AAV vectors expressing LDLR gain-of-function variants demonstrate increased efficacy in mouse models of familial hypercholesterolemia

The low-density lipoprotein receptor: Emerging post-transcriptional regulatory mechanisms

Cholesterol is a vital component of cellular membranes and is an essential molecule in mammalian physiology. Yet dysregulation of hepatic cholesterol metabolism and an increase in plasma cholesterol is linked to development of atherosclerotic cardiovascular disease. Maintaining tight regulation of cholesterol homeostasis is therefore essential, elegantly highlighted by the control of hepatic low-density lipoprotein receptor (LDLR) abundance and associated lipoprotein clearance. The LDLR was discovered in the 1970's in the seminal work of Brown and Goldstein. This was followed by the development of statins, which promote hepatic clearance of LDL via the LDLR pathway. The discovery two decades ago of Proprotein Convertase Subtilisin-Kexin Type 9 (PCSK9), a secreted protein that binds to the LDLR ectodomain and promotes its degradation, and the clinical development of PCSK9 inhibitors has ushered an effort to uncover additional mechanisms that govern the function and abundance of the LDLR. In recent years this has led to the identification of novel post-transcriptional and post-translational mechanisms that govern the LDLR. This review focuses on these emerging regulatory mechanisms and specifically discusses: (1) Regulation of the LDLR mRNA by RNA-binding proteins and microRNAs, (2) Ubiquitin-dependent degradation of the LDLR protein by the E3 ubiquitin ligases inducible degrader of the LDLR (IDOL) and GOLIATH (RNF130), (3) Control of the LDLR pathway by the asialoglycoprotein receptor 1 (ASGR1), and (4) The role of LDLR ectodomain shedding mediated by membrane-type 1 matrix metalloprotease (MT1-MMP), Bone morphogenetic protein 1 (BMP1), and γ-secretase. Understanding the contribution of these emerging mechanisms to regulation of the LDLR is important for the development of novel LDLR-focused lipid-lowering strategies.

Chenodeoxycholic Acid-Modified Polyethyleneimine Nano-Composites Deliver Low-Density Lipoprotein Receptor Genes for Lipid-Lowering Therapy by Targeting the Liver

Lipid-lowering drugs, especially statins, are extensively utilized in clinical settings for the prevention of hyperlipidemia. Nevertheless, prolonged usage of current lipid-lowering medications is associated with significant adverse reactions. Therefore, it is imperative to develop novel therapeutic agents for lipid-lowering therapy. In this study, a chenodeoxycholic acid and lactobionic acid double-modified polyethyleneimine (PDL) nanocomposite as a gene delivery vehicle for lipid-lowering therapy by targeting the liver, are synthesized. Results from the in vitro experiments demonstrate that PDL exhibits superior transfection efficiency compared to polyethyleneimine in alpha mouse liver 12 (AML12) cells and effectively carries plasmids. Moreover, PDL can be internalized by AML12 cells and rapidly escape lysosomal entrapment. Intravenous administration of cyanine5.5 (Cy5.5)-conjugated PDL nanocomposites reveals their preferential accumulation in the liver compared to polyethyleneimine counterparts. Systemic delivery of low-density lipoprotein receptor plasmid-loaded PDL nanocomposites into mice leads to reduced levels of low-density lipoprotein cholesterol (LDL-C) and triglycerides (TC) in the bloodstream without any observed adverse effects on mouse health or well-being. Collectively, these findings suggest that low-density lipoprotein receptor plasmid-loaded PDL nanocomposites hold promise as potential therapeutics for lipid-lowering therapy.

Established and Emerging Nucleic Acid Therapies for Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disease that leads to elevated low-density lipoprotein cholesterol levels and risk of coronary heart disease. Current therapeutic options for FH remain relatively limited and only partially effective in both lowering low-density lipoprotein cholesterol and modifying coronary heart disease risk. The unique characteristics of nucleic acid therapies to target the underlying cause of the disease can offer solutions unachievable with conventional medications. DNA- and RNA-based therapeutics have the potential to transform the care of patients with FH. Recent advances are overcoming obstacles to clinical translation of nucleic acid-based medications, including greater stability of the formulations as well as site-specific delivery, making gene-based therapy for FH an alternative approach for treatment of FH.

Curcumin nicotinate increases LDL cholesterol uptake in hepatocytes through IDOL/LDL-R pathway regulation

BACKGROUND

Curcumin nicotinate (Curtn), derived from curcumin and niacin, reduces serum LDL-C levels, partly due to its influence on PCSK9. This study investigates IDOL's role in Curtn's lipid-lowering effects.

OBJECTIVE

To elucidate Curtn's regulation of the IDOL/LDLR pathway and potential molecular mechanisms in hepatocytes.

METHODS

Differential metabolites in Curtn-treated HepG2 cells were identified via LC-MS. Molecular docking assessed Curtn's affinity with IDOL. Cholesterol content and LDLR expression effects were studied in high-fat diet Wistar rats. In vitro evaluations determined Curtn's influence on IDOL overexpression's LDL-C uptake and LDLR expression in hepatocytes.

RESULTS

Lipids were the main differential metabolites in Curtn-treated HepG2 cells. Docking showed Curtn's higher affinity to IDOL's FERM domain compared to curcumin, suggesting potential competitive inhibition of IDOL's binding to LDLR. Curtn decreased liver cholesterol in Wistar rats and elevated LDLR expression. During in vitro experiments, Curtn significantly enhanced the effects of IDOL overexpression in HepG2 cells, leading to increased LDL-C uptake and elevated expression of LDL receptors.

CONCLUSION

Curtn modulates the IDOL/LDLR pathway, enhancing LDL cholesterol uptake in hepatocytes. Combined with its PCSK9 influence, Curtn emerges as a potential hyperlipidemia therapy.

Antihyperlipidemic Treatment Options in Statin Resistance and Intolerance

Cardiovascular disease is the global leading cause of death and hypercholesterolemia is implicated as one of its top contributors. Moreover, there is growing recognition that lower low-density lipoprotein cholesterol levels offer greater protection against cardiovascular disease. Statins are the first-line lipid-lowering agents for both primary and secondary prevention of cardiovascular disease in patients with hypercholesterolemia. However, statin resistance and intolerance lead to undertreatment in patients who would likely derive the most benefit from antihyperlipidemic drugs. Several non-statin therapies are increasingly prescribed to such patients, most commonly ezetimibe and the PCSK9 monoclonal antibodies, but numerous other options have been developed in recent years and investigations into new therapies are ongoing. The use of these non-statin therapies requires the clinician to take a highly personalized approach to cholesterol reduction in complex patients. In this review, we describe current non-statin options for statin-resistant and statin-intolerant patients in addition to areas of active research.

