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

Apolipoprotein B gene expression and regulation in relation to Alzheimer's disease pathophysiology

Apolipoprotein B (APOB), a receptor-binding protein present in cholesterol-rich lipoproteins, has been implicated in Alzheimer's disease (AD). High levels of APOB-containing low-density lipoproteins (LDL) are linked to the pathogenesis of both early-onset familial and late-onset sporadic AD. Rare coding mutations in the APOB gene are associated with familial AD, suggesting a role for APOB-bound lipoproteins in the central nervous system. This research explores APOB gene regulation across the AD spectrum using four cohorts: BRAINEAC (elderly control brains), DBCBB (controls, AD brains), ROSMAP (controls, MCI, AD brains), and ADNI (control, MCI, AD clinical subjects). APOB protein levels, measured via mass spectrometry and ELISA, positively correlated with AD pathology indices and cognition, while APOB mRNA levels showed negative correlations. Brain APOB protein levels are also correlated with cortical Aβ levels. A common coding variant in the APOB gene locus affected its expression but didn't impact AD risk or brain cholesterol concentrations, except for 24-S-hydroxycholesterol. Polymorphisms in the CYP27A1 gene, notably rs4674344, were associated with APOB protein levels. A negative correlation was observed between brain APOB gene expression and AD biomarker levels. CSF APOB correlated with Tau pathology in presymptomatic subjects, while cortical APOB was strongly associated with cortical Aβ deposition in late-stage AD. The study discusses the potential link between blood-brain barrier dysfunction and AD symptoms in relation to APOB neurobiology. Overall, APOB's involvement in lipoprotein metabolism appears to influence AD pathology across different stages of the disease.

A critical review on diabetes mellitus type 1 and type 2 management approaches: from lifestyle modification to current and novel targets and therapeutic agents

Diabetes mellitus (DM) has emerged as an international health epidemic due to its rapid rise in prevalence. Consequently, scientists and or researchers will continue to find novel, safe, effective, and affordable anti-diabetic medications. The goal of this review is to provide a thorough overview of the role that lifestyle changes play in managing diabetes, as well as the standard medications that are currently being used to treat the condition and the most recent advancements in the development of novel medical treatments that may be used as future interventions for the disease. A literature search was conducted using research databases such as PubMed, Web of Science, Scopus, ScienceDirect, Wiley Online Library, Google Scholar, etc. Data were then abstracted from these publications using words or Phrases like "pathophysiology of diabetes", "Signe and symptoms of diabetes", "types of diabetes", "major risk factors and complication of diabetes", "diagnosis of diabetes", "lifestyle modification for diabetes", "current antidiabetic agents", and "novel drugs and targets for diabetes management" that were published in English and had a strong scientific foundation. Special emphasis was given to the importance of lifestyle modification, as well as current, novel, and emerging/promising drugs and targets helpful for the management of both T1DM and T2DM.

Causal relationship between PCSK9 inhibitor and common neurodegenerative diseases: A drug target Mendelian randomization study

BACKGROUND

In addition to lowering cholesterol levels, the proprotein convertase subtilis kexin 9 (PCSK9) inhibitor has a variety of effects, including anti-neuroapoptosis. However, the effects of PCSK9 inhibitors on neurodegenerative diseases are controversial. Therefore, we used drug-targeted Mendelian randomization (MR) analysis to investigate the effects of PCSK9 inhibitors on different neurodegenerative diseases.

METHODS

We collected single nucleotide polymorphisms (SNPs) of PCSK9 from published statistics of genome-wide association studies and performed drug target MR analyses to detect a causal relationship between PCSK9 inhibitors and the risk of neurodegenerative diseases. We utilized the effects of 3-Hydroxy -3- methylglutaryl-assisted enzyme A reductase (HMGCR) inhibitors (statin targets) for comparison with PCSK9 inhibitors. Coronary heart disease risk was used as a positive control, and primary outcomes included amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and Alzheimer's disease (AD).

RESULTS

PCSK9 inhibitors marginally reduced the risk of ALS (OR [95%] = 0.89 [0.77 to 1.00], p = 0.048), while they increased the risk of PD (OR [95%] = 1.417 [1.178 to 1.657], p = 0.004). However, HMGCR inhibitors increased the risk of PD (OR [95%] = 1.907 [1.502 to 2.312], p = 0.001).

CONCLUSION

PCSK9 inhibitors significantly reduce the risk of ALS but increase the risk of PD. HMGCR inhibitors may be the risk factor for PD.

The Intersection of cerebral cholesterol metabolism and Alzheimer's disease: Mechanisms and therapeutic prospects

Alzheimer's disease (AD) is a common neurodegenerative disease in the elderly, the exact pathogenesis of which remains incompletely understood, and effective preventive and therapeutic drugs are currently lacking. Cholesterol plays a vital role in cell membrane formation and neurotransmitter synthesis, and its abnormal metabolism is associated with the onset of AD. With the continuous advancement of imaging techniques and molecular biology methods, researchers can more accurately explore the relationship between cholesterol metabolism and AD. Elevated cholesterol levels may lead to vascular dysfunction, thereby affecting neuronal function. Additionally, abnormal cholesterol metabolism may affect the metabolism of β-amyloid protein, thereby promoting the onset of AD. Brain cholesterol levels are regulated by multiple factors. This review aims to deepen the understanding of the subtle relationship between cholesterol homeostasis and AD, and to introduce the latest advances in cholesterol-regulating AD treatment strategies, thereby inspiring readers to contemplate deeply on this complex relationship. Although there are still many unresolved important issues regarding the risk of brain cholesterol and AD, and some studies may have opposite conclusions, further research is needed to enrich our understanding. However, these findings are expected to deepen our understanding of the pathogenesis of AD and provide important insights for the future development of AD treatment strategies targeting brain cholesterol homeostasis.

