[Tumor necrosis factor-alpha upregulates the protein levels of adipose differentiation-related protein in rat differentiated adipocytes].

OBJECTIVE

To investigate the effect and basis of tumor necrosis factor-alpha (TNF-alpha) on the lipid droplet associating protein adipose differentiation-related protein(ADRP) in rat differentiated adipocytes.

METHODS

Differentiated rat adipocytes derived from epididymal fat pads of Sprague-Dawley rats were incubated in the presence or absence of TNF-alpha (25 microg/L). Glycerol level released in the culture medium was determined by a colorimetric assay and served as an index of lipolysis. The protein levels of two lipid droplet associating proteins, perilipin and adipose differentiation-related protein, were examined by immunoblotting analysis. The intracellular lipid droplets were stained by nile red and the localizations of perilipin and ADRP on the lipid droplets were determined by immunostaining.

RESULTS

On day 5 or day 8 after the differentiation of adipocytes, TNF-alpha significantly stimulated lipolysis. The lipolysis response to TNF-alpha occurred apparently at hour 8 and remained high 48 h after the stimulation. TNF-alpha increased the protein levels of ADRP, downregulated perilipin proteins but promoted its phosphorylation level. TNF-alpha caused the lipid droplet dispersion, whereas ADRP and perilipin proteins were remained to associate with the surface of the dispersed lipid droplets.

CONCLUSION

Chronic stimulation of lipolysis by TNF-alpha resulted in the dispersion of the lipid droplets and therefore upregulated the levels of ADRP proteins.