Ultrastructural and functional analyses of nephropathy in calmodulin-induced diabetic transgenic mice

Abstract

Background Previous animal models of diabetic nephropathy have used diabetic animals for which the underlying defect was either uncertain or the diabetes was induced by potentially specific toxins. In this report, we describe the renal abnormalities in a transgenic mouse model that develops early‐onset diabetes due to overexpression of calmodulin in pancreatic beta cells. Methods Renal tissues were collected from normal and transgenic mice at 112, 182, and 300 days. These were prepared for light microscopic observation, stained with polyethylenimine (for anionic sites), or rendered acellular by detergent extraction prior to observation by transmission and scanning electron microscopy. Morphometric analysis of glomerular basement membrane thickness was carried out by the “orthogonal intercept” method. Twelve‐hour urine samples of fed and fasting mice were collected for urine volume and glucose and protein analyses. Blood glucose, blood urea nitrogen, serum insulin, and creatinine were determined in 60‐90‐day‐old and 255‐day‐old mice by established methods. Results Morphometric analyses revealed age‐related and transgene‐related increases in glomerular basement membrane thickness. A 22% increase in transgenic diabetics over controls was seen at 112 days of age that developed to increases of 43% and 37% at 182 and 300 days of age, respectively. Mesangial matrix area was also increased markedly in transgenic mice. Surprisingly, even in the oldest diabetic mice, there was no reduction in anionic sites. Moreover, despite an eightfold increase in urine volume, these mice did not become significantly proteinuric. Conclusions These results indicate that proteinuria of diabetes may be delayed or prevented by maintenance of a normal complement of glomerular basement membrane anionic sites. They also demonstrate that transgenic mice can provide a valuble model for discriminating between different aspects of diabetic nephropathy. Anat. Rec. 247:9–19 © 1997 Wiley‐Liss, Inc.

Podocyte Loss in Aging OVE26 Diabetic Mice

“…The OVE26 transgenic diabetic mouse is particularly interesting because, despite substantial pancreatic β‐cell–specific damage (Epstein et al,1989,1992) and blood glucose levels frequently exceeding 600 mg/dl (Zheng et al,2004), insulin secretion is sufficient to allow these mice to live as long as 450 days without treatment. Significantly, these mice show numerous morphological features that parallel chronic complications of DN in humans (Carlson et al,1997,2003; Zheng et al,2004). Moreover, they are prone to early and frequently severe microalbuminuria and the major blood pressure effect is hypertension (Zheng et al,2004).…”

“…These characteristics include significant nephropathic features, which have been well characterized. As examples, OVE26 kidney weights were almost doubled between 2 and 5 months (Zheng et al,2004), and morphometric analyses have shown an increase in GBM thickness (Carlson et al,1997;2003), glomerular volume, and mesangial matrix area (Zheng et al,2004). Interestingly, significant albuminuria was frequently seen by 2 months of age, and urinary albumin excretion (UAE) rates increased progressively with age (Zheng et al,2004).…”

Mammalian Target of Rapamycin Regulates Nox4-Mediated Podocyte Depletion in Diabetic Renal Injury

“…For electron microscopy photomicrographs, kidney cortex was prepared and analyzed as we and others have previously described (7,8,20–24). …”

Impaired Albumin Uptake and Processing Promote Albuminuria in OVE26 Diabetic Mice

“…The most likely cause of too much proximal tubule cell uptake is very high concentrations of albumin in the tubule lumen from leaking glomeruli. We previously described structural abnormalities in the OVE glomerular filtration barrier [12, 13, 21–25] and functional results showing that a subset of OVE glomeruli have severe leakage of albumin [15]. Supplemental Figure 3 shows that OVE glomeruli still filter TR-albumin, despite possessing obviously abnormal podocyte organization, as revealed by a podocyte GFP transgene [26].…”