Pharmacogenetic aspects in familial hypercholesterolemia with the special focus on FHMarburg (FH p.W556R)

Targeting Liver Epsins Ameliorates Dyslipidemia in Atherosclerosis

Rationale

Low density cholesterol receptor (LDLR) in the liver is critical for the clearance of low-density lipoprotein cholesterol (LDL-C) in the blood. In atherogenic conditions, proprotein convertase subtilisin/kexin 9 (PCSK9) secreted by the liver, in a nonenzymatic fashion, binds to LDLR on the surface of hepatocytes, preventing its recycling and enhancing its degradation in lysosomes, resulting in reduced LDL-C clearance. Our recent studies demonstrate that epsins, a family of ubiquitin-binding endocytic adaptors, are critical regulators of atherogenicity. Given the fundamental contribution of circulating LDL-C to atherosclerosis, we hypothesize that liver epsins promote atherosclerosis by controlling LDLR endocytosis and degradation.

Objective

We will determine the role of liver epsins in promoting PCSK9-mediated LDLR degradation and hindering LDL-C clearance to propel atherosclerosis.

Methods and Results

We generated double knockout mice in which both paralogs of epsins, namely, epsin-1 and epsin-2, are specifically deleted in the liver (Liver-DKO) on an ApoE -/- background. We discovered that western diet (WD)-induced atherogenesis was greatly inhibited, along with diminished blood cholesterol and triglyceride levels. Mechanistically, using scRNA-seq analysis on cells isolated from the livers of ApoE-/- and ApoE-/- /Liver-DKO mice on WD, we found lipogenic Alb hi hepatocytes to glycogenic HNF4α hi hepatocytes transition in ApoE-/- /Liver-DKO. Subsequently, gene ontology analysis of hepatocyte-derived data revealed elevated pathways involved in LDL particle clearance and very-low-density lipoprotein (VLDL) particle clearance under WD treatment in ApoE-/- /Liver-DKO, which was coupled with diminished plasma LDL-C levels. Further analysis using the MEBOCOST algorithm revealed enhanced communication score between LDLR and cholesterol, suggesting elevated LDL-C clearance in the ApoE-/- Liver-DKO mice. In addition, we showed that loss of epsins in the liver upregulates of LDLR protein level. We further showed that epsins bind LDLR via the ubiquitin-interacting motif (UIM), and PCSK9-triggered LDLR degradation was abolished by depletion of epsins, preventing atheroma progression. Finally, our therapeutic strategy, which involved targeting liver epsins with nanoparticle-encapsulated siRNAs, was highly efficacious at inhibiting dyslipidemia and impeding atherosclerosis.

Conclusions

Liver epsins promote atherogenesis by mediating PCSK9-triggered degradation of LDLR, thus raising the circulating LDL-C levels. Targeting epsins in the liver may serve as a novel therapeutic strategy to treat atherosclerosis by suppression of PCSK9-mediated LDLR degradation.

Cellular and functional evaluation of LDLR missense variants reported in hypercholesterolemic patients demonstrates their hypomorphic impacts on trafficking and LDL internalization

Background

Familial hypercholesterolemia (FH) is an autosomal dominant disorder characterized by increased LDL-cholesterol levels. About 85% of FH cases are caused by LDLR mutations encoding the low-density lipoprotein receptor (LDLR). LDLR is synthesized in the endoplasmic reticulum (ER) where it undergoes post-translational modifications and then transported through Golgi apparatus to the plasma membrane. Over 2900 LDLR variants have been reported in FH patients with limited information on the pathogenicity and functionality of many of them. This study aims to elucidate the cellular trafficking and functional implications of LDLR missense variants identified in suspected FH patients using biochemical and functional methods.

