Involvement of the TLR4 pathway and related mediators in stress response, neuroinflammation, and behavioral effects in animal models

Animal (strain, sex, size/age)Stress modelBehavioral assessmentMajor findingsModulation of TLR4 pathwayReference
C3H/HeN mice, male
adult		Immobilization stress (1 eCB/7 days)NoneStress induces ↑COX-2, ↑iNOS, and ↑lipid peroxidation in HeN but not in HeJ animalsC3H/HeJ miceCaso et al., 2008 [126]
C57BL/6N mice, male
6–12 weeks old		Single or repeated social defeat stress (4 or 10 days)Social interaction test, EPMRepeated stress induces microglia activation, ↑IL-1α, ↑TNF-α, and social avoidance, all absent in TLR2/4 double KO miceTLR2/4 KO miceNie et al., 2018 [129]
C57Bl/6 mice, male
8–12 weeks old		Footshock stress (one or two sessions of 180 inescapable footshocks, 0.3 mA duration of 6 s)Learned helplessness; number of failures to scape footshocksStress in WT animals but not TLR4 KO promotes ↑HMGB1, ↑TNF-α, ↑IL-6, ↑IL-1β, ↑TLR4, and ↑NLRP3 in PFC
TLR4 KO animals display resistance to learned helplessness depression-like behavior		TLR4 KO miceCheng et al., 2016 [100]
ICR mice, male
Weighing 18–22 g		CUMS (8 weeks) LPS (5 days, 0,83 mg/kg, i.p./day)SPT, OFT, TST, FSTStress: ↑TNF-α, ↑IL-6, ↑IL-1β, and ↑TLR4 in hippocampus and depressive-like behavior
Stress effects were reversed by TAK-242 and baicalin		TAK-242 (3 mg/kg, i.p.) and baicalin (60 or 30 mg/kg, i.g.)Guo et al., 2019 [96]
C57Bl/6 mice, male
8–10 weeks old		CUMS (6 weeks)FST, TST, OFT, SPTStress ↑HMGB1, ↑Iba-1, ↑TNF-α, ↑TNFR1, ↑GM-CSF, ↑IL-1β, ↑IL-5, ↑IL-6, ↑IL-7, ↑IL-9, ↑IL-13, ↑IFNγ, ↑NO, ↑IDO, ↓dopamine, ↓5-HT, ↑TLR4, ↑MyD88, ↑p-IkBα, and ↑p-NFκB p65 in PFC.
Stress induced depressive-like behavior in WT but not TLR4 KO mice
Stress effects were reversed by drug treatment		TLR4 KO mice and arctigenin (25, 50, or 100 mg/kg, i.p.)Xu et al., 2020 [101]
C57Bl/6J mice, male
8 weeks old		LPS (1 mg/kg, i.p.)TST, SPT, FSTLPS ↑IL-1β, ↑Iba-1, ↑RANTES, and ↑MCP-1 in PFCNoneHe et al., 2020 [74]
ICR mice, male
weighing 18–22 g		CUMS (6 weeks)SPT, TST, OFT, FSTStress ↓5-HT, ↓NE, ↑TNF-α, ↑IL-6, ↑IL-1β, ↑TLR4, ↑p-NFκB, ↑p-p38, ↑NLRP3, and ↑caspase-1 in PFC and hippocampus
Stress ↓SOD, ↓GPx, and ↓MDA in the serum
Stress promotes depressive-like behavior prevented by Cli-095		TAK-242 (referred as Cli-095 in this paper) (3 mg/kg, i.g.)Fu et al., 2019 [110]
BALB/c mice, male
8 weeks old		CUMS (4 weeks); i.c.v. administration of fr-HMGB1 or non-oxid HMGBSPT, TST, OFTStress ↑HMGB1 (serum and cortex) and depressive like behavior
fr-HMGB1, but not non-oxid HMGB1, induced depressive-like behavior, ↑TNF-α, and ↓ MBP in hippocampus, which was reversed by TAK-242		TAK-242 (3 mg/kg, i.p.)Lian et al., 2017 [117]
C57Bl/6 mice and ob/ob mice, male
7–8 weeks old		CUMS (3 weeks)SPT, OFT, Morris water mazeStress induced depressive-like behavior and alterations in target quadrant in Morris water maze
Stress ↑TNF-α, ↑IL-6, and ↑IL-1β in hippocampus and frontal cortex
TAK-242 reversed the depressive-like behavior in c57 and ob/ob mice
