Sortilin and Its Multiple Roles in Cardiovascular and Metabolic Diseases

Gene Expression Signature in Patients With Symptomatic Peripheral Artery Disease

[Figure: see text].

The multifaceted role of sortilin/neurotensin receptor 3 in human cancer development

Sortilin (also known as neurotensin receptor 3) is a multitasking protein implicated in numerous pathophysiological processes, including cancer development, cardiovascular impairment, Alzheimer-type dementia, and depression. Although the definitive role of sortilin in human solid and hematological malignancies has been evidenced, few articles reviewed the task. The aim of the current review is to unravel the mechanisms by which sortilin controls oncogenicity and cancer progression; and also to summarize and discuss the original data obtained from international research laboratories on this topic. Questions on how sortilin is involving in the impairment of cell junctions, in exosomes composition and release, as well as in the regulation of epidermal growth factor receptor trafficking are also responded. In addition, we provide a special focus on the regulatory role of sortilin in signal transduction by either neurotrophins or neurotensin in normal and malignant cells. The relevance of sortilin with normal and cancer stem cells is also discussed. The last section provides a general overview of sortilin applications as a diagnostic and prognostic biomarker in the context of cancer detection. Finally, we comment on the future research aspects in which the field of cancer diagnosis, prognosis, and therapy might be developed.

Outcomes of Lower Extremity Endovascular Revascularization: Potential Predictors and Prevention Strategies

Peripheral artery disease (PAD) is a manifestation of atherosclerosis, which may affect arteries of the lower extremities. The most dangerous PAD complication is chronic limb-threatening ischemia (CLTI). Without revascularization, CLTI often causes limb loss. However, neither open surgical revascularization nor endovascular treatment (EVT) ensure long-term success and freedom from restenosis and revascularization failure. In recent years, EVT has gained growing acceptance among all vascular specialties, becoming the primary approach of revascularization in patients with CLTI. In clinical practice, different clinical outcomes after EVT in patients with similar comorbidities undergoing the same procedure (in terms of revascularization technique and localization of the disease) cause unsolved issues that need to be addressed. Nowadays, risk management of revascularization failure is one of the major challenges in the vascular field. The aim of this literature review is to identify potential predictors for lower extremity endovascular revascularization outcomes and possible prevention strategies.

Effect of atorvastatin versus rosuvastatin on inflammatory biomarkers and LV function in type 2 diabetic patients with dyslipidemia

BACKGROUND

Statins are potential drugs for decreasing risk of atherosclerotic cardiovascular complications in type 2 diabetic (T2D) patients.

PURPOSE

To examine the efficacy of both rosuvastatin (ROSUVA) and atorvastatin (ATORVA) on LV function and markers of inflammation in T2D patients with dyslipidemia.

METHODS

One hundred-sixty T2D patients were assigned to receive either atorvastatin (ATORVA group, n = 80, 40 mg) or rosuvastatin (ROSUVA group, n = 80, 10 mg), daily for 6 months. Blood was collected for biochemical analysis. The prevalence of left ventricular abnormalities was determined by echocardiography and two-dimensional Speckle-Strain to assess Global Longitudinal Strain (GLS).

RESULTS

ROSUVA vs. ATORVA resulted in significant (p < 0.001) reduction in HbA1c % (9.13 vs 2.35%), LDL-C (22.23% vs. 14.75%), triglycerides (13.56 % vs. 8.21 %), total cholesterol (16.10 % vs. 10.81 %), atherogenic index (18.08. % vs. 10.97%), hs-CRP (23.51 % vs.18.96%), sortilin (33.33 % % vs. 15.08 %), and leptin (31.81 % vs. 23.17 %) but increased adiponectin (97.99 % vs.76.47.1 %) and HDL-C (76.47 % vs. 0.21 %) compared with baseline, respectively. Negative correlations between adiponectin and each of hs-CRP, HbA1c%, total cholesterol, LDL-C, atherogenic index and leptin were found. Also, left ventricular functions were correlated with adiponectin, lipids, HbA1c% and hs-CRP. The areas under receiver operating characteristic curve (AUC) showed that hs-CRP, leptin, sortlin, leptin, and adiponectin were good predictors for cardiovascular events.

