Circulating smooth muscle progenitor cells in arterial remodeling

Area of Science:

• Cardiovascular Biology
• Stem Cell Research
• Vascular Biology

Background:

• Vascular smooth muscle cell (SMC) proliferation and migration are central to vascular proliferative diseases.
• Bone marrow-derived mononuclear cells (BMMCs) have been implicated in contributing to lesion progression via differentiation into SMCs.
• In vitro studies show BMMCs can adopt SMC-like characteristics, but their in vivo trans-differentiation capacity remains debated.

Purpose of the Study:

• To investigate the controversial role of BMMCs in SMC differentiation in vivo.
• To clarify the contribution of BMMCs to neointima formation and atherosclerotic plaques.
• To reconcile discrepancies in previous findings regarding BMMC-derived SMCs.

Main Methods:

• Analysis of mouse strains with specific smooth muscle-myosin heavy chain (SM-MHC) promoter-driven marker genes.
• Time-course analysis of neointima formation dynamics.
• Utilizing high-resolution microscopy and specific SMC marker proteins for cell identification.

Main Results:

• BMMCs temporarily express alpha-smooth muscle actin but not SM-MHC in neointima formation.
• BM-derived cells are transient and disappear from lesions post-inflammation.
• CD14(+)/CD68(+) BMMCs primarily function as SMC-like macrophages with paracrine effects, rather than definitive SMCs.

Conclusions:

• BMMCs contribute to vascular lesions mainly as SMC-like macrophages, not fully differentiated SMCs in vivo.
• Methodological differences likely explain prior conflicting results on BMMC trans-differentiation.
• The role of BMMCs in cardiovascular stem cell contexts requires re-evaluation.