Angiotensin-II-Evoked Ca²⁺ Entry in Murine Cardiac Fibroblasts Does Not Depend on TRPC Channels

Area of Science:

• Cardiovascular Biology
• Cell Physiology
• Molecular Cardiology

Background:

• Transient Receptor Potential Canonical (TRPC) proteins regulate cellular calcium homeostasis and are expressed in cardiac fibroblasts (CFs).
• TRPC channels are implicated in pathological cardiac remodeling, including fibrosis, a process influenced by angiotensin II (AngII).
• Understanding calcium signaling in CFs is crucial for addressing cardiac fibrosis.

Purpose of the Study:

• To investigate the role of TRPC proteins in angiotensin II (AngII)-induced calcium (Ca2+) homeostasis changes in cardiac fibroblasts (CFs).
• To identify the specific ion channels responsible for AngII-mediated calcium entry in CFs.
• To explore the relationship between CF density, myofibroblast differentiation, and calcium signaling.

Main Methods:

• Utilized Ca2+ imaging techniques and TRPC knockout mouse models (TRPC-hepta KO).
• Quantified TRPC gene expression in CFs using qPCR.
• Assessed AngII- and thrombin-induced Ca2+ transients and entry, and inhibited CRAC channels with GSK7975A.

Main Results:

• All seven TRPC gene transcripts were detected in CFs, with TRPC1, TRPC3, and TRPC4 being most abundant.
• AngII-induced Ca2+ entry and release were dependent on CF density and inversely correlated with α-smooth muscle actin expression.
• TRPC-hepta KO CFs showed no difference in AngII-induced Ca2+ signaling; however, CRAC channel inhibition abolished AngII-induced Ca2+ entry.

Conclusions:

• TRPC channels are dispensable for acute AngII-evoked calcium signaling in isolated cardiac fibroblasts.
• Orai channel family members are suggested as the molecular components responsible for the pathophysiologically important Ca2+ entry pathway.
• These findings provide new insights into calcium signaling mechanisms underlying cardiac fibrosis.