CONCLUSION

ROSUVA is more efficacious in improving lipid profile, atherogenic index and modulation of inflammatory biomarkers in dyslipidemic T2D patients compared with ATROVA. However, both statins are equivalent as cardioprotective agents in dyslipidemic T2D patients.

Neurotensin pathway in digestive cancers and clinical applications: an overview

Initially, NEUROTENSIN (NTS) has been shown to play physiological and biological functions as a neuro-transmitter/modulator in the central nervous system and as an endocrine factor in the periphery, through its binding to two kinds of receptors: NTSR1 and 2 (G protein-coupled receptors) and NTSR3/sortilin (a vacuolar protein-sorting 10-domain receptor). NTS also plays oncogenic roles in many types of cancer, including digestive cancers. In tumor tissues, NTS and NTSR1 expression is higher than in healthy ones and is associated with poor prognosis. NTS and NTRS1 promote cancer progression and play key functions in metastatic processes; they modulate several signaling pathways and they contribute to changes in the tumor microenvironment. Conversely, NTRS2 involvement in digestive cancers is poorly understood. Discovered for mediating NTS biological effects, sortilin recently emerged as a promising target as its expression was found to be increased in various types of cancers. Because it can be secreted, a soluble form of sortilin (sSortilin) appears as a new serum biomarker which, on the basis of recent studies, promises to be useful in both the diagnosis and tumor progression monitoring. More precisely, it appears that soluble sortilin can be associated with other receptors like TRKB. These associations occur in exosomes and trigger the aggressiveness of cancers like glioblastoma, leading to the concept of a possible composite theranostic biomarker. This review summarizes the oncogenic roles of the NTS signaling pathways in digestive cancers and discusses their emergence as promising early diagnostic and/or prognostic biomarkers and therapeutic targets.

Influence of PSRC1, CELSR2, and SORT1 Gene Polymorphisms on the Variability of Warfarin Dosage and Susceptibility to Cardiovascular Disease

Background

Cardiovascular disease is one of the most common causes of morbidity and mortality worldwide. Several cardiovascular diseases require therapy with warfarin, an anticoagulant with large interindividual variability resulting in dosing difficulties. The selected genes and their polymorphisms have been implicated in several Genome-Wide Association Study (GWAS) to be associated with cardiovascular disease.

Objective

The goal of this study is to discover if there are any associations between rs646776 of PSRC1, rs660240 and rs12740374 of CELSR2, and rs602633 of SORT1 to coronary heart disease (CHD) and warfarin dose variability in patients diagnosed with cardiovascular disease undergoing warfarin therapy.

Methods

The study was directed at the Queen Alia Hospital Anticoagulation Clinic in Amman, Jordan. DNA was extracted and genotyped using the Mass ARRAY™ system, statistical analysis was done using SPSS.

Results

The study found several associations between the selected SNPs with warfarin, but none with cardiovascular disease. All 4 studied SNPs were found to be correlated to warfarin sensitivity during the stabilization phase except rs602633 and with warfarin dose variability at the initiation phase. CELSR2 SNPs also showed association with dose variability during the stabilization phase. Also, rs646776 and rs12740374 were linked to warfarin sensitivity over the initiation phase. Only rs602633 was associated with INR treatment outcomes.

Conclusion

The findings presented in this study found new pharmacogenomic associations for warfarin, that warrant further research in the field of genotype-guided warfarin dosing.

