The impact of the PCSK-9/VLDL-Receptor axis on inflammatory cell polarization.

BACKGROUND: Studies have shown that lipoproteins, such as LDL and VLDL, as well as its major protein component ApoE2 impact on macrophage polarization important in atherosclerosis. Proprotein convertase subtilisin/kexin 9 (PCSK9) is a key regulator of lipoprotein receptor expression. The present study investigated the effect of the VLDL/VLDL-receptor (VLDL-R) axis on mononuclear cell polarization, as well as the role of PCSK9 and PCSK9 inhibitors (PCSK9i) within this network. METHODS: Human monocytic THP-1 cells and human monocyte-derived macrophages isolated from peripheral blood mononuclear cells (PBMC) were treated with either LPS/IFN-γ to induce a pro-inflammatory phenotype, or with IL-4/IL-13 to induce an anti-inflammatory phenotype. Cells were then subjected to further treatments by lipoproteins, PCSK9, PCSK9i and lipoprotein receptor blockers. RESULTS: LPS/IFN-γ treatment promoted a pro-inflammatory state with an increased expression of pro-inflammatory mediators such as TNF-α, CD80 and IL-1ß. VLDL co-treatment induced a switch of this pro-inflammatory phenotype to an anti-inflammatory phenotype. In pro-inflammatory cells, VLDL significantly decreased the expression of pro-inflammatory markers e.g., TNF-α, CD80, and IL-1ß. These effects were eliminated by PCSK9 and restored by co-incubation with a specific anti-PCSK9 monoclonal antibody (PCSK9i). Migration assays demonstrated that pro-inflammatory cells displayed a significantly higher invasive capacity when compared to untreated cells or anti-inflammatory cells. Moreover, pro-inflammatory cell chemotaxis was significantly decreased by VLDL-mediated acquisition of the anti-inflammatory phenotype. PCSK9 significantly lessened this VLDL-mediated migration inhibition, which was reversed by the PCSK9i. CONCLUSION: VLDL promotes mononuclear cell differentiation towards an anti-inflammatory phenotype. PCSK9, via its capacity to inhibit VLDL-R expression, reverses the VLDL-mediated anti-inflammatory action, thereby promoting a pro-inflammatory phenotype. Thus, PCSK9 targeting therapies may exert anti-inflammatory properties within the vessel wall.

Male Macrophages and Fibroblasts from C57/BL6J Mice Are More Susceptible to Inflammatory Stimuli.

Mounting evidence argues for the significant impact of sex in numerous cardiac pathologies, including myocarditis. Macrophage polarization and activation of cardiac fibroblasts play a key role in myocardial inflammation and remodeling. However, the role of sex in these processes is still poorly understood. In this study, we investigated sex-specific alterations in the polarization of murine bone marrow-derived macrophages (BMMs) and the polarization-related changes in fibroblast activation. Cultured male and female murine BMMs from C57/BL6J mice were polarized into M1 (LPS) and M2 (IL-4/IL-13) macrophages. Furthermore, male and female cardiac fibroblasts from C57/BL6J mice were activated with TNF-α, TGF-ß, or conditioned medium from M1 BMMs. We found a significant overexpression of M1 markers (c-fos, NFκB, TNF-α, and IL-1ß) and M2 markers (MCP-1 and YM1) in male but not female activated macrophages. In addition, the ROS levels were higher in M1 male BMMs, indicating a stronger polarization. Similarly, the pro-fibrotic markers TGF-ß and IL-1ß were expressed in activated cardiac male fibroblasts at a significantly higher level than in female fibroblasts. In conclusion, the present study provides strong evidence for the male-specific polarization of BMMs and activation of cardiac fibroblasts in an inflammatory environment. The data show an increased inflammatory response and tissue remodeling in male mice.

Zinc Ameliorates the Osteogenic Effects of High Glucose in Vascular Smooth Muscle Cells.

