Behind the Paper

Both sexes develope diabetic kidney disease in type 1 diabetic CD1 mice

Joan Krepinsky Oct 16, 2023

What is diabetic kidney disease and why is it important to study it?

The global prevalence of diabetes is increasing, with an increase by more than 4-fold between 1980 and 2021 [1]. Diabetic kidney disease (DKD) is a common complication of diabetes, developing in up to 40% of patients. Its onset often begins with protein in the urine called albuminuria. Histologically, it is characterized by well-established changes that eventually manifest as fibrosis in all areas of the kidneys. This replacement of the normal kidney structure with fibrosis results in end stage kidney failure that requires dialysis or a kidney transplant to survive [2]. The current standard of care for management of DKD consists of a multipronged approach which includes blood glucose and blood pressure control, the use of renin-angiotensin-aldosterone system inhibitors, and more recently the use of sodium-glucose cotransporter-2 (SGLT2) inhibitors in select individuals. Unfortunately, these therapeutic interventions are unable to prevent the progression of DKD. Therefore, understanding how DKD progresses and testing new drug treatments in the right animal model is of high clinical importance.

 DKD progresses differently in male and females.

Sex is an important factor in DKD progression. Men are more likely to reach end stage kidney disease than women, although progression in women may be faster post-menopausally when levels of hormones such as estrogen and progesterone decline [3][4]. Women also more commonly develop DKD in the absence of proteinuria [5]. These differences could influence treatment decisions and response to treatment. It is thus important to include both male and female participants in clinical studies.

Historically, preclinical DKD studies have predominantly used male mice. Recently, efforts to assess DKD progression in both sexes in rodent models are emerging to promote the incorporation of female mice into therapeutic studies. A commonly used preclinical model of DKD is the induction of type 1 diabetes with the pancreatic beta cell toxin streptozotocin (STZ). Mouse strain was shown to influence development of DKD, with outbred CD1 mice showing more marked kidney fibrosis in comparison to other commonly used strains [6].  Studies in other mouse strains have shown that female mice are relatively resistant to developing hyperglycemia after STZ administration compared to males [7]. This may be due to protection from STZ effects by female hormones like estrogen [8]. However, the effect of sex in CD1 mice on the development of DKD has not yet been assessed and was the focus of our study.

 Key points from our work:

  1. Male and female mice have differing sensitivity to STZ.

We chose to use a single high dose of STZ to induce diabetes since low-dose repeat administration of STZ was previously shown to produce significantly variable induction of DKD in CD1 mice [9]. Surprisingly, we found that the dose used in other studies and which induced diabetes in male mice (200mg/kg) led to very high mortality in females, suggesting that female CD1 mice are more susceptible to STZ than male mice. This necessitated a dose reduction to 150mg/kg, which was well tolerated but which required a reinjection of STZ one week later to induce sufficient diabetes in many mice. We reduced this second dose to 100mg/kg. With this altered administration in females, we were able to induce a similar degree of hyperglycemia in both sexes. However, male mice exhibited a more consistent increase in blood glucose levels with less variability compared to females. 

  1. Male and female CD1 mice both develop DKD, with small differences in some key features.

Once male and female mice had similar levels of diabetes, we observed that both sexes showed signs of typical features of DKD. This included fibrosis and basement membrane thickening in the kidney filtering units (glomeruli), inflammation, protein in the urine (albuminuria) and hypertension. There were some difference in the degree to which some of these features developed, however. Enlarged kidneys and glomeruli as well as albuminuria were greater in female mice, while glomerular basement membrane thickening and blood pressure were greater in male mice.

Why is our study important?

Given the clinical differences in male and female DKD, it is important to include both sexes in preclinical therapeutic studies. Establishing the effects of sex in diabetic models is key to defining whether both sexes of a model can be used for mechanistic and efficacy studies. We have defined a protocol to induce similar type 1 diabetes in male and female CD1 mice. Using this model, we have shown that DKD develops in both sexes, enabling its use in future therapeutic preclinical studies.

References

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