Expression of Trefoil Factor 1 in the Developing and Adult Rat Ventral Mesencephalon

Trefoil factor 1 (TFF1) belongs to a family of secreted peptides with a characteristic tree-looped trefoil structure. TFFs are mainly expressed in the gastrointestinal tract where they play a critical role in the function of the mucosal barrier. TFF1 has been suggested as a neuropeptide, but not much is known about its expression and function in the central nervous system. We investigated the expression of TFF1 in the developing and adult rat midbrain. In the adult ventral mesencephalon, TFF1-immunoreactive (-ir) cells were predominantly found in the substantia nigra pars compacta (SNc), the ventral tegmental area (VTA) and in periaqueductal areas. While around 90% of the TFF1-ir cells in the SNc co-expressed tyrosine hydroxylase (TH), only a subpopulation of the TH-ir neurons expressed TFF1. Some TFF1-ir cells in the SNc co-expressed the calcium-binding proteins calbindin or calretinin and nearly all were NeuN-ir confirming a neuronal phenotype, which was supported by lack of co-localization with the astroglial marker glial fibrillary acidic protein (GFAP). Interestingly, at postnatal (P) day 7 and P14, a significantly higher proportion of TH-ir neurons in the SNc co-expressed TFF1 as compared to P21. In contrast, the proportion of TFF1-ir cells expressing TH remained unchanged during postnatal development. Furthermore, significantly more TH-ir neurons expressed TFF1 in the SNc, compared to the VTA at all four time-points investigated. Injection of the tracer fluorogold into the striatum of adult rats resulted in retrograde labeling of several TFF1 expressing cells in the SNc showing that a significant fraction of the TFF1-ir cells were projection neurons. This was also reflected by unilateral loss of TFF1-ir cells in SNc of 6-hydroxylase-lesioned hemiparkinsonian rats. In conclusion, we show for the first time that distinct subpopulations of midbrain dopaminergic neurons express TFF1, and that this expression pattern is altered in a rat model of Parkinson’s disease.

三叶因子1（TFF1）属于一类具有特征性树状环状三叶结构的分泌性肽类家族。TFFs主要在胃肠道中表达，并在黏膜屏障的功能中发挥关键作用。TFF1曾被提议为一种神经肽，但关于其在中枢神经系统中表达和功能的信息所知甚少。本研究调查了TFF1在大鼠发育期和中枢神经系统中的表达。在成年大鼠的腹侧中脑中，TFF1免疫反应性（-ir）细胞主要分布在黑质致密部（SNc）、腹侧被盖区（VTA）以及周围导水管区。尽管大约90%的SNc中的TFF1-ir细胞共表达酪氨酸羟化酶（TH），但仅有一部分TH-ir神经元表达TFF1。SNc中的一些TFF1-ir细胞与钙结合蛋白钙结合蛋白或钙调素共表达，几乎所有这些细胞均为NeuN-ir，证实了其神经元表型，这一点得到了与星形胶质细胞标记物胶质纤维酸性蛋白（GFAP）无共定位的支持。有趣的是，在出生后（P）第7天和第14天，SNc中TH-ir神经元共表达TFF1的比例明显高于P21。相反，TFF1-ir细胞表达TH的比例在出生后发育过程中保持不变。此外，与VTA相比，在所有四个研究时间点，SNc中表达TH的TH-ir神经元更多。将示踪剂氟金注入成年大鼠的纹状体，导致SNc中多个表达TFF1的细胞发生逆行标记，表明TFF1-ir细胞中有一大部分是投射神经元。这也反映在6-羟基化酶损伤的半侧帕金森病大鼠SNc中TFF1-ir细胞的单侧丢失。总之，我们首次证实了中脑多巴胺能神经元的不同亚群表达TFF1，且这种表达模式在帕金森病大鼠模型中发生了改变。