Fig. 10. BIN1 knockdown rejuvenates the aging heart.

The main findings of our study graphically illustrated and summarized. Top: In healthy young cells, Ca_V1.2 channels undergo endosomal recycling, where channels on endosomes are either marked for degradation through the late endosome pathway or are recycled to the sarcolemma through the fast and slow recycling pathways. Following β-adrenergic receptor (β-AR) stimulation, a pool of channels localized to endosomes are mobilized to the membrane, resulting in larger Ca_V1.2 clusters along t-tubules. Across the dyad, RyR2 clusters on the sarcoplasmic reticulum also increase following βAR stimulation ensuring efficient Ca²⁺-induced Ca²⁺-release. This increase in cytosolic Ca²⁺, along with increased phosphorylation of cardiac Troponin I (cTnI) and cardiac myosin binding protein-C (cMyBP-C) within the sarcomere, allows for enhanced contractility under acute stress to cope with elevated hemodynamic and metabolic demands. Bottom: In aging, Bridging Integrator 1 (BIN1) protein levels are increased, accompanied by a swelling of endosomes and subsequent dysregulation of endosomal trafficking of Ca_V1.2. Ca_V1.2 and RyR2 channels are basally super-clustered at the dyads and lose β-AR responsivity. Reduced phosphorylation of cTnI and cMyBP-C result in systolic and diastolic dysfunction. BIN1 knockdown in aging recovers RyR2 clustering plasticity and Ca²⁺ transient responsivity to β-AR stimulation. Phosphorylation of cMyBP-C is basally restored, and contractility is recovered to youthful levels. Thus, BIN1 knockdown rejuvenates the aging heart. Created with BioRender.com.