Labombarda F, Gonzalez S L, Gonzalez Deniselle M C, Vinson G P, Schumacher M, De Nicola A F, Guennoun R
Instituto de Biologia y Medicina Experimental and Department of Human Biochemistry, Faculty of Medicine, University of Buenos Aires, Argentina.
J Neurochem. 2003 Nov;87(4):902-13. doi: 10.1046/j.1471-4159.2003.02055.x.
Progesterone provides neuroprotection after spinal cord injury, but the molecular mechanisms involved in this effect are not completely understood. In this work, expression of two binding proteins for progesterone was studied in intact and injured rat spinal cord: the classical intracellular progesterone receptor (PR) and 25-Dx, a recently discovered progesterone membrane binding site. RT-PCR was employed to determine their relative mRNA levels, whereas cellular localization and relative protein levels were investigated by immunocytochemistry. We observed that spinal cord PR mRNA was not up-regulated by estrogen in contrast to what is observed in many brain areas and in the uterus, but was abundant as it amounted to a third of that measured in the estradiol-stimulated uterus. In male rats with complete spinal cord transection, levels of PR mRNA were significantly decreased, while those of 25-Dx mRNA remained unchanged with respect to control animals. When spinal cord-injured animals received progesterone treatment during 72 h, PR mRNA levels were not affected and remained low, whereas 25-Dx mRNA levels were significantly increased. Immunostaining of PR showed its intracellular localization in both neurons and glial cells, whereas 25-Dx immunoreactivity was localized to cell membranes of dorsal horn and central canal neurons. As the two binding proteins for progesterone differ with respect to their response to lesion, their regulation by progesterone, their cellular and subcellular localizations, their functions may differ under normal and pathological conditions. These observations point to a novel and potentially important role of the progesterone binding protein 25-Dx after injury of the nervous system and suggest that the neuroprotective effects of progesterone may not necessarily be mediated by the classical progesterone receptor but may involve distinct membrane binding sites.
孕酮在脊髓损伤后具有神经保护作用，但其作用的分子机制尚未完全明确。在本研究中，我们对完整和损伤大鼠脊髓中两种孕酮结合蛋白的表达进行了研究：经典的细胞内孕酮受体（PR）和25-Dx，后者是最近发现的孕酮膜结合位点。采用逆转录聚合酶链反应（RT-PCR）测定其相对mRNA水平，通过免疫细胞化学研究其细胞定位和相对蛋白水平。我们观察到，与许多脑区和子宫中观察到的情况不同，脊髓PR mRNA不受雌激素上调，但含量丰富，达到雌二醇刺激子宫中测量值的三分之一。在完全性脊髓横断的雄性大鼠中，PR mRNA水平显著降低，而25-Dx mRNA水平与对照动物相比保持不变。当脊髓损伤动物接受72小时孕酮治疗时，PR mRNA水平未受影响且保持较低水平，而25-Dx mRNA水平显著升高。PR免疫染色显示其在神经元和胶质细胞内均有定位，而25-Dx免疫反应性定位于背角和中央管神经元的细胞膜。由于两种孕酮结合蛋白在对损伤的反应、孕酮对其的调节、细胞和亚细胞定位方面存在差异，它们在正常和病理条件下的功能可能也不同。这些观察结果表明，孕酮结合蛋白25-Dx在神经系统损伤后具有新的潜在重要作用，并提示孕酮的神经保护作用不一定由经典孕酮受体介导，可能涉及不同的膜结合位点。
