Immunohistochemical study of the autophagy marker microtubule-associated protein 1 light chain 3 in normal and steatotic human livers.

Autophagy has been implicated in lipid droplet (LD) turnover. Adipose differentiation-related protein (ADRP) and microtubule-associated protein 1 light chain 3 (LC3) monitor LD and autophagosomes, respectively. We examined whether immunohistochemical staining of ADRP and LC3 can monitor LD and autophagy, and if so, whether autophagy is related to LD turnover in post-mortem human livers. We performed conventional immunohistochemistry of LC3 in paraffin-embedded human livers with different severities of steatosis, obtained at autopsy. Double immunofluorescence microscopy using anti-LC3 and anti-ADRP antibodies was performed to elucidate the relationship between autophagy and LD turnover. LC3 immunohistochemistry reproducibly delineated puncta in normal human livers, which were preferentially located around the central venal zone. The extent of LC3 immunostaining reduced with progressing steatosis. Double immunofluorescence for ADRP and LC3 demonstrated an inverse relationship between ADRP positive areas and LC3 positive areas, as well as the co-localization of ADRP and LC3 on a part of small LD but not large LD. These findings suggest that impaired autophagy promotes steatosis and that autophagy may be implicated in LD turnover.