A Review of Progress on Targeting LDL Receptor-Dependent and -Independent Pathways for the Treatment of Hypercholesterolemia, a Major Risk Factor of ASCVD

Since the discovery of the LDL receptor in 1973 by Brown and Goldstein as a causative protein in hypercholesterolemia, tremendous amounts of effort have gone into finding ways to manage high LDL cholesterol in familial hypercholesterolemic (HoFH and HeFH) individuals with loss-of-function mutations in the LDL receptor (LDLR) gene. Statins proved to be the first blockbuster drug, helping both HoFH and HeFH individuals by inhibiting the cholesterol synthesis pathway rate-limiting enzyme HMG-CoA reductase and inducing the LDL receptor. However, statins could not achieve the therapeutic goal of LDL. Other therapies targeting LDLR include PCSK9, which lowers LDLR by promoting LDLR degradation. Inducible degrader of LDLR (IDOL) also controls the LDLR protein, but an IDOL-based therapy is yet to be developed. Among the LDLR-independent pathways, such as angiopoietin-like 3 (ANGPTL3), apolipoprotein (apo) B, apoC-III and CETP, only ANGPTL3 offers the advantage of treating both HoFH and HeFH patients and showing relatively better preclinical and clinical efficacy in animal models and hypercholesterolemic individuals, respectively. While loss-of-LDLR-function mutations have been known for decades, gain-of-LDLR-function mutations have recently been identified in some individuals. The new information on gain of LDLR function, together with CRISPR-Cas9 genome/base editing technology to target LDLR and ANGPTL3, offers promise to HoFH and HeFH individuals who are at a higher risk of developing atherosclerotic cardiovascular disease (ASCVD).

Familial Hypercholesterolemia: Challenges for a High-Risk Population: JACC Focus Seminar 1/3

The availability of statins, ezetimibe, and PCSK9 inhibitors has significantly improved the prognosis of familial hypercholesterolemia (FH). However, a great number of individuals with FH do not achieve guideline-recommended low-density lipoprotein (LDL) cholesterol levels despite maximal lipid-lowering therapy. Novel therapies that lower LDL independent of LDL receptor activity can help mitigate atherosclerotic cardiovascular disease risk in most homozygous FH and many heterozygous FH patients. However, access to novel therapies remains limited for heterozygous FH patients with persistent elevation of LDL cholesterol despite treatment with multiple classes of cholesterol-lowering therapies. Conduction of cardiovascular outcomes clinical trials in patients with FH can be challenging because of difficulty in recruitment and long periods of follow-up. In the future, the use of validated surrogate measures of atherosclerosis may allow for clinical trials with fewer study participants and shorter duration, thereby expediting access to novel treatments for patients with FH.

Curcumin nicotinate decreases serum LDL cholesterol through LDL receptor-mediated mechanism

Curcumin nicotinate (Curtn) is a synthesized ester derivative of curcumin and niacin. Our previous study has shown that Curtn lowers serum low-density lipoprotein cholesterol (LDL-C) levels in apoE^-/- mice and promotes LDL-C uptake into HepG2 cells in vitro. The present study was to test the hypothesis that Curtn decreases serum LDL-C levels through decreased expression of pro-protein convertase subtilisin/kexin type 9 (PCSK9) and subsequent increase in LDL receptor expression. Male Wistar rats on high-fat diet (HFD) were treated with Curtn or rosuvastatin. Curtn or rosuvastatin treatment significantly decreased serum levels of total cholesterol (TC) and LDL-C in rats on HFD with increased liver LDL receptor expression. LDL-C-lowering effect of Curtn was not observed in LDL receptor deficient (LDLR^-/-) mice on HFD, while rosuvastatin still decreased serum lipid levels in LDLR^-/- mice, indicating that the reduction of serum LDL-C levels by Curtn treatment was LDL receptor-dependent. Curtn treatment also significantly decreased the protein expression of PCSK9 in Wistar rats and LDLR^-/- mice. In HepG2 cells with overexpression of human PCSK9, Curtn treatment significantly increased LDL-C uptakes into hepatocytes, and increased LDL receptor distribution on cell surface in association with decreased PCSK9 protein expression. RNAi-LDLR significantly attenuated the effect of Curtn on LDLR distribution on cell surface. These data indicates that Curtn would decrease serum LDL-C level at least partially through inhibition of PCSK9 expression, and subsequent increase in LDL receptor expression and distribution in hepatocytes, serving as a potential novel compound to treat hyperlipidemia.

A novel mouse model of diabetes, atherosclerosis and fatty liver disease using an AAV8-PCSK9-D377Y injection and dietary manipulation in db/db mice

Preclinical mouse models of cardiometabolic diseases are crucial to study the pathological mechanisms of cardiometabolic diseases and to explore potential new therapeutic agents. Using double-knockouts in the background of ApoE^-/- or Ldlr^-/- mice requires an extensive amount of breeding and is costly. A significant breakthrough in atherosclerosis research is the use of AAV8-PCSK9-D377Y (a gain-of-function mutant of PCSK9 which promotes LDLR degradation) injection which can induce hyperlipidemia, increased endothelial stiffness, vascular calcification, aneurysm, and atherosclerotic plaque development in normal C57BL/6J mice. The purpose of this study was to assess the possibility that the injection of AAV8-PCSK9 vectors in db/db mice (a well-established animal model of type 2 diabetes mellitus) produces a novel mouse model of diabetes, atherosclerosis and fatty liver disease to study the pathomechanisms of cardiometabolic disease and its complications. Db/db mice were injected with AAV8-PCSK9-D377Y (AAV8-PCSK9 for simplicity) or AAV8-control and fed with high-cholesterol diets for 8 weeks. Levels of total cholesterol (TC) and triglyceride (TG) were significantly elevated in AAV8-PCSK9-injected mice compared to the controls. AAV8-PCSK9 injection led to increased serum level of PCSK9, serious liver steatosis, hypercholesterolemia and atherosclerotic plaque as determined by aortic arch/roots histopathological staining, with Oil Red O, Masson-trichrome and hematoxylin-eosin staining. RNA sequencing and bioinformatics were used to assess the global gene expression in liver tissues. We conclude that AAV8-PCSK9 injection in db/db mice is a promising and time-efficient approach to induce diabetic atherosclerosis with fatty liver. This mouse model can be a new one to investigate the etiology and therapeutics of atherosclerosis with diabetes and fatty liver beyond the traditional model established in ApoE^-/- mice or LDLR^-/- mice receiving streptozotocin (STZ) injection.

