Mitigating mitochondrial epigenetics in bone remodeling by hydrogen sulfide

 描述（由申请方提供）：临床研究报告称，出生时患有严重高同型半胱氨酸血症（HHcy）的儿童，由于胱硫醚-β-合成酶（CBS）基因缺陷，导致血浆同型半胱氨酸（Hcy）水平升高，发生骨骼畸形，骨骼较弱。虽然线粒体功能障碍已参与骨病理学，改变线粒体（Mito）表观遗传学和动力学，促成脆弱的骨尚未研究。本项目的长期目标是了解遗传性HHcy过程中骨结构/功能的有丝分裂-表观遗传重建和变化的机制。线粒体动力学的改变干扰骨细胞（破骨细胞/成骨细胞）分化和基质代谢。研究已经证实，I型胶原（科尔-1），有机骨基质的主要蛋白质，在HHcy期间被同型半胱氨酸化（N-Hcy-科尔-1）。我们的初步研究结果表明，遗传性高同型半胱氨酸通过改变线粒体氧化还原应激、线粒体DNA甲基化/羟甲基化、核分裂融合以及引起N-Hcy-科尔-1交联等途径影响线粒体表观遗传重构。这些过程累积破坏骨基质、骨密度、骨血流，并导致线粒体自噬伴随显著的骨丢失。有趣的是，硫化氢（H2S，抗氧化还原应激和Hcy降低剂）减轻骨损伤。该建议的中心假设是，HHcy通过N-Hcy-科尔-1部分地通过以下途径导致骨基质劣化： 增加线粒体表观遗传重塑和改变线粒体动力学。然而，用H2S治疗可改善HHcy诱导的骨异常。我们将通过以下三个具体目标来测试这一假设：具体目标#1：确定HHcy是否部分地通过改变线粒体分裂和融合来引发线粒体表观遗传重构和DNA甲基化，以及H2S是否减轻线粒体表观遗传重构。具体目标2：确定HHcy是否使骨I型胶原蛋白活化、激活MMP-1、MMP-3、MMP-13、破坏骨基质（MMP/TIMP轴;胶原蛋白/弹性蛋白比率）以及H2S是否改善这些变化。具体目标3：确定HHcy是否改变骨矿物质密度、骨矿物质含量、生物力学承载能力、骨血流并破坏成骨细胞/破骨细胞分化以及H2S是否加剧这些改变。

 DESCRIPTION (provided by applicant): Clinical studies report that children born with severe hyperhomocysteinemia (HHcy), due to deficiency in cystathionine--synthase (CBS) gene, resulting in an elevation in plasma homocysteine (Hcy) levels, develop skeletal malformations with weaker bone. Although mitochondrial dysfunction has been involved in bone pathology, altered mitochondrial (Mito) epigenetics and dynamics contributing to frailer bone have not been studied. The long term goal of this project is to understand the mechanisms of mito-epigenetic remodeling and changes in bone structure/function during genetic HHcy. Alterations in mitochondrial dynamics disturb bone cell (osteoclast/ osteoblast) differentiation and matrix metabolism. Studies have confirmed that type-I collagen (coll-1), a dominant protein of the organic bone matrix, is homocysteinylated (N-Hcy-coll-1) during HHcy. Our preliminary data suggest that genetic HHcy affects mito-epigenetic remodeling by altering mito-redox stress, mito-DNA methylation / hydroxymethylation, fission-fusion and cause N-Hcy-coll-1 cross linking. These processes cumulatively disrupt bone matrix, bone density, bone blood flow and lead to mitophagy accompanying with significant bone loss. Interestingly, hydrogen sulfide (H2S, an anti-redox stress and Hcy lowering agent) mitigates bone damage. The central hypothesis of this proposal is that HHcy contributes to bone-matrix inferiority through N-Hcy-coll-1, in part, by increasing mito- epigenetic remodeling and altering mitochondrial dynamics. However, treatment with H2S ameliorates HHcy-induced bone abnormalities. We will test this hypothesis by following three specific Aims: Specific Aim # 1: To determine whether the HHcy instigates mito-epigenetic remodeling and DNA methylation, in part, by altering mitochondrial fission and fusion, and whether H2S mitigates mito-epigenetic remodeling. Specific Aim # 2: To determine whether the HHcy homocysteinylates bone type-I collagen, activates MMP-1,-3,-13, disrupts bone matrix (MMP/TIMP axis; collagen/elastin ratio) and H2S ameliorates these changes. Specific Aim # 3: To determine whether the HHcy alters bone mineral density, bone mineral content, biomechanical load-bearing capacity, bone blood flow and disrupts osteoblast/osteoclast differentiation and whether H2S alleviates these alterations.