Cognitive Impairment Related to Chronic Kidney Disease Is Associated with a Decreased Abundance of Membrane-Bound Klotho in the Cerebral Cortex

Abstract

Cognitive impairment (CI) is a complication of chronic kidney disease (CKD) that is frequently observed among patients. The aim of this study was to evaluate the potential crosstalk between changes in cognitive function and the levels of Klotho in the brain cortex in an experimental model of CKD. To induce renal damage, Wistar rats received a diet containing 0.25% adenine for six weeks, while the control group was fed a standard diet. The animals underwent different tests for the assessment of cognitive function. At sacrifice, changes in the parameters of mineral metabolism and the expression of Klotho in the kidney and frontal cortex were evaluated. The animals with CKD exhibited impaired behavior in the cognitive tests in comparison with the rats with normal renal function. At sacrifice, CKD-associated mineral disorder was confirmed by the presence of the expected disturbances in the plasma phosphorus, PTH, and both intact and c-terminal FGF23, along with a reduced abundance of renal Klotho. Interestingly, a marked and significant decrease in Klotho was observed in the cerebral cortex of the animals with renal dysfunction. In sum, the loss in cerebral Klotho observed in experimental CKD may contribute to the cognitive dysfunction frequently observed among patients. Although further studies are required, Klotho might have a relevant role in the development of CKD-associated CI and represent a potential target in the management of this complication.

Keywords: Klotho; bone and mineral disorder; chronic kidney disease; cognitive impairment.

Figure 1

The plasma biochemistry of the animals included in this study. The white and black bars represent the data obtained from the control and CKD groups, respectively. The animals with renal dysfunction had similar levels of calcium (A) and magnesium (B). The circulating concentrations of phosphorus (C), creatinine (D), PTH (E), intact FGF23 (F), and c-terminal FGF23 (G) were significantly increased in the groups of animals with renal dysfunction. CKD, chronic kidney disease. n.s., non-significant; * p < 0.05 vs. control.

Figure 2

A scheme of the object location task. This test consisted of three different phases. In the habituation phase, the animals explored the arena for ten minutes during seven days. In the familiarization phase, two identical objects were placed in certain positions in the arena, and the animals could explore them for ten minutes. In the testing phase, which was performed three hours after the familiarization phase, object B was changed to a different position and, again, the animals were allowed to explore them for ten minutes. The time spent exploring both objects was recorded for each animal. N, north; S, south; E, east; W, west.

Figure 3

An assessment of cognitive function. (A) represents the results obtained by the experimental groups in the object location task. There were no differences in the time spent by both groups exploring object A. However, the CKD animals (black bars) spent significantly less time exploring object B in comparison with the healthy rats, which was indicative of an impaired behavior. ** p < 0.01 vs. control; ^# p < 0.05 vs. object A. (B) shows the performance of the animals in the light/dark test. The rats with normal renal function spent statistically equal time in the light (white bars) and the dark (black bars) zones, whereas the animals with renal dysfunction stayed in the dark zone longer, as it was considered a safe environment. CKD, chronic kidney disease. * p < 0.05 vs. control; n.s., non-significant; ^# p < 0.05 vs. light zone.

Figure 4

The determination of the levels of Klotho in the experimental groups. The circulating concentration of Klotho did not differ between the controls and CKD animals (A). However, the concentration of Klotho in urine was substantially higher in the rats with renal damage (B), and such difference persisted when the concentration of Klotho was adjusted by that of creatinine (C). As expected, the rats with CKD had a marked reduction in renal Klotho. Magnification, 10× and 20× (D). When the expression of Klotho was evaluated in the cerebral cortex, a reduction of 50% was observed in the animals with renal dysfunction. Magnification, 10× and 20× (E). CKD, chronic kidney disease. n.s., non-significant; * p < 0.05 vs. control; ** p < 0.01 vs. control; **** p < 0.0001 vs. control.