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Differential Effects of Platelet Factor 4 (CXCL4) and Its Non-Allelic Variant (CXCL4L1) on Cultured Human Vascular
Dawid M Kaczor1, Rafael Kramann2,3,4, Tilman M Hackeng1
1Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
Insights
Platelet factor 4 (CXCL4) and its variant CXCL4L1 affect vascular smooth muscle cells (VSMCs). While both alter gene expression, only CXCL4 promotes VSMC proliferation and calcification, suggesting distinct roles in vascular remodeling.
Area of Science:
- Vascular Biology
- Cellular Signaling
- Atherosclerosis Research
Background:
- Platelet factor 4 (CXCL4) is a platelet chemokine involved in vascular remodeling and atherosclerosis.
- A variant, CXCL4L1, differs slightly from CXCL4 but has distinct functions.
- Vascular smooth muscle cells (VSMCs) are key players in vascular health and disease.
Purpose of the Study:
- To compare the in vitro effects of CXCL4 and CXCL4L1 on human VSMC phenotype and function.
- To investigate the uptake mechanisms of CXCL4 by VSMCs.
- To elucidate the distinct roles of CXCL4 and CXCL4L1 in vascular smooth muscle cell modulation.
Main Methods:
- In vitro incubation of human VSMCs with CXCL4 and CXCL4L1.
- Analysis of VSMC gene expression, proliferation, and calcification.
- Investigation of CXCL4 uptake pathways, including receptor involvement and heparin inhibition.
Main Results:
- Both CXCL4 and CXCL4L1 decreased contractile marker genes and increased KLF4 and NLRP3 mRNA in VSMCs.
- Exogenous CXCL4 was internalized by VSMCs, a process inhibited by heparin.
- Only CXCL4 stimulated VSMC proliferation and calcification, while LDL receptor family members were implicated in CXCL4 uptake.
Conclusions:
- CXCL4 and CXCL4L1 differentially modulate VSMC gene expression.
- CXCL4 promotes VSMC proliferation and calcification, contributing to vascular remodeling.
- Endogenously expressed CXCL4L1 may regulate VSMC homeostasis, warranting further investigation.
Abstract:
Platelet factor 4 (CXCL4) is a chemokine abundantly stored in platelets. Upon injury and during atherosclerosis, CXCL4 is transported through the vessel wall where it modulates the function of vascular smooth muscle cells (VSMCs) by affecting proliferation, migration, gene expression and cytokine release. Variant CXCL4L1 is distinct from CXCL4 in function and expression pattern, despite a minor three-amino acid difference. Here, the effects of CXCL4 and CXCL4L1 on the phenotype and function of human VSMCs were compared in vitro. VSMCs were found to constitutively express CXCL4L1 and only exogenously added CXCL4 was internalized by VSMCs. Pre-treatment with heparin completely blocked CXCL4 uptake. A role of the putative CXCL4 receptors CXCR3 and DARC in endocytosis was excluded, but LDL receptor family members appeared to be involved in the uptake of CXCL4. Incubation of VSMCs with both CXCL4 and CXCL4L1 resulted in decreased expression of contractile marker genes and increased mRNA levels of KLF4 and NLRP3 transcription factors, yet only CXCL4 stimulated proliferation and calcification of VSMCs. In conclusion, CXCL4 and CXCL4L1 both modulate gene expression, yet only CXCL4 increases the division rate and formation of calcium-phosphate crystals in VSMCs. CXCL4 and CXCL4L1 may play distinct roles during vascular remodeling in which CXCL4 induces proliferation and calcification while endogenously expressed CXCL4L1 governs cellular homeostasis. The latter notion remains a subject for future investigation.
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