Hashem et al.pdf

<p>Rationale: Lysosomal associated membrane protein type-2 (LAMP-2) is a highly conserved, ubiquitous protein</p>that is critical for autophagic flux. Loss of function mutations in the LAMP-2 gene cause Danon disease, a rare <p>X-linked disorder characterized by developmental delay, skeletal muscle weakness, and severe cardiomyopathy.</p> <p>We previously found that human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from</p> <p>Danon patients exhibited significant mitochondrial oxidative stress and apoptosis. Understanding how loss of</p> <p>LAMP-2 expression leads to cardiomyocyte dysfunction and heart failure has important implications for the</p> <p>treatment of Danon disease as well as a variety of other cardiac disorders associated with impaired autophagy.</p> <p>Objective: Elucidate the pathophysiology of cardiac dysfunction in Danon disease.</p> <p>Methods and results: We created hiPSCs from two patients with Danon disease and differentiated those cells into</p> <p>hiPSC-CMs using well-established protocols. Danon hiPSC-CMs demonstrated an accumulation of damaged mitochondria,</p> <p>disrupted mitophagic flux, depressed mitochondrial respiratory capacity, and abnormal gene expression</p> <p>of keymitochondrial pathways. Restoring the expression of LAMP-2B, the most abundant LAMP-2 isoformin</p> <p>the heart, rescued mitophagic flux as well as mitochondrial health and bioenergetics. To confirm our findings in</p> <p>vivo,we evaluated Lamp-2 knockout (KO) mice. Impaired autophagic flux was noted in the Lamp-2 KO mice compared</p> <p>toWT reporter mice, as well as an increased number of abnormal mitochondria, evidence of incomplete</p> <p>mitophagy, and impaired mitochondrial respiration. Physiologically, Lamp-2 KO mice demonstrated early features</p> <p>of contractile dysfunction without overt heart failure, indicating that the metabolic abnormalities associated</p> <p>with Danon disease precede the development of end-stage disease and are not merely part of the secondary</p> <p>changes associated with heart failure.</p> <p>Conclusions: Incomplete mitophagic flux and mitochondrial dysfunction are noted in both in vitro and in vivo</p> <p>models of Danon disease, and proceed overt cardiac contractile dysfunction. This suggests that impaired mitochondrial</p> <p>clearance may be central to the pathogenesis of disease and a potential target for therapeutic</p> <p>intervention.</p>