Cell surface thrombospondin is functionally essential for vascular smooth muscle cell proliferation.

Area of Science:

• Vascular Biology
• Cell Cycle Regulation
• Extracellular Matrix

Background:

• Thrombospondin (TS) is an extracellular glycoprotein synthesized by vascular smooth muscle cells (SMC).
• Platelet-derived growth factor regulates TS synthesis and secretion.
• TS plays a role in cell proliferation and extracellular matrix interactions.

Purpose of the Study:

• To investigate the role of thrombospondin (TS) in the proliferation of cultured rat aortic SMC.
• To determine the essentiality of TS for SMC growth using monoclonal antibodies.
• To elucidate the cellular site of action and cell cycle phase affected by TS.

Main Methods:

• Utilized a panel of five monoclonal antibodies against TS to inhibit SMC growth.
• Performed dose-dependent and reversibility assays with anti-TS antibody D4.6.
• Analyzed cell cycle progression using flow cytofluorimetry.
• Investigated TS localization on SMC surface via immunofluorescence and metabolic labeling.
• Assessed the effect of heparin on TS binding and SMC proliferation.

Main Results:

• All five anti-TS monoclonal antibodies significantly inhibited SMC growth.
• Antibody D4.6 demonstrated dose-dependent and reversible inhibition of SMC proliferation.
• SMC treated with D4.6 were arrested in the G1 phase of the cell cycle.
• TS was found to be bound to the cell surface of SMC.
• Heparin and anti-TS antibody D4.6 abolished cell surface TS binding and inhibited SMC growth.

Conclusions:

• Cell surface-associated thrombospondin (TS) is functionally essential for vascular SMC proliferation.
• The requirement for TS is specifically in the G1 phase of the cell cycle.
• Interfering with TS-SMC surface interaction, e.g., with heparin, inhibits SMC proliferation.