Cannabinoid receptor 2 expression in proximal tubule cells exposed to elevated glucose and albumin

Introduction. Hyperglycaemia plays a significant role in the aetiology of diabetic nephropathy. Compounded with this, renal tubule cells are also exposed to high levels of albumin in the filtrate, which is caused by damage to the glomerulus. We have previously identified that the cannabinoid receptor 2 (CB2) is present in proximal tubule cells. In renal tubules, hypertrophy is an early indicator of diabetic nephropathy, and previously we have shown that activation of CB2 reduces tubular hypertrophy (Jenkin et al., 2010). Despite this, to date, there has been little investigation into changes in the expression of the CB2 in the proximal tubule under diabetic conditions. The aim of this research was to quantify the expression of endocannabinoid receptor CB2 in proximal tubule cells exposed to high levels of glucose and albumin. Method. Human kidney (HK2) cells were treated with one of four protocols; a control medium containing physiological normal levels of glucose (5 mM) and no albumin; a high glucose (25 mM) medium with no albumin; a high albumin (1 mg/ml) medium with normal glucose levels (5 mM); or a combination medium composed of high glucose and high albumin. HK2 cells were incubated for 4, 6, 18 or 24 h. Following treatment, mRNA was extracted and DNAse treated. The mRNA was reverse transcribed and the level of the endocannabinoid receptor CB2 mRNA was assessed by real time PCR. Protein expression for the CB2 receptor was investigated using Western blot analysis. Band density was quantified using Image Lab software, and treatment groups were normalized to control treatment. Values were expressed as mean ± SEM. Statistical analysis was performed using one-way ANOVA. Results. High levels of glucose did not significantly alter CB2 mRNA expression in HK2 cells. High albumin treatment alone and in combination with high glucose did result in a significant reduction in CB2 receptor mRNA expression at 6 and 18 h compared to control treatment (P<0.05, n = 9). CB2 protein expression was reduced compared to control treatment at 6 and 24 h treatment periods again in high albumin treatment alone and in combination with high glucose (P