This project focuses on a new cardiac signaling pathway by which mitochondria regulate cytoplasmic regulatory proteins and surface membrane turnover. The pathway relies on the accumulation by mitochondria of coenzyme A (CoA) to a high concentration, such that free CoA gradients to the cytoplasm are greater than 50 to1. For this reason, transient openings of nonselective permeability transition pores (PTP's) in the inner mitochondrial membrane can generate micromolar CoA transients in the cytoplasm without significantly depleting other mitochondrial substrates. CoA transients are then converted to acyl CoA transients because acyl CoA sythetases are limited by the prevailing free cytoplasmic CoA concentration. Numerous signaling proteins will be affected. In extreme metabolic stress, as occurs upon reoxygenation of ischemic cardiac tissue, palmitoylation of surface membrane proteins via this pathway evidently leads to their clustering in liquid ordered (Lo) membrane domains followed by their internalization as massive endocytosis (pMEND). In this context pMEND is detrimental, but preliminary data indicate that the pMEND pathway contributes to constitutive sarcolemma turnover and regulates the activities of Na/K pumps in cardiac myocytes. Using multiple mice lines with deficiencies in this pathway, as well as drugs to block PTP's, we will determine what physiological and pathological roles pMEND-related endocytosis plays in cardiac myocytes. The project will provide insight into fundamental cell regulatory mechanisms that have a high impact for an understanding of the leading cause of death in the developed world.
We recently discovered a cardiac signaling pathway in which mitochondria release a metabolite, coenzyme A, that is used to activate cytoplasmic fatty acids that are then linked to membrane proteins by a process called palmitoylation. At the cell surface, this pathway leads to the removal of proteins into membrane vesicles, and in the wake of ischemic events in the heart large fractions of the cell surface can be removed. We will now determine how this pathway is regulated, is used by, and affects heart cells both in normal physiology and pathological circumstances close to the threshold of death.
