Studies Of Pseudohypoparathyroidism And Related Disorders

假性甲状旁腺功能减退症及相关疾病的研究

• 批准号: 10697751
• 负责人: Lee Weinstein
• 金额: $ 77.02万
• 依托单位: NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10697751
• 关键词: Adult; Age; Alleles; Antibodies; Autoimmunity; Binding; Brain; Calcium; Cell Surface Receptors; Central Nervous System; Characteristics; Chondrocytes; Chromogranin A; Clinical; Congenital Disorders; Cyclic AMP; DNA Methylation; DNA Sequence Alteration; Defect; Deletion Mutation; Development; Disease; Elements; Energy Metabolism; Epiphysial cartilage; Exons; Fathers; GNAS gene; GTP-Binding Protein alpha Subunits, Gs; Generations; Genes; Genetic; Genetic Transcription; Goals; Gonadotropins; Growth; Gs alpha mutations; Hereditary Disease; Heterotopic Ossification; Heterotrimeric GTP-Binding Proteins; Hormones; Human; Hypercalcemia; Hyperparathyroidism; Hypothalamic structure; Inherited; Insulin Resistance; Invaded; Kidney; Knock-out; Knockout Mice; Lesion; Link; Messenger RNA; Metabolic; Modeling; Molecular; Morbid Obesity; Mothers; Mus; Mutate; Mutation; Neurosecretory Systems; Obesity; Operative Surgical Procedures; Osteoblasts; PTH gene; Paper; Parathyroid Hormone Receptor; Parathyroid Neoplasms; Pathogenesis; Patients; Physiologic Ossification; Progressive osseous heteroplasia; Protein Isoforms; Proteins; Proximal Kidney Tubules; Pseudohypoparathyroidism; Pseudopseudohypoparathyroidism; Publishing; Reporting; Resistance; Resistance development; Second Messenger Systems; Signal Pathway; Signal Transduction; Signaling Molecule; Skin; Somatotropin-Releasing Hormone; Thyrotropin; Tissues; United States National Institutes of Health; Vitamin D; Vitamin D Analog; calcification; clinical investigation; clinical phenotype; gene product; glucose metabolism; histone methylation; hormone resistance; hormone sensitivity; imprint; mouse model; neurobehavioral; overexpression; paternal imprint; promoter; response; sex; soft tissue; subcutaneous; transmission process; virtual

Albright hereditary osteodystrophy (AHO) is a congenital disorder resulting from autosomal dominant inheritance of heterozygous mutations in the GNAS gene which disrupt expression of the heterotrimeric G protein Gs-alpha. Gs-alpha is a ubiquitously expressed signaling molecule that is required for the intracellular generation of the second messenger molecule cyclic AMP in response to stimulation of hormone and other cell-surface receptors. Features of AHO include short stature, subcutaneous ossifications, brachydactyly, and neurobehavioral and developmental abnormalities. Patients who inherit the disease from their mother also develop resistance to multiple hormones which activate Gs-alpha signaling pathways (eg. parathyroid hormone PTH, thyroid stimulating hormone, gonadotropins, and growth hormone releasing hormone) as well as obesity, and this form of the disease is also known as pseudohypoparathyroidism type 1A (PHP1A). In contrast patients who inherit the disease from their father only develop features of AHO, and this is also referred to as pseudopseudohypoparathyroidism (PPHP). We and others have shown in mice and humans that Gs-alpha is imprinted in a tissue-specific manner. In some hormone target tissues Gs-alpha is expressed primarily from the maternal allele, and therefore maternal inheritance of Gs-alpha mutations results in hormone resistance while paternal inheritance of these same mutations does not. A few patients with similar mutations develop a severe form of ectopic ossification called progressive osseous heteroplasia (POH) in which the ossifications form cast-like plates and invade deeper soft tissues. While it has reported that POH only occurs when the mutation is inherited paternally, we have recently studied two cases in which POH resulted from maternal transmission. We have generated mice with Gs-alpha deficiency in chondrocytes or osteoblasts, which provides evidence that the Gs-alpha deficiency in growth plate chondrocytes is likely the direct cause of the short stature and brachydactyly observed in AHO. GNAS (Gnas in mice) is a very complicated imprinted gene with multiple gene products generated by several alternative promoters and first exons. NESP55 is a