GUIDE deconstructs genetic architectures using association studies

Genome-wide association studies have revealed that the genetic architecture of most complex traits is characterized by a large number of distinct effects scattered across the genome. Functional enrichment analyses of these results suggest that the associations for any given complex trait are not purely random. Thus, we set out to leverage the genetic association results from many traits with a view to identifying the set of modules, or latent factors, that mediate these associations. The identification of such modules may aid in disease classification as well as the elucidation of complex disease mechanisms. We propose a method, Genetic Unmixing by Independent Decomposition (GUIDE), to estimate a set of statistically independent latent factors that best express the patterns of association across many traits. The resulting latent factors not only have desirable mathematical properties, such as sparsity and a higher variance explained (for both traits and variants), but are also able to single out and prioritize key biological features or pathophysiological mechanisms underlying a given trait or disease. Moreover, we show that these latent factors can index biological pathways as well as epidemiological and environmental influences that compose the genetic architecture of complex traits.

Drug development advances in human genetics-based targets

Drug development is a long and costly process, with a high degree of uncertainty from the identification of a drug target to its market launch. Targeted drugs supported by human genetic evidence are expected to enter phase II/III clinical trials or be approved for marketing more quickly, speeding up the drug development process. Currently, genetic data and technologies such as genome-wide association studies (GWAS), whole-exome sequencing (WES), and whole-genome sequencing (WGS) have identified and validated many potential molecular targets associated with diseases. This review describes the structure, molecular biology, and drug development of human genetics-based validated beneficial loss-of-function (LOF) mutation targets (target mutations that reduce disease incidence) over the past decade. The feasibility of eight beneficial LOF mutation targets (PCSK9, ANGPTL3, ASGR1, HSD17B13, KHK, CIDEB, GPR75, and INHBE) as targets for drug discovery is mainly emphasized, and their research prospects and challenges are discussed. In conclusion, we expect that this review will inspire more researchers to use human genetics and genomics to support the discovery of novel therapeutic drugs and the direction of clinical development, which will contribute to the development of new drug discovery and drug repurposing.

Function of proprotein convertase subtilisin/kexin type 9 and its role in central nervous system diseases: An update on clinical evidence

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has attracted lots of attention in preventing the clearance of plasma low-density lipoprotein cholesterol (LDL-C). PCSK9 inhibitors are developed to primarily reduce the cardiovascular risk by lowering LDL-C level. Recently, a number of pleiotropic extrahepatic functions of PCSK9 beyond the regulation of cholesterol metabolism, particularly its effects on central nervous system (CNS) diseases have been increasingly identified. Emerging clinical evidence have revealed that PCSK9 may play a significant role in neurocognition, depression, Alzheimer's disease, and stroke. The focus of this review is to elucidate the functions of PCSK9 and highlight the effects of PCSK9 in CNS diseases, with the aim of identifying the potential risks that may arise from low PCSK9 level (variant or inhibitor) in the clinical practice.

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.

PCSK9 ablation attenuates Aβ pathology, neuroinflammation and cognitive dysfunctions in 5XFAD mice

BACKGROUND

Increasing evidence highlights the importance of novel players in Alzheimer's disease (AD) pathophysiology, including alterations of lipid metabolism and neuroinflammation. Indeed, a potential involvement of Proprotein convertase subtilisin/kexin type 9 (PCSK9) in AD has been recently postulated. Here, we first investigated the effects of PCSK9 on neuroinflammation in vitro. Then, we examined the impact of a genetic ablation of PCSK9 on cognitive performance in a severe mouse model of AD. Finally, in the same animals we evaluated the effect of PCSK9 loss on Aβ pathology, neuroinflammation, and brain lipids.

METHODS

For in vitro studies, U373 human astrocytoma cells were treated with Aβ fibrils and human recombinant PCSK9. mRNA expression of the proinflammatory cytokines and inflammasome-related genes were evaluated by q-PCR, while MCP-1 secretion was measured by ELISA. For in vivo studies, the cognitive performance of a newly generated mouse line - obtained by crossing 5XFADHet with PCSK9KO mice - was tested by the Morris water maze test. After sacrifice, immunohistochemical analyses were performed to evaluate Aβ plaque deposition, distribution and composition, BACE1 immunoreactivity, as well as microglia and astrocyte reactivity. Cholesterol and hydroxysterols levels in mouse brains were quantified by fluorometric and LC-MS/MS analyses, respectively. Statistical comparisons were performed according to one- or two-way ANOVA, two-way repeated measure ANOVA or Chi-square test.

