Regulation of PTH-induced Osteoanabolism by Inflammatory Lipids

炎症脂质对 PTH 诱导的骨合成代谢的调节

• 批准号: 8423383
• 负责人: Yin Tintut
• 金额: $ 31.68万
• 依托单位: UNIVERSITY OF CALIFORNIA LOS ANGELES
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-05-08 至 2015-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8423383
• 关键词: Accounting; Adenylate Cyclase; Adult; Affect; Age; Agonist; Anabolic Agents; Anabolism; Antioxidants; Apolipoprotein E; Arteries; Atherosclerosis; Attenuated; Blood Vessels; Bone Density; Bone Matrix; Bone Mineral Contents; C57BL/6 Mouse; Cardiovascular Diseases; Cell Count; Cells; Cholesterol; Chronic; Collagen Type I; Connecticut; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Deposition; Diet; Differentiation Antigens; Disease; Enzymes; Epidemiology; Family; Fatty acid glycerol esters; Fibrinogen; GTP-Binding Proteins; Generations; Genes; Goals; Green Fluorescent Proteins; Health; Hormones; Hyperlipidemia; Immediate-Early Genes; In Vitro; Inflammatory; Inflammatory Response; Injection of therapeutic agent; Intervention; Kidney Diseases; Label; Lipids; Lipoproteins; Literature; Liver; Low-Density Lipoproteins; Marrow; Measures; Modification; Molecular; Mus; Nerve Growth Factors; Nuclear Orphan Receptor; Osteoblasts; Osteocytes; Osteoporosis; Paraoxonase 1; Parathyroid Hormone Receptor; Parathyroid gland; Pathway interactions; Patients; Pharmacotherapy; Phospholipids; Plasma; Population; Prevalence; Prevention; Production; Public Health; Rattus; Reaction; Reactive Oxygen Species; Recombinants; Regimen; Regulation; Regulator Genes; Research Personnel; Role; Signal Pathway; Signal Transduction; Site; Stem cells; Teriparatide; Testing; Therapeutic; Thick; Tissues; Transgenes; Transgenic Mice; Treatment Efficacy; United States; Universities; attenuation; base; bone; bone metabolism; bone morphogenetic protein 2; bone turnover; chemokine; cytokine; hormone resistance; hormone sensitivity; hormone therapy; in vitro testing; in vivo; inhibitor/antagonist; insight; member; mouse model; novel; novel strategies; osteoblast differentiation; osteogenic; overexpression; oxidant stress; oxidation; particle; progenitor; promoter; protein activation; receptor; receptor expression; response; trafficking

DESCRIPTION (provided by applicant): Parathyroid hormone (PTH) is a key regulator of bone metabolism and is used as anabolic pharmacotherapy for treatment of osteoporosis. Recent evidence suggests that lipids may affect bone metabolism and that intermittent PTH therapy may fail in the presence of hyperlipidemia. This is clinically important because hyperlipidemia is prevalent in patients with osteoporosis even accounting for age. In the hyperlipidemic condition, bioactive derivatives of low-density lipoproteins (LDL) are generated in the subendothelial space of tissues, triggering chronic inflammatory responses including oxidant stress and expression of cytokines and chemokines. We have found that these inflammatory lipoproteins/lipids are also present in bone and that they inhibit osteoblastic differentiation. In additional studies, we and other investigators demonstrated that hyperlipidemic mice have reduced bone density compared to WT mice. Our preliminary studies, both in vitro and in vivo, now show that lipids inhibit PTH-induced immediate early genes, including Nurr1, a transcriptional regulator of osteoblastic genes, by attenuating cyclic AMP production and that hyperlipidemia blunts PTH-induced osteoanabolism in vivo, primarily in cortical bone. These findings strongly suggest that hyperlipidemia induces PTH resistance. Whether PTH resistance is at the molecular and/or tissue level remains to be determined. Since osteoporosis and hyperlipidemia remain widespread despite treatment, understanding effects of lipids on basal (endogenous) and intermittent (exogenous) PTH may provide new approaches to osteoporosis. We hypothesize that inflammatory lipoproteins, which are increased in hyperlipidemia, reduce PTH anabolic effects. Based on our preliminary studies, in Specific Aim 1, we will test in vitro whether the inhibitory mechanism of lipids on PTH-induced cyclic AMP production is at the level of PTH receptor expression, receptor trafficking, downstream at the level of G-protein activation, or further downstream at the level of adenylate cyclase activation. In Specific Aim 2, we will identify the level at which lipid-induced PTH resistance occurs in vivo: at the level of differentiation of marrow progenitors toward osteogenic vs. adipogenic lineages; anabolic responses of mature osteoblasts/osteocytes; and/or transient expression of osteoclastogenic factors by osteoblasts. We will generate Ldlr-/- mice that express green fluorescent protein targeted to osteoblasts and osteocytes. In Specific Aim 3, we will test whether reducing hyperlipidemia or inhibiting lipid oxidation will reverse PTH resistance in vivo by measuring bone density, histomorphometric parameters and bone turnover markers in the hyperlipidemic (Ldlr-/-) mice that are treated with liver X receptor agonists or that overexpress the anti-oxidant enzyme, paraoxonase-1. These proposed studies will provide insights into how inflammatory lipids inhibit PTH-induced osteoanabolism, pinpoint the site of inhibitory action within the PTH signaling pathway, and demonstrate approaches to reverse lipid-induced PTH dysregulation.

