PCSK9 is present in human cerebrospinal fluid and is maintained at remarkably constant concentrations throughout the course of the day

Association between Apo B, LDL-R and PCSK9 gene polymorphisms with coronary artery diseases in Egyptians

BACKGROUND

Many studies have focused on the significance of lipid regulatory genes in the pathophysiology of Coronary artery disease (CAD). ApoB XbaI (rs693) and EcoRI (rs1042031) single nucleoid polymorphisms (SNPs) were investigated to detect whether they are risk factors for CAD. Till now, this association remains uncertain. SMARCA4 (rs1122608) SNP has directly related to dyslipidemia. Loss of function mutations (LOF) in PCSK9 result in a reduction in LDL cholesterol and are associated with protection from the development of CAD.

METHODS

This study was conducted on 54 CAD patients who were admitted at Internal Medicine Specialized Hospital (Cardiology Department) and 47 healthy controls. Peripheral blood samples were taken from both groups. DNA was extracted from EDTA-blood samples, then PCR- RFLP for ApoB XbaI (rs693) and EcoRI (rs1042031), SMARCA4 (rs1122608) and PCSK9 (rs505151) SNPs was done.

RESULTS

No statistically significant difference was found between patients and controls as regard EcoRI SNP. XbaI (rs693) X + X + genotype was significantly higher in control group (P = 0.0355). SMARCA4 (TT, GT + TT) genotypes, and T allele (P < 0.001); PCSK9 AG genotype and G allele (P = 0.027 and 0.032 respectively) were more frequent in CAD patients than controls.

CONCLUSION

SMARCA4 (rs1122608) and PCSK9 (rs505151) SNPs are significantly accompanying with the risk of CAD development in the Egyptian population. X + X + genotype appeared to have a protective effect against CAD. However, no observed association between EcoRI (rs1042031) and the risk of CAD development was found.

Sex and statin-related genetic associations at the PCSK9 gene locus: results of genome-wide association meta-analysis

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key player of lipid metabolism with higher plasma levels in women throughout their life. Statin treatment affects PCSK9 levels also showing evidence of sex-differential effects. It remains unclear whether these differences can be explained by genetics.

METHODS

We performed genome-wide association meta-analyses (GWAS) of PCSK9 levels stratified for sex and statin treatment in six independent studies of Europeans (8936 women/11,080 men respectively 14,825 statin-free/5191 statin-treated individuals). Loci associated in one of the strata were tested for statin- and sex-interactions considering all independent signals per locus. Independent variants at the PCSK9 gene locus were then used in a stratified Mendelian Randomization analysis (cis-MR) of PCSK9 effects on low-density lipoprotein cholesterol (LDL-C) levels to detect differences of causal effects between the subgroups.

RESULTS

We identified 11 loci associated with PCSK9 in at least one stratified subgroup (p < 1.0 × 10-6), including the PCSK9 gene locus and five other lipid loci: APOB, TM6SF2, FADS1/FADS2, JMJD1C, and HP/HPR. The interaction analysis revealed eight loci with sex- and/or statin-interactions. At the PCSK9 gene locus, there were four independent signals, one with a significant sex-interaction showing stronger effects in men (rs693668). Regarding statin treatment, there were two significant interactions in PCSK9 missense mutations: rs11591147 had stronger effects in statin-free individuals, and rs11583680 had stronger effects in statin-treated individuals. Besides replicating known loci, we detected two novel genome-wide significant associations: one for statin-treated individuals at 6q11.1 (within KHDRBS2) and one for males at 12q24.22 (near KSR2/NOS1), both with significant interactions. In the MR of PCSK9 on LDL-C, we observed significant causal estimates within all subgroups, but significantly stronger causal effects in statin-free subjects compared to statin-treated individuals.

CONCLUSIONS

We performed the first double-stratified GWAS of PCSK9 levels and identified multiple biologically plausible loci with genetic interaction effects. Our results indicate that the observed sexual dimorphism of PCSK9 and its statin-related interactions have a genetic basis. Significant differences in the causal relationship between PCSK9 and LDL-C suggest sex-specific dosages of PCSK9 inhibitors.

Targeting proprotein convertase subtilisin/kexin type 9 (PCSK9): from bench to bedside

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has evolved as a pivotal enzyme in lipid metabolism and a revolutionary therapeutic target for hypercholesterolemia and its related cardiovascular diseases (CVD). This comprehensive review delineates the intricate roles and wide-ranging implications of PCSK9, extending beyond CVD to emphasize its significance in diverse physiological and pathological states, including liver diseases, infectious diseases, autoimmune disorders, and notably, cancer. Our exploration offers insights into the interaction between PCSK9 and low-density lipoprotein receptors (LDLRs), elucidating its substantial impact on cholesterol homeostasis and cardiovascular health. It also details the evolution of PCSK9-targeted therapies, translating foundational bench discoveries into bedside applications for optimized patient care. The advent and clinical approval of innovative PCSK9 inhibitory therapies (PCSK9-iTs), including three monoclonal antibodies (Evolocumab, Alirocumab, and Tafolecimab) and one small interfering RNA (siRNA, Inclisiran), have marked a significant breakthrough in cardiovascular medicine. These therapies have demonstrated unparalleled efficacy in mitigating hypercholesterolemia, reducing cardiovascular risks, and have showcased profound value in clinical applications, offering novel therapeutic avenues and a promising future in personalized medicine for cardiovascular disorders. Furthermore, emerging research, inclusive of our findings, unveils PCSK9's potential role as a pivotal indicator for cancer prognosis and its prospective application as a transformative target for cancer treatment. This review also highlights PCSK9's aberrant expression in various cancer forms, its association with cancer prognosis, and its crucial roles in carcinogenesis and cancer immunity. In conclusion, this synthesized review integrates existing knowledge and novel insights on PCSK9, providing a holistic perspective on its transformative impact in reshaping therapeutic paradigms across various disorders. It emphasizes the clinical value and effect of PCSK9-iT, underscoring its potential in advancing the landscape of biomedical research and its capabilities in heralding new eras in personalized medicine.

The effect of resistance training on PCSK9 levels in patients undergoing cardiac rehabilitation after coronary artery bypass grafting: a randomized study

BACKGROUND

Resistance training is commonly recommended as part of secondary prevention for post-coronary artery bypass graft (CABG) patients in conjunction with aerobic exercise. Despite its potential benefits, there is currently a lack of studies investigating the impact of resistance training on proprotein convertase subtilisin kexin 9 (PCSK9).

