Kidney‐associated brown adipose tissue. Potential relationship to etiology of genetic hypertension in the SHR (spontaneously hypertensive rat)

Abstract

Brown adipose tissue (BAT) is found proximal to many neonate and adult mammalian organ systems. Initial studies of SHR and normotensive BNLx strains found differential expression of uncoupling protein 1 (UCP1) mRNA in the medullary‐pelvic area of the kidney and an association with level of blood pressure. AIMS: The study aims were to identify the location of kidney‐associated BAT, analyze differences in BAT morphology and gene expression and test association with hypertension. METHODS: Immunofluorescent microscopy (IFM) and H&E staining were used to examine cell morphology, perilipin and UCP1 protein staining in 4 and 12 week animals. RT‐PCR quantified expression of genes important to BAT and lipid metabolism and test if different between SHR and BNLx. Cell functional differences were probed by cold exposure experiments. RESULTS: BAT was localized to the kidney ureter‐pelvic junction in proximity to the ureter adventitia, renal nerves and blood vessels. Striking differences were found in BAT cell structure and size between the strains. BAT of both strains responded differentially to cold exposure (morphology and UCP1 expression) but other studies found defective SHR response to ephedrine. CONCLUSIONS: We conclude BAT is located immediately proximal to the major vascular and nerve conduits to the kidney which may enable BAT to affect renal functions. Finding distinct cellular and functional differences between pre‐hypertensive 4 wk old genetically hypertensive and normotensive strains implicate BAT as potentially related to hypertension development. Future studies are warranted into the role of kidney‐associated BAT with regards to the pathology of hypertension and metabolic syndrome. Supported by NIH HL‐35018.