TRAIL Deficiency Contributes to Diabetic Nephropathy in Fat-Fed ApoE^-/- Mice

<div><p>Background</p><p>We recently demonstrated that TNF-related apoptosis-inducing ligand (TRAIL) is protective of diet-induced diabetes in mice. While TRAIL has been implicated in chronic kidney disease, its role <i>in vivo</i> in diabetic nephropathy is not clear. The present study investigated the role of TRAIL in the pathogenesis of diabetic nephropathy using TRAIL^-/-ApoE^-/- mice.</p><p>Methods</p><p>TRAIL^-/-ApoE^-/- and ApoE^-/- mice were fed a high fat diet for 20 w. Plasma glucose and insulin levels were assessed over 0, 5, 8 and 20 w. At 20 w, markers of kidney function including creatinine, phosphate, calcium and cystatin C were measured. Changes in mRNA expression of MMPs, TIMP-1, IL-1β and IL-18 were assessed in the kidney. Functional and histological changes in kidneys were examined. Glucose and insulin tolerance tests were performed.</p><p>Results</p><p>TRAIL^-/-ApoE^-/- mice had significantly increased urine protein, urine protein:creatinine ratio, plasma phosphorous, and plasma cystatin C, with accelerated nephropathy. Histologically, increased extracellular matrix, mesangial expansion and mesangial cell proliferation in the glomeruli were observed. Moreover, TRAIL^-/-ApoE^-/- kidneys displayed loss of the brush border and disorganisation of tubular epithelium, with increased fibrosis. TRAIL-deficient kidneys also had increased expression of MMPs, TIMP-1, PAI-1, IL-1β and IL-18, markers of renal injury and inflammation. Compared with ApoE^-/- mice, TRAIL^-/-ApoE^-/- mice displayed insulin resistance and type-2 diabetic features with reduced renal insulin-receptor expression.</p><p>Conclusions</p><p>Here, we show that TRAIL-deficiency in ApoE^-/- mice exacerbates nephropathy and insulin resistance. Understanding TRAIL signalling in kidney disease and diabetes, may therefore lead to novel strategies for the treatment of diabetic nephropathy.</p></div

Kidneys from TRAIL^-/-ApoE^-/- mice have increased expression of genes indicative of fibrosis.

<p>mRNA expression for (a) fibronectin, (b) PAI-1, (c) TIMP-1, (d) MMP-2 and (e) MMP-9 from kidneys. All levels were normalized to β-actin; n = 6/ genotype. Results are expressed as mean ± SEM, *p<0.05 and **p<0.01 by Mann-Whitney U test.</p

TRAIL^-/-ApoE^-/- mice have increased macrophage infiltration and genes of inflammation.

<p>Representative sections (40X magnification) of mouse kidney after 20 w HFD stained for the pan macrophage marker (a) F4/80. Kidney mRNA expression for (b) IL-1β, (c) IL-18, (d) osteopontin (e) PPAR-γ and (f) TNF-α. All levels were normalized to β-actin; n = 5-6/genotype. Results expressed as mean ± SEM, *p<0.05, **p<0.01 and ****p<0.0001 by Mann-Whitney U test.</p

Organ weights, blood and urine measurements from ApoE^-/- and TRAIL^-/-ApoE^-/- mice after 20 w HFD.

<p>Measurements are from n = 7–11 mice per group. Results are expressed as mean ± SEM, *p< 0.05 and **p<0. 01, by Mann-Whitney U test.</p

Body weights, plasma glucose and insulin levels in HFD-fed ApoE^-/- and TRAIL^-/-ApoE^-/- mice.

<p>Measurements are from n = 5–11 mice per group. Results are expressed as mean ± SEM, *p<0.05 and ****p<0. 0001, by Mann-Whitney U test.</p