Heritable Disorders Of Connective Tissue

骨和细胞外基质分部负责研究骨的细胞外基质以及因基质缺陷引起的疾病。由Joan C.Marini领导的遗传性骨疾病科开展了一项实验室和临床研究的综合计划，重点关注成骨不全(OI)作为一种导致严重骨质疏松的细胞外基质模型障碍。他们已经表明，在成骨不完美的I型胶原的生化筛选中，没有检测到由于阿尔法链氨基末端的甘氨酸替换而导致的过度修饰。完全检测a1(I)链的氨基三分之一和a2(I)链的氨基一半的取代需要通过测序补充(Cabral等(2006)J Med Genet 43：685)。胶原分子的氨基和羧基末端的突变一直是一个主要的研究焦点。在Alpha1(I)螺旋区的氨基末端，他们描述了OI和Ehler Danlos综合征的不同组合表型，并表明它是由一个不同的90个残基折叠区的突变引起的。这些突变会打开邻近的N-蛋白酶裂解部位，干扰前胶原蛋白的加工。在基质中掺入PN-胶原蛋白导致纤维直径显著减小。因此，OI/EDS胶原中的缺陷具有双重作用--它们通过改变骨基质结构直接导致骨质疏松，并通过干扰前胶原的加工间接导致EDS。(Cabral等人(2005年)JBC280：19259；Makareeva等人(2006年)JBC281：6463)该部门还一直在调查前胶原链的羧基末端，在那里他们在II型(致命)、III型(重度)和IV型(中度)OI患者中发现了5个新的突变。这些突变都延迟了突变链与前胶原螺旋的结合。有趣的是，包含这些突变的前胶原分子部分在纤维组装之前被从螺旋上切割下来。因此，突变本身预计不会出现在组织基质中。这意味着这些突变的机制一定不同于胶原螺旋中的机制。细胞外加工以及C-蛋白酶的协同体外消化(David Hulmes，里昂，法国)表明前肽的加工延迟。 该科在OI的治疗中发挥了重要作用，在该科建立的OI Brtl小鼠模型和儿童OI人群中进行了双膦酸盐药物的对照试验。这些研究区分了这些化合物对OI骨骼的有益和有害方面。在小鼠中，骨折时股骨体积和载荷的增加是以材料强度降低和脆性增加为代价的。矿化软骨支架的持续存在增加了骨折的风险，并对Brtl成骨细胞的形态产生了毒性影响。在帕米磷酸钠对III型和IV型OI儿童的随机对照试验中(Letocha等人(2005)JBMR 20：977)，与对照组相比，治疗患者的椎骨BMD z评分显著增加，L1-L4椎体中部高度和总椎体面积增加。然而，治疗1-2年后，骨密度的增加逐渐减少。此外，接受治疗的患者在行走水平、下肢力量或疼痛改善方面未见积极的功能效果。先前报告的这些参数的变化在非对照试验中似乎是安慰剂效应。该科目前正在进行帕米磷酸钠的剂量比较试验，以确定在儿科OI中使用较低剂量的帕米磷酸钠是否可以在减少副作用的情况下提供有益的效果。

The Bone and Extracellular Matrix Branch conducts research on the extracellular matrix of bone and on diseases resulting from defective matrix. The Section on Heritable Bone Disorders, led by Joan C. Marini, conducts an integrated program of laboratory and clinical research, focusing on osteogenesis imperfecta (OI) as a model disorder of extracellular matrix resulting in severe osteoporosis. They have shown that biochemical screening of type I collagen in osteogenesis imperfecta does not detect excess modification resulting from glycine substitutions at the amino ends of the alpha chains. Complete detection of substitutions in the amino third of the a1(I) and amino half of the a2(I) chain requires supplementation by sequencing (Cabral et al (2006) J Med Genet 43:685). Mutations at both the amino and carboxyl ends of the collagen molecule have been a primary research focus. At the amino end of the alpha1(I) helical region, they delineated distinct combined phenotype of OI and Ehlers Danlos Syndrome and showed that it was caused by mutations in a distinct 90-residue folding region. These mutations unfold the adjacent N-proteinase cleavage site and interfere with procollagen processing. Incorporation of pN-collageninto matrix results in fibrils with strikingly decreased diameter. Thus, the defects in OI/EDS collagen have a dual role - they cause osteoporosis directly by altering bone matrix structure and EDS indirectly by interfering with procollagen processing. (Cabral et al (2005) JBC 280:19259; Makareeva et al (2006) JBC 281:6463) The Section has also been investigating the carboxyl end of the procollagen chains, where they have identified 5 novel mutations in patients with types II (lethal), III (severe) and IV (moderate) OI. These mutations all delay incorporation of the mutant chains into the procollagen helix. Interestingly, the portion of the procollagen molecule containing these mutations is cleaved from the helix before fibril assembly. Therefore, the mutations per se are not expected to be present in tissue matrix. This implies that the mechanism of these mutations must differ from those in the collagen helix. Pericellular processing as well as collaborative in vitro digestion with C-proteinase (David Hulmes, Lyon, France) indicates delay in processing of the propeptide. The Section played an important role in OI treatment by conducting controlled trials of bisphosphonate drugs in both the Brtl mouse model for OI generated by this Section, and in the pediatric OI population. These investigations distinguished the beneficial and detrimental aspects of these compounds on OI bone. In the mouse, increased femoral bone volume and load at fracture came at the expense of decreased material strength and increased brittleness. Fracture risk was increased by persistence of mineralized cartilage rests and a toxic effect on the morphology of Brtl osteoblasts was noted. In the randomized controlled trial of pamidronate in children with types III and IV OI (Letocha et al (2005) JBMR 20:977), treated patients experienced a significant increase in vertebral BMD z-scores, increased L1-L4 mid-vertebral height and total vertebral area, compared to controls. However, the increases in BMD tapered after 1-2 years of treatment. Furthermore, treated patients did not experience positive functional effects in ambulation level, lower extremity strength or amelioration of pain. The changes previously reported in these parameters appear to have been placebo effects in uncontrolled trials. The Section is currently engaged in a dose comparison trial of pamidronate, to determine whether a lower dose of pamidronate in pediatric OI can deliver the beneficial effects with reduced side effects.