Association between serum soluble low-density lipoprotein receptor levels and metabolic factors in healthy Japanese individuals

Changes in soluble LDL receptor and lipoprotein fractions in response to diet in the DIETFITS weight loss study

Circulating levels of the soluble ligand-binding ectodomain of the LDL receptor (sLDLR) that is proteolytically cleaved from the cell surface have been shown to correlate with plasma triglycerides, but the lipid and lipoprotein effects of longitudinal changes in sLDLR have not been examined. We sought to assess associations between changes in sLDLR and detailed lipoprotein measurements between baseline and 6 months in participants in the DIETFITS (Diet Intervention Examining The Factors Interacting with Treatment Success) weight loss trial who were randomly assigned to the low-fat (n = 225) or low-carbohydrate (n = 236) diet arms. sLDLR was assayed using a proteomic procedure, lipids and apoprotein (apo) B and apoAI were measured by standard assays, and lipoprotein particle subfractions were quantified by ion mobility methodology. Changes in sLDLR were significantly positively associated with changes in plasma cholesterol, triglycerides, apoB, large-sized and medium-sized VLDL, and small and very small LDL, and inversely with changes in large LDL and HDL. The lipoprotein subfraction associations with sLDLR were independent of age, sex, diet, and BMI, but all except for large LDL were reduced to insignificance when adjusted for triglyceride change. Principal component analysis identified three independent clusters of changes in lipoprotein subfractions that accounted for 78% of their total variance. Change in sLDLR was most strongly correlated with change in the principal component that was loaded positively with large VLDL and small and very small LDL and negatively with large LDL and HDL. In conclusion, sLDLR is a component of a cluster of lipids and lipoproteins that are characteristic of atherogenic dyslipidemia.

Soluble LDL-receptor is induced by TNF-α and inhibits hepatocytic clearance of LDL-cholesterol

Defective LDL-C clearance and hence its elevation in the circulation is an established risk factor for cardiovascular diseases (CVDs) such as myocardial infarction (MI). A soluble LDL-receptor (sLDL-R) has been detected in human plasma which correlates strongly with circulating LDL-C and classical conditions that promote chronic inflammation. However, the mechanistic interplay between sLDL-R, inflammation, and CVDs remains to be investigated. Here, we report that stimulation of HepG2 cells with TNF-α induces the release of sLDL-R into culture supernatants. In addition, TNF-α induces gene expression of peptidases ADAM-17 and MMP-14 in HepG2 cells, and inhibiting these peptidases using TMI 1 significantly reduces the TNF-α induced sLDL-R release. We found that a soluble form of recombinant LDL-R (100 nM) can strongly bind to LDL-C and form a stable complex (KD = E-12). Moreover, incubation of HepG2 cells with this recombinant LDL-R resulted in reduced LDL-C uptake in a dose-dependent manner. In a nested case-control study, we found that baseline sLDL-R in plasma is positively correlated with plasma total cholesterol level. Furthermore, a twofold increase in plasma sLDL-R was associated with a 55% increase in the risk of future MI [AOR = 1.55 (95% CI = 1.10-2.18)]. Nevertheless, mediation analyses revealed that a significant proportion of the association is mediated by elevation in plasma cholesterol level (indirect effect β = 0.21 (95% CI = 0.07-0.38). Collectively, our study shows that sLDL-R is induced by a pro-inflammatory cytokine TNF-α via membrane shedding. Furthermore, an increase in sLDL-R could inhibit hepatic clearance of LDL-C increasing its half-life in the circulation and contributing to the pathogenesis of MI. KEY MESSAGES: TNF-α causes shedding of hepatocytic LDL-R through induction of ADAM-17 and MMP-14. sLDL-R binds strongly to LDL-C and inhibits its uptake by hepatocytic cells. Plasma sLDL-R is positively correlated with TNF-α and cholesterol. Plasma sLDL-R is an independent predictor of myocardial infarction (MI). Plasma cholesterol mediates the association between sLDL-R and MI.