Cellular and Molecular Aspects of Managing Familial Hypercholesterolemia: Recent and Emerging Therapeutic Approaches

Familial hypercholesterolemia (FH) as a high-frequency genetic disorder is diagnosed based on family and/or patient's history of coronary heart disease (CHD) or some other atherosclerotic disease, LDL-C levels and/or clinical signs such as tendonous xantomata, arcus cornealis before age 45 years as well as functional mutation in the LDLR, apoB or PCSK9 gene. Its clinical features are detectable since early childhood. Early diagnosis and timely treatment increase life expectancy in most patients with FH. Current FH therapies decrease the level of low-density lipoprotein up to ≥50% from baseline with diet, pharmacotherapeutic treatment, lipid apheresis, and liver transplantation. The cornerstone of medical therapy is the use of more potent statins in higher doses, to which often ezetimibe has to be added, but some FH patients do not achieve the target LDL-C with this therapy Therefore, besides these and the most recent but already established therapeutic approaches including PCSK9 inhibitors, inclisiran, and bempedoic acid, new therapies are on the horizon such as gene therapy, CRISPR/Cas9 strategy etc. This paper focuses on cellular and molecular potential strategies for the treatment of FH.

Nogo-B promotes angiogenesis and improves cardiac repair after myocardial infarction via activating Notch1 signaling

Nogo-B (Reticulon 4B) is reportedly a regulator of angiogenesis during the development and progression of cancer. However, whether Nogo-B regulates angiogenesis and post-myocardial infarction (MI) cardiac repair remains elusive. In the present study, we aimed to explore the role and underlying mechanisms of Nogo-B in cardiac repair during MI. We observed an increased expression level of Nogo-B in the heart of mouse MI models, as well as in isolated cardiac microvascular endothelial cells (CMECs). Moreover, Nogo-B was significantly upregulated in CMECs exposed to oxygen-glucose deprivation (OGD). Nogo-B overexpression in the endothelium via cardiotropic adeno-associated virus serotype 9 (AAV9) with the mouse endothelial-specific promoter Tie2 improved heart function, reduced scar size, and increased angiogenesis. RNA-seq data indicated that Notch signaling is a deregulated pathway in isolated CMECs along the border zone of the infarct with Nogo-B overexpression. Mechanistically, Nogo-B activated Notch1 signaling and upregulated Hes1 in the MI hearts. Inhibition of Notch signaling using a specific siRNA and γ-secretase inhibitor abolished the promotive effects of Nogo-B overexpression on network formation and migration of isolated cardiac microvascular endothelial cells (CMECs). Furthermore, endothelial Notch1 heterozygous deletion inhibited Nogo-B-induced cardioprotection and angiogenesis in the MI model. Collectively, this study demonstrates that Nogo-B is a positive regulator of angiogenesis by activating the Notch signaling pathway, suggesting that Nogo-B is a novel molecular target for ischemic disease.

Hypoxia inducible factor 1α inhibitor PX-478 reduces atherosclerosis in mice

BACKGROUND AND AIMS

Hypoxia inducible factor 1α (HIF1α) plays a critical role in atherosclerosis as demonstrated in endothelial-targeted HIF1α -deficient mice. However, it has not been shown if specific pharmacological inhibitors of HIF1α can be used as potential drugs for atherosclerosis. PX-478 is a selective inhibitor of HIF1α, which was used to reduce cancer and obesity in animal models. Here, we tested whether PX-478 can be used to inhibit atherosclerosis.

METHODS

We first tested PX-478 in human aortic endothelial cells (HAEC) and found that it significantly inhibited expression of HIF1α and its targets, including Collagen I. Next, two independent atherosclerosis models, C57BL/6 mice treated with AAV-PCSK9 and ApoE^-/- mice, were used to test the efficacy of PX-478. Both mouse models were fed a Western diet for 3 months with bi-weekly treatment with PX-478 (40 mg/kg) or saline.

RESULTS

PX-478 treatment reduced atherosclerotic plaque burden in the aortic trees in both mouse models, while plaque burden in the aortic sinus was reduced in the AAV-PCSK9 mouse model, but not in the ApoE^-/- mice. Russell-Movat's Pentachrome and Picrosirius Red staining showed a significant reduction in extracellular matrix remodeling and collagen maturation, respectively, in the PX-478-treated mice. As expected, PX-478 treatment reduced diet-induced weight-gain and abdominal adipocyte hypertrophy. Interestingly, PX-478 reduced plasma LDL cholesterol by 69% and 30% in AAV-PCSK9 and ApoE^-/- mice, respectively. To explore the cholesterol-lowering mechanisms, we carried out an RNA sequencing study using the liver tissues from the ApoE^-/- mouse study. We found 450 genes upregulated and 381 genes downregulated by PX-478 treatment in the liver. Further, gene ontology analysis showed that PX-478 treatment upregulated fatty acid and lipid catabolic pathways, while downregulating lipid biosynthesis and plasma lipoprotein particle remodeling processes. Of interest, Cfd, Elovl3, and Insig2 were some of the most downregulated genes by PX-478, and have been implicated in fat storage, fatty acid elongation, and cholesterol metabolism. The downregulation of Cfd, Elovl3, and Insig2 was further validated by qPCR in the liver tissues of ApoE^-/- mice treated with PX-478.

CONCLUSIONS

These results suggest that PX-478 is a potential anti-atherogenic drug, which targets vascular endothelium and hepatic cholesterol pathways.