AIM

To evaluate the effect of intensive resistance training on proprotein convertase subtilisin kexin 9 (PCSK9) levels among post-CABG patients undergoing cardiac rehabilitation (CR).

METHODS

In this prospective, open-label, randomized trial, 87 post-coronary artery bypass graft (CABG) patients were randomly assigned into two groups: moderate to high intensity resistance training and aerobic training (n = 44) or aerobic training alone (n = 43) for a total of 12 sessions. Changes in PCSK9 levels was determined as a primary endpoint, while secondary endpoints included changes in the six-minute walk test (6-MWT) results, aerobic capacity, WHO-5 well-being index, fasting blood glucose, and lipid profile. Both groups underwent intention-to-treat analysis.

RESULTS

Following completion of cardiac rehabilitation program, the intervention group demonstrated a significant decrease in mean PCSK9 levels when compared to the control group (β = -55 ng/ml, 95% CI -6.7 to -103.3, p = 0.026), as well as significant improvements in the 6-MWT result (β = 28.2 m, 95% CI 2.4-53.9, p = 0.033), aerobic capacity (β = 0.9 Mets, 95% CI 0.1-1.7, p = 0.021), and WHO-5 well-being index (β = 8.1, 95% CI 2.0-14.4, p = 0.011) in patients who received resistance and aerobic training. No statistically significant changes were observed in fasting blood glucose, cholesterol, LDL-C, HDL-C, and triglyceride levels.

CONCLUSION

Resistance training in CR significantly reduced PCSK-9 levels and increases patient's functional capacity and quality of life. (NCT02674659 04/02/2016).

PCSK9 and the nervous system: a no-brainer?

In the past 20 years, PCSK9 has been shown to play a pivotal role in LDL cholesterol metabolism and cardiovascular health by inducing the lysosomal degradation of the LDL receptor. PCSK9 was discovered by the cloning of genes up-regulated after apoptosis induced by serum deprivation in primary cerebellar neurons, but despite its initial identification in the brain, the precise role of PCSK9 in the nervous system remains to be clearly established. The present article is a comprehensive review of studies published or in print before July 2023 that have investigated the expression pattern of PCSK9, its effects on lipid metabolism as well as its putative roles specifically in the central and peripheral nervous systems, with a special focus on cerebrovascular and neurodegenerative diseases.

Targeting PCSK9 to tackle cardiovascular disease

Lowering blood cholesterol levels efficiently reduces the risk of developing atherosclerotic cardiovascular disease (ASCVD), including coronary artery disease (CAD), which is the main cause of death worldwide. CAD is caused by plaque formation, comprising cholesterol deposits in the coronary arteries. Proprotein convertase subtilisin kexin/type 9 (PCSK9) was discovered in the early 2000s and later identified as a key regulator of cholesterol metabolism. PCSK9 induces lysosomal degradation of the low-density lipoprotein (LDL) receptor in the liver, which is responsible for clearing LDL-cholesterol (LDL-C) from the circulation. Accordingly, gain-of-function PCSK9 mutations are causative of familial hypercholesterolemia, a severe condition with extremely high plasma cholesterol levels and increased ASCVD risk, whereas loss-of-function PCSK9 mutations are associated with very low LDL-C levels and protection against CAD. Since the discovery of PCSK9, extensive investigations in developing PCSK9 targeting therapies have been performed. The combined delineation of clear biology, genetic risk variants, and PCSK9 crystal structures have been major drivers in developing antagonistic molecules. Today, two antibody-based PCSK9 inhibitors have successfully progressed to clinical application and shown to be effective in reducing cholesterol levels and mitigating the risk of ASCVD events, including myocardial infarction, stroke, and death, without any major adverse effects. A third siRNA-based inhibitor has been FDA-approved but awaits cardiovascular outcome data. In this review, we outline the PCSK9 biology, focusing on the structure and nonsynonymous mutations reported in the PCSK9 gene and elaborate on PCSK9-lowering strategies under development. Finally, we discuss future perspectives with PCSK9 inhibition in other severe disorders beyond cardiovascular disease.

Pleiotropy of PCSK9: Functions in Extrahepatic Tissues

PURPOSE OF REVIEW

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a central role in the metabolism of LDL receptors and mainly acts in the liver. However, there are accumulating data that PCSK9 involves in several functions in different organs beyond the liver. Herein we aimed to summarize the effects of PCSK9 in tissues other than the liver.

RECENT FINDINGS

PCSK9 has crucial roles in heart, brain and kidney in addition to the cholesterol metabolism. Targeting PCSK9 for the treatment of hypercholesterolemia is effective in the prevention from cardiovascular diseases and PCSK9 inhibitors are getting to be administered in more cases. Therefore understanding the effects of PCSK9 in other tissues gained importance in the use of PCSK9 inhibitors era. PCSK9 participates in cardiac, renal, and neurologic functions however, current literature reveals that use of PSCSK9 inhibitors have beneficial or neutral effects on these organs. Inhibition of PCSK9 is assigned to be associated with new onset diabetes in experimental studies whereas real world data with PCSK9 inhibitors established no relationship between PCSK9 inhibitors and new onset diabetes. PCSK9 might be used as a target for the treatment of nephrotic syndrome and heart failure in the future.

Serum proteome profiles in patients treated with targeted temperature management after out-of-hospital cardiac arrest

BACKGROUND

Definition of temporal serum proteome profiles after out-of-hospital cardiac arrest may identify biological processes associated with severe hypoxia-ischaemia and reperfusion. It may further explore intervention effects for new mechanistic insights, identify candidate prognostic protein biomarkers and potential therapeutic targets. This pilot study aimed to investigate serum proteome profiles from unconscious patients admitted to hospital after out-of-hospital cardiac arrest according to temperature treatment and neurological outcome.

METHODS

Serum samples at 24, 48, and 72 h after cardiac arrest at three centres included in the Target Temperature Management after out-of-hospital cardiac arrest trial underwent data-independent acquisition mass spectrometry analysis (DIA-MS) to find changes in serum protein concentrations associated with neurological outcome at 6-month follow-up and targeted temperature management (TTM) at 33 °C as compared to 36 °C. Neurological outcome was defined according to Cerebral Performance Category (CPC) scale as "good" (CPC 1-2, good cerebral performance or moderate disability) or "poor" (CPC 3-5, severe disability, unresponsive wakefulness syndrome, or death).

