Sodium-glucose co-transporter (SGLT) inhibitor restores lost axonal varicosities of the myenteric plexus in a mouse model of high-fat diet-induced obesity

Diabetes Renders Photoreceptors Susceptible to Retinal Ischemia-Reperfusion Injury

Purpose

Studies have suggested that photoreceptors (PR) are altered by diabetes, contributing to diabetic retinopathy (DR) pathology. Here, we explored the effect of diabetes on retinal ischemic injury.

Methods

Retinal ischemia-reperfusion (IR) injury was caused by elevation of intraocular pressure in 10-week-old BKS db/db type 2 diabetes mellitus (T2DM) mice or C57BL/6J mice at 4 or 12 weeks after streptozotocin (STZ)-induced type 1 diabetes mellitus (T1DM), and respective nondiabetic controls. Retinal neurodegeneration was evaluated by retinal layer thinning, TUNEL staining, and neuron loss. Vascular permeability was evaluated as retinal accumulation of circulating fluorescent albumin. The effects of pretreatment with a sodium-glucose co-transporter (SGLT1/2) inhibitor, phlorizin, were examined.

Results

Nondiabetic control mice exhibited no significant outer retinal layer thinning or PR loss after IR injury. In contrast, db/db mice exhibited significant outer retina thinning (49%, P < 0.0001), loss of PR nuclei (45%, P < 0.05) and inner segment (IS) length decline (45%, P < 0.0001). STZ-induced diabetic mice at 4 weeks showed progressive thinning of the outer retina (55%, by 14 days, P < 0.0001) and 4.3-fold greater number of TUNEL+ cells in the outer nuclear layer (ONL) than injured retinas of control mice (P < 0.0001). After 12 weeks of diabetes, the retinas exhibited similar outer layer thinning and PR loss after IR. Diabetes also delayed restoration of the blood-retinal barrier after IR injury. Phlorizin reduced outer retinal layer thinning from 49% to 3% (P < 0.0001).

Conclusions

Diabetes caused PR to become highly susceptible to IR injury. The ability of phlorizin pretreatment to block outer retinal thinning after IR suggests that the effects of diabetes on PR are readily reversible.

Treatment of tubular damage in high-fat-diet-fed obese mice using sodium-glucose co-transporter inhibitors

A long-term high-fat diet (HFD) causes obesity and changes in renal lipid metabolism and lysosomal dysfunction in mice, causing renal damage. Sodium-glucose co-transporter inhibitors, including phlorizin, exert nephroprotective effects in patients with chronic kidney disease, but the underlying mechanism remains unclear. A HFD or standard diet was fed to adult C57BL/6J male mice, and phlorizin was administered. Lamellar body components of the proximal tubular epithelial cells (PTECs) were investigated. After phlorizin administration in HFD-fed mice, sphingomyelin and ceramide in urine and tissues were assessed and label-free quantitative proteomics was performed using kidney tissue samples. Mitochondrial elongation by fusion was effective in the PTECs of HFD-fed obese mice under phlorizin administration, and many lamellar bodies were found in the apical portion of the S2 segment of the proximal tubule. Phlorizin functioned as a diuretic, releasing lamellar bodies from the apical membrane of PTECs and clearing the obstruction in nephrons. The main component of the lamellar bodies was sphingomyelin. On the first day of phlorizin administration in HFD-fed obese mice, the diuretic effect was increased, and more sphingomyelin was excreted through urine than in vehicle-treated mice. The expressions of three peroxisomal β-oxidation proteins involved in fatty acid metabolism were downregulated after phlorizin administration in the kidneys of HFD-fed mice. Fatty acid elongation protein levels increased with phlorizin administration, indicating an increase in long-chain fatty acids. Lamellar bodies accumulated in the proximal renal tubule of the S2 segment of the HFD-fed mice, indicating that the urinary excretion of lamellar bodies has nephroprotective effects.

High-Fat Diet and Age-Dependent Effects of IgA-Bearing Cell Populations in the Small Intestinal Lamina Propria in Mice

Several studies highlighted that obesity and diabetes reduce immune function. However, changes in the distribution of immunoglobins (Igs), including immunoglobulin-A (IgA), that have an important function in mucosal immunity in the intestinal tract, are unclear. This study aimed to investigate the impaired immune functions in the context of a diet-induced obese murine model via the assessment of the Igs in the intestinal villi. We used mice fed a high-fat diet (HFD) from four to 12 or 20 weeks of age. The distributions of IgA, IgM, and IgG1 were observed by immunohistochemistry. Interestingly, we observed that IgA was immunolocalized in many cells of the lamina propria and that immunopositive cells increased in mice aged 12 to 20 weeks. Notably, mice fed HFD showed a reduced number of IgA-immunopositive cells in the intestinal villi compared to those fed standard chow. Of note, the levels of IgM and IgG1 were also reduced in HFD fed mice. These results provide insights into the impaired mucosal immune function arising from diet-induced obesity and type 2 diabetes.