Methods

We used HeLa, HEK293T, and LDLR-deficient-CHO-ldlA7 cells to evaluate the subcellular localization and LDL internalization of ten LDLR missense variants (p.C167F, p.D178N, p.C243Y, p.E277K, p.G314R, p.H327Y, p.D477N, p.D622G, p.R744Q, and p.R814Q) reported in multiethnic suspected FH patients. We also analyzed the functional impact of three variants (p.D445E, p.D482H, and p.C677F), two of which previously shown to be retained in the ER.

Results

We show that p.D622G, p.D482H, and p.C667F are largely retained in the ER whereas p.R744Q is partially retained. The other variants were predominantly localized to the plasma membrane. LDL internalization assays in CHO-ldlA7 cells indicate that p.D482H, p.C243Y, p.D622G, and p.C667F have quantitatively lost their ability to internalize Dil-LDL with the others (p.C167F, p.D178N, p.G314R, p.H327Y, p.D445E, p.D477N, p.R744Q and p.R814Q) showing significant losses except for p.E277K which retained full activity. However, the LDL internalization assay is only to able evaluate the impact of the variants on LDL internalization and not the exact functional defects such as failure to bind LDL. The data represented illustrate the hypomorphism nature of variants causing FH which may explain some of the variable expressivity of FH.

Conclusion

Our combinatorial approach of in silico, cellular, and functional analysis is a powerful strategy to determine pathogenicity and FH disease mechanisms which may provide opportunitites for novel therapeutic strategies.

Effects of LDLR variants rs5928, rs750518671 and rs879254797 on protein structure and functional activity in HepG2 cells transfected with CRISPR/Cas9 constructs

Familial Hypercholesterolemia (FH) is a genetic disorder associated with premature atherosclerosis and increased risk of cardiovascular diseases. LDLR deleterious mutations are associated with FH, however the role of some missense variants in FH pathogenicity remains to be elucidated. This study explored the predictive impact of LDLR missense variants on protein structure and investigated their functional effects on LDLR expression in HepG2 cells transfected with CRISPR/Cas9 constructs. FH (n = 287) and non-FH patients (n = 45) were selected, and lipid profile was obtained from medical records. LDLR variants were identified using an exon-targeted gene sequencing strategy, considering its cost-effective to increase accuracy in the identification step of the most likely FH-related variants in a less laborious process. LDLR variants were selected based on conflicting pathogenicity results found in Clinvar, in silico prediction tools, affected LDLR domains, and less common variants considering minor allele frequency < 0.05. Molecular modeling studies were used to predict the effects of LDLR missense variants on protein structure. Recombinant LDLR variants were constructed using CRISPR/Cas9 system and were used to transfect HepG2 cells. Functional assays in transfected cells were performed to assess LDLR expression using flow cytometry and western blotting, and LDLR activity using flow cytometry and confocal microscopy. The variants rs121908039 (c.551G>A, p.C184Y), rs879254797 (c.1118G>A, p.G373D), rs28941776 (c.1646G>A, p.G549D), rs750518671 (c.2389G>C, p.V797L), rs5928 (c.2441G>A, p.R814Q) and rs137853964 (c.2479G>A, p.V827I) were selected for molecular docking analysis. The p.C184Y exhibited a favorable energy change for protein stability due to its interaction with EGF-A/EGF-B regions; p.G373D and p.G549D displayed intermediate energy changes; and p.R814Q and p.V827I showed smaller energy changes. The results of functional assays showed that p.G373D, p.V797L and p.R814Q reduced LDLR expression and activity (p < 0.05). Microscopic analysis of the p.V797L and p.G373D variants revealed altered lipid localization and accumulation in transfected HepG2 cells. Carriers of p.G549D, p.V797L and p.R814Q had higher LDL cholesterol levels than non-FH group, and (p < 0.05). p.G373D and p.G549D were associated with clinical manifestations of FH. In conclusion, the p.C184Y, p.G373D, p.G549D and p.R814Q variants alter protein stability and intramolecular interactions, while p.V797L has a minimal impact on protein stability, and p.V827I has no significant intramolecular interactions. p.G373D, p.V767L and p.R814Q are associated with impaired LDLR expression and activity.

