing insulin resistance.

Methods: The participants included 50 patients with T2DM (M/F 31/19) enrolled in an educational program for controlling blood glucose levels at Hirosaki University Hospital. HbA1c, fasting plasma glucose, insulin, and lipid levels were determined. Plasma miRNA33b, miRNA33a and miRNA148a were quantified using a TaqMan^® MicroRNA Assay, and values were corrected with reference to miRNA16.

Results: Mean BMI of participants were 28.2 ± 6.6 (kg/m²) and the Homeostasis Model Assessment of Insulin Resistance was 4.3 ± 2.7. Patients' laboratory findings indicated diabetic dyslipidemia with insulin resistance. Plasma miRNA33b/16 levels revealed a positive correlation with plasma insulin level (r = 0.326, P = 0.021), serum C-peptide (r = 0.280, P = 0.049), and triglyceride (r = 0.351, P = 0.012), but no association with HDL-C (r = −0.210, P = 0.143). The blood level of miRNA33a was approximately 1/150th of that of miRNA33b and was not correlated with the above parameters.

Conclusion: We postulated that plasma miRNA33b may be useful as a new metabolic biomarker of dyslipidemia in patients with T2DM as well as metabolic syndrome via an insulin/SREBP-1c/miRNA33b/ABCA1 pathway.

Circulating miR-33a and miR-33b are up-regulated in familial hypercholesterolaemia in paediatric age

Circulating miR-33a and miR-33b are up-regulated in familial hypercholesterolaemic children. miR-33a and miR-33b positively correlate with total cholesterol, LDL-cholesterol, LDL-cholesterol/HDL-cholesterol ratio, apolipoprotein B, C-reactive protein and glycaemia. miR-33 could be a novel prognostic marker and therapeutic target for cardiovascular diseases associated with paediatric hypercholesterolaemia.

The cis and trans effects of the risk variants of coronary artery disease in the Chr9p21 region

BACKGROUND

Recent genome-wide association studies (GWAS) have shown that single nucleotide polymorphisms (SNPs) in the Chr9p21 region are associated with coronary artery disease (CAD). Most of the SNPs identified in this region are non-coding SNPs, suggesting that they may influence gene expression by cis or trans mechanisms to affect disease susceptibility. Since all cells from an individual have the same DNA sequence variations, levels of gene expression in immortalized cell lines can reflect the functional effects of DNA sequence variations that influence or regulate gene expression. The objective of this study is to evaluate the functional consequences of the risk variants in the Chr9p21 region on gene expression.

METHODS

We examined the association between the variants in the Chr9p21 region and the transcript-level mRNA expression of the adjacent genes (cis) as well as all other genes across the whole genome (trans) from transformed beta-lymphocytes in 801 non-Hispanic white participants from The Genetic Epidemiology Network of Arteriopathy (GENOA) study.

RESULTS

We found that the CAD risk variants in the Chr9p21 region were significantly associated with the mRNA expression of the ANRIL transcript ENST00000428597 (p = 8.58e-06). Importantly, a few distant transcripts were also found to be associated with the variants in this region, including the well-known CAD risk gene ABCA1 (p = 1.01e-05). Gene enrichment testing suggests that retinol metabolism, N-Glycan biosynthesis, and TGF signaling pathways may be involved.

CONCLUSION

These results suggest that the effect of risk variants in the Chr9p21 region on susceptibility to CAD is likely to be mediated through both cis and trans mechanisms.

Pharmacological treatment of a Sardinian patient affected by Autosomal Recessive Hypercholesterolemia (ARH)

BACKGROUND AND AIM

Previous studies have shown that patients with autosomal recessive hypercholesterolemia (ARH) resulting from mutations in LDLRAP1 gene have a less severe cardiovascular involvement than familial hypercholesterolemia homozygotes, lower levels of low-density lipoprotein cholesterol (LDL-C), and higher levels of high-density lipoprotein cholesterol (HDL-C). In addition, ARH patients seem to be more responsive to the lipid-lowering drugs. The aim was to test the effect of a combined drug treatment in an ARH patient in the absence of plasmapheresis.

METHODS AND RESULTS

Here we report the lipid-lowering effect of rosuvastatin (60 mg/day) associated with ezetimibe (10 mg/day) in a single ARH patient. The sequencing of LDLRAP1 gene showed that the patient was homozygous for the c.432insA mutation. During a 6-month treatment, we observed an 80% reduction of LDL-C and a significant increase of HDL-C and ApoA-I. Some sequence variations in PCSK9 and NPC1L1 genes found in this patient may have contributed to the success of drug treatment.

CONCLUSIONS

Our findings, although limited to a single case, suggest that in many ARH patients the LDL-C goal may be reached with the more potent statins associated with ezetimibe in the absence of extracorporeal procedures.