RESULTS

Of 78 included patients [mean age 66 ± 12 years, 62 (80.0%) male], 37 (47.4%) were randomised to TTM at 36 °C. Six-month outcome was poor in 47 (60.3%) patients. The DIA-MS analysis identified and quantified 403 unique human proteins. Differential protein abundance testing comparing poor to good outcome showed 19 elevated proteins in patients with poor outcome (log₂-fold change (FC) range 0.28-1.17) and 16 reduced proteins (log₂(FC) between - 0.22 and - 0.68), involved in inflammatory/immune responses and apoptotic signalling pathways for poor outcome and proteolysis for good outcome. Analysis according to level of TTM showed a significant protein abundance difference for six proteins [five elevated proteins in TTM 36 °C (log₂(FC) between 0.33 and 0.88), one reduced protein (log₂(FC) - 0.6)] mainly involved in inflammatory/immune responses only at 48 h after cardiac arrest.

CONCLUSIONS

Serum proteome profiling revealed an increase in inflammatory/immune responses and apoptosis in patients with poor outcome. In patients with good outcome, an increase in proteolysis was observed, whereas TTM-level only had a modest effect on the proteome profiles. Further validation of the differentially abundant proteins in response to neurological outcome is necessary to validate novel biomarker candidates that may predict prognosis after cardiac arrest.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) in the central nervous system

The gene encoding proprotein convertase subtilisin/kexin type 9 (PCSK9) and its protein product have been widely studied for their role in cholesterol and lipid metabolism. PCSK9 increases the rate of metabolic degradation of low-density lipoprotein receptors, preventing the diffusion of low-density lipoprotein (LDL) from plasma into cells and contributes to high lipoprotein-bound cholesterol levels in the plasma. While most research has focused on the regulation and disease relevance of PCSK9 to the cardiovascular system and lipid metabolism, there is a growing body of evidence that PCSK9 plays a crucial role in pathogenic processes in other organ systems, including the central nervous system. PCSK9's impact on the brain is not yet fully understood, though several recent studies have sought to illuminate its impact on various neurodegenerative and psychiatric disorders, as well as its connection with ischemic stroke. Cerebral PCSK9 expression is low but is highly upregulated during disease states. Among others, PCSK9 is known to play a role in neurogenesis, neural cell differentiation, central LDL receptor metabolism, neural cell apoptosis, neuroinflammation, Alzheimer's Disease, Alcohol Use Disorder, and stroke. The PCSK9 gene contains several polymorphisms, including both gain-of-function and loss-of-function mutations which profoundly impact normal PCSK9 signaling and cholesterol metabolism. Gain-of-function mutations lead to persistent hypercholesterolemia and poor health outcomes, while loss-of-function mutations generally lead to hypocholesterolemia and may serve as a protective factor against diseases of the liver, cardiovascular system, and central nervous system. Recent genomic studies have sought to identify the end-organ effects of such mutations and continue to identify evidence of a much broader role for PCSK9 in extrahepatic organ systems. Despite this, there remain large gaps in our understanding of PCSK9, its regulation, and its effects on disease risk outside the liver. This review, which incorporates data from a wide range of scientific disciplines and experimental paradigms, is intended to describe PCSK9's role in the central nervous system as it relates to cerebral disease and neuropsychiatric disorders, and to examine the clinical potential of PCSK9 inhibitors and genetic variation in the PCSK9 gene on disease outcomes, including neurological and neuropsychiatric disease.

PCSK9 deficiency alters brain lipid composition without affecting brain development and function

PCSK9 induces lysosomal degradation of the low-density lipoprotein (LDL) receptor (LDLR) in the liver, hereby preventing removal of LDL cholesterol from the circulation. Accordingly, PCSK9 inhibitory antibodies and siRNA potently reduce LDL cholesterol to unprecedented low levels and are approved for treatment of hypercholesterolemia. In addition, PCSK9 inactivation alters the levels of several other circulating lipid classes and species. Brain function is critically influenced by cholesterol and lipid composition. However, it remains unclear how the brain is affected long-term by the reduction in circulating lipids as achieved with potent lipid lowering therapeutics such as PCSK9 inhibitors. Furthermore, it is unknown if locally expressed PCSK9 affects neuronal circuits through regulation of receptor levels. We have studied the effect of lifelong low peripheral cholesterol levels on brain lipid composition and behavior in adult PCSK9 KO mice. In addition, we studied the effect of PCSK9 on neurons in culture and in vivo in the developing cerebral cortex. We found that PCSK9 reduced LDLR and neurite complexity in cultured neurons, but neither PCSK9 KO nor overexpression affected cortical development in vivo. Interestingly, PCSK9 deficiency resulted in changes of several lipid classes in the adult cortex and cerebellum. Despite the observed changes, PCSK9 KO mice had unchanged behavior compared to WT controls. In conclusion, our findings demonstrate that altered PCSK9 levels do not compromise brain development or function in mice, and are in line with clinical trials showing that PCSK9 inhibitors have no adverse effects on cognitive function.

Evolocumab, a PCSK9 inhibitor, protects human endothelial cells against H2O2-induced oxidative stress

CONTEXT

Recent surveys have shown an association between proprotein convertase subtilisin/kexin type 9 (PCSK9) and oxidative stress.

OBJECTIVE

In this investigation, the effect of evolocumab an anti-PCSK9 antibody was assessed against oxidative damage caused by hydrogen peroxide (H₂O₂) in human umbilical vein endothelial cells (HUVEC).

MATERIAL AND METHODS

Viability of HUVEC was measured by MTT assay. Hydroperoxides and malondialdehyde (MDA) levels, and ferric reducing antioxidant power (FRAP) were detected in HUVEC that pre-treated with evolocumab and, then exposed to H₂O₂.

RESULTS

Evolocumab significantly prevented the cytotoxicity induced by H₂O₂ at the concentrations of 5-100 µg/ml. Pre-treatment of HUVEC with evolocumab reduced hydroperoxides and MDA levels and also increased FRAP value in intra- and extra-cellular mediums compared with H₂O₂ stimulated cells at different concentration ranges.

CONCLUSION

This study displayed anti-oxidative and cytoprotective activities of evolocumab against oxidative damage caused by H₂O₂ in endothelial cells.