Pharmacogenomics Variability of Lipid-Lowering Therapies in Familial Hypercholesterolemia

The exponential expansion of genomic data coupled with the lack of appropriate clinical categorization of the variants is posing a major challenge to conventional medications for many common and rare diseases. To narrow this gap and achieve the goals of personalized medicine, a collaborative effort should be made to characterize the genomic variants functionally and clinically with a massive global genomic sequencing of "healthy" subjects from several ethnicities. Familial-based clustered diseases with homogenous genetic backgrounds are amongst the most beneficial tools to help address this challenge. This review will discuss the diagnosis, management, and clinical monitoring of familial hypercholesterolemia patients from a wide angle to cover both the genetic mutations underlying the phenotype, and the pharmacogenomic traits unveiled by the conventional and novel therapeutic approaches. Achieving a drug-related interactive genomic map will potentially benefit populations at risk across the globe who suffer from dyslipidemia.

Pharmacogenomics of statins and familial hypercholesterolemia

PURPOSE OF REVIEW

To collect evidence on statin pharmacogenomics, and review what is known in this field for familial hypercholesterolemia (FH) patients.

RECENT FINDINGS

There are well-known associations between specific single nucleotide polymorphisms involved in statin transport and metabolism and either adverse effects or altered lipid-lowering efficacy. However, the applicability of this knowledge is uncertain, especially in high-risk populations. There are alternative approaches to study plasma concentrations of statins and new insights on why some association studies fail to be replicated.

SUMMARY

Statin therapy recommendations are not always followed in primary and secondary prevention and, even when followed, patients often fail to reach therapeutic target values. Considering the stringent 2019 European Atherosclerosis Society and European Society of Cardiology recommended target lipid levels, as well as the persistently high cost for alternative lipid-lowering therapies such as PCSK9 inhibitors, the variability in low-density lipoprotein cholesterol reductions on statin therapy is still an important factor that needs to be addressed to ensure better cardiovascular disease risk management, especially for FH patients, who have not been well studied historically in this context.

GENetic characteristics and REsponse to lipid-lowering therapy in familial hypercholesterolemia: GENRE-FH study

Among the 146 patients enrolled in the Korean FH registry, 83 patients who had undergone appropriate LLT escalation and were followed-up for ≥ 6 months were analyzed for pathogenic variants (PVs). The achieved percentage of expected low-density lipoprotein-cholesterol (LDL-C) reduction (primary variable) and achievement rates of LDL-C < 70 mg/dL were assessed. The correlations between the treatment response and the characteristics of PVs, and the weighted 4 SNP-based score were evaluated. The primary variables were significantly lower in the PV-positive patients than in the PV-negative patients (p = 0.007). However, the type of PV did not significantly correlate with the primary variable. The achievement rates of LDL-C < 70 mg/dL was very low, regardless of the PV characteristics. Patients with a higher 4-SNP score showed a lower primary variable (R² = 0.045, p = 0.048). Among evolocumab users, PV-negative patients or those with only defective PVs revealed higher primary variable, whereas patients with at least one null PV showed lower primary variables. The adjusted response of patients with FH to LLT showed significant associations with PV positivity and 4-SNP score. These results may be helpful in managing FH patients with diverse genetic backgrounds.

