Phosphoinositide Depletion and Compensatory Phospho-Signaling in Angiotensin II-Induced Heart Disease.

Abstract

Background: Contractile dysfunction, hypertrophy, and cell death during heart failure are linked to altered Ca²⁺ handling and elevated levels of the hormone AngII (angiotensin II), which signals through G_q (Guanine nucleotide-binding protein alpha subunit q)-coupled AT₁Rs (AngII type 1 receptors), initiating hydrolysis of phosphatidylinositol (4,5)-bisphosphate. Chronic elevation of AngII contributes to cardiac pathology, but the mechanisms linking sustained AngII signaling to heart dysfunction remain incompletely understood. Here, we demonstrate that chronic AngII exposure profoundly disrupts cardiac phosphoinositide homeostasis, triggering a cascade of cellular adaptations that ultimately impair cardiac function.

Methods: Mice received 1-week infusions of AngII, bisperoxovanadium (1,10 phenanthroline), both, or saline via osmotic minipumps. We used mass spectrometry, super-resolution microscopy, electrophysiology, confocal imaging, immunoblot, echocardiography, and histology to assess phosphoinositide levels, L-type voltage-gated calcium channel Ca_V1.2 localization, Ca²⁺ handling, protein phosphorylation, cardiac function, and fibrosis.

Results: Chronic AngII infusion caused widespread phosphoinositide imbalance, reducing phosphatidylinositol, phosphatidylinositol phosphate, phosphatidylinositol bisphosphate, and phosphatidylinositol (3,4,5)-trisphosphate levels. Ca_V1.2 channels were partially redistributed from t-tubules to endosomal compartments. Despite reduced sarcolemmal channel expression, Ca²⁺ currents and transients were maintained through enhanced PKA (protein kinase A)-mediated and CaMKII (Ca²⁺/calmodulin-dependent protein kinase II)-mediated phosphorylation of Ca²⁺-handling proteins. However, this compensation proved insufficient as cardiac function progressively declined, marked by pathological hypertrophy, t-tubule disruption, and diastolic dysfunction. PTEN (phosphatase and tensin homolog) inhibition preserved Akt signaling and protected against cardiac dysfunction and fibrosis without preventing cellular remodeling or altered calcium handling.

Conclusions: These findings reveal a complex interplay between phosphoinositide signaling, ion channel trafficking, and compensatory phospho-regulation in AngII-induced cardiac pathology. We establish phosphatidylinositol (3,4,5)-trisphosphate depletion as a critical link between chronic AngII signaling and cardiac dysfunction. The dissociation between persistent cellular remodeling and preserved organ function with PTEN inhibition reveals that cardioprotection occurs primarily through reduced fibrosis. PTEN inhibition, thus, emerges as a promising therapeutic strategy for heart failure associated with pathological renin-angiotensin system activation, with potential to complement existing therapies by targeting antifibrotic responses.