Genetic analysis of the PCSK9 locus in psychological, psychiatric, metabolic and cardiovascular traits in UK Biobank

The association between severe mental illness (SMI) and cardiovascular and metabolic disease (CMD) is poorly understood. PCSK9 is expressed in systems critical to both SMI and CMD and influences lipid homeostasis and brain function. We systematically investigated relationships between genetic variation within the PCSK9 locus and risk for both CMD and SMI. UK Biobank recruited ~500,000 volunteers and assessed a wide range of SMI and CMD phenotypes. We used genetic data from white British ancestry individuals of UK Biobank. Genetic association analyses were conducted in PLINK, with statistical significance defined by the number of independent SNPs. Conditional analyses and linkage disequilibrium assessed the independence of SNPs and the presence of multiple signals. Two genetic risk scores of lipid-lowering alleles were calculated and used as proxies for putative lipid-lowering effects of PCSK9. PCSK9 variants were associated with central adiposity, venous thrombosis embolism, systolic blood pressure, mood instability, and neuroticism (all p < 1.16 × 10-4). No secondary signals were identified. Conditional analyses and high linkage disequilibrium (r2 = 0.98) indicated that mood instability and central obesity may share a genetic signal. Genetic risk scores suggested that the lipid-lowering effects of PCSK9 may be causal for greater mood instability and higher neuroticism. This is the first study to implicate the PCSK9 locus in mood-disorder symptoms and related traits, as well as the shared pathology of SMI and CMD. PCSK9 effects on mood may occur via lipid-lowering mechanisms. Further work is needed to understand whether repurposing PCSK9-targeting therapies might improve SMI symptoms and prevent CMD.

Relationship between Brain Metabolic Disorders and Cognitive Impairment: LDL Receptor Defect

The low-density-lipoprotein receptor (LDLr) removes low-density lipoprotein (LDL), an endovascular transporter that carries cholesterol from the bloodstream to peripheral tissues. The maintenance of cholesterol content in the brain, which is important to protect brain function, is affected by LDLr. LDLr co-localizes with the insulin receptor and complements the internalization of LDL. In LDLr deficiency, LDL blood levels and insulin resistance increase, leading to abnormal cholesterol control and cognitive deficits in atherosclerosis. Defects in brain cholesterol metabolism lead to neuroinflammation and blood–brain-barrier (BBB) degradation. Moreover, interactions between endoplasmic reticulum stress (ER stress) and mitochondria are induced by ox-LDL accumulation, apolipoprotein E (ApoE) regulates the levels of amyloid beta (Aβ) in the brain, and hypoxia is induced by apoptosis induced by the LDLr defect. This review summarizes the association between neurodegenerative brain disease and typical cognitive deficits.

Efficacy and Safety of PCSK9 Monoclonal Antibodies in Patients With Diabetes

PURPOSE

Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors are novel drugs that have proven efficacy in improving cardiovascular outcomes. Roles for the PCSK9 molecule in metabolic pathways beyond LDL receptor processing and cholesterol homeostasis are well established. PCSK9 genetic variants associated with lower LDL-C levels correlate with a higher incidence of type 2 diabetes (T2DM), calling into question the appropriateness of these drugs in patients with T2DM and those at high risk of developing diabetes, and whether cardiovascular benefit seen with PCSK9 inhibitors might be offset by resultant dysglycemia. The purpose of this review was to examine the role of PCSK9 protein in glucose homeostasis, the impact of PCSK9 inhibition in relation to glucose homeostasis, and whether some of the cardiovascular benefit seen with PCSK9 inhibitors and statins might be offset by resultant dysglycemia.

METHODS

Comprehensive literature searches of electronic databases of PubMed, EMBASE, and OVID were conducted by using the search terms hyperlipidaemia, PCSK9, diabetes, and glucose as well as other relevant papers of interest collected by the authors. The retrieved papers were reviewed and shortlisted most relevant ones.

FINDINGS

Genetically determined lower circulating LDL-C and PCSK9 concentrations may have an incremental effect in increasing T2DM incidence, but any perceived harm is outweighed by the reduced risk of atherosclerotic cardiovascular disease achieved through lower lifetime exposure to LDL-C. PCSK9 monoclonal antibodies are effective and safe in patients with T2DM and those at high risk of developing it. The number-needed-to-treat to prevent one atherosclerotic cardiovascular disease event in the FOURIER (Further Cardiovascular Outcomes Research with PCSK9 Inhibition in Subjects with Elevated Risk) study in the subgroup with diabetes is significantly lower than for those without. Therefore, T2DM or being at high risk to develop it should not be a reason to avoid these agents. The safety of PCSK9 inhibition in relation to glucose homeostasis may depend on the method of inhibition and whether it occurs in circulation or the cells. Data from experimental studies and randomized controlled trials suggest no detrimental effect of PCSK9 monoclonal antibodies on glucose homeostasis. More data and large randomized controlled studies are needed to assess the impact of other methods of PCSK9 inhibition on glucose homeostasis.

IMPLICATIONS

PCSK9monoclonal antibodies markedly reduce LDL-C and consistently reduce cardiovascular mortality in patients with and without diabetes. Current evidence does not suggest an adverse effect of PCSK9 monoclonal antibodies on glycemic parameters.

PCSK9 and the Gut-Liver-Brain Axis: A Novel Therapeutic Target for Immune Regulation in Alcohol Use Disorder

Alcohol use disorder (AUD) is a chronic relapsing disorder characterized by an impaired ability to control or stop alcohol intake and is associated with organ damage including alcohol-associated liver disease (ALD) and progressive neurodegeneration. The etiology of AUD is complex, but organ injury due to chronic alcohol use can be partially attributed to systemic and local inflammation along the gut-liver-brain axis. Excessive alcohol use can result in translocation of bacterial products into circulation, increased expression of pro-inflammatory cytokines, and activation of immune cells, including macrophages and/or microglia in the liver and brain. One potential mediator of this alcohol-induced inflammation is proprotein convertase subtilisin/kexin type 9 (PCSK9). PCSK9 is primarily known for its regulation of plasma low-density lipoprotein cholesterol but has more recently been shown to influence inflammatory responses in the liver and brain. In rodent and post-mortem brain studies, chronic alcohol use altered methylation of the PCSK9 gene and increased expression of PCSK9 in the liver and cerebral spinal fluid. Additionally, PCSK9 inhibition in a rat model of ALD attenuated liver inflammation and steatosis. PCSK9 may play an important role in alcohol-induced pathologies along the gut-liver-brain axis and may be a novel therapeutic target for AUD-related liver and brain inflammation.