An Allosteric Binding Site on Sortilin Regulates the Trafficking of VLDL, PCSK9, and LDLR in Hepatocytes

ApoB lipoproteins (apo B-Lp) are produced in hepatocytes, and their secretion requires the cargo receptor sortilin. We examined the secretion of apo B-Lp-containing very low-density lipoprotein (VLDL), an LDL progenitor. Sortilin also regulates the trafficking of the subtilase PCSK9, which when secreted binds the LDL receptor (LDLR), resulting in its endocytosis and destruction at the lysosome. We show that the site 2 binding compound (cpd984) has multiple effects in hepatocytes, including (1) enhanced Apo-Lp secretion, (2) increased cellular PCSK9 retention, and (3) augmented levels of LDLR at the plasma membrane. We postulate that cpd984 enhances apo B-Lp secretion in part through binding the lipid phosphatidylinositol 3,4,5-trisphosphate (PIP₃), which is present at higher levels on circulating VLDL form fed rats relative to after fasting. We attribute the enhanced VLDL secretion to its increased binding affinity for sortilin site 1 induced by cpd984 binding site 2. This hinders PCSK9 binding and secretion, which would subsequently prevent its binding to LDLR leading to its degradation. This suggests that site 2 is an allosteric regulator of site 1 binding. This effect is not limited to VLDL, as cpd984 augments binding of the neuropeptide neurotensin (NT) to sortilin site 1. Molecular dynamics simulations demonstrate that the C-terminus of NT (Ct-NT) stably binds site 1 through an electrostatic interaction. This was bolstered by the ability of Ct-NT to disrupt lower-affinity interactions between sortilin and the site 1 ligand PIP₃. Together, these data show that binding cargo at sortilin site 1 is allosterically regulated through site 2 binding, with important ramifications for cellular lipid homeostasis involving proteins such as PCSK9 and LDLR.

Syntheses and anti-HIV and human cluster of differentiation 4 (CD4) down-modulating potencies of pyridine-fused cyclotriazadisulfonamide (CADA) compounds

CADA compounds selectively down-modulate human cell-surface CD4 protein and are of interest as HIV entry inhibitors and as drugs for asthma, rheumatoid arthritis, diabetes and some cancers. Postulating that fusing a pyridine ring bearing hydrophobic substituents into the macrocyclic scaffold of CADA compounds may lead to potent compounds with improved properties, 17 macrocycles were synthesized, 14 with 12-membered rings having an isobutylene head group, two arenesulfonyl side arms, and fused pyridine rings bearing a para substituent. The analogs display a wide range of CD4 down-modulating and anti-HIV potencies, including some with greater potency than CADA, proving that a highly basic nitrogen atom in the 12-membered ring is not required for potency and that hydrophobic substituents enhance potency of pyridine-fused CADA compounds. Cytotoxicities of the new compounds compared favorably with those of CADA, showing that incorporation of a pyridine ring into the macrocyclic scaffold can produce selective compounds for potently down-modulating proteins of medicinal interest.

Association Study of Coronary Artery Disease-Associated Genome-Wide Significant SNPs with Coronary Stenosis in Pakistani Population

Genome-wide association studies (GWAS) of coronary artery disease (CAD) have revealed multiple genetic risk loci. We assessed the association of 47 genome-wide significant single-nucleotide polymorphisms (SNPs) at 43 CAD loci with coronary stenosis in a Pakistani sample comprising 663 clinically ascertained and angiographically confirmed cases. Genotypes were determined using the iPLEX Gold technology. All statistical analyses were performed using R software. Linkage disequilibrium (LD) between significant SNPs was determined using SNAP web portal, and functional annotation of SNPs was performed using the RegulomeDB and Genotype-Tissue Expression (GTEx) databases. Genotyping comparison was made between cases with severe stenosis (≥70%) and mild/minimal stenosis (<30%). Five SNPs demonstrated significant associations: three with additive genetic models PLG/rs4252120 (p = 0.0078), KIAA1462/rs2505083 (p = 0.005), and SLC22A3/rs2048327 (p = 0.045) and two with recessive models SORT1/rs602633 (p = 0.005) and UBE2Z/rs46522 (p = 0.03). PLG/rs4252120 was in LD with two functional PLG variants (rs4252126 and rs4252135), each with a RegulomeDB score of 1f. Likewise, KIAA1462/rs2505083 was in LD with a functional SNP, KIAA1462/rs3739998, having a RegulomeDB score of 2b. In the GTEx database, KIAA1462/rs2505083, SLC22A3/rs2048327, SORT1/rs602633, and UBE2Z/rs46522 SNPs were found to be expression quantitative trait loci (eQTLs) in CAD-associated tissues. In conclusion, five genome-wide significant SNPs previously reported in European GWAS were replicated in the Pakistani sample. Further association studies on larger non-European populations are needed to understand the worldwide genetic architecture of CAD.