In diabetic patients, medial vascular calcification is common and associated with increased cardiovascular mortality. Excessive glucose concentrations can activate the nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-kB) and trigger pro-calcific effects in vascular smooth muscle cells (VSMCs), which may actively augment vascular calcification. Zinc is able to mitigate phosphate-induced VSMC calcification. Reduced serum zinc levels have been reported in diabetes mellitus. Therefore, in this study the effects of zinc supplementation were investigated in primary human aortic VSMCs exposed to excessive glucose concentrations. Zinc treatment was found to abrogate the stimulating effects of high glucose on VSMC calcification. Furthermore, zinc was found to blunt the increased expression of osteogenic and chondrogenic markers in high glucose-treated VSMCs. High glucose exposure was shown to activate NF-kB in VSMCs, an effect that was blunted by additional zinc treatment. Zinc was further found to increase the expression of TNFα-induced protein 3 (TNFAIP3) in high glucose-treated VSMCs. The silencing of TNFAIP3 was shown to abolish the protective effects of zinc on high glucose-induced NF-kB-dependent transcriptional activation, osteogenic marker expression, and the calcification of VSMCs. Silencing of the zinc-sensing receptor G protein-coupled receptor 39 (GPR39) was shown to abolish zinc-induced TNFAIP3 expression and the effects of zinc on high glucose-induced osteogenic marker expression. These observations indicate that zinc may be a protective factor during vascular calcification in hyperglycemic conditions.

Increased ß-adrenergic stimulation augments vascular smooth muscle cell calcification via PKA/CREB signalling.

In chronic kidney disease (CKD), hyperphosphatemia promotes medial vascular calcification, a process augmented by osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs). VSMC function is regulated by sympathetic innervation, and these cells express α- and ß-adrenergic receptors. The present study explored the effects of ß2-adrenergic stimulation by isoproterenol on VSMC calcification. Experiments were performed in primary human aortic VSMCs treated with isoproterenol during control or high phosphate conditions. As a result, isoproterenol dose dependently up-regulated the expression of osteogenic markers core-binding factor α-1 (CBFA1) and tissue-nonspecific alkaline phosphatase (ALPL) in VSMCs. Furthermore, prolonged isoproterenol exposure augmented phosphate-induced calcification of VSMCs. Isoproterenol increased the activation of PKA and CREB, while knockdown of the PKA catalytic subunit α (PRKACA) or of CREB1 genes was able to suppress the pro-calcific effects of isoproterenol in VSMCs. ß2-adrenergic receptor silencing or inhibition with the selective antagonist ICI 118,551 blocked isoproterenol-induced osteogenic signalling in VSMCs. The present observations imply a pro-calcific effect of ß2-adrenergic overstimulation in VSMCs, which is mediated, at least partly, by PKA/CREB signalling. These observations may support a link between sympathetic overactivity in CKD and vascular calcification.

Circulating uromodulin inhibits vascular calcification by interfering with pro-inflammatory cytokine signalling.

AIMS: Uromodulin is produced exclusively in the kidney and secreted into both urine and blood. Serum levels of uromodulin are correlated with kidney function and reduced in chronic kidney disease (CKD) patients, but physiological functions of serum uromodulin are still elusive. This study investigated the role of uromodulin in medial vascular calcification, a key factor associated with cardiovascular events and mortality in CKD patients. METHODS AND RESULTS: Experiments were performed in primary human (HAoSMCs) and mouse (MOVAS) aortic smooth muscle cells, cholecalciferol overload and subtotal nephrectomy mouse models and serum from CKD patients. In three independent cohorts of CKD patients, serum uromodulin concentrations were inversely correlated with serum calcification propensity. Uromodulin supplementation reduced phosphate-induced osteo-/chondrogenic transdifferentiation and calcification of HAoSMCs. In human serum, pro-inflammatory cytokines tumour necrosis factor α (TNFα) and interleukin-1ß (IL-1ß) co-immunoprecipitated with uromodulin. Uromodulin inhibited TNFα and IL-1ß-induced osteo-/chondrogenic signalling and activation of the transcription factor nuclear factor kappa-light-chain-enhancer of activated ß cells (NF-kB) as well as phosphate-induced NF-kB-dependent transcriptional activity in HAoSMCs. In vivo, adeno-associated virus (AAV)-mediated overexpression of uromodulin ameliorated vascular calcification in mice with cholecalciferol overload. Conversely, cholecalciferol overload-induced vascular calcification was aggravated in uromodulin-deficient mice. In contrast, uromodulin overexpression failed to reduce vascular calcification during renal failure in mice. Carbamylated uromodulin was detected in serum of CKD patients and uromodulin carbamylation inhibited its anti-calcific properties in vitro. CONCLUSIONS: Uromodulin counteracts vascular osteo-/chondrogenic transdifferentiation and calcification, at least in part, through interference with cytokine-dependent pro-calcific signalling. In CKD, reduction and carbamylation of uromodulin may contribute to vascular pathology.

