Topical Nerve Growth Factor (NGF) restores electrophysiological alterations in the Ins2Akita mouse model of diabetic retinopathy

People suffering from diabetes mellitus commonly have to face diabetic retinopathy (DR), an eye disease characterized by early retinal neurodegeneration and microvascular damage, progressively leading to sight loss. The Ins2Akita (Akita) diabetic mouse presents the characteristics of DR and experimental drugs can be tested on this model to check their efficacy before going to the clinic. Topical administration of Nerve Growth Factor (NGF) has been recently demonstrated to prevent DR in the Akita mouse, reverting the thinning of retinal layers and protecting the retinal ganglion cells (RGCs) from death. In this study, we characterize the effects of topical NGF on neuroretina function, quantified with the electroretinogram (ERG). In particular, we show that NGF can ameliorate RGC conduction in the retina of Akita mice, which correlates with a recovery of retinal nerve fiber plus ganglion cell layer (RNFL-GCL) structure. Overall, our preclinical results highlight that topical administration of NGF could be a promising therapeutic approach for DR, being capable of exerting a beneficial impact on retinal functionality.

Effect of chronic administration with human thioredoxin-1 transplastomic lettuce on diabetic mice

SCOPE

Human thioredoxin-1 (hTrx-1) is a defensive protein induced by various stresses and exerts antioxidative and anti-inflammatory effects. Previously, we described a transplastomic lettuce overexpressing hTrx-1 that exerts a protective effect against oxidative damage in a pancreatic β-cell line. In this study, we treated diabetic mice (Akita mice) with exogenous hTrx-1 and evaluated the effects.

METHODS AND RESULTS

Treatment with drinking water and single applications of exogenous hTrx-1 did not influence the feeding, drinking behavior, body weight, blood glucose, or glycosylated hemoglobin (HbA1c) levels in Akita mice. However, chronic administration of a 10% hTrx-1 lettuce-containing diet was associated with a significant reduction from the baseline of HbA1c levels compared with mice fed a wild-type lettuce-containing diet. It also resulted in an increased number of goblet cells in the small intestine, indicating that mucus was synthesized and secreted.

CONCLUSION

Our results revealed that the administration of an hTrx-1 lettuce-containing diet improves the baseline level of HbA1c in Akita mice. This effect is mediated through goblet cell proliferation and possibly related to protection against postprandial hyperglycemia by mucus, which results in the improvement of blood glucose control. These findings suggest that the hTrx-1 lettuce may be a useful tool for the continuous antioxidative and antidiabetic efficacies of the hTrx-1 protein.

Effects of teriparatide on bone in autochthonous transgenic model mice for diabetes mellitus (Akita mice)

OBJECTIVES

The purpose of this study is to evaluate the effects of teriparatide (TPTD) on bone mineral density (BMD), bone strength, and bone quality in Akita mouse models of diabetes mellitus.

METHODS

Twelve-week-old female Akita mice and control mice (C57/BL/6NCrSlc) were divided into 4 groups: control mice treated with vehicle (n = 7) or TPTD (n = 6); and Akita mice treated with vehicle (n = 6) or TPTD (n = 7). TPTD or vehicle was administered subcutaneously 3 times a week for 8 weeks. Blood glucose, serum sclerostin, total tibial BMD, femoral shaft bone strength, and bone quality using Fourier-transform infrared spectroscopy imaging were evaluated.

RESULTS

No significant differences in serum sclerostin levels were evident among these groups after 8 weeks of treatment. TPTD significantly increased BMD in control mice (+12.7%, P = 0.02) and Akita mice (+29.2%, P = 0.001) compared with vehicle. Maximum load and stiffness were significantly higher in Akita mice treated with TPTD than in Akita mice treated with vehicle (+56.6%, P = 0.03 and + 90.5%, P = 0.02, respectively). On Fourier-transform infrared spectroscopy imaging, the mineral/matrix ratio was significantly lower in Akita mice treated with vehicle than in control mice (-12.2%, P = 0.02), and TPTD treatment significantly increased the mineral/matrix ratio (P = 0.003).

CONCLUSIONS

TPTD thus improved BMD and bone strength in both control mice and Akita mice, with improvements in the mineral/matrix ratio among Akita mice.

