Multiple physiological roles of cytosolic 3,5,3'-triiodothyronine binding protein (CTBP)

以前，我们在大鼠胞浆中发现了NADPH依赖的胞浆T3结合蛋白(CTBP)。CTBP与m-晶体蛋白(CRYM)相同。最近，在非综合征型遗传性耳聋患者中发现了CRYM突变。虽然已经证实CRYM在体外储存和转运T3到细胞核中起着关键作用，并对听力有临床影响，但CRYM的确切功能在体内仍有待阐明。为了进一步研究CRYM基因产物在体内的功能，我们建立了靶向阻断CRYM基因的小鼠，从而取消了CRYM的产生。CRYM基因敲除会在脑、肾、心脏和肝脏的胞浆中失去依赖NADPH的T3结合活性。在甲状腺功能正常的状态下，尽管发育、心率和听力正常，基因敲除仍显著抑制血清中T3和T4的浓度。该基因的破坏不会改变脑下垂体中TSHb mRNA的表达，也不会改变肝脏和肾脏中谷胱甘肽S转移酶α2和脱碘酶1mRNAs的表达。当静脉注射放射性标记的T3时，标记的T3在CRYM基因敲除小鼠体内迅速进入组织，然后从组织中逃逸。这些数据表明，由于快速的T3周转，CRYM基因的破坏降低了组织和血清中的T3浓度，而不改变体内外周T3的作用。

Previously, we identified NADPH-dependent cytosolic T3 binding protein (CTBP) in rat cytosol. CTBP is identical to m-crystallin (CRYM). Recently, CRYM mutations were found in patients with non-syndromic hereditary deafness. Although it has been established that CRYM plays pivotal roles in reserving and transporting T3 into the nuclei in vitro and has a clinical impact on hearing ability, the precise functions of CRYM remain to be elucidated in vivo.To further investigate the in vivo functions of CRYM gene products, we have generated mice with targeted disruption of the CRYM gene, which abrogates the production of CRYM. CRYM knockout loses the NADPH-dependent T3 binding activity in the cytosol of the brain, kidney, heart, and liver. At the euthyroid state, knockout significantly suppresses the serum concentration of T3 and T4 despite normal growth, heart rate and hearing ability. The disruption of the gene does not alter the expression of TSHb mRNA in the pituitary gland or glutathione S transferase alpha 2 and deiodinase 1 mRNAs in either the liver or kidney. When radiolabeled T3 is injected intravenously, labeled T3 rapidly enters into then escapes from the tissues in CRYM-knockout mice. These data suggest that because of rapid T3 turnover, disruption of the CRYM gene decreases T3 concentrations in tissues and serum without alteration of peripheral T3 action in vivo.