RESULTS

In vitro, PCSK9 significantly increased IL6, IL1B and TNFΑ mRNA levels in Aβ fibrils-treated U373 cells, without influencing inflammasome gene expression, except for an increase in NLRC4 mRNA levels. In vivo, PCSK9 ablation in 5XFAD mice significantly improved the performance at the Morris water maze test; these changes were accompanied by a reduced corticohippocampal Aβ burden without affecting plaque spatial/regional distribution and composition or global BACE1 expression. Furthermore, PCSK9 loss in 5XFAD mice induced decreased microgliosis and astrocyte reactivity in several brain regions. Conversely, knocking out PCSK9 had minimal impact on brain cholesterol and hydroxysterol levels.

CONCLUSIONS

In vitro studies showed a pro-inflammatory effect of PCSK9. Consistently, in vivo data indicated a protective role of PCSK9 ablation against cognitive impairments, associated with improved Aβ pathology and attenuated neuroinflammation in a severe mouse model of AD. PCSK9 may thus be considered a novel pharmacological target for the treatment of AD.

Blockade of Hepatocyte PCSK9 Ameliorates Hepatic Ischemia-Reperfusion Injury by Promoting Pink1-Parkin-Mediated Mitophagy

BACKGROUND & AIMS

Hepatic ischemia-reperfusion injury is a significant complication of partial hepatic resection and liver transplantation, impacting the prognosis of patients undergoing liver surgery. The protein proprotein convertase subtilisin/kexin type 9 (PCSK9) is primarily synthesized by hepatocytes and has been implicated in myocardial ischemic diseases. However, the role of PCSK9 in hepatic ischemia-reperfusion injury remains unclear. This study aims to investigate the role and mechanism of PCSK9 in hepatic ischemia-reperfusion injury.

METHODS

We first examined the expression of PCSK9 in mouse warm ischemia-reperfusion models and AML12 cells subjected to hypoxia/reoxygenation. Subsequently, we explored the impact of PCSK9 on liver ischemia-reperfusion injury by assessing mitochondrial damage and the resulting inflammatory response.

RESULTS

Our findings reveal that PCSK9 is up-regulated in response to ischemia-reperfusion injury and exacerbates hepatic ischemia-reperfusion injury. Blocking PCSK9 can alleviate hepatocyte mitochondrial damage and the consequent inflammatory response mediated by ischemia-reperfusion. Mechanistically, this protective effect is dependent on mitophagy.

CONCLUSIONS

Inhibiting PCSK9 in hepatocytes attenuates the inflammatory responses triggered by reactive oxygen species and mitochondrial DNA by promoting PINK1-Parkin-mediated mitophagy. This, in turn, ameliorates hepatic ischemia-reperfusion injury.

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.

Resveratrol Attenuates the Disruption of Lipid Metabolism Observed in Amyloid Precursor Protein/Presenilin 1 Mouse Brains and Cultured Primary Neurons Exposed to Aβ

To examine whether resveratrol (RSV), an activator of silent mating-type information regulation 2 homolog 1 (SIRT1), can reverse the disruption of lipid metabolism caused by β-amyloid peptide (Aβ), APP/PS1 mice or cultured primary rat neurons were treated with RSV, suramin (inhibitor of SIRT1), ZLN005, a stimulator of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), or PGC-1α silencing RNA. In the brains of the APP/PS1 mice, expressions of SIRT1, PGC-1α, low-density lipoprotein receptor (LDLR) and very LDLR (VLDLR) were reduced at the protein and, in some cases, mRNA levels; while the levels of the proprotein convertase subtilisin/kexin type 9 (PCSK9), apolipoprotein E (ApoE), total cholesterol and LDL were all elevated. Interestingly, these changes were reversed by administration of RSV, while being aggravated by suramin. Furthermore, activation of PGC-1α, but inhibition of SIRT1, decreased the levels of PCSK9 and ApoE, while increased those of LDLR and VLDLR in the neurons exposed to Aβ, and silencing PGC-1α, but activation of SIRT1, did not influence the levels of any of these proteins. These findings indicate that RSV can attenuate the disruption of lipid metabolism observed in the brains of APP mice and in primary neurons exposed to Aβ by activating SIRT1, in which the mechanism may involve subsequently affecting PGC-1α.

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.

Neurocognitive Disorders Associated with PCSK9 Inhibitors: a Pharmacovigilance Disproportionality Analysis

PURPOSE

PCSK9 might affect central nervous system development, neuronal apoptosis, and differentiation. We investigate the neurocognitive adverse events associated with the use of PCSK9 inhibitors (alirocumab and evolocumab) using pharmacovigilance reports.

METHODS

We used the World Health Organization pharmacovigilance database (VigiBase) to perform a disproportionality analysis comparing the proportion of neurocognitive adverse events reported with PCSK9 inhibitors versus the proportion of these effects reported since August 14, 2015 (date of first post-marketing report suspecting a PCSK9 inhibitor), for all drugs in the database. Associations between PCSK9 inhibitor use and neurocognitive adverse events were assessed using both proportional reporting ratio (PRR) and information component (IC). Complementary analyses were performed on other neurologic events, and different sensitivity analyses were conducted to evaluate the robustness of results.

RESULTS

Among the 81,108 reports involving at least one PCSK9 inhibitor, 1,941 concerned the occurrence of neurocognitive disorders. Most of patients (52.3%) were aged 45-74 years, and 58.0% were women. Signals of disproportionate reporting were found for PCSK9 inhibitors (PRR 1.22, 95% CI 1.17; 1.28; IC 0.28, IC₀₂₅ 0.21) and for each drug individually. No signal of disproportionality was found for any of the other neurologic events investigated. Signals of disproportionate reporting were found for the positive control (benzodiazepines), but not for the negative control (aspirin). The results of the main analysis were confirmed by sensitivity analyses.

