Aim: 

Excess energy is stored as neutral lipids in lipid droplets whose surface is coated by PAT proteins, each playing distinct cellular function. The adipocyte differentiation-related protein (ADRP) and tail-interacting protein (TIP47) are expressed almost ubiquitously, whereas the oxidative tissue-enriched PAT protein (OXPAT) is expressed in specific tissues such as liver where till now only ADRP expression is documented.

Methods: 

In this study we investigated OXPAT and TIP47 transcripts and the effects exhibited in their expression by a lipid excess, using fat-enriched hepatocytes to mimic different degrees of steatosis. Primary adult rat hepatocytes were exposed to fatty acids (FFAs) for 12, 24 and 36h. Afterwards lipid accumulation was estimated by triacylglycerol quantification and PAT protein as well as of PPAR-gamma expression were evaluated by real-time RT-PCR.

Results: 

Hepatocytes exposed to FFAs showed progressive lipid accumulation accompanied by up-regulation of PPAR-gamma expression together with an induction of PAT protein expression. At 12h, OXPAT and TIP47 expression was up-regulated. At longer times, the level of OXPAT transcripts remained high, whereas that of TIP47 slowly declined. Conversely, ADRP expression showed a time-dependent increase with exposure to FFAs.

Conclusion: 

These results demonstrate the presence of OXPAT and TIP47 transcripts in rat hepatocytes, as well as their up-regulation with lipid accumulation. Up-regulation of OXPAT and TIP47 may represent an early response to lipid accumulation while, in correspondence with a lipid overload, up-regulation of ADRP could address lipids towards storage.