Abstract 498: Increased Proliferative Cells in the Medullary Thick Ascending Limb of the Loop of Henle in the Dahl Salt-Sensitive Rat
Studies of transcriptome profiles have provided new insights into mechanisms underlying the development of hypertension. Cell type heterogeneity in tissue samples, however, has been a significant hindrance in these studies. We performed a transcriptome analysis in medullary thick ascending limbs (mTALs) of the loop of Henle isolated from Dahl salt-sensitive (SS) rats and salt-insensitive consomic SS.13BN rats on either 0.4% or 7 days of 8% NaCl diet (n=4). The mTAL is a nephron segment importantly implicated in the development of hypertension in SS rats. Pathway analysis was performed based on genes differentially expressed between the two rat strains or by a Bayesian model analysis. The Bayesian model analysis was independent of a priori determination of differential expression and selected pathways by incorporating biological knowledge and expression profiles. Both analytical approaches identified pathways involving cell proliferation, cell cycle regulation, and cytokine signaling. The proliferative state of mTAL cells was analyzed by immunofluorescent staining of Ki-67 and p-H3. Of approximately 4,000 mTAL cells counted in each individual rat, 2.3% to 4.4% were in a proliferative state (positive for Ki-67 staining) when the rats were on the 0.4% salt diet (not significantly different between SS and SS.13BN rats). Exposure to the 8% salt diet for 7 days substantially increased the number of proliferative mTAL cells in both strains. In SS rats on the 8% salt diet, 15.0% of mTAL cells analyzed were in a proliferative state, which was significantly higher than the 10.1% in SS.13BN rats (n=7-9, P<0.05). The total number of cells per mTAL section analyzed was not different between the two strains. The number of cells that were in the G2/M phases (positive for p-H3 staining) tended to be higher in SS rats on the 8% salt diet, but the numbers were small in all treatment groups. The study revealed alterations in regulatory pathways in SS rats in a single cell type, leading to the unexpected finding of a greater increase in the number of proliferative mTAL cells in SS rats on a high-salt diet.
- © 2012 by American Heart Association, Inc.