Podocyte-Specific Overexpression of the Antioxidant Metallothionein Reduces Diabetic Nephropathy

Abstract

Podocytes are critical components of the selective filtration barrier of the glomerulus and are susceptible to oxidative damage. For investigation of the role of oxidative stress and podocyte damage in diabetic nephropathy, transgenic mice that overexpress the antioxidant protein metallothionein (MT) specifically in podocytes (Nmt mice) were produced. MT expression was increased six-and 18-fold in glomeruli of two independent lines of Nmt mice, and podocyte-specific overexpression was confirmed. Glomerular morphology and urinary albumin excretion were normal in Nmt mice. OVE26 transgenic mice, a previously reported model of diabetic nephropathy, were crossed with Nmt mice to determine whether an antioxidant transgene targeted to podocytes could reduce diabetic nephropathy. Double-transgenic OVE26Nmt mice developed diabetes similar to OVE26 mice, but MT overexpression reduced podocyte damage, indicated by more podocytes, less glomerular cell death, and higher density of podocyte foot processes. In addition, expansion of glomerular and mesangial volume were significantly less in OVE26Nmt mice compared with OVE26 mice. Four-month-old OVE26Nmt mice had a 70 to 90% reduction in 24-h albumin excretion, but this protection does not seem to be permanent. These results provide evidence for the role of oxidative damage to the podocyte in diabetic mice and show that protection of the podocyte can reduce or delay primary features of diabetic nephropathy.

Adriamycin nephrotoxicity is reduced by metallothionein over-expression and kidney gene expression is modified by diabetes in the OVE26 diabetic model.

“…Metallothionein is a low molecular weight, cysteine-rich, inducible protein, which is capable of scavenging many different types of ROS. Our lab developed a transgenic mouse line in FVB mice designated Nmt, which we have recently described [40]. In Nmt mice MT is over-expressed in podocytes using the podocyte-specific nephrin promoter (a more complete description of the Nmt trans gene is 13 contained in Zheng et al [40]).…”

“…Our lab developed a transgenic mouse line in FVB mice designated Nmt, which we have recently described [40]. In Nmt mice MT is over-expressed in podocytes using the podocyte-specific nephrin promoter (a more complete description of the Nmt trans gene is 13 contained in Zheng et al [40]). The morphology ofNmt glomeruli appears normal and MT staining is clearly increased in Nmt glomeruli compared to FVB glomeruli, as shown in Figure 2.…”

“…Our lab developed a transgenic line of mice (called NMT mice) with the antioxidant protein metallothionein (MT) over-expressed in podocytes [40]. We demonstrated that this line of mice was significantly protected from diabetic nephropathy.…”

Differential expression of endoplasmic reticulum stress-response proteins in different renal tubule subtypes of OVE26 diabetic mice

“…To determine whether excessive proteinuria plays a role in this induction, CHOP expression was analyzed in kidney sections from diabetic OVE26 and OVE26-Nmt7 mice. The OVE26-Nmt7 mice are a cross of OVE26 diabetic mice with Nmt transgenic mice which have podocyte-specific expression of metallothionein (Zheng et al 2008). The OVE26-Nmt7 mice are similar to OVE26 diabetic mice in developing diabetes but exhibit much less podocyte and glomerular damage.…”

“…The OVE26-Nmt7 mice are similar to OVE26 diabetic mice in developing diabetes but exhibit much less podocyte and glomerular damage. For this set of studies, we used 4-month-old mice in each group since OVE26-Nmt7 diabetic mice have a fourfold reduction in albuminuria, compared with OVE26 mice at this age (Zheng et al 2008). Average urinary albumin excretion of OVE-Nmt7 mice used for this study was 722.7±192 μg/24 h, compared with 12,410.3± 4498 in 4-month-old OVE26 diabetic mice.…”