Studies with apolipoprotein A-II transgenic mice indicate a role for HDLs in adiposity and insulin resistance.
Apolipoprotein A-II (apoA-II) is the second most abundant protein in HDLs. Genetic studies in humans have provided evidence of linkage of the apoA-II gene locus to plasma free fatty acid (FFA) levels and to type 2 diabetes, and transgenic mice overexpressing mouse apoA-II have elevated levels of both FFA and triglycerides. We now show that apoA-II promotes insulin resistance and has diverse effects on fat homeostasis. ApoA-II transgenic mice have increased adipose mass and higher plasma leptin levels than C57BL/6J control mice. Fasting glucose levels were similar between apoA-II transgenic and control mice, but plasma insulin levels were elevated approximately twofold in the apoA-II transgenic mice. Compared with control mice, apoA-II transgenic mice exhibited a delay in plasma clearance of a glucose bolus. Adipose tissue isolated from fasted apoA-II transgenic mice exhibited a 50% decrease in triglyceride hydrolysis compared with adipose tissue from control mice. This is consistent with a normal response of adipose tissue to the increased insulin levels in the apoA-II transgenic mice and may partially explain the increased fat deposition. Skeletal muscle isolated from fasted apoA-II transgenic mice exhibited reduced uptake of 2-deoxyglucose compared with muscles isolated from control mice. Our observations indicate that a primary disturbance in lipoprotein metabolism can result in several traits associated with insulin resistance, consistent with the hypothesis that insulin resistance and type 2 diabetes can, under certain circumstances, be related primarily to altered lipid metabolism rather than glucose metabolism.
Department of Medicine, University of California, Los Angeles 90095, USA. lcastellani@mednet.ucla.edu
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Castellani
A M
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Goto
A J
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Lusis
D000273:Adipose Tissue / Q000033:anatomy & histology* / Q000378:metabolism; D000818:Animals; D016633:Apolipoprotein A-II / Q000235:genetics / Q000502:physiology*; D001786:Blood Glucose / Q000378:metabolism; D003847:Deoxyglucose / Q000493:pharmacokinetics; D005215:Fasting / Q000378:metabolism; D006868:Hydrolysis; D007333:Insulin Resistance / Q000502:physiology*; D008075:Lipoproteins, HDL / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic / Q000235:genetics; D018482:Muscle, Skeletal / Q000378:metabolism; D012016:Reference Values; D014280:Triglycerides / Q000378:metabolism
D016633:Apolipoprotein A-II; D001786:Blood Glucose; D008075:Lipoproteins, HDL; D014280:Triglycerides; D003847:Deoxyglucose