Sex-Specific Association of Endogenous PCSK9 With Memory Function in Elderly Subjects at High Cardiovascular Risk

Background: Growing evidence indicates that cognitive decline and cardiovascular diseases (CVDs) share common vascular risk factors. Protease proprotein convertase subtilisin/kexin type 9 (PCSK9) is associated with CV disease risk and has been also involved in neuronal differentiation.

Aim: Evaluate whether in patients at high CV risk cognitive function is related to PCSK9 levels.

Methods. One hundred sixty-six patients (67 female) were enrolled. A detailed neuropsychological (NP) assessment was performed. PCSK9 levels were measured with ELISA.

Results: Men had significantly higher short-term memory, executive function, and praxic and mental representation skills, as reflected by Forward Digit Span (FDS) (p = 0.005), Trail Making Test-A (TMT-A) (p = 0.047), Clock Drawing Test (CDT) (0.016). Endogenous PCSK9 levels were higher in female (p = 0.005). On linear regression analysis PCSK9 predicts short term memory only in females (Beta = 0.408, p = 0.001), with an interaction between PCSK9 and gender (p = 0.004 for interaction PCSK9 by sex). The association of PCSK9 with FDS in female was partially mediated by waist circumference (mediation effect 8.5%).

Conclusions: In patients at high CV risk short term memory was directly related to PCSK9 levels only in women, revealing the relevance of sex in this relationship. The association of PCSK9 with memory function may be mediated, at least in part, by waist circumference.

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) in the Brain and Relevance for Neuropsychiatric Disorders

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has long been studied in the liver due to its regulation of plasma low-density lipoprotein cholesterol (LDL-C) and its causal role in familial hypercholesterolemia. Although PCSK9 was first discovered in cerebellar neurons undergoing apoptosis, its function in the central nervous system (CNS) is less clear. PCSK9 has been shown to be involved in neuronal differentiation, LDL receptor family metabolism, apoptosis, and inflammation in the brain, but in vitro and in vivo studies offer contradictory findings. PCSK9 expression in the adult brain is low but is highly upregulated during disease states. Cerebral spinal fluid (CSF) PCSK9 concentrations are correlated with neural tube defects and neurodegenerative diseases in human patients. Epigenetic studies reveal that chronic alcohol use may modulate methylation of the PCSK9 gene and genetic studies show that patients with gain-of-function PCSK9 variants have higher LDL-C and an increased risk of ischemic stroke. Early safety studies of the PCSK9 inhibitors evolocumab and alirocumab, used to treat hypercholesterolemia, hinted that PCSK9 inhibition may negatively impact cognition but more recent, longer-term clinical trials found no adverse neurocognitive events. The purpose of this review is to elucidate the role of PCSK9 in the brain, particularly its role in disease pathogenesis.

The role of proprotein convertase subtilisin-kexin type 9 (PCSK9) in the vascular aging process - is there a link?

Lately there are many new, promising low-density lipoprotein cholesterol reducing therapies with PCSK9 inhibitors. We performed selected sampling of the publications in PubMed and made a review according to selected keywords. It summarizes the effect of PCSK9 on vascular aging, directly associated with lipid and glucose metabolism, chronic inflammation, atherosclerosis and hypertension. Serum level of PCSK9 is different in patients affected by certain illnesses (whose risk increases with age) than in healthy individuals. The same could be observed in the case of chronic inflammation. In this review we summarize what is known about the role PCSK9 in human metabolism and how this could affect the vascular aging process. Based on the available sources, we prove that PCSK9 is involved in many biochemical pathways associated with vascular aging. In the future, treatments using PCSK9 inhibition may not only reduce the cardiovascular risk but also slow down this process.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) in Alzheimer's disease: A genetic and proteomic multi-cohort study

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a hepatic enzyme that regulates circulating low-density lipoprotein (LDL) cholesterol levels by binding to LDL receptors (LDLR) and promoting their degradation. Although PCSK9 inhibitors were shown to reduce the risk of cardiovascular disease, a warning was issued concerning their possible impact on cognitive functions. In Alzheimer's disease (AD), it is believed that cognitive impairment is associated with cholesterol metabolism alterations, which could involve PCSK9. The main objective of this study is to determine if PCSK9 plays a significant role in the pre-symptomatic phase of the disease when the pathophysiological markers of AD unfolds and, later, when cognitive symptoms emerge.

METHODS AND FINDINGS

To test if PCSK9 is associated with AD pathology, we measured its expression levels in 65 autopsy confirmed AD brains and 45 age and gender matched controls. Messenger ribonucleic acid (mRNA) were quantified using real-time polymerase chain reaction (RT-PCR) and protein levels were quantified using enzyme-linked immunosorbent assay (ELISA). PCSK9 was elevated in frontal cortices of AD subjects compared to controls, both at the mRNA and protein levels. LDLR protein levels were unchanged in AD frontal cortices, despite and upregulation at the mRNA level. To verify if PCSK9 dysregulation was observable before the onset of AD, we measured its expression in the cerebrospinal fluid (CSF) of 104 "at-risk" subjects and contrasted it with known apolipoproteins levels and specific AD biomarkers using ELISAs. Positive correlations were found between CSF PCSK9 and apolipoprotein E (APOE), apolipoprotein J (APOJ or CLU), apolipoprotein B (APOB), phospho Tau (pTau) and total Tau. To investigate if PCSK9 levels were driven by genetic variants, we conducted an expression quantitative trait loci (eQTL) study using bioinformatic tools and found two polymorphisms in strong association. Further investigation of these variants in two independent cohorts showed a female specific association with AD risk and with CSF Tau levels in cognitively impaired individuals.

CONCLUSIONS

PCSK9 levels differ between control and AD brains and its protein levels correlate with those of other lipoproteins and AD biomarkers even before the onset of the disease. PCSK9 regulation seems to be under tight genetic control in females only, with specific variants that could predispose to increased AD risk.