Developing a second-generation clinical candidate AAV vector for gene therapy of familial hypercholesterolemia

Gene therapy for hypercholesterolemia offers the potential to sustainably ameliorate disease for life with a single dose. In this study, we demonstrate the combinatorial effects of codon and vector optimization, which significantly improve the efficacy of an adeno-associated virus (AAV) vector in the low-density lipoprotein receptor (LDLR)-deficient mouse model (Ldlr -/-, Apobec1 -/- double knockout [DKO]). This study investigated vector efficacy following the combination of intervening sequence 2 (IVS2) of the human beta-globin gene and codon optimization with the previously developed gain-of-function, human LDLR triple-mutant variant (hLDLR-L318D/K809R/C818A) in the treatment of homozygous familial hypercholesterolemia (HoFH). Vector doses as low as 3 × 1011 genome copies (GC)/kg achieved a robust reduction of serum low-density lipoprotein cholesterol (LDL-C) by 98% in male LDLR-deficient mice. Less efficient LDL-C reduction was observed in female mice, which was attributable to lower gene transfer efficiency in liver. We also observed persistent and stable transgene expression for 120 days, with LDL-C levels being undetectable in male DKO mice treated with the second-generation vector. In conclusion, codon and vector optimization enhanced transgene expression and reduced serum LDL-C levels effectively at a lower dose in LDLR-deficient mice. The second-generation clinical candidate vector we have developed has the potential to achieve therapeutic effects in HoFH patients.

Narciclasine attenuates sepsis-induced myocardial injury by modulating autophagy

Acute myocardial injury (AMI) is often secondary to sepsis, which is a life-threatening disease associated with severe cardiac inflammation. Narciclasine, a plant alkaloid isolated from different members of the Amaryllidaceae family, has been extensively characterized as an antitumor and anti-inflammatory compound. In addition, autophagy is critical for sepsis-induced myocardial injury. However, the role and mechanism of autophagy by which narciclasine confers cardioprotection are still unclear. The present study aimed to investigate the underlying mechanism by which narciclasine affects the pathogenesis of sepsis-induced myocardial injury. Narciclasine effectively attenuated LPS-induced myocardial inflammation in vitro and in vivo. In addition, narciclasine protected cardiac function and suppressed the expression of inflammatory cytokines in LPS-induced heart tissue. Furthermore, narciclasine upregulated LPS-induced autophagic activity, and the autophagy inhibitor 3-MA abrogated narciclasine-mediated protection against LPS-induced AMI. Importantly, narciclasine exerted an inhibitory effect on the JNK signaling pathway, and JNK activity was tightly associated with narciclasine-induced autophagy and the consequent protective effects during AMI. Taken together, our findings indicate that narciclasine protects against LPS-induced AMI by inducing JNK-dependent autophagic flux; hence, narciclasine may be an effective and novel agent for the clinical treatment of sepsis-induced myocardial injury.

Hypoxia-inducible factor 2-alpha-dependent induction of IL-6 protects the heart from ischemia/reperfusion injury

Myocardial ischemia-reperfusion injury (MIRI) results in increased myocardial infarct size and leads to poor clinical outcomes. Hypoxia-inducible factor 2-alpha (HIF2α) exerts myocardial protective effects during MIRI through as yet unclear mechanisms. Here, we show that knockdown of HIF2α with cardiotropic recombinant adeno-associated virus serotype 9 (rAAV9) in mouse hearts significantly increased the infarct sizes during myocardial ischemia/reperfusion (MI/R). In addition, HIF2α transcriptionally regulated the expression of interleukin 6 (IL-6) in cardiomyocytes to elicit cardioprotection. Likewise, IL-6 deficiency aggravated MIRI, while treatment with recombinant IL-6 had cardioprotective effects and rescued the mice with HIF2α knockdown. Furthermore, IL-6 treatment significantly activated the PI3K/Akt and STAT3 signaling pathways in the myocardium during MI/R, and the specific inhibitors wortmannin (specific phosphoinositide 3-kinase inhibitor) and Stattic (specific STAT3 inhibitor) substantially abolished HIF2α/IL-6-induced cardioprotection. These studies suggest that HIF2α transcription regulates the expression of IL-6 in cardiomyocytes and plays a protective role during MI/R.

Cardioprotective Natural Compound Pinocembrin Attenuates Acute Ischemic Myocardial Injury via Enhancing Glycolysis

Purpose

Emerging evidence has shown that pinocembrin protects the myocardium from ischemic injury in animals. However, it is unknown whether it has cardioprotection when given at the onset of reperfusion. Also, mechanisms mediating the cardioprotective actions of pinocembrin were largely unknown. Thus, this study is aimed at investigating the effects of pinocembrin postconditioning on ischemia-reperfusion (I/R) injury and the underlying mechanisms.

Methods

The in vivo mouse model of myocardial I/R injury, ex vivo isolated rat heart with global I/R, and in vitro hypoxia/reoxygenation (H/R) injury model for primary cardiomyocytes were used.

Results

We found that pinocembrin postconditioning significantly reduced the infarct size and improved cardiac contractile function after acute myocardial I/R. Mechanically, in primary cardiomyocytes, we found that pinocembrin may confer protection in part via direct stimulation of cardiac glycolysis via promoting the expression of the glycolytic enzyme, PFKFB3. Besides, PFKFB3 inhibition abolished pinocembrin-induced glycolysis and protection in cardiomyocytes. More importantly, PFKFB3 knockdown via cardiotropic adeno-associated virus (AAV) abrogated cardioprotective effects of pinocembrin. Moreover, we demonstrated that HIF1α is a key transcription factor driving pinocembrin-induced PFKFB3 expression in cardiomyocytes.

Conclusions

In conclusion, these results established that the acute cardioprotective benefits of pinocembrin are mediated in part via enhancing PFKFB3-mediated glycolysis via HIF1α, which may provide a new therapeutic target to impede the progression of myocardial I/R injury.

Review of the scientific evolution of gene therapy for the treatment of homozygous familial hypercholesterolaemia: past, present and future perspectives

Familial hypercholesterolaemia (FH) is a devastating genetic disease that leads to extremely high cholesterol levels and severe cardiovascular disease, mainly caused by mutations in any of the main genes involved in low-density lipoprotein cholesterol (LDL-C) uptake. Among these genes, mutations in the LDL receptor (LDLR) are responsible for 80%–90% of the FH cases. The severe homozygous variety (HoFH) is not successfully treated with standard cholesterol-lowering therapies, and more aggressive strategies must be considered to mitigate the effects of this disease, such as weekly/biweekly LDL apheresis. However, development of new therapeutic approaches is needed to cure HoFH. Because HoFH is mainly due to mutations in theLDLR, this disease has been proposed as an ideal candidate for gene therapy. Several preclinical studies have proposed that the transference of functional copies of theLDLRgene reduces circulating LDL-C levels in several models of HoFH, which has led to the first clinical trials in humans. Additionally, the recent development of clustered regularly interspaced short palindromic repeat/CRISPR-associated 9 technology for genome editing has opened the door to therapies aimed at directly correcting the specific mutation in the endogenousLDLRgene. In this article, we review the genetic basis of the FH disease, paying special attention to the severe HoFH as well as the challenges in its diagnosis and clinical management. Additionally, we discuss the current therapies for this disease and the new emerging advances in gene therapy to target a definitive cure for this disease.