Identification of amino acid residues in the MT-loop of MT1-MMP critical for its ability to cleave low-density lipoprotein receptor

Low-density lipoprotein receptor (LDLR) mediates clearance of plasma LDL cholesterol, preventing the development of atherosclerosis. We previously demonstrated that membrane type 1-matrix metalloproteinase (MT1-MMP) cleaves LDLR and exacerbates the development of atherosclerosis. Here, we investigated determinants in LDLR and MT1-MMP that were critical for MT1-MMP-induced LDLR cleavage. We observed that deletion of various functional domains in LDLR or removal of each of the five predicted cleavage sites of MT1-MMP on LDLR did not affect MT1-MMP-induced cleavage of the receptor. Removal of the hemopexin domain or the C-terminal cytoplasmic tail of MT1-MMP also did not impair its ability to cleave LDLR. On the other hand, mutant MT1-MMP, in which the catalytic domain or the MT-loop was deleted, could not cleave LDLR. Further Ala-scanning analysis revealed an important role for Ile at position 167 of the MT-loop in MT1-MMP’s action on LDLR. Replacement of Ile167 with Ala, Thr, Glu, or Lys resulted in a marked loss of the ability to cleave LDLR, whereas mutation of Ile167 to a non-polar amino acid residue, including Leu, Val, Met, and Phe, had no effect. Therefore, our studies indicate that MT1-MMP does not require a specific cleavage site on LDLR. In contrast, an amino acid residue with a hydrophobic side chain at position 167 in the MT-loop is critical for MT1-MMP-induced LDLR cleavage.

Associations of pro-protein convertase subtilisin-like kexin type 9, soluble low-density lipoprotein receptor and coronary artery disease: A case-control study

BACKGROUND

Low-density lipoprotein receptor (LDLR) is the primary pathway for removal of cholesterol from the circulation, pro-protein convertase subtilisin-like kexin type 9 (PCSK9) is a secreted protease that binds to and promotes degradation of the LDLR protein. The goal of this case-control study was to investigate the role of soluble LDLR (sLDLR) and PCSK9 in coronary artery disease (CAD) and investigate the relationship between these two indices and CAD.

METHODS

In a sample of 144 Chinese patients recruited between January 2018 and August 2018, 81 cases with mild and severe stenosis characterized by coronary angiograph (CAG) and 63 healthy controls were selected using the propensity score matching (PSM) based on demographics and medical history. sLDLR and PCSK9 concentrations were determined using enzyme-linked immunosorbent assay (ELISA), Immuno-precipitation (IP) and western blotting. Multivariable logistic models were used to assess the associations between the degree of coronary artery stenosis and the biomarkers of interest.

RESULTS

Higher PCSK9 was found to be a significant predictor of coronary artery stenosis when comparing cases who had severe stenosis vs. controls (OR = 1.016, 95%CI: 1.009-1.024), and cases who had mild stenosis vs. controls (OR = 1.009, 95%CI: 1.003-1.015). sLDLR was positively corrected with PCSK9, which confounded the association between CAD and PCSK9. Compared to patients with mild-stenosis, patients with severe-stenosis also showed a higher level of PCSK9 (OR = 1.005, 95%CI: 1.007-1.013).

CONCLUSIONS

These findings suggest that elevated PSCK9 may contribute to the odds of developing CAD, with a higher degree of coronary artery stenosis.

PCSK9/LDLR System and Rheumatoid Arthritis-Related Atherosclerosis

Background/Aims: Rheumatoid arthritis (RA) is associated with the emergence of cardiovascular disease, while chronic inflammation is considered a common denominator for their parallel progression. The Proprotein convertase subtilisin/kexin type 9 (PCSK9)/LDL-Receptor (LDLR) system is of high importance during atherogenesis, via regulating the clearance of LDL from the circulation; nevertheless the role of this molecular mechanism during RA-related atheromatosis is not known.

Methods: Herein, high-resolution ultrasound measurements for arterial hypertrophy, atheromatosis and arterial stiffness as well as comprehensive biochemical profiling were performed in 85 RA patients. The circulating levels of PCSK9 and LDLR were measured and their potential associations as well as of the PCSK9/LDLR ratio with patients' characteristics and the degree of atherosclerosis were investigated.

Results: Increased LDLR levels and decreased PCSK9/LDLR ratio were found in RA patients with at least 2 atheromatic plaques as compared to the ones without any plaques. In addition the levels of both PCSK9 and LDLR were positively correlated with the presence of atheromatic plaques as an age- and gender- adjusted multivariate analysis revealed.

Conclusions: Our data imply that the PCSK9/LDLR system plays a significant role during RA-related atherosclerosis and may therefore be used as a screening tool for disease progression in the future.