描述(申请人提供)：甲状旁腺激素(PTH)是骨代谢的关键调节剂，用于治疗骨质疏松症的合成代谢药物。最近的证据表明，血脂可能会影响骨代谢，间歇性甲状旁腺素治疗在高脂血症的情况下可能失败。这在临床上很重要，因为高脂血症在骨质疏松症患者中很普遍，即使考虑到年龄。在高脂血症条件下，低密度脂蛋白(LDL)的生物活性衍生物在组织的内皮下间隙产生，引发包括氧化应激、细胞因子和趋化因子表达在内的慢性炎症反应。我们发现，这些炎性脂蛋白/脂类也存在于骨骼中，它们抑制成骨细胞的分化。在其他研究中，我们和其他研究人员证明，与WT小鼠相比，高脂血症小鼠的骨密度降低。我们在体外和体内的初步研究表明，脂类通过抑制环磷酸腺苷的产生来抑制甲状旁腺素诱导的即刻早期基因，包括成骨基因的转录调节因子Nurr1；高脂血症可以钝化甲状旁腺素诱导的体内骨合成代谢，主要是在皮质骨中。这些发现强烈提示高脂血症可诱导甲状旁腺素抵抗。甲状旁腺激素抵抗是否在分子和/或组织水平上仍有待确定。由于骨质疏松症和高脂血症在治疗后仍然普遍存在，了解血脂对基础(内源性)和间歇性(外源性)甲状旁腺素的影响可能会提供治疗骨质疏松症的新方法。我们假设在高脂血症中增加的炎性脂蛋白减少了甲状旁腺素的合成代谢作用。在前期研究的基础上，具体目标1，我们将在体外检验脂质对甲状旁腺素诱导的环磷酸腺苷生成的抑制机制是在甲状旁腺素受体表达、受体转运水平，还是在G蛋白激活的下游水平，还是在腺苷环化酶激活的下游水平。在特定的目标2中，我们将确定体内发生脂质诱导的甲状旁腺素抵抗的水平：骨髓前体细胞向成骨和成脂分化的水平；成熟成骨细胞/骨细胞的合成代谢反应；和/或成骨细胞瞬时表达破骨细胞因子。我们将产生表达针对成骨细胞和骨细胞的绿色荧光蛋白的Ldlr-/-小鼠。在具体目标3中，我们将通过测量接受肝脏X受体激动剂治疗或过度表达抗氧化酶对氧磷酶-1的高脂血症(Ldlr-/-)小鼠的骨密度、组织形态计量学参数和骨转换标志物，来测试降低高脂血症或抑制脂质氧化是否会在体内逆转PTH抵抗。这些拟议的研究将提供关于炎性脂类如何抑制PTH诱导的骨合成代谢的见解，准确地确定PTH信号通路中抑制作用的位置，并展示逆转脂质诱导的PTH失调的方法。