PCSK9 Concentrations in Cerebrospinal Fluid Are Not Specifically Increased in Alzheimer's Disease

The role of PCSK9 in Alzheimer's disease (AD) is controversial. We compared cerebrospinal fluid (CSF) PCSK9 concentrations in 36 AD and 31 non-AD patients. CSF PCSK9 levels did not differ between AD and non-AD groups (2.80 versus 2.62 ng/mL). However, PCSK9 CSF levels were increased in AD and non-AD patients with other neurodegenerative process (non-AD ND, n = 20) compared to patients without neurodegenerative disorders (non-ND, n = 11): 2.80 versus 2.30 (p < 0.005) and 2.83 versus 2.30 ng/mL (p = NS), respectively. CSF PCSK9 were positively correlated with AD biomarkers (Aβ1-42, T-tau, and P-tau). PCSK9 concentrations in CSF are increased in neurodegenerative disorders rather than specifically in AD.

Proprotein Convertase Subtilisin/Kexin Type 9, Brain Cholesterol Homeostasis and Potential Implication for Alzheimer's Disease

Alzheimer’s disease (AD) has been associated with dysregulation of brain cholesterol homeostasis. Proprotein convertase subtilisin/kexin type 9 (PCSK9), beyond the known role in the regulation of plasma low-density lipoprotein cholesterol, was first identified in the brain with a potential involvement in brain development and apoptosis. However, its role in the central nervous system (CNS) and in AD pathogenesis is still far from being understood. While in vitro and in vivo evidence led to controversial results, genetic studies apparently did not find an association between PCSK9 loss of function mutations and AD risk or prevalence. In addition, a potential impairment of cognitive performances by the treatment with the PCSK9 inhibitors, alirocumab and evolocumab, have been excluded, although ongoing studies with longer follow-up will provide further insights. PCSK9 is able to affect the expression of neuronal receptors involved in cholesterol homeostasis and neuroinflammation, and higher PCSK9 concentrations have been found in the cerebrospinal fluid (CSF) of AD patients. In this review article, we critically examined the science of PCSK9 with respect to its modulatory role of the mechanisms underlying the pathogenesis of AD. In addition, based on literature data, we made the hypothesis to consider brain PCSK9 as a negative modulator of brain cholesterol homeostasis and neuroinflammation and a potential pharmacological target for treatment.

PCSK9 is Increased in Cerebrospinal Fluid of Individuals With Alcohol Use Disorder

BACKGROUND

Recent studies have shown that alcohol use affects the regulation and expression of proprotein convertase subtilisin/kexin 9 (PCSK9). While a major role of PCSK9 in hepatic function and lipid regulation has been clearly established, other pleiotropic effects remain poorly understood. Existing research suggests a positive association between PCSK9 expression in the brain and psychopathology, with increased levels of PCSK9 in the cerebrospinal fluid (CSF) of individuals with dementia and epigenetic modifications of PCSK9 associated with alcohol use disorder (AUD). In this study, we hypothesized that chronic alcohol use would increase PCSK9 expression in CSF.

METHODS

PCSK9 levels in CSF were measured in individuals with AUD (n = 42) admitted to an inpatient rehabilitation program and controls (n = 25). CSF samples in AUD were assessed at 2 time points, at day 5 and day 21 after admission. Furthermore, plasma samples were collected and measured from the individuals with AUD.

RESULTS

PCSK9 in CSF was significantly increased in the AUD group at day 5 and day 21 compared to the controls (p < 0.0001). Plasma PCSK9 levels were correlated positively with CSF PCSK9 levels in AUD (p = 0.0493).

CONCLUSIONS

Our data suggest that PCSK9 is elevated in the CSF of individuals with AUD, which may indicate a potential role of PCSK9 in AUD. Additional studies are necessary to further elucidate the functions of PCSK9 in the brain.

Effect of Physical Activity on Plasma PCSK9 in Subjects With High Risk for Type 2 Diabetes

Background

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a liver serine protease regulating LDL cholesterol metabolism. PCSK9 binds to LDL receptors and guides them to lysosomes for degradation, thus increasing the amount of circulating LDL cholesterol. The aim of the study was to investigate associations between physical activity and plasma PCSK9 in subjects with high risk for type 2 diabetes (T2D).

Methods

Sixty-eight subjects from both genders with a high risk for T2D were included to a randomized controlled trial with a 3-month physical activity intervention. Physical activity intensities and frequencies were monitored throughout the intervention using a hip worn portable accelerometer. The plasma was collected before and after intervention for analysis of PCSK9 and cardiovascular biomarkers.

Results

Plasma PCSK9 did not relate to physical activity although number of steps were 46% higher in the intervention group than in the control group (p < 0.029). Total cholesterol was positively correlated with plasma PCSK9 (R = 0.320, p = 0.008), while maximal oxygen uptake was negatively associated (R = -0.252, p = 0.044). After the physical activity intervention PCSK9 levels were even stronger inversely associated with maximal oxygen uptake (R = -0.410, p = 0.0008) and positively correlated with HDL cholesterol (R = 0.264, p = 0.030). Interestingly, plasma PCSK9 levels were higher in the beginning than at the end of the study.

Conclusion

The low physical activity that our subjects with high risk for T2D could perform did not influence plasma PCSK9 levels. Intervention with higher physical activities might be more effective in influencing PCSK9 levels.

PCSK9 and neurocognitive function: Should it be still an issue after FOURIER and EBBINGHAUS results?

The serine protease proprotein convertase subtilisin/kexin type 9 (PCSK9) modulates the levels of low-density lipoprotein cholesterol and cardiovascular risk. Potential risks of adverse neurological effects of intensive lipid-lowering treatment have been hypothesized, as cholesterol is a component of the central nervous system. Moreover, several observations suggest that PCSK9 might play a role in neurogenesis, neuronal migration and apoptosis. In rodents, increased expression of PCSK9 has been detected in specific areas of the central nervous system during embryonic development; also, PCSK9 modulates low-density lipoprotein receptor levels in the ischemic brain areas. Despite a putative participation of PCSK9 in nervous system physiology, the absence of PCSK9 in knockout mice or in humans with loss-of-function mutations of PCSK9 gene has not been linked to neurological alterations. In recent years, some concerns have been raised about the potential neurological side effects of cholesterol-lowering treatments and, more specifically of PCSK9 inhibitors. In this review, the evidence regarding the function of PCSK9 in neuron differentiation, apoptosis, and migration and in nervous system development and latest clinical trials evaluating the effects of PCSK9 inhibitors on neurocognitive function will be described.

