# TRIC-A Loss Sensitizes the Heart to β-Adrenergic Stress and Drives Cardiomyocyte Death and Fibrosis

## TL;DR

TRIC-A protects the heart from stress-induced damage by regulating calcium balance and preventing cell death and fibrosis.

## Contribution

This study identifies TRIC-A as a critical regulator of cardiac resilience during β-adrenergic stress.

## Key findings

- TRIC-A deficiency leads to SR Ca2+ overload and mitochondrial damage during β-adrenergic stimulation.
- Mitochondrial Ca2+ overload is the proximal trigger of cardiomyocyte necrosis in Tric-a−/− hearts.
- TRIC-A loss causes fibrosis without hypertrophy, driven by cardiomyocyte injury rather than fibroblast dysfunction.

## Abstract

Trimeric intracellular cation channel A (TRIC-A) provides counter-ion support for sarcoplasmic reticulum (SR) Ca2+ release, yet its physiological role in the intact heart under stress remains poorly defined. Here, we demonstrate that TRIC-A is essential for maintaining balanced SR Ca2+ release, mitochondrial integrity, and cardiac resilience during β-adrenergic stimulation. Tric-a−/− cardiomyocytes exhibited Ca2+ transients evoked by electrical stimuli and exaggerated isoproterenol (ISO)-evoked Ca2+ release, consistent with SR Ca2+ overload. These defects were accompanied by selective upregulation of protein kinase A (PKA)-dependent phosphorylation of ryanodine receptor 2 (RyR2) (S2808) and phospholamban (PLB) (S16). Acute ISO challenge induced mitochondrial swelling, cristae disruption, and Evans Blue Dye uptake, and elevated circulating troponin T in Tric-a−/− hearts, hallmarks of necrosis-like cell death. Mitochondrial Ca2+ uptake inhibition with Ru360 markedly reduced membrane injury, establishing mitochondrial Ca2+ overload as the proximal trigger of cardiac cell death. With sustained β-adrenergic stimulation by ISO, Tric-a−/− hearts developed extensive interstitial and perivascular fibrosis without exaggerated hypertrophy. Cardiac fibroblasts lacked TRIC-A expression and displayed normal Ca2+ signaling and activation, indicating that fibrosis arises secondarily from cardiomyocyte injury rather than fibroblast-intrinsic abnormalities. These findings identify TRIC-A as a critical regulator of SR-mitochondrial Ca2+ coupling and a key molecular safeguard that protects the heart from catecholamine-induced injury and maladaptive remodeling.