Proprotein convertase subtilisin/kexin type 9 (PCSK9) induces the hepatic degradation of the low-density lipoprotein receptor (LDLR), thereby increasing the concentration of LDL-cholesterol in the blood. Beyond its effects on LDL, recent studies have reported pleiotropic effects of PCSK9, notably in septic shock, vascular inflammation, viral infection, and cancer. While the functional and structural integrity of peripheral nerves are critically influenced by circulating lipids, the effect of PCSK9 on the peripheral nervous system remains unknown. In this study, we investigated the consequences of PCSK9 deficiency on peripheral nerves. We found that PCSK9 deletion in mice leads to peripheral neuropathy, characterized by reduced thermal and mechanical pain sensations. PCSK9-deficient mice also presented with skin structural changes, including a reduction in nociceptive Schwann cell number, axonal swelling of Remak fibers, and hypomyelination of small nerve fibers. Interestingly, the peripheral nerves of PCSK9-deficient mice showed an upregulation of CD36, a fatty acid transporter, which correlated with increased nerve lipid content, structural mitochondrial abnormalities, and acylcarnitine accumulation. Our findings demonstrate that PCSK9 plays a critical role in peripheral nerves by regulating lipid homeostasis and that its deficiency results in symptoms related to peripheral neuropathy.

Diabetic peripheral neuropathy (DPN) is characterized by progressive and symmetrical sensory abnormalities and constitutes one of the earliest and main complications of diabetes. DPN is characterized by heterogeneous sensory symptoms such as chronic pain, tingling, burning or loss of sensation. Nociceptive Schwann cells (nSCs), a recently identified subtypes of dermal Schwann cells support terminal nerve fibers in mouse skin and contribute to mechanical sensation and neuropathic pain. While terminal nerve fibers density is evaluated in DPN models, there is currently no data about nSCs number and integrity during the early stages of the disease. In the present study, we determined the quantitative differences in terminal nerve fiber density as well as nSCs number and cellular extensions between control and high-fat diet (HFD) induced diabetic mice presenting with a neuropathic phenotype. We also characterized L1CAM as a reliable and specific marker of nSCs, a cell type previously assessed by the expression of S100β and Sox10. Interestingly, we observed a decrease in intraepidermal nerve fiber density (IENFD) associated with a significant reduction of nSCs in the glabrous foot skin of neuropathic mice. Overall, this study identifies L1CAM as a new marker of nSCs and indicates that these cells are impacted in diabetic peripheral neuropathy.### Competing Interest StatementThe authors have declared no competing interest.

Background In the SPARCL (Stroke Prevention by Aggressive Reduction in Cholesterol Levels) trial, atorvastatin (80 mg per day) was compared with placebo in patients with recent stroke or transient ischemic attack and no known coronary artery disease. Given the central role of apoE (apolipoprotein E) in lipoprotein metabolism and in the central nervous system, we assessed the contribution of apoE to subsequent cerebrovascular and cardiovascular events in this trial. Methods and Results ApoE concentrations and major isoforms (E2/E3/E4) were determined by liquid‐chromatography high resolution mass‐spectrometry in plasma samples collected at baseline from 4348 SPARCL participants. Patients in the lowest quartile were compared with those in the highest quartiles of apoE concentrations. Multivariable‐adjusted hazard‐ratios (HR) and 95% CIs were calculated using Cox proportional hazards regression models. We found a significant association between low apoE concentrations and the risk of recurrent strokes or cerebrovascular events (HR, 1.401 [95% CI, 1.154–1.701], P<0.001 and 1.467 [95% CI, 1.260–1.708], P<0.001) driven by a higher incidence of ischemic strokes and transient ischemic attacks in the entire cohort as well as separately in each treatment arm of SPARCL. In contrast, apoE concentrations did not significantly associate with the incidence of hemorrhagic strokes in SPARCL. We also found a significant association between reduced apoE concentrations and the risk of subsequent coronary events (HR, 1.373 ([95% CI, 1.064–1.772], P=0.015) in the entire cohort that was, however, significant only in the placebo arm of SPARCL. Conclusions Low apoE concentrations are predictive of recurring cerebrovascular events in patients with a history of stroke or transient ischemic attack. Registration URL: https://www.clinicaltrials.gov; Identifier: NTC00147602.

