Role of Trk Receptors in the Development and Function of Non-neuronal Structures

缺乏激酶结构域的截断Trk受体同工型在发育和成人中大量表达；然而，它们的功能和信号能力在很大程度上是未知的。有趣的是，神经营养因子-3 （NT3）截断的TrkCT1-受体的细胞质尾部在物种中高度保守，表明其在体内可能具有重要功能。我们最近发现NT3与TrkCT1的相互作用通过支架蛋白Tamalin激活Arf6-Rac1信号。我们发现TrkCT1还结合Tamalin同源Cybr，一种在免疫系统中高度表达的支架蛋白。NT3治疗内源性表达TrkCT1和Cybr的EL4淋巴瘤细胞系，诱导Cybr的细胞内再定位。由于Cybr参与促炎细胞因子调节的细胞迁移，我们的研究结果表明TrkCT1可能调节特定白细胞细胞群的募集和迁移。事实上，在我们删除Cybr的小鼠中，我们发现血液循环中的白细胞和淋巴结中的淋巴细胞存在特异性缺陷。此外，在th1极化小鼠模型中，淋巴细胞运输因Cybr缺失而受损，无菌性腹膜炎Cybr缺陷小鼠的腹腔细胞比对照组少，离开血流的白细胞也更少。注射moloney -小鼠肉瘤/白血病病毒的突变小鼠肿瘤明显大于野生型小鼠，淋巴结肿大减小，表明细胞毒性T淋巴细胞迁移减少。综上所述，这些数据支持Cybr在白细胞运输中的作用，特别是在应激条件下对促炎细胞因子的反应中。我们现在正在调查NT-3/TrkC.T1对这些网络功能的影响。在另一个项目中，我们研究了TrkB受体在神经系统之外是否有其他功能。令人惊讶的是，我们发现这些受体控制着哺乳动物心脏的收缩和长期稳态。例如，BDNF通过TrkB增加心肌细胞的收缩力和钙释放。T1和缺乏TrkB的小鼠。T1-/-小鼠表现为心肌肥厚、钙通道改变、扩张性心肌病和心脏功能下降。这些数据表明BDNF/TrkB受损。T1信号可能与心肌病的病因有关。

Truncated Trk receptor isoforms lacking the kinase domain are abundantly expressed during development and in the adult; however, their function and signaling capacity is largely unknown. Interestingly, the cytoplasmic tail of the neurotrophin-3 (NT3) truncated TrkCT1- receptor is highly conserved among species, suggesting the potential for important functions in vivo. We have recently shown that NT3 interaction with TrkCT1 activates Arf6-Rac1 signaling through the scaffold protein Tamalin. We found that TrkCT1 binds also the Tamalin homolog Cybr, a scaffold protein highly expressed in the immune system. NT3 treatment of the EL4 lymphoma cell line that express endogenously both TrkCT1 and Cybr, induces intracellular re-localization of Cybr. Since Cybr is involved in pro-inflammatory cytokine-modulated cell migration, our results suggest that TrkCT1 may modulate the recruitment and migration of specific leukocyte cell populations. Indeed, in mouse in which we have deleted Cybr we find specific deficits in blood circulating leukocytes and lymphocytes present in the lymph nodes. Moreover, in a Th1-polarized-mouse model, lymphocyte trafficking is impaired by loss of Cybr and Cybr-deficient mice with aseptic peritonitis have fewer cells than controls present in the peritoneal cavity and fewer leukocytes leaving the blood stream. Mutant mice injected with Moloney-murine sarcoma/leukemia virus develop significantly larger tumors than wild type mice and have reduced lymph node enlargement suggesting reduced cytotoxic T lymphocytes migration. Taken together, these data support a role for Cybr in leukocyte trafficking, especially in response to pro-inflammatory cytokines in stress conditions. We are now investigating which of these Cybr functions are affected by NT-3/TrkC.T1. In a separate project we have investigated whether TrkB Receptors have other functions outside the nervous system. Surprisingly, we found that these receptors control contraction and long-term homeostasis of the mammalian heart. For example, BDNF increases the cardiac contraction force and calcium release in cardiomyocytes through TrkB.T1 and mice lacking TrkB.T1-/- mice show cardiac hypertrophy, calcium channel alteration, dilated cardiomyopathy and reduced heart performances. Together these data suggest that impairment in BDNF/TrkB.T1 signaling can contribute to the etiology of cardiomyopathies.