chromogranin-like protein that is maternally expressed while XL-alpha-s is a paternally expressed Gs-alpha isoform with a long amino-terminal extension. Both are primarily expressed in neuroendocrine tissues. We have shown that NESP imprinting is not established until postimplantation development. We identified another alternative first exon (exon 1A) that generates paternally expressed untranslated mRNAs and that is a maternal germline imprint mark. We have shown that this region has allele-specific differences in DNA and histone methylation. We also have shown that the Gs-alpha promoter and first exon also has allele-specific differences in histone methylation which correlates to its tissue-specific imprinting, even though this region does not undergo DNA methylation. We have shown that PHPIB (parathyroid hormone resistance in the absence of AHO) is virtually always associated with loss of maternal exon 1A imprinting. A detailed analysis of GNAS imprinting in PHP IB patients showed that familial cases tend to only have abnormal exon 1A imprinting associated with a deletion mutation within a closely-linked gene, while sporadic cases often have additional imprinting defects involving NESP and XL-alpha-s. We have generated exon 1A knockout mice, and show that this region is not required for Nesp and XL-alpha-s imprinting, but is required for tissue-specific Gs-alpha imprinting. Mice with paternal exon 1A deletion, which have Gs-alpha overexpression in renal proximal tubules due to loss of paternal Gs-alpha imprinting, have increased parathyroid hormone sensitivity with low circulating parathyroid hormone levels. We have also published a paper showing that PHPIB patients who are inadequately treated with calcium and vitamin D analogs can develop tertiary hyperparathyroidism (autonomous parathyroid tumors leading to hypercalcemia) which need to be removed by surgery. We have preliminarily identified a factor that binds to the exon 1A region on the unmethylated paternal allele and may be required for tissue-specific Gs-alpha imprinting. Studies confirming this are ongoing. A recent mouse model showed that loss of Gs-alpha in renal proximal tubules in mice leads to renal PTH resistance with reduced generation of 1, 25 vitamin D (the activated form). Although obesity has been previously considered to be a general feature of AHO present in both PHP1A and PPHP patients, we have recently shown that obesity is a specific feature of PHP1A and therefore is a result of loss of Gs-alpha expression in one or more tissues due to the combined effects of maternal mutation and paternal imprinting. These clinical observations are consistent with findings in mice with germline Gs-alpha mutations showing that mice with maternal mutations develop severe obesity with lower energy expenditure and insulin resistance and that these effects are reversed by the presence of a paternal 1A deletion which reverses Gs-alpha imprinting (Z01-DK043313-03). Results in a brain-specific Gs-alpha knockout model suggest that this imprinting effect is localized to one or more regions in the central nervous system (Z01-DK043315-01). Most recently we localized this imprinting effect to the dorsomedial hypothalamus. We have conducted studies in the NIH Obesity/Clinical Phenotyping Center examining the metabolic characteristics of AHO and related patients in detail to better characterize the metabolic defect and gain understanding of its pathogenesis. Results to date show that adult PHP1A patients, similar to the mouse models, are more insulin resistant, even when compared to other subjects matched for age, sex, and degree of adiposity, indicating that these patients have a primary defect in glucose metabolism. In addition we have shown that mice with the equivalent genetic mutation can develop skin calcifications, although they are associated with fibrous lesions and not true ossifications. Studies are ongoing to confirm that a putative transcriptional element is involved in tissue-specific Gs imprinting. We have also identified two patients with acquired parathyroid hormone resistance and features of autoimmunity associated with antibodies to the parathyroid hormone receptor which block PTH signaling.