CONCLUSIONS

This study identified a signal of neurocognitive disorders associated with PCSK9 inhibitors and encourages paying attention to at-risk populations.

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.

Is type 2 diabetes associated dementia a microvascular early-Alzheimer's phenotype induced by aberrations in the peripheral metabolism of lipoprotein-amyloid?

There is increasing evidence of a positive association of type 2 diabetes with Alzheimer's disease (AD), the most prevalent form of dementia. Suggested pathways include cerebral vascular dysfunction; central insulin resistance, or exaggerated brain abundance of potentially cytotoxic amyloid-β (Aβ), a hallmark feature of AD. However, contemporary studies find that Aβ is secreted in the periphery by lipogenic organs and secreted as nascent triglyceride-rich lipoproteins (TRL's). Pre-clinical models show that exaggerated abundance in blood of TRL-Aβ compromises blood-brain barrier (BBB) integrity, resulting in extravasation of the TRL-Aβ moiety to brain parenchyme, neurovascular inflammation and neuronal degeneration concomitant with cognitive decline. Inhibiting secretion of TRL-Aβ by peripheral lipogenic organs attenuates the early-AD phenotype indicated in animal models, consistent with causality. Poorly controlled type 2 diabetes commonly features hypertriglyceridemia because of exaggerated TRL secretion and reduced rates of catabolism. Alzheimer's in diabetes may therefore be a consequence of heightened abundance in blood of lipoprotein-Aβ and accelerated breakdown of the BBB. This review reconciles the prevailing dogma of amyloid associated cytotoxicity as a primary risk factor in late-onset AD, with substantial evidence of a microvascular axis for dementia-in-diabetes. Consideration of potentially relevant pharmacotherapies to treat insulin resistance, dyslipidaemia and by extension plasma amyloidemia in type 2 diabetes are discussed.

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.

PCSK9 Affects Astrocyte Cholesterol Metabolism and Reduces Neuron Cholesterol Supplying In Vitro: Potential Implications in Alzheimer's Disease

The Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) involvement in Alzheimer’s disease (AD) is poorly investigated. We evaluated the in vitro PCSK9 modulation of astrocyte cholesterol metabolism and neuronal cholesterol supplying, which is fundamental for neuronal functions. Moreover, we investigated PCSK9 neurotoxic effects. In human astrocytoma cells, PCSK9 reduced cholesterol content (−20%; p < 0.05), with a greater effect in presence of beta amyloid peptide (Aβ) (−37%; p < 0.01). PCSK9 increased cholesterol synthesis and reduced the uptake of apoE-HDL-derived cholesterol (−36%; p < 0.0001), as well as the LDL receptor (LDLR) and the apoE receptor 2 (ApoER2) expression (−66% and −31%, respectively; p < 0.01). PCSK9 did not modulate ABCA1- and ABCG1-cholesterol efflux, ABCA1 levels, or membrane cholesterol. Conversely, ABCA1 expression and activity, as well as membrane cholesterol, were reduced by Aβ (p < 0.05). In human neuronal cells, PCSK9 reduced apoE-HDL-derived cholesterol uptake (−41%; p < 0.001) and LDLR/apoER2 expression (p < 0.05). Reduced cholesterol internalization occurred also in PCSK9-overexpressing neurons exposed to an astrocyte-conditioned medium (−39%; p < 0.001). PCSK9 reduced neuronal cholesterol content overall (−29%; p < 0.05) and increased the Aβ-induced neurotoxicity (p < 0.0001). Our data revealed an interfering effect of PCSK9, in cooperation with Aβ, on brain cholesterol metabolism leading to neuronal cholesterol reduction, a potentially deleterious effect. PCSK9 also exerted a neurotoxic effect, and thus represents a potential pharmacological target in AD.

HDL-like-Mediated Cell Cholesterol Trafficking in the Central Nervous System and Alzheimer's Disease Pathogenesis

The main aim of this work is to review the mechanisms via which high-density lipoprotein (HDL)-mediated cholesterol trafficking through the central nervous system (CNS) occurs in the context of Alzheimer’s disease (AD). Alzheimer’s disease is characterized by the accumulation of extracellular amyloid beta (Aβ) and abnormally hyperphosphorylated intracellular tau filaments in neurons. Cholesterol metabolism has been extensively implicated in the pathogenesis of AD through biological, epidemiological, and genetic studies, with the APOE gene being the most reproducible genetic risk factor for the development of AD. This manuscript explores how HDL-mediated cholesterol is transported in the CNS, with a special emphasis on its relationship to Aβ peptide accumulation and apolipoprotein E (ApoE)-mediated cholesterol transport. Indeed, we reviewed all existing works exploring HDL-like-mediated cholesterol efflux and cholesterol uptake in the context of AD pathogenesis. Existing data seem to point in the direction of decreased cholesterol efflux and the impaired entry of cholesterol into neurons among patients with AD, which could be related to impaired Aβ clearance and tau protein accumulation. However, most of the reviewed studies have been performed in cells that are not physiologically relevant for CNS pathology, representing a major flaw in this field. The ApoE4 genotype seems to be a disruptive element in HDL-like-mediated cholesterol transport through the brain. Overall, further investigations are needed to clarify the role of cholesterol trafficking in AD pathogenesis.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a psoriasis susceptibility locus that is negatively related to IL36G