Acetaldehyde dehydrogenase 2 interactions with LDLR and AMPK regulate foam cell formation

Acetaldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme detoxifying acetaldehyde and endogenous lipid aldehydes; previous studies suggest a protective role of ALDH2 against cardiovascular disease (CVD). Around 40% of East Asians carrying the single nucleotide polymorphism (SNP) ALDH2 rs671 have an increased incidence of CVD. However, the role of ALDH2 in CVD beyond alcohol consumption remains poorly defined. Here we report that ALDH2/LDLR double knockout (DKO) mice have decreased atherosclerosis compared with LDLR-KO mice, whereas ALDH2/APOE-DKO mice have increased atherosclerosis, suggesting an unexpected interaction of ALDH2 with LDLR. Further studies demonstrate that in the absence of LDLR, AMPK phosphorylates ALDH2 at threonine 356 and enables its nuclear translocation. Nuclear ALDH2 interacts with HDAC3 and represses transcription of a lysosomal proton pump protein ATP6V0E2, critical for maintaining lysosomal function, autophagy, and degradation of oxidized low-density lipid protein. Interestingly, an interaction of cytosolic LDLR C-terminus with AMPK blocks ALDH2 phosphorylation and subsequent nuclear translocation, whereas ALDH2 rs671 mutant in human macrophages attenuates this interaction, which releases ALDH2 to the nucleus to suppress ATP6V0E2 expression, resulting in increased foam cells due to impaired lysosomal function. Our studies reveal a novel role of ALDH2 and LDLR in atherosclerosis and provide a molecular mechanism by which ALDH2 rs671 SNP increases CVD.

Familial Hypercholesterolemia: New Horizons for Diagnosis and Effective Management

Familial hypercholesterolemia (FH) is a common genetic cause of premature cardiovascular disease (CVD). The reported prevalence rates for both heterozygous FH (HeFH) and homozygous FH (HoFH) vary significantly, and this can be attributed, at least in part, to the variable diagnostic criteria used across different populations. Due to lack of consistent data, new global registries and unified guidelines are being formed, which are expected to advance current knowledge and improve the care of FH patients. This review presents a comprehensive overview of the pathophysiology, epidemiology, manifestations, and pharmacological treatment of FH, whilst summarizing the up-to-date relevant recommendations and guidelines. Ongoing research in FH seems promising and novel therapies are expected to be introduced in clinical practice in order to compliment or even substitute current treatment options, aiming for better lipid-lowering effects, fewer side effects, and improved clinical outcomes.

Familial hypercholesterolaemia

Familial hypercholesterolaemia is a common inherited disorder characterized by abnormally elevated serum levels of low-density lipoprotein (LDL) cholesterol from birth, which in time can lead to cardiovascular disease (CVD). Most cases are caused by autosomal dominant mutations in LDLR, which encodes the LDL receptor, although mutations in other genes coding for proteins involved in cholesterol metabolism or LDLR function and processing, such as APOB and PCSK9, can also be causative, although less frequently. Several sets of diagnostic criteria for familial hypercholesterolaemia are available; common diagnostic features are an elevated LDL cholesterol level and a family history of hypercholesterolaemia or (premature) CVD. DNA-based methods to identify the underlying genetic defect are desirable but not essential for diagnosis. Cascade screening can contribute to early diagnosis of the disease in family members of an affected individual, which is crucial because familial hypercholesterolaemia can be asymptomatic for decades. Clinical severity depends on the nature of the gene that harbours the causative mutation, among other factors, and is further modulated by the type of mutation. Lifelong LDL cholesterol-lowering treatment substantially improves CVD-free survival and longevity. Statins are the first-line therapy, but additional drugs, such as ezetimibe, bile acid sequestrants, PCSK9 inhibitors and other emerging therapies, are often required.

A human APOC3 missense variant and monoclonal antibody accelerate apoC-III clearance and lower triglyceride-rich lipoprotein levels

Recent large-scale genetic sequencing efforts have identified rare coding variants in genes in the triglyceride-rich lipoprotein (TRL) clearance pathway that are protective against coronary heart disease (CHD), independently of LDL cholesterol (LDL-C) levels. Insight into the mechanisms of protection of these variants may facilitate the development of new therapies for lowering TRL levels. The gene APOC3 encodes apoC-III, a critical inhibitor of triglyceride (TG) lipolysis and remnant TRL clearance. Here we report a detailed interrogation of the mechanism of TRL lowering by the APOC3 Ala43Thr (A43T) variant, the only missense (rather than protein-truncating) variant in APOC3 reported to be TG lowering and protective against CHD. We found that both human APOC3 A43T heterozygotes and mice expressing human APOC3 A43T display markedly reduced circulating apoC-III levels. In mice, this reduction is due to impaired binding of A43T apoC-III to lipoproteins and accelerated renal catabolism of free apoC-III. Moreover, the reduced content of apoC-III in TRLs resulted in accelerated clearance of circulating TRLs. On the basis of this protective mechanism, we developed a monoclonal antibody targeting lipoprotein-bound human apoC-III that promotes circulating apoC-III clearance in mice expressing human APOC3 and enhances TRL catabolism in vivo. These data reveal the molecular mechanism by which a missense variant in APOC3 causes reduced circulating TG levels and, hence, protects from CHD. This protective mechanism has the potential to be exploited as a new therapeutic approach to reduce apoC-III levels and circulating TRL burden.

