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Light-Induced Changes in Retinoic Acid Critical to Liver

Constant darkness may lead to molecular changes underlying defective hepatic fat metabolism

WEDNESDAY, Nov. 26 (HealthDay News) -- Exposure to light leads to synthesis of all-trans retinoic acid (ATRA) not only in the retina, but also in the general blood circulation, thereby boosting hepatic lipid homeostasis, researchers report in the December issue of Endocrinology.

Wenqiang Pang, Ph.D., of Nanjing University of Science & Technology in Nanjing, China, and colleagues used genetically engineered mice to identify the mechanism by which environmental light signals changes in gene expression and physiological functions in peripheral tissues. In particular, they investigated the relationship between light-mediated increase in retinal and circulatory ATRA and changes in hepatic fat genes encoding murine procolipase (mClps), and pancreatic lipase related protein 2 (mPlrp2), involved in postnatal development and body weight regulation.

The results suggest that mice living under constant darkness had decreased circulatory levels of ATRA, which were increased by light exposure. Hepatic fat genes (mPlrp2 and mClps), but not hepatic lipase (mHl), were activated in response to lack of light, leading to lowered hepatic and serum triglycerides and liver weight.

"The decline of retinoic acid results in decreasing Cd73 expression and increasing 5'-AMP levels of blood, leading to the expression of mPlrp2 and mClps, which causes hydrolysis of hepatic fat and retinyl esters," the authors conclude. "Our results suggest environmental light influences hepatic lipid homeostasis by light-modulated retinoic acid signaling associated with mPlrp2 and mClps gene expression in livers."

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