The liver plays a key role in the metabolism of lipoproteins, controlling both production and catabolism. To accelerate the development of new lipid-lowering therapies in humans, it is essential to have a relevant in vitro study model available. The current hepatocyte-like cells (HLCs) models derived from hiPSC can be used to model many genetically driven diseases but require further improvement to better recapitulate the complexity of liver functions. Here, we aimed to improve the maturation of HLCs using a three-dimensional (3D) approach using Biomimesys®, a hyaluronic acid-based hydroscaffold in which hiPSCs may directly form aggregates and differentiate toward a functional liver organoid model. After a 28-day differentiation 3D protocol, we showed that many hepatic genes were upregulated in the 3D model (liver organoids) in comparison with the 2D model (HLCs). Liver organoids, grown on Biomimesys®, exhibited an autonomous cell organization, were composed of different cell types and displayed enhanced cytochromes P450 activities compared to HLCs. Regarding the functional capacities of these organoids, we showed that they were able to accumulate lipids (hepatic steatosis), internalize low-density lipoprotein and secrete apolipoprotein B. Interestingly, we showed for the first time that this model was also able to produce apolipoprotein (a), the apolipoprotein (a) specific of Lp(a). This innovative hiPSC-derived liver organoid model may serve as a relevant model for studying human lipopoprotein metabolism, including Lp(a).

Diabetic peripheral neuropathy (DPN) characterized by progressive and symmetrical sensory abnormalities is one of the earliest and main complications of diabetes. DPN is characterized by heterogeneous sensory symptoms such as chronic pain, tingling, burning or loss of sensation. Nociceptive Schwann cells (nSCs), a recently identified subtypes of dermal Schwann cells support terminal nerve fibers in mouse skin and contribute to mechanical sensation and neuropathic pain. While terminal nerve fibers density is basically evaluated in DPN models, there is currently few data about nSCs number and integrity during early stage of DPN. In the present study, we used a mouse model of prediabetes by using high-fat diet (HFD) fed mice to determine if there are quantitative differences in terminal nerve fiber density, nSCs number and cellular extensions between control and prediabetic neuropathic mice. In this study, we identified L1CAM as a reliable marker of nSCs currently characterized by the expression of S100beta and Sox10. Interestingly, we observed a decrease in intraepidermal nerve fiber density (IENFD) associated to a significant reduction of nSCs in the glabrous foot skin of neuropathic mice. Overall, this study identifies L1CAM as a new marker of nSCs and indicates that these cells are impaired during prediabetic peripheral neuropathy.

In 2022, the European Atherosclerosis Society (EAS) published a new consensus statement on lipoprotein(a) [Lp(a)], summarizing current knowledge about its causal association with atherosclerotic cardiovascular disease (ASCVD) and aortic stenosis. One of the novelties of this statement is a new risk calculator showing how Lp(a) influences lifetime risk for ASCVD and that global risk may be underestimated substantially in individuals with high or very high Lp(a) concentration. The statement also provides practical advice on how knowledge about Lp(a) concentration can be used to modulate risk factor management, given that specific and highly effective mRNA-targeted Lp(a)-lowering therapies are still in clinical development. This advice counters the attitude: "Why should I measure Lp(a) if I can't lower it?". Subsequent to publication, questions have arisen relating to how the recommendations of this statement impact everyday clinical practice and ASCVD management. This review addresses 30 of the most frequently asked questions about Lp(a) epidemiology, its contribution to cardiovascular risk, Lp(a) measurement, risk factor management and existing therapeutic options.

In the SPARCL (Stroke Prevention by Aggressive Reduction in Cholesterol levels) trial, atorvastatin (80 mg/d) was compared to placebo in patients with recent stroke or transient ischemic attack (TIA) and no known coronary artery disease. This study aimed to assess the contribution of lipoprotein(a) [Lp(a)] to subsequent cerebrovascular and cardiovascular events in stroke/TIA survivors. Lp(a) levels and apolipoprotein(a) [apo(a)] isoform size were determined by liquid-chromatography mass spectrometry in samples collected at baseline from 2,814 SPARCL participants (1,418 randomized to atorvastatin and 1,396 to placebo). Within each treatment arm, patients in the highest quartile (≥84.0 nmol/L) were compared with those in the lowest quartiles of Lp(a) concentrations. Patients in the lowest quartile (≤25.9 Kringle IV domains) of apo(a) isoform sizes were compared with those in the highest quartiles. Multivariable-adjusted HRs were calculated using Cox proportional regression models. There was no significant association between Lp(a) concentrations or apo(a) isoform sizes and the risk of recurrent stroke, the primary outcome of SPARCL, or cerebrovascular events in patients randomized to atorvastatin or placebo. In contrast, in patients randomized to atorvastatin, elevated Lp(a) concentrations and short apo(a) isoforms were positively and independently associated with an increased risk of coronary events (HR: 1.607 [95% CI: 1.007-2.563] and HR: 2.052 [95% CI: 1.303-3.232]). No such association was found in patients randomized to placebo (HR: 1.025 [95% CI: 0.675-1.555] and HR: 1.097 [95% CI: 0.735-1.637]). Lp(a) contributes to the residual coronary artery disease risk of statin-treated stroke/TIA survivors, paving the way for use of therapies targeting Lp(a) in this population with stroke. (Lipitor In The Prevention Of Stroke, For Patients Who Have Had A Previous Stroke [SPARCL]; NCT00147602).