Accelerated atherosclerosis development in C57Bl6 mice by overexpressing AAV-mediated PCSK9 and partial carotid ligation

Studying the role of a particular gene in atherosclerosis typically requires a time-consuming and often difficult process of generating double knockouts or transgenics on ApoE^-/- or LDL receptor (LDLR)^-/- background. Recently, it was reported that adeno-associated-virus-8 (AAV8)-mediated overexpression of PCSK9 (AAV8-PCSK9) rapidly induced hyperlipidemia. However, using this method in C57BL6 wild-type (C57) mice, it took ~3 months to develop atherosclerosis. Our partial carotid ligation model is used to rapidly develop atherosclerosis by inducing disturbed flow in the left common carotid artery within 2 weeks in ApoE^-/- or LDLR^-/- mice. Here, we combined these two approaches to develop an accelerated model of atherosclerosis in C57 mice. C57 mice were injected with AAV9-PCSK9 or AAV9-luciferase (control) and high-fat diet was initiated. A week later, partial ligation was performed. Compared to the control, AAV-PCSK9 led to elevated serum PCSK9, hypercholesterolemia, and rapid atherosclerosis development within 3 weeks as determined by gross plaque imaging, and staining with Oil-Red-O, Movat's pentachrome, and CD45 antibody. These plaque lesions were comparable to the atherosclerotic lesions that have been previously observed in ApoE^-/- or LDLR^-/- mice that were subjected to partial carotid ligation and high-fat diet. Next, we tested whether our method can be utilized to rapidly determine the role of a particular gene in atherosclerosis. Using eNOS^-/- and NOX1^-/y mice on C57 background, we found that the eNOS^-/- mice developed more advanced lesions, while the NOX1^-/y mice developed less atherosclerotic lesions as compared to the C57 controls. These results are consistent with the previous findings using double knockouts (eNOS^-/-_ApoE^-/- and NOX1^-/y_ApoE^-/-). AAV9-PCSK9 injection followed by partial carotid ligation is an effective and time-saving approach to rapidly induce atherosclerosis. This accelerated model is well-suited to quickly determine the role of gene(s) interest without generating double or triple knockouts.

Defining severe familial hypercholesterolaemia and the implications for clinical management: a consensus statement from the International Atherosclerosis Society Severe Familial Hypercholesterolemia Panel

Familial hypercholesterolaemia is common in individuals who had a myocardial infarction at a young age. As many as one in 200 people could have heterozygous familial hypercholesterolaemia, and up to one in 300 000 individuals could be homozygous. The phenotypes of heterozygous and homozygous familial hypercholesterolaemia overlap considerably; the response to treatment is also heterogeneous. In this Review, we aim to define a phenotype for severe familial hypercholesterolaemia and identify people at highest risk for cardiovascular disease, based on the concentration of LDL cholesterol in blood and individuals' responsiveness to conventional lipid-lowering treatment. We assess the importance of molecular characterisation and define the role of other cardiovascular risk factors and advanced subclinical coronary atherosclerosis in risk stratification. Individuals with severe familial hypercholesterolaemia might benefit in particular from early and more aggressive cholesterol-lowering treatment (eg, with PCSK9 inhibitors). In addition to better tailored therapy, more precise characterisation of individuals with severe familial hypercholesterolaemia could improve resource use.

Recent Developments in Gene Therapy for Homozygous Familial Hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) is a life-threatening Mendelian disorder with a mean life expectancy of 33 years despite maximally tolerated standard lipid-lowering therapies. This disease is an ideal candidate for gene therapy, and in the last few years, a number of exciting developments have brought this approach closer to the clinic than ever before. In this review, we discuss in detail the most advanced of these developments, a recombinant adeno-associated virus (AAV) vector carrying a low-density lipoprotein receptor (LDLR) transgene which has recently entered phase 1/2a testing. We also review ongoing development of approaches to enhance transgene expression, improve the efficiency of hepatocyte transduction, and minimize the AAV capsid-specific adaptive immune response. We include a summary of key gene therapy approaches for HoFH in pre-clinical development, including RNA silencing of the gene encoding HMG-CoA reductase (HMGCR) and induced pluripotent stem cell transplant therapy.

From Loci to Biology: Functional Genomics of Genome-Wide Association for Coronary Disease

Genome-wide association studies have provided a rich collection of ≈ 58 coronary artery disease (CAD) loci that suggest the existence of previously unsuspected new biology relevant to atherosclerosis. However, these studies only identify genomic loci associated with CAD, and many questions remain even after a genomic locus is definitively implicated, including the nature of the causal variant(s) and the causal gene(s), as well as the directionality of effect. There are several tools that can be used for investigation of the functional genomics of these loci, and progress has been made on a limited number of novel CAD loci. New biology regarding atherosclerosis and CAD will be learned through the functional genomics of these loci, and the hope is that at least some of these new pathways relevant to CAD pathogenesis will yield new therapeutic targets for the prevention and treatment of CAD.

Novel therapies for severe dyslipidemia originating from human genetics

PURPOSE OF REVIEW

Novel therapies for severe dyslipidemia target a wide range of unmet medical needs: severe familial hypercholesterolemia, severe hypertriglyceridemia and chylomicronemia, elevated lipoprotein (a), lipodystrophies, high-density lipoprotein particle diseases, lysosomal acid lipase deficiency and storage diseases, nonalcoholic fatty liver disease and others. The purpose of this review is to describe the contribution of human genetics to the development of therapeutic approaches targeting severe dyslipidemia.

RECENT FINDINGS

Recent advances in human genetics and the identification of rare genetic variants having strong effects on disease risk not only accelerated the development of therapies for severe dyslipidemia, they also revealed new pathways, genes and mechanisms of health, disease or drug response, and facilitated molecular diagnosis, which may prove essential as the authorized use of some of these novel drugs is limited to specific conditions. In addition, the dissection of the gene and cell machinery gave rise to new technologies, gene-based therapies and biodrugs covering a broad range of novel agents currently available or in clinical development to treat severe lipid disorders.

SUMMARY

Several novel therapies are recently available or under development to treat severe dyslipidemia and associated risk stem directly from genetic research. Altogether, these therapies target a broad variety of severe dyslipidemia pathways or mechanisms and illustrate that clinical lipidology has now entered the era of precision medicine.

