Complement 3 activates the KLF5 gene in rat vascular smooth muscle cells

Area of Science:

• Cardiovascular Biology
• Molecular Mechanisms of Disease
• Immunology

Background:

• Spontaneously hypertensive rat (SHR)-derived vascular smooth muscle cells (VSMCs) exhibit a phenotypic switch to a synthetic state.
• Complement 3 (C3) expression is increased in this synthetic VSMC phenotype.
• C3 plays a role in mediating the VSMC phenotypic transition.

Purpose of the Study:

• To elucidate the molecular mechanisms by which C3 influences VSMC phenotypic modulation.
• To investigate the effect of C3a on key transcription factors regulating VSMC phenotype.
• To identify the signaling pathways involved in C3-mediated transcriptional regulation.

Main Methods:

• Analysis of C3a effects on transcription factor mRNA expression in VSMCs.
• Luciferase reporter assays to assess KLF5 promoter activity.
• Deletion analysis of the KLF5 gene promoter region.
• Assessment of extracellular signal-regulated kinase (ERK) phosphorylation.
• Pharmacological inhibition of MEK signaling pathway.

Main Results:

• C3a significantly increased Krüppel-like zinc-finger transcription factor 5 (KLF5) mRNA expression.
• C3a dose-dependently enhanced KLF5 promoter activity.
• A specific promoter region (-991 to -699) was identified as crucial for C3a-induced KLF5 activation.
• C3a induced ERK phosphorylation.
• MEK inhibition abolished C3a-mediated KLF5 promoter activation.

Conclusions:

• C3a enhances KLF5 gene expression through transcriptional regulation.
• The ERK signaling pathway is essential for C3a-induced KLF5 promoter activity.
• These findings reveal a novel mechanism linking complement activation to VSMC phenotypic plasticity via KLF5 and ERK signaling.