The signal peptide as a new target for drug design

Many current and potential drug targets are membrane-bound or secreted proteins that are expressed and transported via the Sec61 secretory pathway. They are targeted to translocon channels across the membrane of the endoplasmic reticulum (ER) by signal peptides (SPs), which are temporary structures on the N-termini of their nascent chains. During translation, such proteins enter the lumen and membrane of the ER by a process known as co-translational translocation. Small molecules have been found that interfere with this process, decreasing protein expression by recognizing the unique structures of the SPs of particular proteins. The SP may thus become a validated target for designing drugs for numerous disorders, including certain hereditary diseases.

PTH/PTHrP Receptor Signaling Restricts Arterial Fibrosis in Diabetic LDLR-/- Mice by Inhibiting Myocardin-Related Transcription Factor Relays

RATIONALE

The PTH1R (PTH [parathyroid hormone]/PTHrP [PTH-related protein] receptor) is expressed in vascular smooth muscle (VSM) and increased VSM PTH1R signaling mitigates diet-induced arteriosclerosis in LDLR-/- mice.

OBJECTIVE

To study the impact of VSM PTH1R deficiency, we generated mice SM22-Cre:PTH1R(fl/fl);LDLR-/- mice (PTH1R-VKO) and Cre-negative controls.

METHODS AND RESULTS

Immunofluorescence and Western blot confirmed PTH1R expression in arterial VSM that was reduced by Cre-mediated knockout. PTH1R-VKO cohorts exhibited increased aortic collagen accumulation in vivo, and VSM cultures from PTH1R-VKO mice elaborated more collagen (2.5-fold; P=0.01) with elevated Col3a1 and Col1a1 expression. To better understand these profibrotic responses, we performed mass spectrometry on nuclear proteins extracted from Cre-negative controls and PTH1R-VKO VSM. PTH1R deficiency reduced Gata6 but upregulated the MADS (MCM1, Agamous, Deficiens, and Srf DNA-binding domain)-box transcriptional co-regulator, Mkl-1 (megakaryoblastic leukemia [translocation] 1). Co-transfection assays (Col3a1 promoter-luciferase reporter) confirmed PTH1R-mediated inhibition and Mkl-1-mediated activation of Col3a1 transcription. Regulation mapped to a conserved hybrid CT(A/T)6GG MADS-box cognate in the Col3a1 promoter. Mutations of C/G in this motif markedly reduced Col3a1 transcriptional regulation by PTH1R and Mkl-1. Upregulation of Col3a1 and Col1a1 in PTH1R-VKO VSM was inhibited by small interfering RNA targeting Mkl1 and by treatment with the Mkl-1 antagonist CCG1423 or the Rock (Rho-associated coiled-coil containing protein kinase)-2 inhibitor KD025. Chromatin precipitation demonstrated that VSM PTH1R deficiency increased Mkl-1 binding to Col3a1 and Col1a1, but not TNF, promoters. Proteomic studies of plasma extracellular vesicles and VSM from PTH1R-VKO mice identified C1r (complement component 1, r) and C1s (complement component 1, s), complement proteins involved in vascular collagen metabolism, as potential biomarkers. VSM C1r protein and C1r message were increased with PTH1R deficiency, mediated by Mkl-1-dependent transcription and inhibited by CCG1423 or KD025.

CONCLUSIONS

PTH1R signaling restricts collagen production in the VSM lineage, in part, via Mkl-1 regulatory circuits that control collagen gene transcription. Strategies that maintain homeostatic VSM PTH1R signaling, as reflected in extracellular vesicle biomarkers of VSM PTH1R/Mkl-1 action, may help mitigate arteriosclerosis and vascular fibrosis.