Rare variant in scavenger receptor BI raises HDL cholesterol and increases risk of coronary heart disease

Scavenger receptor BI (SR-BI) is the major receptor for high-density lipoprotein (HDL) cholesterol (HDL-C). In humans, high amounts of HDL-C in plasma are associated with a lower risk of coronary heart disease (CHD). Mice that have depleted Scarb1 (SR-BI knockout mice) have markedly elevated HDL-C levels but, paradoxically, increased atherosclerosis. The impact of SR-BI on HDL metabolism and CHD risk in humans remains unclear. Through targeted sequencing of coding regions of lipid-modifying genes in 328 individuals with extremely high plasma HDL-C levels, we identified a homozygote for a loss-of-function variant, in which leucine replaces proline 376 (P376L), in SCARB1, the gene encoding SR-BI. The P376L variant impairs posttranslational processing of SR-BI and abrogates selective HDL cholesterol uptake in transfected cells, in hepatocyte-like cells derived from induced pluripotent stem cells from the homozygous subject, and in mice. Large population-based studies revealed that subjects who are heterozygous carriers of the P376L variant have significantly increased levels of plasma HDL-C. P376L carriers have a profound HDL-related phenotype and an increased risk of CHD (odds ratio = 1.79, which is statistically significant).

Human PCSK9 promotes hepatic lipogenesis and atherosclerosis development via apoE- and LDLR-mediated mechanisms

AIMS

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of hepatic low-density lipoprotein (LDL) receptors (LDLR), thereby, decreasing hepatocyte LDL-cholesterol (LDL-C) uptake. However, it is unknown whether PCSK9 has effects on atherogenesis that are independent of lipid changes. The present study investigated the effect of human (h) PCSK9 on plasma lipids, hepatic lipogenesis, and atherosclerotic lesion size and composition in transgenic mice expressing hPCSK9 (hPCSK9tg) on wild-type (WT), LDLR⁻/⁻, or apoE⁻/⁻ background.

METHODS AND RESULTS

hPCSK9 expression significantly increased plasma cholesterol (+91%), triglycerides (+18%), and apoB (+57%) levels only in WT mice. The increase in plasma lipids was a consequence of both decreased hepatic LDLR and increased hepatic lipid production, mediated transcriptionally and post-transcriptionally by PCSK9 and dependent on both LDLR and apoE. Despite the lack of changes in plasma lipids in mice expressing hPCSK9 and lacking LDLR (the main target for PCSK9) or apoE (a canonical ligand for the LDLR), hPCSK9 expression increased aortic lesion size in the absence of apoE (268 655 ± 97 972 µm² in hPCSK9tg/apoE⁻/⁻ vs. 189 423 ± 65 700 µm(2) in apoE⁻/⁻) but not in the absence of LDLR. Additionally, hPCSK9 accumulated in the atheroma and increased lesion Ly6C(hi) monocytes (by 21%) in apoE⁻/⁻ mice, but not in LDLR⁻/⁻ mice.

CONCLUSIONS

PCSK9 increases hepatic lipid and lipoprotein production via apoE- and LDLR-dependent mechanisms. However, hPCSK9 also accumulate in the artery wall and directly affects atherosclerosis lesion size and composition independently of such plasma lipid and lipoprotein changes. These effects of hPCSK9 are dependent on LDLR but are independent of apoE.

Stable liver-specific expression of human IDOL in humanized mice raises plasma cholesterol

AIMS

IDOL (inducible degrader of the low-density lipoprotein receptor, LDLR) is an E3 ubiquitin ligase that promotes the ubiquitination and degradation of the LDLR. IDOL is a potential therapeutic target for the development of a novel class of low-density lipoprotein cholesterol (LDL-C)-lowering therapies. In an attempt to develop a mouse model for testing IDOL inhibitors, we examined the effects of adeno-associated virus (AAV)-mediated stable expression of human IDOL in the livers of mice 'humanized' with regard to lipoprotein metabolism.

METHODS AND RESULTS

Using a liver-specific AAV serotype 8 (AAV8)-mediated delivery, AAV-hIDOL produced a dose-dependent increase in LDL-C levels and a decrease in liver LDLR protein. Furthermore, we expressed hIDOL in a 'humanized' mouse model of heterozygous familial hypercholesterolaemia (LDLR(+/-)/Apobec1(-/-)/hApoB-Tg, LAhB). In this model, total cholesterol (TC) and LDL-C levels were increased by ∼60% starting from 1 week and were sustainable for at least 3 weeks post-injection. Finally, we demonstrate that the effects caused by hIDOL expression are LDLR- dependent given the unchanged plasma lipids in LAhB mice lacking LDLR.

CONCLUSION

In conclusion, our study demonstrates a dose-dependent physiological effect of human IDOL on LDL metabolism in mice. This provides a potential model for preclinical testing of IDOL inhibitors for reduction of LDL-C levels.

Sleeping Beauty Transposon Vectors in Liver-directed Gene Delivery of LDLR and VLDLR for Gene Therapy of Familial Hypercholesterolemia

Plasmid-based Sleeping Beauty (SB) transposon vectors were developed and used to deliver genes for low-density lipoprotein and very-low-density lipoprotein receptors (LDLR and VLDLR, respectively) or lacZ reporter into liver of an LDLR-deficient mouse model of familial hypercholesterolemia (FH). SB transposase, SB100x, was used to integrate the therapeutic transposons into mice livers for evaluating the feasibility of the vectors in reducing high blood cholesterol and the progression of atherosclerosis. Hydrodynamic gene delivery of transposon-VLDLR into the livers of the mice resulted in initial 17-19% reductions in plasma cholesterol, and at the later time points, in a significant stabilization of the cholesterol level for the 6.5-month duration of the study compared to the control mice. Transposon-LDLR-treated animals also demonstrated a trend of stabilization in the cholesterol levels in the long term. Vector-treated mice had slightly less lipid accumulation in the liver and reduced aortic atherosclerosis. Clinical chemistry and histological analyses revealed normal liver function and morphology comparable to that of the controls during the follow-up with no safety issues regarding the vector type, transgenes, or the gene transfer method. The study demonstrates the safety and potential benefits of the SB transposon vectors in the treatment of FH.

Gene-based therapies in lipidology: current status and future challenges

PURPOSE OF REVIEW

Gene-based therapies are designed to modulate gene expression in specific tissues by introducing into cells transgenes, antisense oligonucleotides, RNA interference, microRNAs, or a variety of other oligonucleotide-based compounds and their delivery systems. Several types of gene-based therapies are already available or in clinical development to treat severe lipid-related disorders and associated risk. The review briefly presents the current status and future challenges of these therapies in clinical lipidology, focusing on most advanced and promising agents or mechanisms.

