Targeting Altered Mitochondrial Biogenesis in the Brain of Diabetic Rats: Potential Effect of Pioglitazone and Exendin-4

Abstract

Background: Neuroprotective mechanisms triggered by peroxisome proliferator-activated receptor-gamma agonist: pioglitazone (PIO) and glucagon-like peptide 1 analog: exendin-4 (Ex-4) in neurological diseases were reported, but whether mitochondrial biogenesis is involved or not in their neuro-protective mechanisms in type 1 Diabetes Mellitus (T1DM); has not been studied before. To bridge this gap, we investigated the effect of PIO and Ex-4 on brain mitochondrial biogenesis in streptozotocin- induced diabetes in rats.

Methods: Seven weeks after induction of diabetes in rats, serum fasting glucose and insulin were measured in studied groups. The brain was removed for histological analysis and assessment of: mitochondrial complexes I and II, ATP, H₂O₂, brain derived neurotrophic factor (BDNF), cytochrome c and hemeoxygenase (HO)-1 activity, and relative gene expression of the nuclear factor; Nrf2 and the apoptotic markers: bax & bcl2 and mitochondrial biogenesis markers; peroxisome proliferator-activated receptor γ coactivator (PGC) 1-α and sirtuin 1 (SIRT-1) and AMP-activated protein kinase (AMPK) and c-Jun-N-terminal kinase (JNK) proteins.

Results: Brain in untreated rats showed neurodegeneration area and significantly rising H₂O₂ and JNK, up-regulation of bax, down-regulation of bcl2. These changes were paralleled with significant reduction in Nrf2, HO-1, BDNF, complex I, II and ATP and SIRT-1/ PGC1-α expression. PIO and Ex-4 significantly improved the reported changes. Combined modality showed better improvement relative to each drug alone.

Conclusion: PIO and Ex-4 may have neuroprotective effects in T1DM, via targeting altered mitochondrial biogenesis probably due to modulation of brain SIRT-1 signaling, improvement of oxidative stress and equilibrating the balance between pro-apoptotic and anti-apoptotic mediators.

Keywords: Brain derived neurotrophic factor; Diabetic neurodegeneration; Exendin-4; PGC1- α; oxidative stress.

Fig.1

Levels of: hydrogen peroxide (H2O2); heme oxygenase-1 activity (HO-1) in all studied groups. Values are represented as mean ± S.D, (n = 6), *Statistically significant as compared with control at P ≤ 0.05, # Statistically significant as compared with the diabetic group at P ≤ 0.05.

Fig.2

Levels of BDNF protein and brain relative expression of NF-E2 related factor (Nrf) 2; level in brain tissue in all studied groups. Values are represented as mean ± SD, (n = 6), *Statistically significant as compared with control at P ≤ 0.05; #Statistically significant as compared with the diabetic group at P ≤ 0.05.

Fig.3

Relative gene expression of studied genes and the levels of AMPK and JNK proteins A: Western blot of AMPK and JNK proteins. B: The relative gene expression of AMPK; JNK; SIRT-1; PGC 1-α in all studied groups. AMPK: AMP-activated protein kinase; JNK: c-Jun-N-terminal kinase; SIRT-1: sirtuin 1; PGC1 α: Peroxisome proliferator-activated receptor gamma coactivator1-alpha. Values are represented as mean ± S.D, (n = 6), *Statistically significant as compared with control at P ≤ 0.05; #Statistically significant as compared with the diabetic group at P ≤ 0.05.

Fig.4

Sections in the frontal cerebral cortex of all studied groups (H&E ×200) for EPL (H&E ×400) for IPL: a) EPL in the control group, b) IPL in the control group, c) EPL in the diabetic rats, d) IPL in the diabetic rats, e) EPL with Ex-4 treatment, f) IPL with Ex-4 treatment, g) EPL with PIO treatment, h) IPL with PIO treatment, i) EPL with combined Ex-4 +PIO treatment, j) IPL with combined Ex-4 +PIO treatment. H&E: Hematoxylin & Eosin, EPL; external pyramidal layer, IPL; internal pyramidal layer, Ex-4; Exendin-4, PIO; pioglitazone, p; pyramidal cells, g; glial cells, s; stellate cells, gr; granule cells, d; deformed neurons, a; acidophilic neurons with dark nuclei.