Also, reversed stress effects in TNF-α, IL-6, and IL-1β levels in the brain		TAK-242 (3 mg/kg, i.p.)Wang et al., 2018 [43]
ICR mice, male
6–8 weeks old		LPS (0,83 mg/kg, i.p.)OFT, TST, FST, SPTLPS induced ↑TNF-α, ↑IL-6, ↑IL-1β, ↑CD89, ↑TLR4, ↑p-IkBα, ↑NFκB p65, and ↑HMGB1 in hippocampus
LPS also induced depressive-like behavior reversed by the drug used		Saikosaponin-d (1 mg/kg, i.g.)Su et al., 2020 [112]
ICR mice, male
8–10 weeks old		LPS (1 mg/kg, i.p.)FST, SPT, NSFTLPS induced ↑Iba-1, ↑GFAP, ↑TNF-α, ↑IL-6, ↑IL-1β, ↑TLR4, ↑p-NFκB, ↑MyD88, ↓BDNF in hippocampus, and depressive- like behavior
These effects are reversed by the pre-treatment with fast green FCF		Molecular docking simulation indicates possible interaction between TLR4 and fast green FCF (100 mg/kg, i.p.)Yang et al., 2019 [73]
NMRI mice, male
Adult
Weighing20–25 g		LPS (0,83 mg/kg, i.p.)OFT, FSTLPS induced ↑expression of TLR4, p-NFκB, and IDO in mice hippocampus and depressive-like behavior
GM-CSF inhibited the LPS effects		Modulation of TLR4 pathway with GM- CSF (30 μg/kg, i.p.)Hemmati et al., 2019 [111]
Wistar rats, male
Weighing 150–180 g		CRS (6 eCB/day, 28 days)SPT, OFT, FST, social interaction testCRS induced ↑TNF-α, ↑IL-6, ↑IL-1β, and ↓BDNF in rat hippocampus and PFC. CRS also induced alterations in neurotransmitters, ↓GABA, ↑glutamate, and ↓GAD in hippocampus and PFC
CRS also promoted depressive-like behavior and ↓social interaction
All effects were reversed in a dose-dependent manner by eritoran		TLR4 antagonist, eritoran (5 mg/kg, i.p.)Aboul-Fotouh et al., 2018 [98]
Wistar rats, male
adult
Weighing 250–300g		LPS (20 μg or 80 μg, i.c.v.)OFT, EPM, FST, Morris water mazeLPS induced ↑TNF-α, ↑IL-1β
LPS induced depressive- and anxiety-like behaviors and cognitive impairments in Morris water maze		NoneNa et al., 2021 [131]
Wistar Hannover rats, male
Weighing 200–225g		CMS (21 days)FST, SPT, splash test, EPMCMS induces bacterial translocation, ↑plasma LPS and depressive-like behaviorNoneMartín-Hernández et al., 2016 [130]
Offspring of C57BL/6 mice, male and femaleMIA (single dose of LPS on embryonic day 12, 50 μg/kg, i.p.)NonePro-inflammatory profile of cytokines and ↑TLR4 in amygdala of MIA offspringNoneO’Loughlin et al., 2017 [114]

↑: increase; ↓: decrease; EPM: elevated plus-maze; WT: wild-type; SPT: sucrose preference test; OFT: open field test; TST: tail suspension test; FST: forced swim test; Iba-1: ionized calcium binding adaptor molecule 1; TNFR1: tumor necrosis factor receptor 1; GM-CSF: granulocyte-macrophage colony-stimulating factor; NO: nitric oxide; 5-HT: 5-hydroxytriptamine; p-NFκB: phosphorylated NFκB; RANTES: regulated on activation, normal T cell expressed and secreted; MCP-1: monocyte chemoattractant protein-1; NE: norepinephrine; p-p38: phosphorylated p38; SOD: superoxide dismutase; GPx: glutathione peroxidase; MDA: malondialdehyde; MBP: myelin basic protein; NSFT: novelty suppressed feeding test; GFAP: Glial fibrillary acidic protein; GABA: γ-aminobutyric acid; GAD: glutamate decarboxylase; CMS: chronic mild stress; MIA: maternal immune activation