Abstract P452: Evaluation of Pathological Basis of a Shrsp-based Congenic Strain Characterized by Early Stroke Occurrence

Abstract

Objectives: The stroke-prone spontaneously hypertensive rat (SHRSP) is a well-known model for essential hypertension and cerebral stroke. In the previous studies, we have identified a major blood pressure (BP) QTL on chromosome (chr) 1 of SHRSP and have explored gene(s) on the BP QTL responsible for hypertensive phenotypes of this strain through physiological analyses using reciprocal congenic strains between SHRSP and a normotensive control (Wistar-Kyoto rat, WKY). In a recent observation, we unexpectedly found that a SHRSP-based congenic strain, harboring a 0.3-Mbp fragment of the chr1 QTL, has developed stroke earlier than SHRSP. Here, we investigated pathological basis of this congenic strain and attempted to identify gene(s) related to early stroke occurrence. Methods: SHRSP and a SHRSP-based congenic strain SHRSP.WKY-( D1Smu13 )/Izm, abbreviated as SPwch1.71 were used in this study. The rats were housed 12-hour light phase-controlled environment with freely accessible SP diet (Funabashi Farm) and drinking water until at least one suggestive sign of stroke (diminished motor activity, paralytic gait, and so on) was found. MRI by MRmini SA 1508 (DS Pharma Biomedical) was employed to confirm stroke occurrence. BP measurement was performed by the tail-cuff method. Cerebral cortex, brainstem, kidney, adrenal gland and heart obtained from 14 weeks old rats (n=5) were snap-frozen for RNA extraction. Quantitative RT-PCR (qRT-PCR) was performed about 15 of candidate genes located on the chr1 QTL covered by SPwch1.71. Nonsynonymous SNPs were scanned based on the whole-genome sequence of SHRSP and WKY. Results: SPwch1.71 showed significantly high stroke susceptibility compared with SHRSP stroke-free rate until 22 weeks old; SPwch1.71: 0% (0/7), SHRSP: 62.5% (5/8), p <0.001. Systolic BP at 12 weeks old of SPwch1.71 was significantly higher than that of SHRSP (222±4 vs. 206±5, p <0.01, n=5 for each). qRT-PCR identified genes showing modest (<1.5-fold change), but statistically significant different ( p <0.05), in the expression in each tissue examined. Nonsynonymous variations were found in Pde2a , Inppl1 and Folr1 . Pathological significance of expression/sequence variations in the genes remain unclear.