Hashem et al.pdf

Rationale: Lysosomal associated membrane protein type-2 (LAMP-2) is a highly conserved, ubiquitous protein

that is critical for autophagic flux. Loss of function mutations in the LAMP-2 gene cause Danon disease, a rare

X-linked disorder characterized by developmental delay, skeletal muscle weakness, and severe cardiomyopathy.

We previously found that human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from

Danon patients exhibited significant mitochondrial oxidative stress and apoptosis. Understanding how loss of

LAMP-2 expression leads to cardiomyocyte dysfunction and heart failure has important implications for the

treatment of Danon disease as well as a variety of other cardiac disorders associated with impaired autophagy.

Objective: Elucidate the pathophysiology of cardiac dysfunction in Danon disease.

Methods and results: We created hiPSCs from two patients with Danon disease and differentiated those cells into

hiPSC-CMs using well-established protocols. Danon hiPSC-CMs demonstrated an accumulation of damaged mitochondria,

disrupted mitophagic flux, depressed mitochondrial respiratory capacity, and abnormal gene expression

of keymitochondrial pathways. Restoring the expression of LAMP-2B, the most abundant LAMP-2 isoformin

the heart, rescued mitophagic flux as well as mitochondrial health and bioenergetics. To confirm our findings in

vivo,we evaluated Lamp-2 knockout (KO) mice. Impaired autophagic flux was noted in the Lamp-2 KO mice compared

toWT reporter mice, as well as an increased number of abnormal mitochondria, evidence of incomplete

mitophagy, and impaired mitochondrial respiration. Physiologically, Lamp-2 KO mice demonstrated early features

of contractile dysfunction without overt heart failure, indicating that the metabolic abnormalities associated

with Danon disease precede the development of end-stage disease and are not merely part of the secondary

changes associated with heart failure.

Conclusions: Incomplete mitophagic flux and mitochondrial dysfunction are noted in both in vitro and in vivo

models of Danon disease, and proceed overt cardiac contractile dysfunction. This suggests that impaired mitochondrial

clearance may be central to the pathogenesis of disease and a potential target for therapeutic

intervention.