Résumé
Abstract
Background and Aims
An increasing number of studies demonstrate a significant association between chronic kidney disease (CKD) and a higher risk of cognitive impairment. This involves several interconnected mechanisms between kidney and brain, particularly evident in end-stage renal disease. Uremic toxin accumulation, including neurotoxic compounds like indoxyl sulfate, could contribute to oxidative stress and cellular dysfunction in the brain. This can lead to modifications in glial cells that can impair their protective functions and potentially exacerbating neuronal damage. The blood-brain barrier can be disrupted, allowing harmful substances to infiltrate brain tissue, thus further promoting neurological dysfunction. The aim of this study was to evaluate brain morphology changes and pathological processes induced by CKD, using a long-term 5/6 nephrectomy rat model to investigate potential mechanisms involved in such pathology.
Method
Twelve-week-old Sprague Dawley rats were randomly assigned to undergo either 5/6Nx or sham surgery. Twenty-four weeks after surgery, renal function and brain histopathological changes were assessed. Plasma and brain tissue levels of indoxyl sulfate were measured using high performance liquid chromatography coupled with Triple Quad mass spectrometry (LC-MS/MS). Brain modifications were evaluated through western blot analysis of tight junction protein Claudin-5, Perls’ Prussian blue staining for cerebral microbleeds, and immunostaining for GFAP and Iba1 to assess perivascular astrocytes and microglial cell densities, respectively.
Results
5/6Nx rats developed CKD, evidenced by increased plasma levels of creatinine (P = 0.0402) and urea (P = 0.0043) (Fig. 1). The presence of macrophage infiltration in 5/6Nx rats, highlighted by CD68 staining, was noticed as a sign of inflammation of the renal tissue. Indoxyl sulfate levels were elevated in both plasma (P = 0.0519) and brain tissue (P = 0.0063) of the 5/6Nx group compared to the sham group. Notable brain modifications, including disruption of the blood-brain barrier (BBB) were observed in CKD group: (i) reduced expression of the tight junction protein Claudin-5 (P = 0.0087), (ii) appearance of cerebral microbleeds, (iii) decreased density of perivascular astrocytes (P = 0.0442) and microglial cells (P = 0.0029).
Conclusion
Our results demonstrate significant CKD-induced brain tissue alterations. This provide evidences in favor of an increased risk of cognitive impairment associated with CKD. To further investigate these findings, potential cognitive deficits should be evaluated using behavioral tests, which would help to determine whether the observed brain tissue changes can be linked to specific cognitive impairments as observed with patients.
Figure 1:
Blood creatinine (A1), urea (A2) and number of CD68+ cells in the kidney (B1) were significantly increased in the 5/6Nx group compared to the Sham group. Representative images of kidney CD68 immunostaining (B2). Plasma (C1) and brain (C2) indoxyl sulfate concentration increased in the 5/6Nx group compared to the Sham group. Claudin-5 expression was significantly decreased in the brains of 5/6Nx group compared to the Sham group (D1). Representative images of brain Claudin-5 western blot (D2). The appearance of microbleeds was detected only in the brain of the 5/6Nx group (E1). Representative brain Perls’ Prussian blue staining images and magnification in the red square of microbleeds (E2). Perivascular astrocyte (F1) and microglia (F2) densities in the brain were significantly decreased in the 5/6Nx group compared to the Sham group. Representative images of brain green GFAP (astrocytes), red Iba1 (microglia) and blue DAPI (nucleus) immunostaining (F3). Mean ± SEM; * = P < 0.05; ** = P < 0.01; *** = P < 0.0001.