High Elmo1 expression aggravates and low Elmo1 expression prevents diabetic nephropathy.

Human genome-wide association studies have demonstrated that polymorphisms in the engulfment and cell motility protein 1 gene (ELMO1) are strongly associated with susceptibility to diabetic nephropathy. However, proof of causation is lacking. To test whether modest changes in its expression alter the severity of the renal phenotype in diabetic mice, we have generated mice that are type 1 diabetic because they have the Ins2(Akita) gene, and also have genetically graded expression of Elmo1 in all tissues ranging in five steps from ∼30% to ∼200% normal. We here show that the Elmo1 hypermorphs have albuminuria, glomerulosclerosis, and changes in the ultrastructure of the glomerular basement membrane that increase in severity in parallel with the expression of Elmo 1. Progressive changes in renal mRNA expression of transforming growth factor ß1 (TGFß1), endothelin-1, and NAD(P)H oxidase 4 also occur in parallel with Elmo1, as do the plasma levels of cystatin C, lipid peroxides, and TGFß1, and erythrocyte levels of reduced glutathione. In contrast, Akita type 1 diabetic mice with below-normal Elmo1 expression have reduced expression of these various factors and less severe diabetic complications. Remarkably, the reduced Elmo1 expression in the 30% hypomorphs almost abolishes the pathological features of diabetic nephropathy, although it does not affect the hyperglycemia caused by the Akita mutation. Thus, ELMO1 plays an important role in the development of type 1 diabetic nephropathy, and its inhibition could be a promising option for slowing or preventing progression of the condition to end-stage renal disease.

Transforming growth factor-ß1 and diabetic nephropathy.

Transforming growth factor-ß1 (TGF-ß1) is established to be involved in the pathogenesis of diabetic nephropathy. The diabetic milieu enhances oxidative stress and induces the expression of TGF-ß1. TGF-ß1 promotes cell hypertrophy and extracellular matrix accumulation in the mesangium, which decreases glomerular filtration rate and leads to chronic renal failure. Recently, TGF-ß1 has been demonstrated to regulate urinary albumin excretion by both increasing glomerular permeability and decreasing reabsorption in the proximal tubules. TGF-ß1 also increases urinary excretion of water, electrolytes and glucose by suppressing tubular reabsorption in both normal and diabetic conditions. Although TGF-ß1 exerts hypertrophic and fibrogenic effects in diabetic nephropathy, whether suppression of the function of TGF-ß1 can be an option to prevent or treat the complication is still controversial. This is partly because adrenal production of mineralocorticoids could be augmented by the suppression of TGF-ß1. However, differentiating the molecular mechanisms for glomerulosclerosis from those for the suppression of the effects of mineralocorticoids by TGF-ß1 may assist in developing novel therapeutic strategies for diabetic nephropathy. In this review, we discuss recent findings on the role of TGF-ß1 in diabetic nephropathy.

Low TGFß1 expression prevents and high expression exacerbates diabetic nephropathy in mice.

Nephropathy develops in many but not all patients with long-standing type 1 diabetes. Substantial efforts to identify genotypic differences explaining this differential susceptibility have been made, with limited success. Here, we show that the expression of the transforming growth factor ß1 gene (Tgfb1) affects the development of diabetic nephropathy in mice. To do this we genetically varied Tgfb1 expression in five steps, 10%, 60%, 100%, 150%, and 300% of normal, in mice with type 1 diabetes caused by the Akita mutation in the insulin gene (Ins2(Akita)). Although plasma glucose levels were not affected by Tgfb1 genotype, many features of diabetic nephropathy (mesangial expansion, elevated plasma creatinine and urea, decreased creatinine clearance and albuminuria) were progressively ameliorated as Tgfb1 expression decreased and were progressively exacerbated when expression was increased. The diabetic 10% hypomorphs had comparable creatinine clearance and albumin excretion to wild-type mice and no harmful changes in renal morphology. The diabetic 300% hypermorphs had ∼1/3 the creatinine clearance of wild-type mice, >20× their albumin excretion, ∼3× thicker glomerular basement membranes and severe podocyte effacement, matching human diabetic nephropathy. Switching Tgfb1 expression from low to high in the tubules of the hypomorphs increased their albumin excretion more than 10-fold but creatinine clearance remained high. Switching Tgfb1 expression from low to high in the podocytes markedly decreased creatinine clearance, but minimally increased albumin excretion. Decreasing expression of Tgfb1 could be a promising option for preventing loss of renal function in diabetes.