Proteostasis Regulation in the Endoplasmic Reticulum: An Emerging Theme in the Molecular Pathology and Therapeutic Management of Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal genetic disease characterized by high serum low-density lipoprotein (LDL) content leading to premature coronary artery disease. The main genetic and molecular causes of FH are mutations in low-density lipoprotein receptor gene (LDLR) resulting in the non-clearance of LDL from the blood by hepatocytes and consequently the formation of plaques. LDLR is synthesized and glycosylated in the endoplasmic reticulum (ER) and then transported to the plasma membrane via Golgi. It is estimated that more than 50% of reported FH-causing mutations in LDLR result in misfolded proteins that are transport-defective and hence retained in ER. ER accumulation of misfolded proteins causes ER-stress and activates unfolded protein response (UPR). UPR aids protein folding, blocks further protein synthesis, and eliminates misfolded proteins via ER-associated degradation (ERAD) to alleviate ER stress. Various studies demonstrated that ER-retained LDLR mutants are subjected to ERAD. Interestingly, chemical chaperones and genetic or pharmacological inhibition of ERAD have been reported to rescue the transport defective mutant LDLR alleles from ERAD and restore their ER-Golgi transport resulting in the expression of functional plasma membrane LDLR. This suggests the possibility of pharmacological modulation of proteostasis in the ER as a therapeutic strategy for FH. In this review, we picture a detailed analysis of UPR and the ERAD processes activated by ER-retained LDLR mutants associated with FH. In addition, we discuss and critically evaluate the potential role of chemical chaperones and ERAD modulators in the therapeutic management of FH.

In Silico Insights into Protein-protein Interaction Disruptive Mutations in the PCSK9-LDLR complex

Gain-of-function mutations in PCSK9 (proprotein convertase subtilisin/kexin type 9) lead to reduced uptake of LDL (low density lipoprotein) cholesterol and, therefore, increased plasma LDL levels. However, the mechanism by which these mutants reduce LDL reuptake is not fully understood. Here, we have used molecular dynamics simulations, MM/PBSA (Molecular Mechanics/Poisson-Boltzmann Surface Area) binding affinity calculations, and residue interaction networks, to investigate the protein-protein interaction (PPI) disruptive effects of two of PCSK9's gain-of-function mutations, Ser127Arg and Asp374Tyr on the PCSK9 and LDL receptor complex. In addition to these PPI disruptive mutants, a third, non-interface mutation (Arg496Trp) is included as a positive control. Our results indicate that Ser127Arg and Asp374Tyr confer significantly improved binding affinity, as well as different binding modes, when compared to the wild-type. These PPI disruptive mutations lie between the EGF(A) (epidermal growth factor precursor homology domain A) of the LDL receptor and the catalytic domain of PCSK9 (Asp374Tyr) and between the prodomain of PCSK9 and the β-propeller of the LDL receptor (Ser127Arg). The interactions involved in these two interfaces result in an LDL receptor that is sterically inhibited from entering its closed conformation. This could potentially implicate the prodomain as a target for small molecule inhibitors.

Translating Pharmacogenetics and Pharmacogenomics to the Clinic: Progress in Human and Veterinary Medicine

As targeted personalized therapy becomes more widely used in human medicine, clients will expect the veterinary clinician to be able to implement an evidence-based strategy regarding both the prescribing of medicines and also recognition of the potential for adverse drug reactions (ADR) for their pet, at breed and individual level. This review aims to provide an overview of current developments and challenges in pharmacogenetics in medicine for a veterinary audience and to map these to developments in veterinary pharmacogenetics. Pharmacogenetics has been in development over the past 100 years but has been revolutionized following the publication of the human, and then veterinary species genomes. Genetic biomarkers called pharmacogenes have been identified as specific genetic loci on chromosomes which are associated with either positive or adverse drug responses. Pharmacogene variation may be classified according to the associated drug response, such as a change in (1) the pharmacokinetics; (2) the pharmacodynamics; (3) genes in the downstream pathway of the drug or (4) the effect of “off-target” genes resulting in a response that is unrelated to the intended target. There are many barriers to translation of pharmacogenetic information to the clinic, however, in human medicine, international initiatives are promising real change in the delivery of personalized medicine by 2025. We argue that for effective translation into the veterinary clinic, clinicians, international experts, and stakeholders must collaborate to ensure quality assurance and genetic test validation so that animals may also benefit from this genomics revolution.

