1.ATP-binding cassette (ABC) transporters form a large superfamily of proteins that mediate the transport of a largc variety of diverse molecules across biological membranes in an ATP-dependent manner.ABC transporter subfamily G member 4, abcg4, involved in lipid metabolism, highly expressed in the brain and eyes, may play an important role in the neurodegenerative (Alzheimers) disease, but direct evidence in vivo was lacking.In the present study, by injecting the synthesized small interference RNA (siRNA) targeting to abcg4 into the Intracerebroventricular region of the brain, we found that when the expression of abcg4 in the brain was successfully inhibited, the amyloid beta precursor protein APPs expression was greatly upregulated, and some other genes related to lipid metabolism were changed accordingly in the brain.These data we generated in the study will help us better understand the link between the transport of cholesterol/lipid in the brain and the pathogenesis of Alzheimers disease (AD).2.Our previous study using abcg4-knock-out/GFP knock-in mouse has indicated an increased gonadal fat/body weight ratio and suppressed brain gluconeogenesis in female mouse, compared to its wildtype littermate.It was found that expression of lipid-related genes such as HMGS, FAS, HMGR, SREBP2 and SR-B 1 in the brains of Abcg4 knockout female mice were significantly upregulated.The relation between lipid homeostasis and APP production will be further studied.