Neuroinflammation increases GABAergic tone and impairs cognitive and motor function in hyperammonemia by increasing GAT-3 membrane expression. Reversal by sulforaphane by promoting M2 polarization of microglia

Abstract

BackgroundHyperammonemia induces neuroinflammation and increases GABAergic tone in the cerebellum which contributes to cognitive and motor impairment in hepatic encephalopathy (HE). The link between neuroinflammation and GABAergic tone remains unknown. New treatments reducing neuroinflammation and GABAergic tone could improve neurological impairment. The aims were, in hyperammonemic rats, to assess whether:Enhancing endogenous anti-inflammatory mechanisms by sulforaphane treatment reduces neuroinflammation and restores learning and motor coordination.Reduction of neuroinflammation by sulforaphane normalizes extracellular GABA and glutamate-NO-cGMP pathway and identify underlying mechanisms.Identify steps by which hyperammonemia-induced microglial activation impairs cognitive and motor function and how sulforaphane restores them.MethodsWe analyzed in control and hyperammonemic rats, treated or not with sulforaphane, (a) learning in the Y maze; (b) motor coordination in the beam walking; (c) glutamate-NO-cGMP pathway and extracellular GABA by microdialysis; (d) microglial activation, by analyzing by immunohistochemistry or Western blot markers of pro-inflammatory (M1) (IL-1b, Iba-1) and anti-inflammatory (M2) microglia (Iba1, IL-4, IL-10, Arg1, YM-1); and (e) membrane expression of the GABA transporter GAT-3.ResultsHyperammonemia induces activation of astrocytes and microglia in the cerebellum as assessed by immunohistochemistry. Hyperammonemia-induced neuroinflammation is associated with increased membrane expression of the GABA transporter GAT-3, mainly in activated astrocytes. This is also associated with increased extracellular GABA in the cerebellum and with motor in-coordination and impaired learning ability in the Y maze. Sulforaphane promotes polarization of microglia from the M1 to the M2 phenotype, reducing IL-1b and increasing IL-4, IL-10, Arg1, and YM-1 in the cerebellum. This is associated with astrocytes deactivation and normalization of GAT-3 membrane expression, extracellular GABA, glutamate-nitric oxide-cGMP pathway, and learning and motor coordination.ConclusionsNeuroinflammation increases GABAergic tone in the cerebellum by increasing GAT-3 membrane expression. This impairs motor coordination and learning in the Y maze. Sulforaphane could be a new therapeutic approach to improve cognitive and motor function in hyperammonemia, hepatic encephalopathy, and other pathologies associated with neuroinflammation by promoting microglia differentiation from M1 to M2.

Sildenafil reduces neuroinflammation in cerebellum, restores GABAergic tone, and improves motor in‐coordination in rats with hepatic encephalopathy

“…Reversal of GAT3 function and GABA release through it has been also reported in activated astrocytes of a mouse model of Alzheimer's disease . A similar GAT3‐mediated release of GABA has been suggested in activated astrocytes in cerebellum of hyperammonemic rats . Neuroinflammation would therefore contribute to increased release of GABA through GAT3 in activated astrocytes also in PCS rats.…”

“…cGMP may also modulate IL‐1b levels by modulating NF‐kB. IL‐1β transcription is mainly modulated by NF‐kB . cGMP may reduce activation of NF‐kB by a mechanism mediated by increased HSP70 protein and of its binding to IkB, the inhibitor of NF‐kB translocation to the nucleus and activation .…”

Modulators of microglial activation and polarization after intracerebral haemorrhage

“…Astrocytes also participate in microglial M1 to M2 phenotype switching. In hyperammonaemic rats, sulforaphane promoted a switch in microglial polarization from the M1 to the M2 phenotype by decreasing membrane expression of sodium-dependent and chloride-dependent GABA transporter GAT3, mainly in activated astrocytes 190 .…”

Peripheral inflammation induces neuroinflammation that alters neurotransmission and cognitive and motor function in hepatic encephalopathy: Underlying mechanisms and therapeutic implications

“…To investigate the mechanisms involved in the interplay between neuroinflammation, cGMP and GABAergic/glutamatergic neurotransmission to modulate each other and contribute to impairment of learning in the Y maze and motor coordination in hyperammonaemic rats (Figure ), Hernandez‐Rabaza et al assessed whether reducing neuroinflammation by treating hyperammonaemic rats with sulphoraphane has the following effects: normalizes extracellular GABA in the cerebellum; normalizes the glutamate‐nitric oxide‐cGMP pathway in the cerebellum in vivo; and restores learning in the Y maze and motor coordination. …”

“…As mentioned above, in activated astrocytes, the function of GAT3 was reversed, leading to the release of GABA into the extracellular fluid. This was therefore associated with increased extracellular GABA in the cerebellum, which impaired motor coordination and learning ability in the Y maze …”