Multimodal lipid-lowering treatment in pediatric patients with homozygous familial hypercholesterolemia-target attainment requires further increase of intensity

BACKGROUND

Familial hypercholesterolemia (FH) causes premature cardiovascular disease (CVD). Lipoprotein apheresis (LA) is recommended as first-line lipid-lowering treatment (LLT) for homozygous (ho) FH.

METHODS

Efficacy of multimodal LLT including lifestyle counseling, drug treatment, and LA was analyzed in 17 pediatric hoFH or compound heterozygous (c-het) FH patients, who commenced chronic LA in Germany before the age of 18.

RESULTS

At time of diagnosis, mean low-density lipoprotein cholesterol (LDL-C) concentration was 19.6 mmol/l (756 mg/dl). Multimodal LLT resulted in 73% reduction of mean LDL-C concentration including a 62% contribution of LA. Only three children (18%) achieved mean LDL-C concentrations below the recommended pediatric target of 3.5 mmol/l (135 mg/dl). In 13 patients (76%) during chronic LA, neither cardiovascular events occurred nor was CVD progression detected clinically or by routine imaging techniques. In four patients (24%), cardiovascular events documented progression of CVD despite weekly LA, including one death due to coronary and cerebrovascular CVD which was not stabilized after commencing LA. Based on the mutational status, only 6 out of the 17 children were candidates for proprotein convertase subtilisin-kexin type 9 (PCSK9) inhibition. Two already responded with further LDL-C decrease by 40%.

CONCLUSIONS

Next to drug therapy, regular LA is an essential component of LLT for approaching LDL-C targets in children with hoFH or c-hetFH, which was successful only in a minority of children. Progression of CVD morbidity and resulting mortality remain unresolved issues. Early and intensified multimodal LLT guided by risk factors beyond LDL-C concentration is needed to improve outcome.

Homozygous familial hypercholesterolemia: Summarized case reports

BACKGROUND AND AIMS

Homozygous familial hypercholesterolemia (hoFH) is a rare genetic disorder with potential severe atherosclerosis in the pediatric age.

METHODS

We report on 9 patients with hoFH, who had been diagnosed within the last 30 years and who were consequently treated with apheresis and drugs.

RESULTS

Two deaths occurred: one at age 36 years and the other at age four and a half years before effective treatment was commenced. All other patients are still in good clinical condition today, although four of them have proven aortic stenosis or arterial plaques.

CONCLUSIONS

Our case report highlights that adequate treatment should start as early as possible to delay the onset of clinical manifestations of atherosclerosis. It can be assumed that the introduction of new drugs can improve the outcome and possibly lengthen the life expectancy of patients affected by hoFH.

Seventeen years of statin pharmacogenetics: a systematic review

AIM

We evaluated the evidence of pharmacogenetic associations with statins in a systematic review.

METHODS

Two separate outcomes were considered of interest: modification of low-density lipoprotein cholesterol (LDL-C) response and modification of risk for cardiovascular events.

RESULTS

In candidate gene studies, 141 loci were claimed to be associated with LDL-C response. Only 5% of these associations were positively replicated. In addition, six genome-wide association studies of LDL-C response identified common SNPs in APOE, LPA, SLCO1B1, SORT1 and ABCG2 at genome-wide significance. None of the investigated SNPs consistently affected the risk reduction for cardiovascular events.

CONCLUSION

Only five genetic loci were consistently associated with LDL-C response. However, as effect sizes are modest, there is no evidence for the value of genetic testing in clinical practice.

