Autophagy of Fats

New evidence suggests that in periods of starvation or fasting the body may undergo autophagic breakdown of lipids. As most of us understand autophagy is the process where cells self-degrade unused components using lysosomal machinery. To do this cellular components are trapped in double-membrane bound vesicles called autophagosomes that fuse with and are broken down by lysosomes. What the new research posits is that in a similar way, under fasting conditions, cytoplasmic proteins are recruited to lipids to form similar double membrane enclosures. These enclosures, dubbed "autolipophagosomes," can then fuse with the lysosomes for degradation.

For years its been thought that catabolizing lipids has been the task of regulatory proteins and lipases--most notably hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL). But this understanding left a number of aspects unexplained. For example, why the hepatocytes of liver cells could turnover triglycerides and cholesteryl esters so quickly, despite having low concentrations of HSL and ATGL. The new model suggests and shows that an autophagic mechanism may be at work.

One further poitn of interest: the study also showed that the efficiency of this process varied with nutritional status. Mice fed a high-fat diet for an extended period of 16 weeks showed an impaired autophagy-mediated breakdown in the liver. This would force the conclusion that increased fat ingestion might actually decrease fat removal.

Sources:
"Cell Biology Another Way to get rid of fat"
http://www.nature.com/nature/journal/v458/n7242/full/4581118a.html

"Autophagy regulates lipid metabolism" (Original Research Article)
http://www.nature.com/nature/journal/v458/n7242/full/nature07976.html