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a posttranslational regulator of the LDL receptor (LDLR). Recent studies have proposed a role for PCSK9 in regulating immune responses. Using RNA-Seq–based variant discovery, we identified a possible psoriasis-susceptibility locus at 1p32.3, located within PCSK9 (rs662145 C > T). This finding was verified in independently acquired genomic and RNA-Seq data sets. Single-cell RNA-Seq (scRNA-Seq) identified keratinocytes as the primary source of PCSK9 in human skin. PCSK9 expression, however, was not uniform across keratinocyte subpopulations. scRNA-Seq and IHC demonstrated an epidermal gradient of PCSK9, with expression being highest in basal and early spinous layer keratinocytes and lowest in granular layer keratinocytes. IL36G expression followed the opposite pattern, with expression highest in granular layer keratinocytes. PCSK9 siRNA knockdown experiments confirmed this inverse relationship between PCSK9 and IL36G expression. Other immune genes were also linked to PCSK9 expression, including IL27RA, IL1RL1, ISG20, and STX3. In both cultured keratinocytes and nonlesional human skin, homozygosity for PCSK9 SNP rs662145 C > T was associated with lower PCSK9 expression and higher IL36G expression, when compared with heterozygous skin or cell lines. Together, these results support PCSK9 as a psoriasis-susceptibility locus and establish a putative link between PCSK9 and inflammatory cytokine expression.

No association between APOE genotype and lipid lowering with cognitive function in a randomized controlled trial of evolocumab

APOE encodes a cholesterol transporter, and the ε4 allele is associated with higher circulating cholesterol levels, ß-amyloid burden, and risk of Alzheimer's disease. Prior studies demonstrated no significant differences in objective or subjective cognitive function for patients receiving the PCSK9 inhibitor evolocumab vs. placebo added to statin therapy. There is some evidence that cholesterol-lowering medications may confer greater cognitive benefits in APOE ε4 carriers. Thus, the purpose of this study was to determine whether APOE genotype moderates the relationships between evolocumab use and cognitive function. APOE-genotyped patients (N = 13,481; 28% ε4 carriers) from FOURIER, a randomized, placebo-controlled trial of evolocumab added to statin therapy in patients with stable atherosclerotic cardiovascular disease followed for a median of 2.2 years, completed the Everyday Cognition Scale (ECog) to self-report cognitive changes from the end of the trial compared to its beginning; a subset (N = 835) underwent objective cognitive testing using the Cambridge Neuropsychological Test Automated Battery as part of the EBBINGHAUS trial. There was a dose-dependent relationship between APOE ε4 genotype and patient-reported memory decline on the ECog in the placebo arm (p = .003 for trend across genotypes; ε4/ε4 carriers vs. non-carriers: OR = 1.46, 95% CI [1.03, 2.08]) but not in the evolocumab arm (p = .50, OR = 1.18, 95% CI [.83,1.66]). However, the genotype by treatment interaction was not significant (p = .30). In the subset of participants who underwent objective cognitive testing with the CANTAB, APOE genotype did not significantly modify the relationship between treatment arm and CANTAB performance after adjustment for demographic and medical covariates, (p's>.05). Although analyses were limited by the low population frequency of the ε4/ε4 genotype, this supports the cognitive safety of evolocumab among ε4 carriers, guiding future research on possible benefits of cholesterol-lowering medications in people at genetic risk for Alzheimer's disease.

Guidelines for bioinformatics of single-cell sequencing data analysis in Alzheimer's disease: review, recommendation, implementation and application

Alzheimer's disease (AD) is the most common form of dementia, characterized by progressive cognitive impairment and neurodegeneration. Extensive clinical and genomic studies have revealed biomarkers, risk factors, pathways, and targets of AD in the past decade. However, the exact molecular basis of AD development and progression remains elusive. The emerging single-cell sequencing technology can potentially provide cell-level insights into the disease. Here we systematically review the state-of-the-art bioinformatics approaches to analyze single-cell sequencing data and their applications to AD in 14 major directions, including 1) quality control and normalization, 2) dimension reduction and feature extraction, 3) cell clustering analysis, 4) cell type inference and annotation, 5) differential expression, 6) trajectory inference, 7) copy number variation analysis, 8) integration of single-cell multi-omics, 9) epigenomic analysis, 10) gene network inference, 11) prioritization of cell subpopulations, 12) integrative analysis of human and mouse sc-RNA-seq data, 13) spatial transcriptomics, and 14) comparison of single cell AD mouse model studies and single cell human AD studies. We also address challenges in using human postmortem and mouse tissues and outline future developments in single cell sequencing data analysis. Importantly, we have implemented our recommended workflow for each major analytic direction and applied them to a large single nucleus RNA-sequencing (snRNA-seq) dataset in AD. Key analytic results are reported while the scripts and the data are shared with the research community through  GitHub. In summary, this comprehensive review provides insights into various approaches to analyze single cell sequencing data and offers specific guidelines for study design and a variety of analytic directions. The review and the accompanied software tools will serve as a valuable resource for studying cellular and molecular mechanisms of AD, other diseases, or biological systems at the single cell level.