Role of PCSK9 in lipid metabolism and atherosclerosis

Elevated plasma low-density lipoprotein cholesterol (LDL-C) is an important risk factor for cardiovascular diseases. Statins are the most widely used therapy for patients with hyperlipidemia. However, a significant residual cardiovascular risk remains in some patients even after maximally tolerated statin therapy. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a new pharmacologically therapeutic target for decreasing LDL-C. PCSK9 reduces LDL intake from circulation by enhancing LDLR degradation and preventing LDLR recirculation to the cell surface. Moreover, PCSK9 inhibitors have been approved for patients with either familial hypercholesterolemia or atherosclerotic cardiovascular disease, who require additional reduction of LDL-C. In addition, PCSK9 inhibition combined with statins has been used as a new approach to help reduce LDL-C levels in patients with either statin intolerance or unattainable LDL goal. This review will discuss the emerging anti-PCSK9 therapies in the regulation of cholesterol metabolism and atherosclerosis.

Potential Link Between Proprotein Convertase Subtilisin/Kexin Type 9 and Alzheimer's Disease

Alzheimer's disease [AD] is not only the most common neurodegenerative disease but is also currently incurable. Proprotein convertase subtilisin/kexin-9 [PCSK9] is an indirect regulator of plasma low density lipoprotein [LDL] levels controlling LDL receptor expression at the plasma membrane. PCSK9 also appears to regulate the development of glucose intolerance, insulin resistance, abdominal obesity, inflammation, and hypertension, conditions that have been identified as risk factors for AD. PCSK9 levels also depend on age, sex, and ethnic background, factors associated with AD. Herein, we will review indirect evidence that suggests a link between PCSK9 levels and AD.

Decreased serum PCSK9 levels after ischaemic stroke predict worse outcomes

BACKGROUND

Soluble mediators have been investigated to predict the prognosis of acute ischaemic stroke (AIS). Among them, proprotein convertase subtilisin/kexin type 9 (PCSK9) might have both clinical and pathophysiological relevance.

MATERIALS AND METHODS

All available serum samples from a cohort of patients with first AIS (n = 72) were tested for PCSK9 and included in this substudy analysis. The primary endpoint investigated the predictive value of early PCSK9 level variations (ΔPCSK9) from AIS onset to day 7 or from day 1 to day 7, towards a 90-day outcome by modified Rankin Scale (mRS). The secondary endpoint explored the association between ΔPCSK9 and the risk of major adverse cardiovascular events (MACEs).

RESULTS

Decreased serum PCSK9 levels at days 1 and 7 were associated with poor clinical outcomes at day 90. At the cut-off point identified by ROC curve analysis (-61·28 ng/mL), ΔPCSK9 day 7-day 1 predicted a poor mRS at day 90 after AIS. ΔPCSK9 day 7-day 1 ≤ -61·28 ng/mL was associated with an increased rate of MACEs.

CONCLUSION

A decrease in PCSK9 levels was a predictor for poor outcome and increased MACEs after AIS. Additional studies targeting post-AIS PCSK9 levels and activity are required to clarify the prognostic and pathophysiological relevance of PCSK9 after AIS.

Biology of proprotein convertase subtilisin kexin 9: beyond low-density lipoprotein cholesterol lowering

Proprotein convertase subtilisin kexin 9 (PCSK9) is a key regulator of low-density lipoprotein receptor levels and LDL-cholesterol levels. Loss-of-function mutations in PCSK9 gene are associated with hypocholesterolaemia and protection against cardiovascular disease, identifying PCSK9 inhibition as a valid therapeutic approach to manage hypercholesterolaemia and related diseases. Although PCSK9 is expressed mainly in the liver, it is present also in other tissues and organs with specific functions, raising the question of whether a pharmacological inhibition of PCSK9 to treat hypercholesterolaemia and associated cardiovascular diseases might be helpful or deleterious in non-hepatic tissues. For example, PCSK9 is expressed in the vascular wall, in the kidneys, and in the brain, where it was proposed to play a role in development, neurocognitive process, and neuronal apoptosis. A link between PCSK9 and immunity was also proposed as both sepsis and viral infections are differentially affected in the presence or absence of PCSK9. Despite the increasing number of observations, the debate on the exact roles of PCSK9 in extrahepatic tissues is still ongoing, and as very effective drugs that inhibit PCSK9 have become available to the clinician, a better understanding of the biological roles of PCSK9 is warranted.

Identification of PCSK9 as a novel serum biomarker for the prenatal diagnosis of neural tube defects using iTRAQ quantitative proteomics

To identify candidate serum molecule biomarkers for the non-invasive early prenatal diagnosis of neural tube defects (NTDs), we employed an iTRAQ-based quantitative proteomic approach to analyze the proteomic changes in serum samples from embryonic day (E) 11 and E13 pregnant rats with spina bifida aperta (SBA) induced by all-trans retinoic acid. Among the 390 proteins identified, 40 proteins at E11 and 26 proteins at E13 displayed significant differential expression in the SBA groups. We confirmed 5 candidate proteins by ELISA. We observed the space-time expression changes of proprotein convertase subtilisin/kexin type 9 (PCSK9) at different stages of fetal development, including a marked decrease in the sera of NTD pregnancies and gradual increase in the sera of normal pregnancies with embryonic development. PCSK9 demonstrated the diagnostic efficacy of potential NTD biomarkers [with an area under the receiver operating characteristic curve of 0.763, 95% CI: 065-0.88]. Additionally, PCSK9 expression in the spinal cords and placentas of SBA rat fetuses was markedly decreased. PCSK9 could serve as a novel molecular biomarker for the non-invasive prenatal screening of NTDs and may be involved in the pathogenesis of NTDs at critical periods of fetal development.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) in lipid metabolism, atherosclerosis and ischemic stroke

Proprotein convertase subtilisin/kexin 9 (PCSK9) is the ninth member of the proprotein convertase family. It is an important regulator of cholesterol metabolism. PCSK9 can bind to low-density lipoprotein receptors (LDLRs) and induce the degradation of these receptors through the endosome/lysosome pathway, thus decreasing the LDLR levels on the cell surface of hepatocytes, resulting in increased serum low-density lipoprotein cholesterol (LDL-C) concentrations. Recent studies have found that gene polymorphisms of PCSK9 are associated with hypercholesterolemia, risk of atherosclerosis, and ischemic stroke. Furthermore, monoclonal antibodies, peptide mimetics, small molecule inhibitors and gene silencing agents that are associated with PCSK9 are some of the newer pharmaceutical therapeutic strategies and approaches for lowering serum LDL-C levels. In this review, we will discuss recent advances in PCSK9 research, which show that PCSK9 is correlated with lipid metabolism, atherosclerosis, and, in particular, ischemic stroke. We will also discuss the current state of PCSK9 therapeutics and their potential in modulating these diseases.