Endothelial or vascular smooth muscle cell-specific expression of human NOX5 exacerbates renal inflammation, fibrosis and albuminuria in the Akita mouse

AIMS/HYPOTHESIS

Excessive production of reactive oxygen species (ROS) plays a detrimental role in the progression of diabetic kidney disease (DKD). Renal oxidative stress activates proinflammatory cytokines, chemokines and profibrotic factors in DKD. Increased expression of the prooxidant enzyme NADPH oxidase (NOX) 5 in kidneys of diabetic individuals has been hypothesised to correlate with renal injury and progression of DKD. Since the gene encoding NOX5 is not expressed in the mouse genome, we examined the effect of inducible human NOX5 expression in renal cells, selectively in either endothelial cells or vascular smooth muscle cells (VSMCs)/mesangial cells in a model of insulin-deficient diabetes, the Akita mouse.

METHODS

Renal structural injury, including glomerulosclerosis, mesangial expansion and extracellular matrix protein accumulation, as well as renal inflammation, ROS formation and albuminuria, were examined in the NOX5 transgenic Akita mouse model of DKD.

RESULTS

Expression of NOX5 in either endothelial cells or VSMCs/mesangial cells in diabetic Akita mice was associated with increased renal inflammation (monocyte chemoattractant protein-1, NF-κB and toll-like receptor-4) and glomerulosclerosis, as well as upregulation of protein kinase C-α and increased expression of extracellular matrix genes (encoding collagen III, fibronectin and α-smooth muscle actin) and proteins (collagen IV), most likely mediated via enhanced renal ROS production. The effect of VSMC/mesangial cell-specific NOX5 expression resulted in more pronounced renal fibrosis in comparison with endothelial cell-specific NOX5 expression in diabetic mice. In addition, albuminuria was significantly increased in diabetic VEcad⁺NOX5⁺ mice (1192 ± 194 μg/24 h) when compared with diabetic VEcad⁺NOX5^- mice (770 ± 98 μg/24 h). Furthermore, the regulatory components of NOX5 activation, including heat shock protein 90 and transient receptor potential cation channel subfamily C member 6, were upregulated only in the presence of both NOX5 and diabetes.

CONCLUSIONS/INTERPRETATION

The findings from this study highlight the importance of NOX5 in promoting diabetes-related renal injury and provide the rationale for the development of a selective NOX5 inhibitor for the prevention and/or treatment of DKD.

QRS/T-wave and calcium alternans in a type I diabetic mouse model for spontaneous postmyocardial infarction ventricular tachycardia: A mechanism for the antiarrhythmic effect of statins

BACKGROUND

The incidence of sudden arrhythmic death is markedly increased in diabetics.

OBJECTIVE

The purpose of this study was to develop a mouse model for postmyocardial infarction (post-MI) ventricular tachycardia (VT) in the diabetic heart and determine the mechanism of an antiarrhythmic effect of statins.

METHODS

ECG transmitters were implanted in wild-type (WT), placebo, and pravastatin-treated type I diabetic Akita mice. MIs were induced by coronary ligation, and Ca²⁺ transients were studied by optical mapping, and Ca²⁺ transients and sparks in left ventricular myocytes (VM) by the Ionoptix system and confocal microscopy.

RESULTS

Burst pacing of Akita mouse hearts resulted in rate-related QRS/T-wave alternans, which was attenuated in pravastatin-treated mice. Post-MI Akita mice developed QRS/T-wave alternans and VT at 2820 ± 879 beats per mouse, which decreased to 343 ± 115 in pravastatin-treated mice (n = 13, P <.05). Optical mapping demonstrated pacing-induced VT originating in the peri-infarction zone and Ca²⁺ alternans, both attenuated in hearts of statin-treated mice. Akita VM displayed Ca²⁺ alternans, and triggered activity as well as increased Ca²⁺ transient decay time (Tau), Ca²⁺ sparks, and cytosolic Ca²⁺ and decreased SR Ca²⁺ stores all of which were in part reversed in cells from statin treated mice. Homogenates of Akita ventricles demonstrated decreased SERCA2a/PLB ratio and increased ratio of protein phosphatase (PP-1) to the PP-1 inhibitor PPI-1 which were reversed in homogenates of pravastatin-treated Akita mice.

CONCLUSION

Pravastatin decreased the incidence of post-MI VT and Ca²⁺ alternans in Akita mouse hearts in part by revering abnormalities of Ca²⁺ handling via the PP-1/PPI-1 pathway.