水解磷酸酯受器於早衰症中扮演角色之研究

Abstract

早衰症(Hutchinson-Gilford progeria syndrome, HGPS)為造成個體提前衰老之罕見疾病，此病症由細胞核中突變的A型合纖層蛋(Lamin A)所形成的早衰蛋白(Progerin)引起。帶有早衰蛋白的細胞，其明顯病徵為細胞核型態異變、細胞分裂緩慢、活性氧物種(Reactive oxygen species)累積及促使細胞進入細胞凋亡(Apoptosis)。水解磷酸脂(Lysophosphatidic acid, LPA)為一透過其六個受器於體內廣泛地調控生理現象之脂質生長因子，本實驗室研究中發現帶有早衰蛋白的細胞，第三型水解磷酸脂受器表現量經由大量內吞作用，並且最終由溶酶體降解而造成第三型水解磷酸脂受器所調控之細胞訊號路徑受到明顯抑制。因此，在此細胞中利用水解磷酸脂第三型受器之促進劑活化兩型受器和短髮夾 RNA(short hairpin RNA)抑制受器表現，並透過 CM-H2DCHDA 染劑和 ß-gal 染劑分別偵測活性氧物種的產生，以及細胞的老化程度。我們發現第三型水解磷酸脂受器具有能夠調控細胞中抗氧化酵素之能力，並達成延緩細胞老化的效果。藉由早衰症病患所提供之皮膚纖維母細胞反覆驗證，證實第三型水解磷酸脂受器極有可能在早衰症致病機轉中扮演重要調控角色。此外，我們於斑馬魚系統中更發現第三型水解磷酸脂受器剔除會造成早衰症。在本研究中，我們釐清第三型水解磷酸脂受器在老化過程中的的調控機轉，其中包括水解磷酸脂透過何種酵素造成活性氧化物的產生，進而影響早衰細胞中的老化。未來，專一的水解磷酸脂第三型受器之受體也期望能應用於臨床使用，增加治療老化相關疾病之可能性。

Hutchinson-Gilford progeria syndrome (HGPS) is a rare laminopathy that produces a mutant form of prelamin A, known as Progerin, resulting in premature aging. HGPS cells show morphological abnormalities of the nuclear membrane, reduced cell proliferation rates, accumulation of reactive oxygen species (ROS), and expression of senescence markers. Lysophosphatidic acid (LPA) is a growth factor-like lipid mediator that regulates various physiological functions via activating multiple LPA G proteincoupled receptors. Here, the roles of LPA and LPA receptors in premature aging are investigated in this study. It’s shown that the protein level of LPA3 was highly downregulated through internalization and the lysosomal degradation pathway in Progerin-transfected HEK293 cells. By treating Progerin transfected HEK293 cells with an LPA3 agonist (OMPT, 1-Oleoyl-2-O-methyl-rac-glycerophosphothionate) and performing shRNA knockdown of the Lpa3r transcript in these cells, LPA3 activation is shown to increase expression levels of antioxidant enzymes, consequently inhibiting ROS accumulation and ameliorating cell senescence. LPA3 was shown to be downregulated in HGPS patient fibroblasts through the lysosomal pathway, and it was shown to be crucial for ameliorating ROS accumulation and cell senescence in fibroblasts. Moreover, in a zebrafish model, LPA3 deficiency was sufficient to cause premature aging phenotypes in multiple organs, as well as a shorter life span. Taken together, these findings identify the decline of LPA3 as a key contributor to the premature aging phenotypes of HGPS cells and zebrafish.