The role of mitochondrial dysfunction in white adipose tissues (WAT) under different metabolic conditions is not well understood. Here, we report that under high fat diet (HFD) conditions, endogenous production of APP is significantly induced and, instead of being secreted, the protein is highly enriched in WAT mitochondria. To better understand the role of APP, we established an inducible model by directing the full-length APP with a mitochondrial targeting presequence quantitatively to mitochondria, selectively in adipocytes. We validated that APP mRNA and protein levels were significantly elevated in subcutaneous WAT, and the protein was markedly accumulated in isolated mitochondria from sWAT. EM imaging suggested widespread loss of mitochondrial cristae. Respiratory measurements on a Seahorse instrument revealed a rapid impairment in mitochondrial functions in sWAT, concomitant with an increase in adipocyte size within a few days. APP transgenic mice displayed significantly enhanced fat mass, along with impaired glucose tolerance and reduced insulin sensitivity under a long term HFD challenge. By H and E staining, we observed widespread inflammatory cell infiltration in WAT, and consistent with the adipose tissue dysfunction, we also noticed massive hepatic steatosis. Adiponectin levels in plasma and sWAT were significantly reduced. We specifically eliminated endogenous APP in WAT through a conditioned knock-out mouse model (Appflox/flox) to demonstrate that adipocyte-specific deletion of APP can ameliorate high fat diet-induced mitochondrial dysfunction.
In summary, accumulated APP in WAT mitochondria significantly induces mitochondrial dysfunction in adipocytes, leading to unhealthy adipose tissue expansion and eventually resulting in obesity and systemic insulin resistance.
Y.A. An: None. P.E. Scherer: None.