Homocysteine downregulates cardiac homeobox transcription factor NKX2.5 via IGFBP5

Area of Science:

• Cardiovascular Biology
• Developmental Biology
• Biochemistry

Background:

• Homocysteine (Hcy) is an established risk factor for congenital heart disease (CHD).
• The precise molecular mechanisms linking Hcy to CHD remain largely unelucidated.
• Understanding these mechanisms is crucial for identifying potential therapeutic targets and diagnostic markers.

Purpose of the Study:

• To investigate the role of homocysteine (Hcy) in congenital heart disease (CHD) pathogenesis.
• To explore the relationship between Hcy, NK2 homeobox 5 (NKX2.5), and insulin-like growth factor binding protein 5 (IGFBP5) in the context of CHD.
• To elucidate the molecular pathway through which Hcy influences cardiac development.

Main Methods:

• Analysis of amniotic fluid (AF) supernatant samples from pregnant women with CHD-affected and normal fetuses.
• Western blot analysis to quantify protein levels of NKX2.5 and IGFBP5.
• In vitro experiments using H9C2 cell cultures treated with Hcy and IGFBP5.
• Real-time PCR, luciferase reporter gene assays, chromatin immunoprecipitation, and electrophoretic mobility shift assays to assess gene expression and protein-DNA interactions.

Main Results:

• Elevated Hcy concentrations were observed in the AF of fetuses with CHD compared to controls.
• NKX2.5 protein levels were decreased, while IGFBP5 levels were increased in the AF of the CHD group.
• In vitro, Hcy downregulated NKX2.5 and upregulated IGFBP5 expression in H9C2 cells.
• IGFBP5 treatment led to reduced NKX2.5 expression and transcriptional activity, with evidence of IGFBP5 binding to the NKX2.5 promoter region.

Conclusions:

• Hcy may contribute to CHD development by inhibiting NKX2.5 expression.
• This inhibition appears to be mediated, at least in part, by IGFBP5, which is upregulated by Hcy.
• IGFBP5 directly suppresses NKX2.5 transcription, suggesting a novel molecular mechanism in Hcy-induced cardiac malformations.