Type of LDLR mutation and the pharmacogenetics of familial hypercholesterolemia treatment

Familial hypercholesterolemia (FH) is an autosomal dominant disease mainly caused by mutations in the low-density lipoprotein receptor (LDLR) gene. FH patients present a wide variability regarding response to drugs and they are usually undertreated. Here, we review studies that evaluated the association between the type of LDLR mutation and the response to lipid-lowering therapy. The main findings were that patients with a null LDLR mutation had: higher baseline LDL-C, higher LDL-C after drug therapy, lower proportion of patients within the LDL-C target value and higher frequencies of CVD. Thus, we conclude that FH patients harboring a null mutation have a trend to an increased risk, even if diagnosis is early established and lipid-lowering treatment instituted. It is suggested that these individuals may benefit from the use of newly approved lipid-lowering agents.

Familial Hypercholesterolemia: a Review of the Natural History, Diagnosis, and Management

Familial hypercholesterolemia (FH) is an inherited disorder of lipid metabolism characterized by premature cardiovascular disease. It is one of the most common metabolic disorders affecting humans. There are two clinical manifestations: the milder heterozygous form and more severe homozygous form. Despite posing a significant health risk, FH is inadequately diagnosed and managed. As the clinical outcome is related to the degree and duration of exposure to elevated low-density lipoprotein cholesterol (LDL-C) levels, early treatment is vital. Diagnosis can usually be made using a combination of clinical characteristics such as family history, lipid levels, and genetic testing. Mutations in the gene encoding the LDL receptor (LDLR), apolipoprotein B, the pro-protein convertase subtilisin/kexin 9 (PCSK9), and LDLR adaptor protein are the commonest abnormalities. Early identification and treatment of patients, as well as screening of relatives, helps significantly reduce the risk of premature disease. Although statins remain the first-line therapy in most cases, monotherapy is usually inadequate to control elevated LDL-C levels. Additional therapy with ezetimibe and bile acid sequestrants may be required. Newer classes of pharmacotherapy currently under investigation include lomitapide, mipomersen, and monoclonal antibodies to PCSK9. Lipoprotein apheresis may be required when multiple pharmacotherapies are inadequate, especially in the homozygous form. Effective early detection and treatment of the index individual and initiation of cascade screening will help reduce the complications associated with FH. In this article, we review the disease of FH, complexity of diagnosis and management, and the challenges faced in preventing the significant morbidity and mortality associated with it.

Presence and type of low density lipoprotein receptor (LDLR) mutation influences the lipid profile and response to lipid-lowering therapy in Brazilian patients with heterozygous familial hypercholesterolemia

OBJECTIVES

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused mainly by LDLR mutations. This study assessed the influence of the presence and type of LDLR mutation on lipid profile and the response to lipid-lowering therapy in Brazilian patients with heterozygous FH.

METHODS

For 14 ± 3 months, 156 patients with heterozygous FH receiving atorvastatin were followed. Coding sequences of the LDLR gene were bidirectionally sequenced, and the type of LDLR mutations were classified according to their probable functional class.

RESULTS

The frequencies of the types of LDLR mutations were: null-mutation (n = 40, 25.6%), defective-mutation (n = 59, 37.8%), and without an identified mutation (n = 57, 36.6%). Baseline total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were higher in patients carrying a null mutation (9.9 ± 1.9 mmol/L, 7.9 ± 1.7 mmol/L), compared to those with a defective (8.9 ± 2.2 mmol/L, 7.0 ± 2.0 mmol/L), or no mutation (7.9 ± 1.9 mmol/L, 5.8 ± 1.9 mmol/L) (p < 0.001). After treatment, the proportion of patients attaining an LDL-C<3.4 mmol/L was significantly different among groups: null (22.5%), defective (27.1%), and without mutations (47.4%) (p = 0.02). The presence of LDLR mutations was independently associated with higher odds of not achieving the LDL-C cut-off (OR 9.07, 95% CI 1.41-58.16, p = 0.02).

CONCLUSIONS

Our findings indicate that the presence and type of LDLR mutations influence lipid profile and response to lipid-lowering therapy in Brazilian patients with heterozygous FH. Thus, more intensive care with pharmacological therapeutics should be performed in patients who have a molecular analysis indicating the presence of a LDLR mutation.