The pathogenesis of alcohol-induced liver injury is normally accompanied by profound changes in the composition and concentration of lipids and lipoproteins at each stage. Plasma high density lipoproteins (HDL) is a normal constituent in both rat and human, and its role in the regulation of body cholesterol via reverse cholesterol transport is well documented. Apoprotein (apo)A and E, major components of HDL play important regulatory roles in cholesterol homeostasis. Recently, Apo J, a 70-kDa protein has been identified as an integral component of human plasma HDL and its role in the reverse cholesterol transport has been suggested. Sulfated glycoprotein-2 (SGP-2), is the major secretory protein product of sertoli cells in rat and has ben suggested as a homolog of human plasma apo J. [We have previously shown that chronic ethanol affects the synthesis, glycosylation and secretion of many N- and O-glycosylated proteins including HDL-apo E and transferrin. The physiological role of Apo J remains unclear]. No studies have been done on Apo J as an integral component of HDL in rats. Our preliminary results clearly established the presence of Apo J in rat liver, plasma and plasma HDL fractions and its involvement in the [reverse cholesterol transport] process. Further, our results suggest that Apo J is strongly susceptible to deleterious actions of chronic ethanol [as evidenced by the loss of sialic acid residues from Apo J]. These facts provide a compelling rationale for studying the effects of chronic ethanol on the structure and function of Apo J in rats.
The specific aims of this proposal, using rat as a model are; 1. to determine plasma Apo J levels and its distribution in HDL subspecies and effects of chronic ethanol treatment on the normal distribution profile. 2. to study how chronic ethanol affects the synthesis, post-translational modifications and secretion of Apo J, 3. to investigate the microheterogeneity pattern of Apo J [and effects of ethanol on sialic acid composition of apo J, thus, exploring its potential as a viable marker for alcohol consumption]. 4. to evaluate the participation of Apo J in HDL assembly and its role in the 'Reverse cholesterol transport' and alterations, if any, induced by chronic ethanol, and 5. to explore the structural designing of rat HDL=Apo J, its similarities and differences with rat SGP-2 and human apo J and effects of chronic ethanol on the structural framework of rat HDL-Apo J. The systems to be used to accomplish the above specific aims: (i) the macrophage and hepatocyte system to study reverse cholesterol transport, (ii) Apo J purification by SDS-PAGE and immunoaffinity columns, (iii) hepatocyte study reverse cholesterol transport, (ii) Apo J purification by SDS-PAGE and immunoaffinity columns, (iii) hepatocyte system for the synthesis, glycosylation and subcellular transit studies on Apo J,(v) iso- electric focussing for microheterogeneity studies, and (vi) HPLC and gas chromatography for studies on structural aspects of rat Apo J. An animal model provides a good tool to explore the metabolic and physiological activities of biological systems. Studies on alcohol and HDL remain unclear. The results of this study may provide a new insight into HDL metabolism and role of Apo J under alcoholic conditions. [More significantly, our recent findings suggest the viability of the index of the loss of sialic acid residues from Apo J as a clinical marker for chronic alcohol consumption. This method may prove to be simple, improved and cost-effective compared to those currently used in clinics.
| Ghosh, P; Hale, E A; Lakshman, R (1999) Long-term ethanol exposure alters the sialylation index of plasma apolipoprotein J (Apo J) in rats. Alcohol Clin Exp Res 23:720-5 |
