BOLD-fMRI reveals the association between renal oxygenation and functional connectivity in the aging brain

Aging is accompanied by a decline in physical and cognitive function. Vascular aging may provide a major influence on these measures. The purpose of this study was to explore the relationship between renal oxygenation and functional connectivity of the aging brain because of the anatomic and hemodynamic similarities between cerebral and renal vessels. Fifty-two healthy older adults were recruited to undergo a BOLD-fMRI scan of the brain and kidneys, and forty-four healthy younger subjects were recruited as the control group. First, cerebral functional connectivity density (FCD) was used to evaluate functional connectivity. Renal medullary and cortical R2* values were extracted respectively, and the ratio of medullary and cortical R2* values (MCR) was calculated. Then, the association between brain FCD and renal MCR was analyzed. Compared with younger adults, the elderly group showed higher renal medullary R2* and MCR, which might reflect a slight abnormality of renal oxygenation with aging. The older subjects also showed enhanced FCD in bilateral motor-related regions and decreased FCD in regions of the default mode network (DMN). The findings indicated that the functional connectivity in the DMN and motor cortices was vulnerable to aging. Moreover, the altered brain FCD values in the watershed regions, DMN and motor cortices were significantly correlated with the renal MCR value in the elderly group. The association between renal oxygenation abnormalities and spontaneous activity in the brain might reflect vascular aging and its influence on the kidney and brain during aging to some extent. This study provided a new perspective for understanding the relationship between tissue oxygenation and brain functional connectivity.