Addressing Peroxisome Proliferator-Activated Receptor-gamma in 3-Nitropropionic Acid-Induced Striatal Neurotoxicity in Rats

Abstract

Telmisartan (TEL) is an angiotensin II type 1 receptor blocker and a partial activator of peroxisome proliferator-activated receptor-gamma (PPARγ), which regulates inflammatory and apoptotic pathways. Increasing evidence has demonstrated the PPARγ agonistic property of TEL in several brain disorders. This study aims to explore the neuroprotective impact of TEL in 3-nitropropionic acid (3-NP)-induced neurotoxicity in rats. The PPARγ effect of TEL was affirmed by using the PPARγ agonist pioglitazone (PIO), and the antagonist GW9662. 3-NP led to a significant reduction in body weight alongside motor and cognitive functioning. The striata of the 3-NP-treated rats showed energy-deficit, microglia-mediated inflammatory reactions, apoptotic damage as well as histopathological lesions. PIO and TEL improved motor and cognitive perturbations induced by 3-NP, as confirmed by striatal histopathological examination, energy restoration, and neuronal preservation. Both drugs improved mitochondrial biogenesis evidenced by elevated mRNA expression of PPARγ, PGC-1α, and TFAM, alongside increased striatal ATP and SDH. The mitochondrial effect of TEL was beyond PPARγ activation. As well, their anti-inflammatory effect was attributed to suppression of microglial activation, and protein expression of pS536 p65 NF-κB with marked attenuation of striatal inflammatory mediator's release. Anti-inflammatory cytokine IL-10 expression was concurrently increased. TEL effectively participated in neuronal survival as it promoted phosphorylation of Akt/GSK-3β, further increased Bcl-2 expression, and inhibited cleavage of caspase-3. Interestingly, co-treatment with GW9662 partially revoked the beneficial effects of TEL. These findings recommend that TEL improves motor and cognitive performance, while reducing neuronal inflammation and apoptosis in 3-NP-induced neurotoxicity via a PPARγ-dependent mechanism.

Keywords: 3-nitropropionic acid; Neurotoxicity; Peroxisome proliferator-activated receptor gamma (PPARγ); Striatum.

Fig. 1

Schedule of the experimental study. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; IHC: immunohistochemistry; WB: Western blot; BW: body weight; OFT: open field test; NOR: novel object recognition test)

Fig. 2

Effects of PIO and TEL with and without PPARγ blocker on (a) number of squares, (b) latency time, (c) rearing frequency, (d) grooming frequency, and (e) fall-off time in 3-NP-treated rats. Data are presented as means ± SD (n = 15) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)

Fig. 3

Effects of PIO and TEL with and without PPARγ blocker on (a) body weights, (b) discrimination index, and (c) recognition index in 3-NP-treated rats. Data are presented as means ± SD (n = 15) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)

Fig. 4

Effects of PIO and TEL with and without PPARγ blocker on striatal gene expressions of (a) PPARγ, (b) PGC-1α, and (c) TFAM, as well as striatal levels of (d) SDH, and (e) ATP in 3-NP-treated rats. Data are presented as means ± SD (n = 6) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)

Fig. 5

Effects of PIO and TEL with and without PPARγ blocker on striatal protein/gene expressions of (a) p65 NF- κB and (b) IL-10, as well as striatal levels of (c) TNF-α, (d) IL-1β, and (e) IL-6 in 3-NP-treated rats. Data are presented as means ± SD (n = 6) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)

Fig. 6

Effects of PIO and TEL with and without PPARγ blocker on striatal protein/gene expression of (a) pS473 Akt, (b) pS9 GSK-3β, (c) Cleaved caspase-3, and (d) Bcl-2 in 3-NP-treated rats. Data are presented as means ± SD (n = 6) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)

Fig. 7

Effects of PIO and TEL with and without PPARγ blocker on histopathological alterations in 3-NP-treated rats. Representative H&E-stained striatal sections: (a) control, (b) 3NP group, (c) PIO-pre-treated group, (d) PIO&GW-pre-treated group, (e) TEL-pre-treated group, and (f) TEL&GW-pre-treated group. Black arrows indicate intact neurons, red arrows indicate necrotic neurons, while black heads indicate microglial infiltrates

Fig. 8

Effects of PIO and TEL with and without PPARγ blocker on neuronal survival in 3-NP rats. Representative cresyl violet-stained striatal sections: (a) control, (b) 3NP group, (c) PIO-pre-treated group, (d) PIO&GW-pre-treated group, (e) TEL pre-treated group, and (f) TEL&GW-pre-treated group. (g) Quantification of intact neurons in striatal sections of the experimental groups. Data are presented as means ± SD (n = 3) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)

Fig. 9

Effects of PIO and TEL with and without PPARγ blocker on immunoreactivity of Iba-1⁺ in the striatum of 3-NP-treated rats. (a) Control, (b) 3-NP group, (c) PIO-pre-treated group, (d) PIO&GW-pre-treated group, (e) TEL-pre-treated group, and (f) TEL&GW-pre-treated group. (g) Quantification of Iba-1-positive microglial cells in striatal sections of the experimental groups. Data are presented as means ± SD (n = 3) and analyzed by one-way ANOVA followed by the Tukey’s post hoc test. @ vs control, # vs 3-NP group, $ vs PIO-pre-treated group, & vs TEL-pre-treated group. (PIO: pioglitazone; TEL: telmisartan; 3-NP: 3-nitropropionic acid; GW: GW9662)