Endothelin-1 critically influences cardiac function via superoxide-MMP9 cascade.

We have generated low-expressing and high-expressing endothelin-1 genes (L and H) and have bred mice with four levels of expression: L/L, ∼20%; L/+, ∼65%; +/+ (wild type), 100%; and H/+, ∼350%. The hypomorphic L allele can be spatiotemporally switched to the hypermorphic H allele by Cre-loxP recombination. Young adult L/L and L/+ mice have dilated cardiomyopathy, hypertension, and increased plasma volumes, together with increased ventricular superoxide levels, increased matrix metalloproteinase 9 (Mmp9) expression, and reduced ventricular stiffness. H/+ mice have decreased plasma volumes and significantly heavy stiff hearts. Global or cardiomyocyte-specific switching expression from L to H normalized the abnormalities already present in young adult L/L mice. An epithelial sodium channel antagonist normalized plasma volume and blood pressure, but only partially corrected the cardiomyopathy. A superoxide dismutase mimetic made superoxide levels subnormal, reduced Mmp9 overexpression, and substantially improved cardiac function. Genetic absence of Mmp9 also improved cardiac function, but increased superoxide remained. We conclude that endothelin-1 is critical for maintaining normal contractile function, for controlling superoxide and Mmp9 levels, and for ensuring that the myocardium has sufficient collagen to prevent overstretching. Even a modest (∼35%) decrease in endothelin-1 gene (Edn1) expression is sufficient to cause cardiac dysfunction.

Transforming growth factor beta1 and aldosterone.

PURPOSE OF REVIEW: It is well established that blocking the renin-angiotensin-aldosterone system (RAAS) is effective for the treatment of cardiovascular and renal complications in hypertension and diabetes mellitus. Although the induction of transforming growth factor beta1 (TGFbeta1) by components of the RAAS mediates the hypertrophic and fibrogenic changes in cardiovascular-renal complications, it is still controversial as to whether TGFbeta1 can be a target to prevent such complications. Here, we review recent findings on the role of TGFbeta1 in fluid homeostasis, focusing on the relationship with aldosterone. RECENT FINDINGS: TGFbeta1 suppresses the adrenal production of aldosterone and renal tubular sodium reabsorption. We have generated mice with TGFbeta1 mRNA expression graded in five steps, from 10 to 300% of normal, and found that blood pressure and plasma volume are negatively regulated by TGFbeta1. Notably, the 10% hypomorph exhibits primary aldosteronism and sodium and water retention due to markedly impaired urinary excretion of water and electrolytes. SUMMARY: These results identify TGFbeta signalling as an important counterregulatory system against aldosterone. Understanding the molecular mechanisms for the suppressive effects of TGFbeta1 on adrenocortical and renal function may further our understanding of primary aldosteronism, as well as assist in the development of novel therapeutic strategies for hypertension.

The role of transforming growth factor ß1 in the regulation of blood pressure.

Although human association studies suggest a link between polymorphisms in the gene encoding transforming growth factor (TGF) ß1 and differing blood pressure levels, a causative mechanism for this correlation remains elusive. Recently we have generated a series of mice with graded expression of TGFß1, ranging from approximately 10% to 300% compared to normal. We have found that blood pressure and plasma volume are negatively regulated by TGFß1. Of note, the 10% hypomorph exhibits primary aldosteronism and markedly impaired urinary excretion of water and electrolytes. We here review previous literature highlighting the importance of TGFß signaling as a natriuretic system, which we postulate is a causative mechanism explaining how polymorphisms in TGFß1 could influence blood pressure levels.