Rice R H, Wong V J, Price V H, Hohl D, Pinkerton K E
Department of Environmental Toxicology, University of California, Davis 95616-8588, USA.
Anat Rec. 1996 Dec;246(4):433-40. doi: 10.1002/(SICI)1097-0185(199612)246:4<433::AID-AR2>3.0.CO;2-W.
The biochemical bases for fragility in most of the rare brittle hair shaft syndromes are unknown. The hypothesis being investigated in several syndromes is that the hair cuticle cells show defects in cross-linked protein features. Since transglutaminases stabilize protein structures by cross-linking them, hair from autosomal recessive lamellar ichthyosis patients lacking keratinocyte transglutaminase was examined to find whether this enzyme participates in hair shaft stabilization.
Hair shaft samples from patients afflicted with lamellar ichthyosis or several brittle hair syndromes were examined ultrastructurally by transmission electron microscopy after vigorous extraction with detergent and reducing agent to reveal cross-linked protein features.
In hair cuticle cells from three patients with lamellar ichthyosis the marginal band (A layer) was present but nonuniform and subject to breakage, while in a fourth sample it was missing altogether. The exocuticle appeared less dense than in normal hair, consistent with extensive protein loss during detergent extraction. In cuticle cells from trichothiodystrophy hair, the exocuticle layer was essentially fully extractable in one sample, while in two others (from siblings) the exocuticle appeared less dense and the A layer was absent or greatly reduced in thickness. A sample of proximal trichorrhexis nodosa also displayed defects in cuticle cells, in which the endocuticle layer appeared subject to rupture. The outer cuticle cells in monilethrix hair displayed a thinning of the A layer and less dense exocuticle, while the cortex exhibited regions lacking remnant cell borders. Pili annulati hair displayed large gaps in the cortex, presumably reflecting the air-filled cavities characteristic of this syndrome, and wavy borders of some cuticle cells.
Observations with autosomal recessive lamellar ichthyosis hair indicate that keratinocyte transglutaminase has a major role in maturation of the cuticle but appears unnecessary for stabilization of cell borders in the cortex. Defective cross-linking was also evident in cuticle cells of trichothiodystrophy and monilethrix.
大多数罕见的脆发综合征中毛发脆弱的生化基础尚不清楚。在几种综合征中正在研究的假设是，毛小皮细胞在交联蛋白特征方面存在缺陷。由于转谷氨酰胺酶通过交联来稳定蛋白质结构，因此对缺乏角质形成细胞转谷氨酰胺酶的常染色体隐性板层状鱼鳞病患者的毛发进行了检查，以确定该酶是否参与毛干的稳定。
对患有板层状鱼鳞病或几种脆发综合征的患者的毛干样本，在用去污剂和还原剂进行强力提取后，通过透射电子显微镜进行超微结构检查，以揭示交联蛋白特征。
在三名板层状鱼鳞病患者的毛小皮细胞中，边缘带（A层）存在但不均匀且易断裂，而在第四个样本中则完全缺失。外角质层看起来比正常毛发中的密度低，这与去污剂提取过程中大量蛋白质流失一致。在毛发硫营养不良症毛发的小皮细胞中，一个样本中的外角质层基本上完全可提取，而在另外两个样本（来自兄弟姐妹）中，外角质层看起来密度较低，A层缺失或厚度大大减小。近端结节性脆发病的一个样本在小皮细胞中也显示出缺陷，其中内角质层似乎容易破裂。念珠状发的外部小皮细胞显示A层变薄且外角质层密度较低，而皮质则表现出缺乏残余细胞边界的区域。竹节状发的皮质中有大的间隙，推测反映了该综合征特有的充满空气的腔隙，以及一些小皮细胞的波浪状边界。
对常染色体隐性板层状鱼鳞病毛发的观察表明，角质形成细胞转谷氨酰胺酶在小皮成熟中起主要作用，但对于皮质中细胞边界的稳定似乎并非必需。毛发硫营养不良症和念珠状发的小皮细胞中也明显存在交联缺陷。
