RhoA-mediated signaling up-regulates hepatocyte growth factor gene and protein expression in response to apoptotic...

Area of Science:

• Cellular Biology
• Immunology
• Molecular Signaling

Background:

• Macrophages play a critical role in clearing apoptotic cells, a process essential for tissue homeostasis.
• Hepatocyte Growth Factor (HGF) is a key signaling molecule involved in tissue repair and regeneration.

Purpose of the Study:

• To elucidate the molecular mechanisms regulating HGF mRNA and protein expression in macrophages upon encountering apoptotic cells.
• To investigate the role of specific signaling pathways, including RhoA and PI3K/Akt, in HGF production during efferocytosis.

Main Methods:

• Utilized RAW 264.7 macrophage cell lines and primary peritoneal macrophages co-cultured with various apoptotic cell types (Jurkat, HeLa, thymocytes).
• Employed pharmacological inhibitors and siRNA to down-regulate RhoA/Rho kinase, PI3K/Akt, and MAPK pathways (p38, ERK, JNK).
• Assessed HGF mRNA and protein expression via quantitative PCR and Western blotting; analyzed pathway activation through phosphorylation status.

Main Results:

• Interaction with apoptotic cells, but not viable cells, induced HGF mRNA and protein expression in macrophages.
• Activation of RhoA, PI3K/Akt, and MAPKs (p38, ERK, JNK) was observed upon exposure to apoptotic cells.
• Down-regulation of the RhoA/Rho kinase pathway significantly suppressed HGF production, impacting Akt and MAPK phosphorylation; PI3K and JNK inhibition also affected these pathways and HGF expression.

Conclusions:

• The RhoA/Rho kinase signaling pathway is a critical upstream regulator of transcriptional HGF production in macrophages responding to apoptotic cells.
• This pathway influences HGF production through the modulation of PI3K/Akt and MAPK signaling cascades.
• The findings highlight a novel mechanism linking efferocytosis to the induction of regenerative factor HGF production.