Role of SGK1 in the Osteogenic Transdifferentiation and Calcification of Vascular Smooth Muscle Cells Promoted by Hyperglycemic Conditions.

In diabetes mellitus, hyperglycemia promotes the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) to enhance medial vascular calcification, a common complication strongly associated with cardiovascular disease and mortality. The mechanisms involved are, however, still poorly understood. Therefore, the present study explored the potential role of serum- and glucocorticoid-inducible kinase 1 (SGK1) during vascular calcification promoted by hyperglycemic conditions. Exposure to high-glucose conditions up-regulated the SGK1 expression in primary human aortic VSMCs. High glucose increased osteogenic marker expression and activity and, thus, promoted the osteogenic transdifferentiation of VSMCs, effects significantly suppressed by additional treatment with the SGK1 inhibitor EMD638683. Moreover, high glucose augmented the mineralization of VSMCs in the presence of calcification medium, effects again significantly reduced by SGK1 inhibition. Similarly, SGK1 knockdown blunted the high glucose-induced osteogenic transdifferentiation of VSMCs. The osteoinductive signaling promoted by high glucose required SGK1-dependent NF-kB activation. In addition, advanced glycation end products (AGEs) increased the SGK1 expression in VSMCs, and SGK1 inhibition was able to interfere with AGEs-induced osteogenic signaling. In conclusion, SGK1 is up-regulated and mediates, at least partly, the osteogenic transdifferentiation and calcification of VSMCs during hyperglycemic conditions. Thus, SGK1 inhibition may reduce the development of vascular calcification promoted by hyperglycemia in diabetes.

Inhibition of vascular smooth muscle cell calcification by vasorin through interference with TGFß1 signaling.

Elevated transforming growth factor ß1 (TGFß1) levels are frequently observed in chronic kidney disease (CKD) patients. TGFß1 contributes to development of medial vascular calcification during hyperphosphatemia, a pathological process promoted by osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). Vasorin is a transmembrane glycoprotein highly expressed in VSMCs, which is able to bind TGFß to inhibit TGFß signaling. Thus, the present study explored the effects of vasorin on osteo-/chondrogenic transdifferentiation and calcification of VSMCs. Primary human aortic smooth muscle cells (HAoSMCs) were treated with recombinant human TGFß1 or ß-glycerophosphate without or with recombinant human vasorin or vasorin gene silencing by siRNA. As a result, TGFß1 down-regulated vasorin mRNA expression in HAoSMCs. Vasorin supplementation inhibited TGFß1-induced pathway activation, SMAD2 phosphorylation and downstream target genes expression in HAoSMCs. Furthermore, treatment with exogenous vasorin blunted, while vasorin knockdown augmented TGFß1-induced osteo-/chondrogenic transdifferentiation of HAoSMCs. In addition, phosphate down-regulated vasorin mRNA expression in HAoSMCs. Phosphate-induced TGFß1 expression was not affected by addition of exogenous vasorin. Nonetheless, the phosphate-induced TGFß1 signaling, osteo-/chondrogenic transdifferentiation and calcification of HAoSMCs were all blunted by vasorin. Conversely, silencing of vasorin aggravated osteoinduction in HAoSMCs during high phosphate conditions. Aortic vasorin expression was reduced in the hyperphosphatemic klotho-hypomorphic mouse model of CKD-related vascular calcification. In conclusion, vasorin, which suppresses TGFß1 signaling and protects against osteo-/chondrogenic transdifferentiation and calcification of VSMCs, is reduced by pro-calcifying conditions. Thus, vasorin is a novel key regulator of VSMC calcification and may represent a potential therapeutic target for vascular calcification during CKD.