Elevated circulating TGFβ1 during acute liver failure activates TGFβR2 on cortical neurons and exacerbates neuroinflammation and hepatic encephalopathy in mice

Abstract

Background Acute liver failure resulting from drug-induced liver injury can lead to the development of neurological complications called hepatic encephalopathy (HE). Hepatic transforming growth factor beta 1 (TGFβ1) is upregulated due to liver failure in mice and inhibiting circulating TGFβ reduced HE progression. However, the specific contributions of TGFβ1 on brain cell populations and neuroinflammation during HE are not known. Therefore, the aim of this study was to characterize hepatic and brain TGFβ1 signaling during acute liver failure and its contribution to HE progression using a combination of pharmacological and genetic approaches. Methods C57Bl/6 or neuron-specific transforming growth factor beta receptor 2 (TGFβR2) null mice (TGFβR2 ΔNeu ) were treated with azoxymethane (AOM) to induce acute liver failure and HE. The activity of circulating TGFβ1 was inhibited in C57Bl/6 mice via injection of a neutralizing antibody against TGFβ1 (anti-TGFβ1) prior to AOM injection. In all mouse treatment groups, liver damage, neuroinflammation, and neurological deficits were assessed. Inflammatory signaling between neurons and microglia were investigated in in vitro studies through the use of pharmacological inhibitors of TGFβ1 signaling in HT-22 and EOC-20 cells. Results TGFβ1 was expressed and upregulated in the liver following AOM injection. Pharmacological inhibition of TGFβ1 after AOM injection attenuated neurological decline, microglia activation, and neuroinflammation with no significant changes in liver damage. TGFβR2 ΔNeu mice administered AOM showed no effect on liver pathology but significantly reduced neurological decline compared to control mice. Microglia activation and neuroinflammation were attenuated in mice with pharmacological inhibition of TGFβ1 or in TGFβR2 ΔNeu mice. TGFβ1 increased chemokine ligand 2 (CCL2) and decreased C-X3-C motif ligand 1 (CX3CL1) expression in HT-22 cells and reduced interleukin-1 beta (IL-1ß) expression, tumor necrosis factor alpha (TNFα) expression, and phagocytosis activity in EOC-20 cells. Conclusion Increased circulating TGFβ1 following acute liver failure results in activation of neuronal TGFβR2 signaling, driving neuroinflammation and neurological decline during AOM-induced HE. Electronic supplementary material The online version of this article (10.1186/s12974-019-1455-y) contains supplementary material, which is available to authorized users.

CX3CL1/CX3CR1 axis attenuates early brain injury via promoting the delivery of exosomal microRNA-124 from neuron to microglia after subarachnoid hemorrhage

“…As previously reported, cell-cell contacts in the CX3CL1/CX3CR1 axis were involved in the transfer of miR-124 [16], and this conjugation kept microglia "quiescent" [53,54]. In CNS, CX3CL1 mainly expressed in neurons and had two different forms: one is a membrane-bound glycoprotein providing direct interaction with CX3CR1, which expressed in microglia; the other is a soluble form working as an extracellular mediator [25].…”

The Direct Contribution of Astrocytes and Microglia to the Pathogenesis of Hepatic Encephalopathy

“…107 In azoxymethane-treated mice, cortex IL-1b, IL-6, TNFa and CCL2 protein expression were increased. 108 The use of anti-TGFb1 antibodies or genetic ablation of transforming growth factor beta receptor 2 (known as TGFbR2) in neurons of azoxymethane-treated mice led to reduced microglia activation and normalized levels of IL-1b, IL-6, TNFa and CCL2, giving support that TGFbR2-mediated signaling contributes to neuroinflammation during HE. 108 Interestingly, the use of the gamma aminobutyric acid antagonist bicuculine was found to reduce the expression of IL-1b, but not effect microglia activation in ammonium chloride-fed rats.…”

“…108 The use of anti-TGFb1 antibodies or genetic ablation of transforming growth factor beta receptor 2 (known as TGFbR2) in neurons of azoxymethane-treated mice led to reduced microglia activation and normalized levels of IL-1b, IL-6, TNFa and CCL2, giving support that TGFbR2-mediated signaling contributes to neuroinflammation during HE. 108 Interestingly, the use of the gamma aminobutyric acid antagonist bicuculine was found to reduce the expression of IL-1b, but not effect microglia activation in ammonium chloride-fed rats. 109 This gives support that the pro-inflammatory state during elevated levels of ammonia in the brain may not be directly linked to microglia activation, though more studies are need in this area to better characterize this.…”

Substantia nigra Smad3 signaling deficiency: relevance to aging and Parkinson’s disease and roles of microglia, proinflammatory factors, and MAPK

“…Canonical TGF-β1 signal transduction pathway is comprised of ligand binding to the type II receptor (TβR-II) and subsequently phosphorylating the type I receptor (TβR-I). Upon phosphorylation, the receptor complex leads to the recruitment and phosphorylation of Smad2 and Smad3, which form a heteromeric complex with Smad4 and translocate into nucleus to regulate the expression of targeted genes [ 17 , 18 ]. Smad3 signaling has been shown to be required for the development and homeostasis of microglia and plays a key role in the regulation of microglial activity [ 19 ].…”