Elevated serum sortilin is related to carotid plaque concomitant with calcification

Aim: To explore whether elevated serum sortilin was associated with calcified carotid plaque and ischemic stroke. Methods: A total of 171 patients with cardiovascular risk factors were enrolled. Ultrasonography was performed to evaluate calcified plaques and noncalcified plaques. Serum sortilin concentration was measured by ELISA. Results: Serum sortilin level was higher in patients with calcified carotid plaque and positively related to carotid plaque burden, but not with ischemic stroke during the follow-up. Multivariable logistic regression analysis revealed serum sortilin level was an independent determinant for calcified carotid plaque (p = 0.001). Receiving operating characteristic analysis showed an area under the curve of sortilin for carotid calcification was 0.759. Conclusion: Higher serum sortilin level was associated with carotid calcification and severe carotid plaque score.

Biomarkers of vascular disease in diabetes: the adipose-immune system cross talk

Experimental and clinical studies aimed at investigating the mechanism(s) underlying vascular complications of diabetes indicate that a great number of molecules are involved in the pathogenesis of these complications. Most of these molecules are inflammatory mediators or markers generated by immune or adipose tissue. Some of them, i.e. resistin and sortilin, have been shown to be involved in the cross talk between adipocytes and inflammatory cells. This interaction is an attractive area of research, particularly in type 2 diabetes and obesity. Other proteins, such as adiponectin and visfatin, appear to be more promising as possible vascular markers. In addition, some molecules involved in calcium/phosphorus metabolism, such as klotho and FGF23, have an involvement in the pathogenesis of diabetic vasculopathy, which appears to be dependent on the degree of vascular impairment. Inflammatory markers are a promising tool for treatment decisions while measuring plasma levels of adipokines, sortilin, Klotho and FGF23 in adequately sized longitudinal studies is expected to allow a more precise characterization of diabetic vascular disease and the optimal use of personalized treatment strategies.

Mechanisms of Arterial Stiffening: From Mechanotransduction to Epigenetics

Arterial stiffness is a major independent risk factor for cardiovascular complications causing isolated systolic hypertension and increased pulse pressure in the microvasculature of target organs. Stiffening of the arterial wall is determined by common mechanisms including reduced elastin/collagen ratio, production of elastin cross-linking, reactive oxygen species-induced inflammation, calcification, vascular smooth muscle cell stiffness, and endothelial dysfunction. This brief review will discuss current biological mechanisms by which other cardiovascular risk factors (eg, aging, hypertension, diabetes mellitus, and chronic kidney disease) cause arterial stiffness, with a particular focus on recent advances regarding nuclear mechanotransduction, mitochondrial oxidative stress, metabolism and dyslipidemia, genome mutations, and epigenetics. Targeting these different molecular pathways at different time of cardiovascular risk factor exposure may be a novel approach for discovering drugs to reduce arterial stiffening without affecting artery strength and normal remodeling.

Role of Sortilin and Matrix Vesicles in Nε-Carboxymethyl-Lysine-Induced Diabetic Atherosclerotic Calcification

BACKGROUND AND AIMS

To investigate the role of Sortilin and matrix vesicles (MVs) in Nε-Carboxymethyl-lysine (CML)-induced diabetic atherosclerotic calcification (AC).

METHODS

At human level, the correlation between Sortilin and CD9 (marker proteins of MVs) in serum MVs and CML in serum was explored by enzyme-linked immunosorbent assay (ELISA) detection and Pearson correlation analysis. After a diabetic apoE^-/- mouse model was constructed, the calcification of aorta and the expressions of related proteins under CML and MVs injection were observed by calcification staining, immunofluorescence staining, and Western blot. MVs levels released by smooth muscle cells (SMCs) under different treatments was detected by nanometer tracking analysis (NTA). After treating SMCs with MVs and Anti-Sortilin, cell calcification was observed by Alizarin red staining.