Emerging role of HDL in brain cholesterol metabolism and neurodegenerative disorders

High-density lipoproteins (HDLs play a key role in cholesterol homeostasis maintenance in the central nervous system (CNS), by carrying newly synthesized cholesterol from astrocytes to neurons, to support their lipid-related physiological functions. As occurs for plasma HDLs, brain lipoproteins are assembled through the activity of membrane cholesterol transporters, undergo remodeling mediated by specific enzymes and transport proteins, and finally deliver cholesterol to neurons by a receptor-mediated internalization process. A growing number of evidences indicates a strong association between alterations of CNS cholesterol homeostasis and neurodegenerative disorders, in particular Alzheimer's disease (AD), and a possible role in this relationship may be played by defects in brain HDL metabolism. In the present review, we summarize and critically examine the current state of knowledge on major modifications of HDL and HDL-mediated brain cholesterol transport in AD, by taking into consideration the individual steps of this process. We also describe potential and encouraging HDL-based therapies that could represent new therapeutic strategies for AD treatment. Finally, we revise the main plasma and brain HDL modifications in other neurodegenerative disorders including Parkinson's disease (PD), Huntington's disease (HD), and frontotemporal dementia (FTD).

Cholesterol metabolism in aging simultaneously altered in liver and nervous system

In humans, aging, triggers increased plasma concentrations of triglycerides, cholesterol, low-density lipoproteins and lower capacity of high-density lipoproteins to remove cellular cholesterol. Studies in rodents showed that aging led to cholesterol accumulation in the liver and decrease in the brain with reduced cholesterol synthesis and increased levels of cholesterol 24-hydroxylase, an enzyme responsible for removing cholesterol from the brain. Liver diseases are also related to brain aging, inducing changes in cholesterol metabolism in the brain and liver of rats. It has been suggested that late onset Alzheimer's disease is associated with metabolic syndrome. Non-alcoholic fatty liver is associated with lower total brain volume in the Framingham Heart Study offspring cohort study. Furthermore, disorders of cholesterol homeostasis in the adult brain are associated with neurological diseases such as Niemann-Pick, Alzheimer, Parkinson, Huntington and epilepsy. Apolipoprotein E (apoE) is important in transporting cholesterol from astrocytes to neurons in the etiology of sporadic Alzheimer's disease, an aging-related dementia. Desmosterol and 24S-hydroxycholesterol are reduced in ApoE KO hypercholesterolemic mice. ApoE KO mice have synaptic loss, cognitive dysfunction, and elevated plasma lipid levels that can affect brain function. In contrast to cholesterol itself, there is a continuous uptake of 27- hydroxycholesterol in the brain as it crosses the blood-brain barrier and this flow can be an important link between intra- and extracerebral cholesterol homeostasis. Not surprisingly, changes in cholesterol metabolism occur simultaneously in the liver and nervous tissues and may be considered possible biomarkers of the liver and nervous system aging.

Lipids and peripheral neuropathy

PURPOSE OF REVIEW

Hyperlipidaemia is associated with the development of neuropathy. Indeed, a mechanistic link between altered lipid metabolism and peripheral nerve dysfunction has been demonstrated in a number of experimental and clinical studies. Furthermore, post hoc analyses of clinical trials of cholesterol and triglyceride-lowering pharmacotherapy have shown reduced rates of progression of diabetic neuropathy. Given, there are currently no FDA approved disease-modifying therapies for diabetic neuropathy, modulation of lipids may represent a key therapeutic target for the treatment of diabetic nerve damage. This review summarizes the current evidence base on the role of hyperlipidaemia and lipid lowering therapy on the development and progression of peripheral neuropathy.

RECENT FINDINGS

A body of literature supports a detrimental effect of dyslipidaemia on nerve fibres resulting in somatic and autonomic neuropathy. The case for an important modulating role of hypertriglyceridemia is stronger than for low-density lipoprotein cholesterol (LDL-C) in relation to peripheral neuropathy. This is reflected in the outcomes of clinical trials with the different therapeutic agents targeting hyperlipidaemia reporting beneficial or neutral effects with statins and fibrates. The potential concern with the association between proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor therapy and cognitive decline raised the possibility that extreme LDL-C lowering may result in neurodegeneration. However, studies in murine models and data from small observational studies indicate an association between increased circulating PCSK9 levels and small nerve fibre damage with a protective effect of PCSK9i therapy against small fibre neuropathy. Additionally, weight loss with bariatric surgery leads to an improvement in peripheral neuropathy and regeneration of small nerve fibres measured with corneal confocal microscopy in people with obesity with or without type 2 diabetes. These improvements correlate inversely with changes in triglyceride levels.

SUMMARY

Hyperlipidaemia, particularly hypertriglyceridemia, is associated with the development and progression of neuropathy. Lipid modifying agents may represent a potential therapeutic option for peripheral neuropathy. Post hoc analyses indicate that lipid-lowering therapies may halt the progression of neuropathy or even lead to regeneration of nerve fibres. Well designed randomized controlled trials are needed to establish if intensive targeted lipid lowering therapy as a part of holistic metabolic control leads to nerve fibre regeneration and improvement in neuropathy symptoms.

