Abstract
Ischemia/reperfusion injury is a major cause of acute kidney injury (AKI). AKI is characterized by a sudden decrease in kidney function, systemic inflammation, oxidative stress, and dysregulation of the sodium, potassium, and water channels. While AKI leads to uremic encephalopathy, epidemiological studies have shown that AKI is associated with a subsequent risk for developing stroke and dementia. To get more insights into kidney–brain crosstalk, we have created an in vitro co-culture model based on human kidney cells of the proximal tubule (HK-2) and brain microvascular endothelial cells (BMEC). The HK-2 cell line was grown to confluence on 6-well plates and exposed to oxygen/glucose deprivation (OGD) for 4 h. Control HK-2 cells were grown under normal conditions. The BMEC cell line cerebED was grown to confluence on transwells with 0.4 μm pores. The transwell filters seeded and grown to confluence with cereEND were inserted into the plates with HK-2 cells with or without OGD treatment. In addition, cerebEND were left untreated or treated with uremic toxins, indole-3-acetic acid (IAA) and indoxyl sulfate (IS). The protein and mRNA expression of selected BBB-typical influx transporters, efflux transporters, cellular receptors, and tight junction proteins was measured in BMECs. To validate this in vitro model of kidney–brain interaction, we isolated brain capillaries from mice exposed to bilateral renal ischemia (30 min)/reperfusion injury (24 h) and measured mRNA and protein expression as described above. Both in vitro and in vivo systems showed similar changes in the expression of drug transporters, cellular receptors, and tight junction proteins. Efflux pumps, in particular Abcb1b, Abcc1, and Abcg2, have shown increased expression in our model. Thus, our in vitro co-culture system can be used to study the cellular mechanism of kidney and brain crosstalk in renal ischemia/reperfusion injury.
Highlights
Decreased kidney function in patients with chronic kidney disease (CKD) or acute kidney injury (AKI) often leads to neurological effects such as cognitive impairment, neuropathy and cerebrovascular disease (Tanaka and Okusa, 2020)
indoxyl sulfate (IS) and Indole-3-acetic acid (IAA) are uremic toxins that are upregulated in kidney ischemia/reperfusion injury
IS/IAA were selected for the treatment of brain microvascular endothelial cells (BMEC) to mimic the uremic conditions in the cell culture medium (Yu et al, 2011; Edamatsu et al, 2014)
Summary
Decreased kidney function in patients with chronic kidney disease (CKD) or acute kidney injury (AKI) often leads to neurological effects such as cognitive impairment, neuropathy and cerebrovascular disease (Tanaka and Okusa, 2020). In ischemia/reperfusion injury, reduced GFR is usually due to decreased glomerular perfusion and tubular obstruction due to necrotic and shed tubular epithelial cells. This leads to the accumulation of uremic toxins in the body. In a rat model of a chronic renal failure, a significant decrease of influx and efflux drug transporters on mRNA and protein level have been shown (Naud et al, 2012). We analyze here brain microvessels isolated from mice exposed to bilateral renal ischemia (30 min)/reperfusion (24 h) injury and measured protein and mRNA expression of influx and efflux transporters, cellular receptors and tight junction proteins. We demonstrate the induction of selected efflux transporters in BMECs and altered tight junction protein expression using this in vitro model
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