奥尔布赖特遗传性骨营养不良 (AHO) 是一种先天性疾病，由常染色体显性遗传 GNAS 基因杂合突变引起，该突变破坏异三聚体 G 蛋白 Gs-α 的表达。 Gs-α 是一种普遍表达的信号分子，是响应激素和其他细胞表面受体刺激而在细胞内生成第二信使分子环 AMP 所必需的。 AHO 的特征包括身材矮小、皮下骨化、短指、神经行为和发育异常。从母亲那里继承该疾病的患者还会对激活 Gs-α 信号通路的多种激素（例如甲状旁腺激素 PTH、促甲状腺激素、促性腺激素和生长激素释放激素）产生抵抗力，并出现肥胖，这种疾病也称为 1A 型假性甲状旁腺功能减退症 (PHP1A)。相比之下，从父亲那里继承该疾病的患者只会出现 AHO 的特征，这也称为假性甲状旁腺功能减退症 (PPHP)。我们和其他人已经在小鼠和人类身上证明，Gs-α 以组织特异性方式印记。在一些激素靶组织中，Gs-α 主要由母体等位基因表达，因此母系遗传的 Gs-α 突变会导致激素抵抗，而父系遗传的这些相同突变则不会。一些具有类似突变的患者会出现一种严重的异位骨化，称为进行性骨异型增生 (POH)，其中骨化形成铸型板并侵入更深的软组织。虽然有报道称 POH 仅在突变为父系遗传时才会发生，但我们最近研究了两例 POH 是由母体传播引起的。我们培育了软骨细胞或成骨细胞中 Gs-α 缺乏的小鼠，这提供了证据表明生长板软骨细胞中的 Gs-α 缺乏可能是 AHO 中观察到的身材矮小和短指的直接原因。 GNAS（小鼠中的Gnas）是一个非常复杂的印记基因，由多个替代启动子和第一个外显子产生多个基因产物。 NESP55 是一种母源表达的嗜铬粒蛋白样蛋白，而 XL-α-s 是父源表达的 Gs-α 亚型，具有长氨基末端延伸。两者主要在神经内分泌组织中表达。我们已经证明，NESP 印记直到植入后发育才建立。我们确定了另一个替代的第一外显子（外显子 1A），它产生父系表达的非翻译 mRNA，并且是母系种系印记标记。我们已经证明该区域在 DNA 和组蛋白甲基化方面具有等位基因特异性差异。我们还表明，Gs-alpha 启动子和第一个外显子在组蛋白甲基化方面也具有等位基因特异性差异，这与其组织特异性印记相关，即使该区域不经历 DNA 甲基化。我们已经证明 PHPIB（没有 AHO 时的甲状旁腺激素抵抗）实际上总是与母体外显子 1A 印记的丧失相关。对 PHP IB 患者 GNAS 印记的详细分析表明，家族性病例往往仅具有与紧密连锁基因内的缺失突变相关的异常外显子 1A 印记，而散发病例通常具有涉及 NESP 和 XL-alpha-s 的额外印记缺陷。我们已经生成了外显子 1A 敲除小鼠，并表明该区域不是 Nesp 和 XL-alpha-s 印记所必需的，但是组织特异性 Gs-alpha 印记所必需的。父系外显子 1A 缺失的小鼠，由于父系 Gs-α 印记的缺失，肾近曲小管中 Gs-α 过度表达，甲状旁腺激素敏感性增加，循环甲状旁腺激素水平较低。我们还发表了一篇论文，表明钙和维生素 D 类似物治疗不充分的 PHPIB 患者可能会出现三级甲状旁腺功能亢进症（导致高钙血症的自主性甲状旁腺肿瘤），需要通过手术切除。我们初步鉴定了一个与未甲基化父本等位基因上的外显子 1A 区域结合的因子，并且可能是组织特异性 Gs-α 印记所必需的。证实这一点的研究正在进行中。最近的小鼠模型表明，小鼠肾近曲小管中 Gs-α 的缺失会导致肾 PTH 抵抗，并减少 1, 25 维生素 D（活化形式）的产生。 虽然肥胖以前被认为是 PHP1A 和 PPHP 患者中存在的 AHO 的一般特征，但我们最近表明，肥胖是 PHP1A 的一个特定特征，因此是由于母体突变和父系印记的综合影响，一个或多个组织中 Gs-α 表达缺失的结果。这些临床观察结果与在具有种系 Gs-α 突变的小鼠中的研究结果一致，表明具有母体突变的小鼠会出现严重肥胖、能量消耗较低和胰岛素抵抗，并且这些影响会因父系 1A 缺失的存在而逆转，从而逆转 Gs-α 印记 (Z01-DK043313-03)。大脑特异性 Gs-alpha 敲除模型的结果表明，这种印记效应局限于中枢神经系统的一个或多个区域 (Z01-DK043315-01)。最近，我们将这种印记效应定位于下丘脑背内侧。我们在 NIH 肥胖/临床表型中心进行了研究，详细检查了 AHO 和相关患者的代谢特征，以更好地表征代谢缺陷并了解其发病机制。迄今为止的结果表明，与小鼠模型类似，成年 PHP1A 患者的胰岛素抵抗程度更高，即使与年龄、性别和肥胖程度匹配的其他受试者相比，这表明这些患者在葡萄糖代谢方面存在主要缺陷。 此外，我们还表明，具有相同基因突变的小鼠可以出现皮肤钙化，尽管它们与纤维性病变有关，而不是真正的骨化。 正在进行的研究证实组织特异性 Gs 印记涉及假定的转录元件。我们还发现了两名患有获得性甲状旁腺激素抵抗的患者，以及与甲状旁腺激素受体抗体相关的自身免疫特征，这些抗体会阻断 PTH 信号传导。