Sodium-glucose transporter type 3-mediated neuroprotective effect of acetylcholine suppresses the development of cerebral ischemic neuronal damage

Cerebral ischemia can be exacerbated by post-ischemic hyperglycemia, which may involve the cerebral sodium-glucose transporter (SGLT). However, the contribution of each SGLT isoform in cerebral ischemia is still unclear. SGLT-1, -3, -4, and -6 have been reported to be expressed in various brain regions. Among these isoforms, only SGLT-3 does not transport glucose, but depolarizes the plasma membrane when glucose is bound, suggesting that SGLT-3 is a glucose sensor. Therefore, in this study, we investigated the involvement of cerebral SGLT-3 in the development of ischemia. The mouse model of focal ischemia was generated by middle cerebral artery occlusion (MCAO). Neuronal damage was assessed by histological and behavioral analyses. Fasting blood glucose levels on day 1 after MCAO were not affected in SGLT-3 siRNA-mediated knockdown of SGLT-3. The development of infarct volume and behavioral abnormalities on day 1 after MCAO were exacerbated in SGLT-3 knockdown mice (control group: n = 7, 94.2 ± 21.8 mm3, 2 (1.6-2.4), SGLT-3 knockdown group: n = 6, 1414.8 ± 492.4 mm3, 6 (5.8-6.3), P < 0.05). Moreover, SGLT-3 expression levels were significantly decreased in the striatum (65.0 ± 8.1%, P < 0.05) on day 1, and in the hippocampus (67.6 ± 7.2%, P < 0.05) and hypothalamus (47.5 ± 5.1%, P < 0.01) on day 3 after MCAO (n = 12-13). These effects were significantly inhibited by donepezil (DPZ) treatment (SGLT-3 knockdown group: n = 6, 1419.0 ± 181.5 mm3, 3.6 (3.4-3.7), SGLT-3 knockdown and 3 mg/kg DPZ-treated group: n = 5, 611.3 ± 205.3 mm3, 1.5 (1.4-1.8), P < 0.05). Immunofluorescence revealed that SGLT-3 and choline acetyltransferase were co-localized in the cortex. Our results indicated that cerebral SGLT-3 suppressed neuronal damage by the activation of cholinergic neurons, which are neuroprotective. In contrast, other cerebral SGLT isoforms may be involved in the development of ischemia.