BACKGROUND In the SPARCL (Stroke Prevention by Aggressive Reduction in Cholesterol levels) trial, atorvastatin (80 mg/d) was compared to placebo in patients with recent stroke or transient ischemic attack (TIA) and no known coronary artery disease. OBJECTIVES This study aimed to assess the contribution of lipoprotein(a) [Lp(a)] to subsequent cerebrovascular and cardiovascular events in stroke/TIA survivors. METHODS Lp(a) levels and apolipoprotein(a) [apo(a)] isoform size were determined by liquid-chromatography mass spectrometry in samples collected at baseline from 2,814 SPARCL participants (1,418 randomized to atorvastatin and 1,396 to placebo). Within each treatment arm, patients in the highest quartile (>= 84.0 nmol/L) were compared with those in the lowest quartiles of Lp(a) concentrations. Patients in the lowest quartile (<= 25.9 Kringle IV domains) of apo(a) isoform sizes were compared with those in the highest quartiles. Multivariable-adjusted HRs were calculated using Cox proportional regression models. RESULTS There was no significant association between Lp(a) concentrations or apo(a) isoform sizes and the risk of recurrent stroke, the primary outcome of SPARCL, or cerebrovascular events in patients randomized to atorvastatin or placebo. In contrast, in patients randomized to atorvastatin, elevated Lp(a) concentrations and short apo(a) isoforms were positively and independently associated with an increased risk of coronary events (HR: 1.607 [95% CI: 1.007-2.563] and HR: 2.052 [95% CI: 1.303-3.232]). No such association was found in patients randomized to placebo (HR: 1.025 [95% CI: 0.675-1.555] and HR: 1.097 [95% CI: 0.735-1.637]). CONCLUSIONS Lp(a) contributes to the residual coronary artery disease risk of statin-treated stroke/TIA survivors, paving the way for use of therapies targeting Lp(a) in this population with stroke. (Lipitor In The Prevention Of Stroke, For Patients Who Have Had A Previous Stroke [SPARCL]; NCT00147602) (JACC Adv 2023;2:100557) (c) 2023 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Elevated circulating lipoprotein(a) (Lp(a)) is a genetically determined risk factor for coronary artery disease and aortic valve stenosis (Tsimikas, 2017). Importantly, the LPA gene, which encodes the apolipoprotein(a) (protein-component of Lp(a)), is missing in most species, and human liver cell-lines do not secrete Lp(a). There is a need for the development of human in vitro models suitable for investigating biological mechanisms involved in Lp(a) metabolism. We here generated and characterized iPSCs from a patient with extremely high Lp(a) plasma levels genetically determined (Coassin et al., 2022). This unique cellular model offers great opportunities and new perspectives for investigations on biological mechanisms involved in Lp(a) metabolism.

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.

Proprotein convertase subtilisin kexin 9 (PCSK9) is a major modulator of low-density lipoprotein cholesterol (LDL-C) plasma concentrations through its inhibitory action on LDL receptor (LDLR) expression. As a result, PCSK9 inhibitors lower the circulating concentrations of LDL. Surprisingly, these therapeutic agents also reduce the plasma levels of another class of atherogenic lipoproteins, lipoprotein(a) [Lp(a)]. This observation has driven research aimed at elucidating the role of PCSK9 in Lp(a) metabolism. Is the interaction between PCSK9 and Lp(a) particles LDLR dependent? What are the molecular mechanisms involved? This chapter aims at providing the key insights into the PCSK9-Lp(a) axis based on recent fundamental and clinical research findings.