Role of PCSK9 beyond liver involvement

PURPOSE OF REVIEW

Proprotein convertase subtilisin kexin type 9 (PCSK9) acts as an endogenous natural inhibitor of the LDL receptor pathway, by targeting the receptor to lysosomes for degradation. Beside the liver, PCSK9 is also expressed at significant levels in other tissues, where its function remains unclear. The current review focuses on the extrahepatic actions of PCSK9.

RECENT FINDINGS

The generation of liver-specific PCSK9 knockout mice has clearly indicated that PCSK9 affects cholesterol homeostasis via its action on extrahepatic organs. PCSK9 is highly expressed in the intestine, where it controls the production of triglyceride-rich lipoproteins and the transintestinal cholesterol excretion. The role of PCSK9 in the endocrine pancreas and glucose homeostasis remains unclear because conflicting data exist concerning the metabolic phenotype of PCSK9-deficient mice. Sparse data suggest that PCSK9 might also play a role in kidneys, vascular smooth muscle cells, and neurons.

SUMMARY

Based on the virtuous combination of genetic and pharmacological approaches, the major function of PCSK9 as a key regulator of hepatic LDL receptor metabolism had quickly emerged. Accumulating evidence indicates that intestinal PCSK9 is also involved in the modulation of lipid homeostasis. Additional studies are warranted to decipher the physiological function of PCSK9 in other extrahepatic tissues and thus to better assess the safety of PCSK9 inhibitors.

Impacts of ezetimibe on PCSK9 in rats: study on the expression in different organs and the potential mechanisms

Background

Previous studies including our group have indicated the effects of ezetimibe on increased plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) concentration, while the rapid expression in different organs and the potential molecular mechanisms for this impact have not been carefully evaluated.

Methods

Thirty rats were randomly divided into two groups (n = 15 for each), which were orally administrated with ezetimibe (10 mg/kg/day) or normal saline. Blood samples were obtained at day 3 after orally administration, and the PCSK9 levels were determined by ELISA. We further analyzed the mRNA expression of PCSK9, low-density lipoprotein receptor (LDLR), sterol regulator element-binding protein 2 (SREBP2), and hepatocyte nuclear factor 1 alpha (HNF-1α) by real-time PCR, as well as the protein expression by western blot, in liver, intestine and kidney respectively.

Results

Ezetimibe significantly increased plasma PCSK9 levels compared with control group, while there was no significant difference between the two groups with regard to lipid profile at day 3. Moreover, ezetimibe remarkably increased the expression of PCSK9, LDLR, SREBP2 and HNF-1α in liver. Enhanced expression of PCSK9, LDLR and SREBP2 protein were found in intestine and kidney, while no changes in the expression of HNF-1α were observed in intestine and kidney of rats with ezetimibe treatment.

Conclusions

The data demonstrated that ezetimibe increased PCSK9 expression through the SREBP2 and HNF-1α pathways in different organs, subsequently resulting in elevated plasma PCSK9 levels prior to the alterations of lipid profile in rats.

Molecular and cellular function of the proprotein convertase subtilisin/kexin type 9 (PCSK9)

The proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a promising treatment target to lower serum cholesterol, a major risk factor of cardiovascular diseases. Gain-of-function mutations of PCSK9 are associated with hypercholesterolemia and increased risk of cardiovascular events. Conversely, loss-of-function mutations cause low-plasma LDL-C levels and a reduction of cardiovascular risk without known unwanted effects on individual health. Experimental studies have revealed that PCSK9 reduces the hepatic uptake of LDL-C by increasing the endosomal and lysosomal degradation of LDL receptors (LDLR). A number of clinical studies have demonstrated that inhibition of PCSK9 alone and in addition to statins potently reduces serum LDL-C concentrations. This review summarizes the current data on the regulation of PCSK9, its molecular function in lipid homeostasis and the emerging evidence on the extra-hepatic effects of PCSK9.

PCSK9 and its modulation

Proprotein convertase subtilisin/kexin type 9 (PCSK9), a newly-recognized protein, plays a key role in regulating cholesterol homeostasis. PCSK9 reduces hepatic low-density lipoprotein receptors (LDLRs) thereby increasing LDL-cholesterol (LDL-C). Recently, biologic and genetic research proposed several approaches to inhibit or reduce PCSK9 to improve lipid profile and cardiovascular performance in patients with dyslipidemia, particularly hypercholesterolemia. Of note, PCSK9 is a secreted protein under tight control by multiple modulators. Therefore, elucidating the factors that influence PCSK9 would enhance our understanding of PCSK9 and potentially day-to-day management of these patients at high cardiovascular risk. This review will focus on genetic variants, physiologic processes, pharmacologic agents and pathologic conditions related to PCSK9 in order to assess current and future therapeutic strategies targeting this molecule.

PCSK9 inhibition for the treatment of hypercholesterolemia: promises and emerging challenges

Hypercholesterolemia, is a prominent risk factor for cardiovascular disease (CVD). Undestanding of the biochemical mechanisms that regulate the expression of the low density lipoproteins receptor (LDLR) and the hepatic clearance of LDL cholesterol (LDL-C) paved the way to the statin therapy as the gold standard for CVD prevention. The discovery of proteins that regulate - at a post-translational level - the activity of the LDLR has been a major breakthrough in developing new cholesterol-lowering drugs. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key modulator of the LDLR degradation in the liver. Genetic studies confirmed that in humans PCSK9 mutations associate with hypercholesterolemia and hypocholesterolemia (gain-of-function or loss-of-function variants respectively). Moreover, PCSK9 is up-regulated by statin treatment and limits the efficacy of these agents. These findings led to the development of PCSK9 inhibitors. Anti-PCSK9 monoclonal antibodies showed encouraging results and are currently being evaluated in phase III clinical trials. The aim of this short review is to describe the new frontier of PCSK9 inhibition in the treatment of hypercholesterolemia. Emphasis here is given to critical emerging issues linked to PCSK9 physiology and pharmacology, which will require future investigation to definitely address the potential of anti-PCSK9 drugs in clinical practice.