A tale of two fronts : novel experimental strategies to improve stroke outcome in type 2 diabetes

Background

Type 2 Diabetes (T2D) constitutes a critical health issue worldwide, which is associated with poor stroke outcome and lasting disability. However, the exact mechanisms through which T2D worsens stroke outcome are not determined and despite the high medical need for therapies, no treatment is currently available. The hypothesis behind this thesis was built on the concept that by targeting the impaired T2D metabolism either before or after stroke, stroke outcome could be improved.

Aim

The aim of this thesis was to therefore investigate whether a weight loss (WL) intervention (mimicking a lifestyle intervention) before stroke (Paper I: diet change) as well as several pharmacological interventions with antidiabetic treatments implemented either before (Paper II: Glucagon-like peptide-1 receptor (GLP-1R)/Neuropeptide Y receptor Y2 (NPY2R) co-activation) or after stroke (Papers III, IV: GLP-1R activation & Sodium-glucose cotransporter-2 (SGLT2) inhibition) improve stroke outcome in T2D mice and to identify some of the underlying mechanisms.

Methods

To achieve these aims, C57BL/6J mice were fed with high-fat diet (HFD) for several months to induce obesity and T2D features (i.e. hyperglycemia and insulin resistance). Thereafter, the mice received either a diet change leading to WL or pharmacological interventions before (Papers I, II) or after (Papers III, IV) a stroke induced by transient middle cerebral artery occlusion (tMCAO). The chronic stroke outcome was assessed by measuring the recovery of the grip strength and/or the lateralized sensorimotor integration of the mice several weeks after tMCAO, until sacrifice. Mouse brains were then collected and various immunohistochemical assessments were performed.

Results

All the aforementioned interventions (Papers I-IV) in the T2D mice resulted in better stroke outcome compared to the diabetic controls, suggesting that the improved metabolism in T2D before or after stroke, was beneficial to improve stroke outcome. Several mechanisms by which stroke outcome was ameliorated in the treatment groups were also identified.

In Paper I, the 4-month dietary change leading to WL before tMCAO, which improved fasting glycemia and insulin sensitivity, resulted in improved stroke outcome in association with decreased cellular atrophy of GABAergic parvalbumin (PV)+ interneurons and neuroinflammation, as well as reduced astrocyte reactivity in contralateral striatum.

In Paper II, GLP-1R activation by Semaglutide induced a significant WL before tMCAO, upstream of glycemia regulation, which resulted in improved post-stroke outcome. These effects were further enhanced by NPY2R co-activation by the NPY2R agonist BI8271 in association with the normalization of peripheral insulin- like growth factor 1 (IGF-1) and homocysteine levels. Furthermore, GLP-1R and NPY2R activation exerted acute neuroprotection, which was independent of their metabolic effects.

In Paper III, the GLP-1R activation by Exendin-4 after tMCAO improved glucose metabolism and resulted in improved stroke outcome in association with the counteraction of T2D-induced atrophy of PV+ interneurons and the reduction of T2D-induced microglial neuroinflammatory response.

In Paper IV, the SGLT2 inhibition by Empagliflozin after tMCAO resulted in improved stroke outcome in the diabetic mice via the normalization of glycemia, but not insulin sensitivity, in association with increased serum fibroblast growth factor 21 (FGF-21) and normalized parenchymal pericyte density.

Conclusion

In an era of obesity and diabetes, with a high prevalence of cardiovascular complications, including stroke, specific strategies to ameliorate the poor stroke outcome in T2D are highly needed. To this end, four strategies are proposed in this thesis that could be evaluated in future clinical trials; two offering a prophylactic (Papers I, II; before stroke) and two a curative (Papers III, IV; after stroke) value. A pre-stroke dietary intervention and the repurposing of several clinically used antidiabetic treatments, either pre- or post-stroke, are hereby suggested to offer novel therapeutic options to improve stroke outcome for numerous people.

List of scientific papers

I. Karampatsi, D. et al. Diet-induced weight loss in obese/diabetic mice normalizes glucose metabolism and promotes functional recovery after stroke. Cardiovasc Diabetol 20, 240. https://doi.org/10.1186/s12933-021-01426-z

II. Karampatsi, D. et al. Pre-Stroke Weight Loss by Glucagon-like Peptide 1 Receptor and Neuropeptide Y Receptor Y2 Activation improves Post-Stroke Functional Recovery in T2D mice. [Submitted]

III. Augestad, I. L. & Dekens, D., Karampatsi, D. et al. Normalisation of glucose metabolism by exendin-4 in the chronic phase after stroke promotes functional recovery in male diabetic mice. Br J Pharmacol. https://doi.org/10.1111/bph.15524

IV. Vercalsteren, E., Karampatsi D., et al. The SGLT2 inhibitor Empagliflozin promotes post-stroke functional recovery in diabetic mice. Cardiovasc Diabetol 23, 88, (2024). https://doi.org/10.1186/s12933