Anti-PCSK 9 antibodies increase the ratios of the brain-specific oxysterol 24S-hydroxycholesterol to cholesterol and to 27-hydroxycholesterol in the serum

AIMS

The serum ratios of the brain-specific oxysterol 24S-hydroxycholesterol (24S-OHC) to cholesterol and to 27-OHC reflect brain cholesterol turnover. We studied the effect of proprotein convertase subtilisin/kexin type 9 monoclonal antibodies (PCSK9ab) that enhance low-density lipoprotein receptor activity on serum cholesterol and oxysterol concentrations.

METHODS

Twenty-eight hypercholesterolaemic patients (15 males and 13 females) responding insufficiently to maximally tolerated statin and/or ezetimibe therapy were additionally subcutanously treated biweekly with either the PCSK9ab alirocumab (150 mg, n = 13) or evolocumab (140 mg, n = 15). Fasting serum cholesterol was measured by gas chromatography and the oxysterols 24S-OHC and 27-OHC using gas chromatography-mass spectrometry before, after 1-month (n = 28) and after 3-month (n = 13) treatment.

RESULTS

As expected, PCSK9ab treatment lowered serum cholesterol and oxysterol levels after 1 month. The serum ratio of 24S-OHC to cholesterol increased after 1 month by 17 ± 28% (mean ± standard deviation; 95% confidence interval [CI]: 5.8 to 28%; P < .01) and 24S-OHC to 27-OHC by 15 ± 39% (95% CI: 0.2 to 30%; P < .01). Within 3 months, 24S-OHC to cholesterol increased by 2.8 μg g^-1 mo^-1 (95% CI: 2.1 to 3.6; P < .01) and 24S-OHC to 27-OHC by 0.019 mo^-1 (95% CI: 0.007 to 0.032; P < .01).

CONCLUSION

The serum ratios of 24S-OHC to cholesterol and to 27-OHC increased after treatment with PCSK9ab. We hypothesize that this is caused by a reduced entrance of 27-OHC into the brain, increased synthesis of brain cholesterol, increased production of 24S-OHC and its secretion across the blood-brain barrier.

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.

PCSK9 Inhibitors and Neurocognitive Adverse Drug Reactions: Analysis of Individual Case Safety Reports from the Eudravigilance Database

Introduction

Proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9Is) were associated with a risk of neurocognitive adverse drug reactions (ADRs).

Objective

We aimed to investigate the occurrence of neuropsychiatric ADRs related to PCSK9Is.

Methods

We analyzed Individual Case Safety Reports (ICSRs) sent through the European pharmacovigilance database that reported alirocumab or evolocumab as the suspected drug and at least one neurological or psychiatric ADR. The reporting odds ratio (ROR) was computed to compare the probability of reporting ICSRs with neuropsychiatric ADRs between alirocumab, evolocumab and statins.

Results

Overall, 2041 ICSRs with alirocumab and/or evolocumab as the suspected drug described the occurrence of neuropsychiatric ADRs. The most reported preferred terms for both drugs were headache, insomnia and depression. No difference between alirocumab and evolocumab was observed for the RORs of ICSRs with ADRs belonging to the System Organ Classes (SOCs) ‘Nervous system disorders’ or ‘Psychiatric disorders’ (ROR 1.02, 95% confidence interval 0.91–1.14; and 1.12, 95% CI 0.94–1.34, respectively), while evolocumab and alirocumab had a higher reporting probability of ICSRs with ADRs belonging to the SOC ‘Nervous system disorders’ compared with atorvastatin and fluvastatin. A lower reporting probability was instead found for ICSRs with ADRs belonging to the SOC ‘Psychiatric disorders’ for evolocumab and alirocumab versus simvastatin, pravastatin and rosuvastatin.

Conclusion

Our results demonstrated that 22.7% of all ICSRs reporting alirocumab or evolocumab as suspect drugs described the occurrence of neuropsychiatric ADRs. The ROR showed that evolocumab and alirocumab had a higher reporting probability of neurological ADRs compared with statins. Further data from real-life contexts are needed.

Electronic supplementary material

The online version of this article (10.1007/s40264-020-01021-3) contains supplementary material, which is available to authorized users.

From Brain to Heart: Possible Role of Amyloid-β in Ischemic Heart Disease and Ischemia-Reperfusion Injury

Ischemic heart disease (IHD) is among the leading causes of death in developed countries. Its pathological origin is traced back to coronary atherosclerosis, a lipid-driven immuno-inflammatory disease of the arteries that leads to multifocal plaque development. The primary clinical manifestation of IHD is acute myocardial infarction (AMI),) whose prognosis is ameliorated with optimal timing of revascularization. Paradoxically, myocardium re-perfusion can be detrimental because of ischemia-reperfusion injury (IRI), an oxidative-driven process that damages other organs. Amyloid-β (Aβ) plays a physiological role in the central nervous system (CNS). Alterations in its synthesis, concentration and clearance have been connected to several pathologies, such as Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Aβ has been suggested to play a role in the pathogenesis of IHD and cerebral IRI. The purpose of this review is to summarize what is known about the pathological role of Aβ in the CNS; starting from this evidence, we will illustrate the role played by Aβ in the development of coronary atherosclerosis and its possible implications in the pathophysiology of IHD and myocardial IRI. Better elucidation of Aβ's contribution to the molecular pathways underlying IHD and IRI could be of great help in developing new therapeutic strategies.