RESULTS

Serological analysis of patients showed that the concentrations of Sortilin and CD9 in serum MVs were positively correlated with the concentration of CML in serum. Animal experiments showed that CML could promote the progression of diabetic AC and the high expression of Sortilin in plaques. Diabetic apoE^-/- mouse tail vein injection of CML-induced SMCs-derived MVs obviously aggravated AC. Cell experiment results showed that a high concentration of CML significantly promoted the release of MVs from SMCs. MVs from this source could markedly worsen cell calcification, while the administration of GW4869 (a widely used extracellular vesicles biogenesis inhibitor) significantly reduced cell calcification. Finally, treatment of high concentrations of CML could also promote the recruitment of Sortilin to MVs, and administration of Anti-Sortilin could markedly reduce cell calcification caused by MVs.

CONCLUSION

We proved that CML not only affects the release of MVs from SMCs but also affects the recruitment of Sortilin to MVs, thereby promoting diabetic AC. This discovery may provide a new strategy for targeted prevention of vascular calcification in diabetes.

Relation of Decreased Circulating Sortilin Levels With Unfavorable Metabolic Profiles in Subjects With Newly Diagnosed Type 2 Diabetes Mellitus

BACKGROUND

Sortilin, a pluripotent peptide hormone, plays a role in glucose and lipid metabolism. A link between sortilin and insulin sensitivity has been implicated. However, the clinical implications of this link remain elusive. Our aims were to investigate whether sortilin levels were altered in subjects with newly diagnosed type 2 diabetes mellitus (nT2DM) compared with subjects with normal glucose tolerance (NGT) and to determine whether a link exist between sortilin levels and metabolic parameters.

MATERIALS AND METHODS

A total of 150 subjects including 75 nT2DM patients and 75 subjects with NGT who were matched in age, body mass index, and sex were enrolled into this case-control study. The circulating levels of sortilin were measured using enzyme-linked immunosorbent assay. A 2-hour 75-g oral glucose tolerance test was used for diagnosis of T2DM. Metabolic parameters of enrolled subjects were also determined.

RESULTS

The circulating levels of sortilin were found to be significantly lower in subjects with nT2DM than in controls (138.44 ± 38.39 vs. 184.93 ± 49.67 pg/mL, P < 0.001). Sortilin levels showed a negative correlation with insulin resistance and unfavorable lipid profiles, while they were positively correlated with high-density lipoprotein cholesterol in subjects with nT2DM. Linear regression analysis showed an independent and inverse link between sortilin and insulin resistance and unfavorable lipid profiles. Moreover, logistic regression analysis revealed that the subjects with the lowest sortilin levels had an increased risk of nT2DM compared with those subjects with the highest sortilin levels.

CONCLUSIONS

Decreased circulating levels of sortilin were associated with unfavorable metabolic profiles in subjects with nT2DM.

Metabolism, Obesity, and Diabetes Mellitus

Obesity and diabetes remain leading causes of reduced health span and life span throughout the world. Hence, it is not surprising that these areas are at the center of highly active areas of research. The identification of novel mechanisms underlying these metabolic disorders sets the stage for uncovering new potential therapeutic strategies. In this issue of Highlights in Arteriosclerosis, Thrombosis and Vascular Biology, we review recently published papers in the journal that add to our understanding of causes and consequences of obesity and diabetes and how these disorders impact metabolic function. Collectively, these studies in cultured cells to in vivo animal models to human subjects add to the growing body of evidence that both cell-intrinsic and cell-cell communication mechanisms collaborate in metabolic disorders to cause obesity, insulin resistance and diabetes and its complications.

