Rationale: Hepatic Scavenger Receptor Class B, Type I receptor (SRBI), a highly glycosylated 82 kDa protein, is primarily responsible for hepatic cholesterol ester uptake from high density lipoproteins (HDL), a process termed Reverse Cholesterol Transport (RCT). PI's central hypothesis is that SRBI is a, hitherto unexplored, potential target for chronic alcohol-induced defective RCT that is due to corresponding impaired SRB1 expression and/or post-translational modifications, which in turn, could affect its intracellular trafficking. The net result would be the concomitant onset of alcoholic hyperlipidemia. Therefore, it is important and clinically relevant to delineate the actions of alcohol on SRB1 function and status in relation to alcoholic hyperlipidemia. Similarly, since dietary betaine has significant lowering effects on plasma and liver lipids, it is equally important to investigate whether betaine elicits its hypolipidemic actions by regulating the expression, post-translational modification and function of SRB1. Preliminary Results: PI has the following preliminary data in support of this proposal: 1. Liver uptake of cholesterol from normal HDL is decreased by 48% (p<0.05) when tested with hepatocytes from alcohol-fed rats compared to the control group. 2. Ethanol down regulates liver SRB1 gene expression by 51% (p<0.05). 3. Ethanol inhibits hepatic relative glycosylation rate of SRB1 by 41% (p<0.05). 4. These effects of ethanol are attenuated by dietary betaine. Based on these data and our novel hypotheses, we wish to accomplish the following specific aims:
Specific Aim 1. Possible action/s of chronic ethanol and betaine on the synergistic functions of SRB1 and HDL in the regulation of RCT and correlation with plasma lipids &lipoproteins, liver lipids and liver histopathology.
Specific Aim 2. Possible action/s of chronic ethanol and betaine in the transcriptional and post- transcriptional regulation of SRB1 expression.
Specific Aim 3. Possible action/s of chronic ethanol and betaine in the regulation of hepatic relative synthetic &glycosylation rates and trafficking of SRB1. Thus, the major emphasis on this R21 grant application will be to establish a central role for SRB1 as a new target of chronic alcohol exposure and can potentially and logically lead to a more detailed R01 application on this novel role of SRB1 status and function in the pathogenesis of alcoholic hyperlipidemia. Finally, it is therapeutically pertinent to test whether dietary betaine can attenuate deleterious actions of ethanol by restoring the normal SRB1 status &function. Methods of Approach: We will accomplish our specific aims using an in vivo animal model &liver cell systems applying molecular biology, immuno-histochemistry and biochemical approaches. PI has a strong molecular biology &biochemical group with expertise in all aspects of this proposal.
It is goal of this exploratory grant application to establish that chronic ethanol exposure affects the cholesterol uptake function of SRB1, a specific receptor for HDL cholesterol leading to alcoholic steatosis. If so, it is clinically important to verify whether this defect is due to impaired SRB1 gene expression, its post-translational modification and its disposition.
| Varatharajalu, Ravi; Garige, Mamatha; Leckey, Leslie C et al. (2014) Adverse signaling of scavenger receptor class B1 and PGC1s in alcoholic hepatosteatosis and steatohepatitis and protection by betaine in rat. Am J Pathol 184:2035-44 |