Coming Back to Physiology: Extra Hepatic Functions of Proprotein Convertase Subtilisin/Kexin Type 9

Neuronal apoptosis regulated convertase-1 (NARC-1), now mostly known as proprotein convertase subtilisin/kexin type 9 (PCSK9), has received a lot of attention due to the fact that it is a key regulator of the low-density lipoprotein (LDL) receptor (LDL-R) and is therefore involved in hepatic LDL clearance. Within a few years, therapies targeting PCSK9 have reached clinical practice and they offer an additional tool to reduce blood cholesterol concentrations. However, PCSK9 is almost ubiquitously expressed in the body but has less well-understood functions and target proteins in extra hepatic tissues. As such, PCSK9 is involved in the regulation of neuronal survival and protein degradation, it affects the expression of the epithelial sodium channel (ENaC) in the kidney, it interacts with white blood cells and with cells of the vascular wall, and it modifies contractile activity of cardiomyocytes, and contributes to the regulation of cholesterol uptake in the intestine. Moreover, under stress conditions, signals from the kidney and heart can affect hepatic expression and thereby the plasma concentration of PCSK9 which then in turn can affect other target organs. Therefore, there is an intense relationship between the local (autocrine) and systemic (endocrine) effects of PCSK9. Although, PCSK9 has been recognized as a ubiquitously expressed modifier of cellular function and signaling molecules, its physiological role in different organs is not well-understood. The current review summarizes these findings.

HDL Proteome and Alzheimer's Disease: Evidence of a Link

Several lines of epidemiological evidence link increased levels of high-density lipoprotein-cholesterol (HDL-C) with lower risk of Alzheimer's disease (AD). This observed relationship might reflect the beneficial effects of HDL on the cardiovascular system, likely due to the implication of vascular dysregulation in AD development. The atheroprotective properties of this lipoprotein are mostly due to its proteome. In particular, apolipoprotein (Apo) A-I, E, and J and the antioxidant accessory protein paraoxonase 1 (PON1), are the main determinants of the biological function of HDL. Intriguingly, these HDL constituent proteins are also present in the brain, either from in situ expression, or derived from the periphery. Growing preclinical evidence suggests that these HDL proteins may prevent the aberrant changes in the brain that characterize AD pathogenesis. In the present review, we summarize and critically examine the current state of knowledge on the role of these atheroprotective HDL-associated proteins in AD pathogenesis and physiopathology.

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.

Autophagy Modulators Profoundly Alter the Astrocyte Cellular Proteome

Autophagy is a key cellular process that involves constituent degradation and recycling during cellular development and homeostasis. Autophagy also plays key roles in antimicrobial host defense and numerous pathogenic organisms have developed strategies to take advantage of and/or modulate cellular autophagy. Several pharmacologic compounds, such as BafilomycinA1, an autophagy inducer, and Rapamycin, an autophagy inhibitor, have been used to modulate autophagy, and their effects upon notable autophagy markers, such as LC3 protein lipidation and Sequestosome-1/p62 alterations are well defined. We sought to understand whether such autophagy modulators have a more global effect upon host cells and used a recently developed aptamer-based proteomic platform (SOMAscan^®) to examine 1305 U-251 astrocytic cell proteins after the cells were treated with each compound. These analyses, and complementary cytokine array analyses of culture supernatants after drug treatment, revealed substantial perturbations in the U-251 astrocyte cellular proteome. Several proteins, including cathepsins, which have a role in autophagy, were differentially dysregulated by the two drugs as might be expected. Many proteins, not previously known to be involved in autophagy, were significantly dysregulated by the compounds, and several, including lactadherin and granulins, were up-regulated by both drugs. These data indicate that these two compounds, routinely used to help dissect cellular autophagy, have much more profound effects upon cellular proteins.

Genome-Wide DNA Methylation Analysis in Male Methamphetamine Users With Different Addiction Qualities

This paper aimed to explore the genome-wide DNA methylation status of methamphetamine (MA) abusers with different qualities to addiction and to identify differentially methylated candidate genes. A total of 207 male MA abusers with an MA abuse frequency of ≥10 times and an MA abuse duration of ≥1 year were assigned to the high MA addiction quality group (HMAQ group; 168 subjects who met the diagnostic criteria for MA dependence according to the DSM-IV) or to the low MA addictive quality group (LMAQ group; 39 subjects who did not meet the criteria for MA dependence). In addition 105 healthy controls were recruited. Eight HMAQ subjects, eight LMAQ subjects, and eight healthy controls underwent genome-wide DNA methylation scans with an Infinium Human Methylation 450 array (Illumina). The differentially methylated region (DMR) data were entered into pathway analysis, and the differentially methylated position (DMP) data were screened for candidate genes and verified by MethyLight qPCR with all samples. Seven specific pathways with an abnormal methylation status were identified, including the circadian entrainment, cholinergic synapse, glutamatergic synapse, retrograde endocannabinoid signaling, GABAergic synapse, morphine addiction and PI3K-Akt signaling pathways. SLC1A6, BHLHB9, LYNX1, CAV2, and PCSK9 showed differences in their methylation levels in the three groups. Only the number of methylated copies of CAV2 was significantly higher in the LMAQ group than in the HMAQ group. Our findings suggest that the circadian entrainment pathway and the caveolin-2 gene may play key roles in MA addiction quality. Further studies on their functions and mechanisms will help us to better understand the pathogenesis of MA addiction and to explore new targets for drug intervention.