Non-antibody Approaches to Proprotein Convertase Subtilisin Kexin 9 Inhibition: siRNA, Antisense Oligonucleotides, Adnectins, Vaccination, and New Attempts at Small-Molecule Inhibitors Based on New Discoveries

Low-density lipoprotein (LDL) is one of the principal risk factors for atherosclerosis. Circulating LDL particles can penetrate into the sub-endothelial space of arterial walls. These particles undergo oxidation and promote an inflammatory response, resulting in injury to the vascular endothelial wall. Persistent elevation of LDL-cholesterol (LDL-C) is linked to the progression of fatty streaks to lipid-rich plaque and thus atherosclerosis. LDL-C is a causal factor for atherosclerotic cardiovascular disease and lowering it is beneficial across a range of conditions associated with high risk of cardiovascular events. Therefore, all guidelines-recommended initiations of statin therapy for patients at high cardiovascular risk is irrespective of LDL-C. In addition, intensive LDL-C lowering therapy with statins has been demonstrated to result in a greater reduction of cardiovascular event risk in large clinical trials. However, many high-risk patients receiving statins fail to achieve the guideline-recommended reduction in LDL-C levels in routine clinical practice. Moreover, low levels of adherence and often high rates of discontinuation demand the need for further therapies. Ezetimibe has typically been used as a complement to statins when further LDL-C reduction is required. More recently, proprotein convertase subtilisin kexin 9 (PCSK9) has emerged as a novel therapeutic target for lowering LDL-C levels, with PCSK9 inhibitors offering greater reductions than feasible through the addition of ezetimibe. PCSK9 monoclonal antibodies have been shown to not only considerably lower LDL-C levels but also cardiovascular events. However, PCSK9 monoclonal antibodies require once- or twice-monthly subcutaneous injections. Further, their manufacturing process is expensive, increasing the cost of therapy. Therefore, several non-antibody treatments to inhibit PCSK9 function are being developed as alternative approaches to monoclonal antibodies. These include gene-silencing or editing technologies, such as antisense oligonucleotides, small interfering RNA, and the clustered regularly interspaced short palindromic repeats/Cas9 platform; small-molecule inhibitors; mimetic peptides; adnectins; and vaccination. In this review, we summarize the current knowledge base on the role of PCSK9 in lipid metabolism and an overview of non-antibody approaches for PCSK9 inhibition and their limitations. The subsequent development of alternative approaches to PCSK9 inhibition may give us more affordable and convenient therapeutic options for the management of high-risk patients.

Hepatocyte sortilin 1 knockout and treatment with a sortilin 1 inhibitor reduced plasma cholesterol in Western diet-fed mice

Sortilin 1 (Sort1) is a member of the Vps10p domain intracellular trafficking receptor family. Genetic variations of the SORT1 gene are strongly associated with plasma cholesterol levels in humans. Recent studies have linked Sort1 to regulation of cholesterol metabolism in hepatocytes and pro-inflammatory response in macrophages, but the tissue-specific roles of Sort1 in lipid metabolism have not been well defined. We developed Sort1 floxed mice and investigated the development of Western diet (WD)-induced steatosis, hepatic inflammatory response, and hyperlipidemia in hepatocyte Sort1 KO mice and myeloid cell Sort1 KO mice. Our findings suggest that hepatocyte Sort1 deficiency attenuated diet-induced hepatic steatosis and hypercholesterolemia in mice. In contrast, myeloid Sort1 deficiency did not reduce hepatic cytokine expression or plasma cholesterol levels, but exacerbated hepatic triglyceride accumulation in WD-fed mice. Finally, we showed that treating WD-fed mice with an orally bioavailable Sort1 inhibitor, AF38469, decreased plasma cholesterol and hepatic cytokine expression. AF38469 treatment did not affect diet-induced obesity or insulin resistance, but was associated with reduced hepatic VLDL secretion and higher hepatic cholesterol 7α-hydrolase expression in WD-fed mice. In conclusion, findings from this study suggest that Sort1 loss-of-function in hepatocytes contributes to lower plasma cholesterol, and pharmacological inhibition of Sort1 attenuates diet-induced hypercholesterolemia in mice.

Sortilin levels are associated with peripheral arterial disease in type 2 diabetic subjects

BACKGROUND

Sortilin is a 95-kDa protein which has recently been linked to circulating cholesterol concentration and lifetime risk of developing significant atherosclerotic disease. Sortilin is found inside different cell types and circulating in blood. Higher circulating sortilin concentration has been found in patients with coronary atherosclerosis compared to control subjects. Sortilin concentration is influenced by statin therapy.

