Antiadipogenic Influence of HIV Protease Inhibitors

拟议研究的主要目的是阐明接受HIV蛋白酶抑制剂（PI）治疗的HIV+患者中脂肪代谢障碍综合征（LDS）的分子基础。 LDS的特征在于皮下脂肪组织的脂肪萎缩伴随内脏脂肪组织的肥大。LDS患者通常表现出胰岛素抵抗和高血糖症的体征。 我们的中心假设是脂肪萎缩与PI对皮下脂肪细胞的选择性萎缩作用有关，导致内脏脂肪代偿性增加。 增加的内脏肥胖促进胰岛素抵抗、增加的非酯化脂肪酸到肝脏的流量和增加的极低密度脂蛋白-甘油三酯产生和分泌。 我们使用模型前脂肪细胞系（3 T3-L1和-F442 A）的初步结果表明，几种PI抑制前脂肪细胞分化和/或拮抗脂肪细胞表型（促进甘油三酯的损失，脂肪细胞特异性蛋白表达的损失和可能通过凋亡机制降低生存力）。 因此，PI可能通过损害脂肪细胞活力和/或通过抑制脂肪生成防止替代丢失的脂肪细胞来促进LDS患者的皮下脂肪萎缩。 我们假设PI通过阻止脂肪形成转录因子CCAAT/增强子结合蛋白（C/EBP）α和过氧化物酶体增殖物激活受体（PPAR）γ的表达来阻断脂肪形成，因为这些是PI抑制的最早可观察到的分子标志物。 待研究的可能阻断C/EBPalpha和/或PPARgamma表达的潜在PI依赖性效应包括：1）抑制C/EBPalpha和PPARgamma基因表达的C/EBP β/δ依赖性转录激活，2）未能抑制C/EBPalpha基因表达的C/EBP未分化蛋白（CUP）/AP-2 α和Sp1依赖性抑制，3）未能抑制抗脂肪形成Wnt信号通路。我们假设皮下脂肪细胞比内脏脂肪细胞更容易受到PI的拮抗作用。 将从皮下和内脏贮库中分离人原代脂肪细胞，并检查PI诱导的差异效应。 待研究的潜在PI依赖性机制包括：1）TNF α信号转导途径中下游信号传导组分的激活和2）GLUT 4葡萄糖转运蛋白功能的抑制。 将使用小鼠体内前脂肪细胞植入技术来测试PI作用的拟议分子机制。 拟议研究的长期目标是促进缺乏脂肪萎缩潜力的抗HIV治疗剂的设计。

The primary objective of the proposed studies is to elucidate the molecular basis of the lipodystrophy syndrome (LDS) in HIV+ patients treated with HIV protease inhibitors (PIs). LDS is characterized by lipoatrophy of subcutaneous adipose tissue with accompanying hypertrophy of visceral adipose tissue. Patients with LDS often show signs of insulin resistance and hypertriglyceridemia. Our central hypothesis is that the lipoatrophy is related to a selective atrophic effect of PIs on the subcutaneous adipocyte leading to a compensatory increase in visceral adiposity. The increased visceral adiposity promotes insulin resistance, increased flux of non-esterified fatty acid to the liver and increased very low density lipoprotein- triglyceride production and secretion. Our preliminary results using model preadipocyte cell lines (3T3-L1 and -F442A) demonstrate that several PIs inhibit preadipocyte differentiation and/or antagonize the adipocyte phenotype (promote loss of triglyceride, loss of adipocyte-specific protein expression and decreased viability perhaps via an apoptotic mechanism). Thus, PIs may promote subcutaneous lipoatrophy in patients with LDS by compromising adipocyte viability and/or preventing replacement of lost adipocytes by inhibiting adipogenesis. We hypothesize that PIs block adipogenesis by preventing expression of the adipogenic transcription factors CCAAT/enhancer-binding protein (C/EBP) alpha and peroxisome proliferator-activated receptor (PPAR) gamma as these are the earliest observable molecular markers to be repressed by PIs. Potential PI-dependent effects to be investigated and that may block expression of C/EBPalpha and/or PPARgamma include: 1) Inhibition of C/EBPbeta/delta-dependent transcriptional activation of C/EBPalpha and PPARgamma gene expression, 2) Failure to derepress C/EBP undifferentiated protein (CUP)/AP-2alpha- and Sp1-dependent repression of C/EBPalpha gene expression and 3) Failure to inactivate antiadipogenic Wnt signaling pathways. We hypothesize that subcutaneous adipocytes are more susceptible than visceral adipocytes to the antagonistic effects of PIs. Human primary adipocytes will be isolated from subcutaneous and visceral depots and examined for differential PI-induced effects. Potential PI- dependent mechanisms to be investigated include: 1) Activation of downstream signaling components in the TNFalpha signal transduction pathway and 2) Inhibition of GLUT4 glucose transporter function. An in vivo preadipocyte implantation technique in mice will be used to test proposed molecular mechanisms of PI action. The long term objective of the proposed research is to facilitate the design of anti-HIV therapeutics that lack lipoatrophic potential.