RECENT FINDINGS

Gene-based agents address several unmet medical needs in lipidology such as homozygous familial hypercholesterolemia, familial or multifactorial chylomicronemia, severe hypertriglyceridemia, elevated lipoprotein (a), familial partial lipodystrophy, nonalcoholic fatty liver disease, and hypoalphalipoproteinemia. Most advanced antisense oligonucleotide drugs target apolipoprotein C-III, apolipoprotein (a), angiopoietin-like 3, and diacylglycerol o-acyltransferase-2. Long-term efficacy and safety data are now available for two gene-based agents, mipomersen, approved in the USA for homozygous familial hypercholesterolemia and Glybera, AAV1-LPLS447X gene therapy, conditionally approved in Europe for lipoprotein lipase deficiency.

SUMMARY

Although positive to date, the overall benefit-risk ratio of gene-based therapies is yet to be documented long term across additional patients and conditions. The next generation of such therapies might improve their therapeutic index.

IDOL, inducible degrader of low-density lipoprotein receptor, serves as a potential therapeutic target for dyslipidemia

Low-density lipoprotein cholesterol (LDL-C) is the hall marker for the atherosclerotic cardiovascular disease (ASCVD). It has been shown that over 70% of circulating LDL-C is metabolized through binding and activation of hepatic LDL receptor (LDLR). Genetic LDLR mutations cause hypercholesterolemia in the patients. Therefore, elevation of LDLR levels is beneficial for the treatment of dyslipidemia. LDLR expression is regulated by the SREBP2/PCSK9 pathways. Targeting SREBP2/PCSK9 pathways by statins and human monoclonal PCSK9 antibody has been shown to reduce the progression of ASVCD. Recent studies identified that inducible degrader of LDLR (IDOL) is a novel regulator of LDLR. IDOL is an E3-ubiquitin ligase regulated via liver X receptors (LXRs) binding to the upstream of translation start site of IDOL. IDOL modulates LDLR distribution through ubiquitination and degradation of LDLR in lysosomes. Genome-wide association studies (GWAS) have revealed that the nonsynonymous substitution rs9370867 of IDOL probably contributes to the variability of circulating LDL levels. Recently studies also demonstrated that IDOL influences PCSK9 expression in a LDLR/SREBP2-dependent manner. Based upon these novel findings, we hypothesize that IDOL and PCSK9 would have a synergistic effect on LDLR distribution. Specifically, loss of IDOL increases LDLR distribution in the hepatic cell, and subsequently reduces serum LDL-C levels in dyslipidemic patients. IDOL might be a potential therapeutic target for the treatment of ASCVD.

PCSK9 inhibition to reduce cardiovascular disease risk: recent findings from the biology of PCSK9

PURPOSE OF REVIEW

Review novel insights into the biology of proprotein convertase subtilisin/kexin 9 (PCSK9) that may explain the extreme efficiency of PCSK9 inhibition and the unexpected metabolic effects resulting from PCSK9 monoclonal antibody therapy, and may identify additional patients as target of therapy.

RECENT FINDINGS

For over 20 years, the practical knowledge of cholesterol metabolism has centered around cellular mechanisms, and around the idea that statin therapy is the essential step to control metabolic abnormalities for cardiovascular risk management. This view has been embraced by the recent AHA/ACC guidelines, but is being challenged by recent studies including nonstatin medications and by the development of a new class of cholesterol-lowering agents that seems destined to early US Food and Drug Administration approval. The discovery of PCSK9 - a circulating protein that regulates hepatic low-density lipoprotein (LDL) receptor and serum LDL cholesterol levels - has led to a race for its therapeutic inhibition. Recent findings on PCSK9 regulation and pleiotropic effects will help identify additional patient groups likely to benefit from the inhibitory therapy and unravel the full potential of PCSK9 inhibition therapy.

SUMMARY

Injectable human monoclonal antibodies to block the interaction between PCSK9 and LDL receptor are demonstrating extraordinary efficacy (LDL reductions of up to 70%) and almost the absence of any side-effects. A more moderate effect is seen on other lipoprotein parameters, with the exception of lipoprotein(a) levels. We describe mechanisms that can explain the effect on lipoprotein(a), predict a potential effect on postprandial triglyderides, and suggest a new category of patients for anti-PCSK9 therapy.

Macrophage sortilin promotes LDL uptake, foam cell formation, and atherosclerosis

RATIONALE

Noncoding gene variants at the SORT1 locus are strongly associated with low-density lipoprotein cholesterol (LDL-C) levels, as well as with coronary artery disease. SORT1 encodes a protein called sortilin, and hepatic sortilin modulates LDL metabolism by targeting apolipoprotein B-containing lipoproteins to the lysosome. Sortilin is also expressed in macrophages, but its role in macrophage uptake of LDL and in atherosclerosis independent of plasma LDL-C levels is unknown.

OBJECTIVE

To determine the effect of macrophage sortilin expression on LDL uptake, foam cell formation, and atherosclerosis.

METHODS AND RESULTS

We crossed Sort1(-/-) mice onto a humanized Apobec1(-/-); hAPOB transgenic background and determined that Sort1 deficiency on this background had no effect on plasma LDL-C levels but dramatically reduced atherosclerosis in the aorta and aortic root. To test whether this effect was a result of macrophage sortilin deficiency, we transplanted Sort1(-/-);LDLR(-/-) or Sort1(+/+);LDLR(-/-) bone marrow into Ldlr(-/-) mice and observed a similar reduction in atherosclerosis in mice lacking hematopoetic sortilin without an effect on plasma LDL-C levels. In an effort to determine the mechanism by which hematopoetic sortilin deficiency reduced atherosclerosis, we found no effect of sortilin deficiency on macrophage recruitment or lipopolysaccharide-induced cytokine release in vivo. In contrast, sortilin-deficient macrophages had significantly reduced uptake of native LDL ex vivo and reduced foam cell formation in vivo, whereas sortilin overexpression in macrophages resulted in increased LDL uptake and foam cell formation.

CONCLUSIONS

Macrophage sortilin deficiency protects against atherosclerosis by reducing macrophage uptake of LDL. Sortilin-mediated uptake of native LDL into macrophages may be an important mechanism of foam cell formation and contributor to atherosclerosis development.