Membrane-type I matrix metalloproteinase (MT1-MMP), lipid metabolism and therapeutic implications

Lipids exert many essential physiological functions, such as serving as a structural component of biological membranes, storing energy, and regulating cell signal transduction. Dysregulation of lipid metabolism can lead to dyslipidemia related to various human diseases, such as obesity, diabetes, and cardiovascular disease. Therefore, lipid metabolism is strictly regulated through multiple mechanisms at different levels, including the extracellular matrix. Membrane-type I matrix metalloproteinase (MT1-MMP), a zinc-dependent endopeptidase, proteolytically cleaves extracellular matrix components, and non-matrix proteins, thereby regulating many physiological and pathophysiological processes. Emerging evidence supports the vital role of MT1-MMP in lipid metabolism. For example, MT1-MMP mediates ectodomain shedding of low-density lipoprotein receptor and increases plasma low-density lipoprotein cholesterol levels and the development of atherosclerosis. It also increases the vulnerability of atherosclerotic plaque by promoting collagen cleavage. Furthermore, it can cleave the extracellular matrix of adipocytes, affecting adipogenesis and the development of obesity. Therefore, the activity of MT1-MMP is strictly regulated by multiple mechanisms, such as autocatalytic cleavage, endocytosis and exocytosis, and post-translational modifications. Here, we summarize the latest advances in MT1-MMP, mainly focusing on its role in lipid metabolism, the molecular mechanisms regulating the function and expression of MT1-MMP, and their pharmacotherapeutic implications.

Membrane type 1 matrix metalloproteinase promotes LDL receptor shedding and accelerates the development of atherosclerosis

Plasma low-density lipoprotein (LDL) is primarily cleared by LDL receptor (LDLR). LDLR can be proteolytically cleaved to release its soluble ectodomain (sLDLR) into extracellular milieu. However, the proteinase responsible for LDLR cleavage is unknown. Here we report that membrane type 1-matrix metalloproteinase (MT1-MMP) co-immunoprecipitates and co-localizes with LDLR and promotes LDLR cleavage. Plasma sLDLR and cholesterol levels are reduced while hepatic LDLR is increased in mice lacking hepatic MT1-MMP. Opposite effects are observed when MT1-MMP is overexpressed. MT1-MMP overexpression significantly increases atherosclerotic lesions, while MT1-MMP knockdown significantly reduces cholesteryl ester accumulation in the aortas of apolipoprotein E (apoE) knockout mice. Furthermore, sLDLR is associated with apoB and apoE-containing lipoproteins in mouse and human plasma. Plasma levels of sLDLR are significantly increased in subjects with high plasma LDL cholesterol levels. Thus, we demonstrate that MT1-MMP promotes ectodomain shedding of hepatic LDLR, thereby regulating plasma cholesterol levels and the development of atherosclerosis.

The enigma of soluble LDLR: could inflammation be the key?

Soluble low-density lipoprotein receptor (sLDLR) is the circulating ectodomain of transmembrane LDLR. Its blood level strongly correlates with that of triglycerides (TG). This correlation has eluded satisfactory explanation. Hypertriglyceridemia and shedding of the ectodomain of many transmembrane receptors often accompany inflammatory states. The shedding mostly occurs through cleavage by a disintegrin-and-metalloproteinase-17 (ADAM-17), an enzyme activated by inflammation. It reduces the cellular uptake of TG-loaded lipoproteins, causing their accumulation in circulation; hence the correlation between plasma sLDLR and TG. Soluble LDLR could become a new surrogate marker of inflammation.

Relationship between XspI Site Polymorphisms of LDL-R Gene and Serum IL-2 and IL-10 in Patients with Hypercholesterolemia

BACKGROUND

Relationship has been identified in sporadic reports between polymorphisms and hypercholesterolemia. However, the relationship between inflammatory cytokines and polymorphism of low-density lipoprotein receptor (LDL-R) gene in hypercholesterolemia is unclear. This study aimed to explore the relationship and significance between polymorphisms of LDL-R gene and serum Interleukin-2 (IL-2), IL-10 in patients with hypercholesterolemia.

METHODS

PCR-RFLP and direct DNA sequencing assay were employed to determine polymorphism of LDL-R gene in 900 patients with hypercholesterolemia and 400 healthy cases. ELISA was applied to assay serum concentration of IL-2 and IL-10. Blood lipid indexes were tested in all cases.

RESULTS

Compared with the healthy controls, level of IL-2 increased significantly, while IL-10 decreased significantly (P < 0.05). Correlation analysis showed that IL-2 was positively correlated with total cholesterol (TC), LDL-c, and genotype (r = 0.542, 0.410, 0.598, P < 0.05) and negatively correlated with HDL-c (r = -0.352, P < 0.05). Negative relationship also was found between TC, LDL-c, genotype, and IL-10 (r = -0.452, -0.390, -0.613, P < 0.05), and positive correlation between HDL-c and IL-10 (r = 0.398, P < 0.05). Multiple linear regression showed that genotypes and TC were independent factors affecting the levels of IL-2 and IL-10 (P < 0.05).

CONCLUSION

IL-2 and IL-10 were related to gene polymorphisms of LDL-R, which might be involved in the development and progress of hypercholesterolemia.