METHODS

We enrolled statin-naïve subjects with type 2 diabetes mellitus and we performed a cross-sectional study to evaluate the association between sortilin levels and the presence of clinically significant lower limb peripheral artery disease (PAD) in a population of statin-free diabetic subjects.

RESULTS

Out of the 154 patients enrolled in our study, 80 patients were free from PAD, while 74 had clinically significant PAD. Sortilin concentration was significantly higher in the latter group compared to the former (1.61 ± 0.54 ng/mL versus 0.67 ± 0.30 ng/mL, P < 0.01) and there was a trend toward increased sortilin levels as disease severity increased. The association of sortilin levels with PAD remained after adjusting for major risk factors in a multivariate analysis.

CONCLUSIONS

We showed that sortilin is significantly and independently associated with the presence of lower limb PAD in a statin-free diabetic population and it may be a promising marker for clinically significant atherosclerosis of the lower limbs. Further studies are needed to confirm this finding and to evaluate its clinical usefulness.

Regulatory Roles of Sortilin and SorLA in Immune-Related Processes

Sortilin, also known as Neurotensin Receptor-3, and the sorting-related receptor with type-A repeats (SorLA) are both members of the Vps10p domain receptor family. Initially identified in CNS cells, they are expressed in various other cell types where they exert multiple functions. Although mostly studied for its involvement in Alzheimer’s disease, SorLA has recently been shown to be implicated in immune response by regulating IL-6-mediated signaling, as well as driving monocyte migration. Sortilin has been shown to act as a receptor, as a co-receptor and as an intra- and extracellular trafficking regulator. In the last two decades, deregulation of sortilin has been demonstrated to be involved in many human pathophysiologies, including neurodegenerative disorders (Alzheimer and Parkinson diseases), type 2 diabetes and obesity, cancer, and cardiovascular pathologies such as atherosclerosis. Several studies highlighted different functions of sortilin in the immune system, notably in microglia, pro-inflammatory cytokine regulation, phagosome fusion and pathogen clearance. In this review, we will analyze the multiple roles of sortilin and SorLA in the human immune system and how their deregulation may be involved in disease development.

Dimerization of sortilin regulates its trafficking to extracellular vesicles

Extracellular vesicles (EVs) play a critical role in intercellular communication by transferring microRNAs, lipids, and proteins to neighboring cells. Sortilin, a sorting receptor that directs target proteins to the secretory or endocytic compartments of cells, is found in both EVs and cells. In many human diseases, including cancer and cardiovascular disorders, sortilin expression levels are atypically high. To elucidate the relationship between cardiovascular disease, particularly vascular calcification, and sortilin expression levels, we explored the trafficking of sortilin in both the intracellular and extracellular milieu. We previously demonstrated that sortilin promotes vascular calcification via its trafficking of tissue-nonspecific alkaline phosphatase to EVs. Although recent reports have noted that sortilin is regulated by multiple post-translational modifications, the precise mechanisms of sortilin trafficking still need to be determined. Here, we show that sortilin forms homodimers with an intermolecular disulfide bond at the cysteine 783 (Cys⁷⁸³) residue, and because Cys⁷⁸³ can be palmitoylated, it could be shared via palmitoylation and an intermolecular disulfide bond. Formation of this intermolecular disulfide bond leads to trafficking of sortilin to EVs by preventing palmitoylation, which further promotes sortilin trafficking to the Golgi apparatus. Moreover, we found that sortilin-derived propeptide decreased sortilin homodimers within EVs. In conclusion, sortilin is transported to EVs via the formation of homodimers with an intermolecular disulfide bond, which is endogenously regulated by its own propeptide. Therefore, we propose that inhibiting dimerization of sortilin acts as a new therapeutic strategy for the treatment of EV-associated diseases, including vascular calcification and cancer.