Early Activation of STAT3 Regulates Reactive Astrogliosis Induced by Diverse Forms of Neurotoxicity

Abstract

Astrogliosis, a cellular response characterized by astrocytic hypertrophy and accumulation of GFAP, is a hallmark of all types of central nervous system (CNS) injuries. Potential signaling mechanisms driving the conversion of astrocytes into “reactive” phenotypes differ with respect to the injury models employed and can be complicated by factors such as disruption of the blood-brain barrier (BBB). As denervation tools, neurotoxicants have the advantage of selective targeting of brain regions and cell types, often with sparing of the BBB. Previously, we found that neuroinflammation and activation of the JAK2-STAT3 pathway in astrocytes precedes up regulation of GFAP in the MPTP mouse model of dopaminergic neurotoxicity. Here we show that multiple mechanistically distinct mouse models of neurotoxicity (MPTP, AMP, METH, MDA, MDMA, KA, TMT) engender the same neuroinflammatory and STAT3 activation responses in specific regions of the brain targeted by each neurotoxicant. The STAT3 effects seen for TMT in the mouse could be generalized to the rat, demonstrating cross-species validity for STAT3 activation. Pharmacological antagonists of the neurotoxic effects blocked neuroinflammatory responses, pSTAT3tyr705 and GFAP induction, indicating that damage to neuronal targets instigated astrogliosis. Selective deletion of STAT3 from astrocytes in STAT3 conditional knockout mice markedly attenuated MPTP-induced astrogliosis. Monitoring STAT3 translocation in GFAP-positive cells indicated that effects of MPTP, METH and KA on pSTAT3tyr705 were localized to astrocytes. These findings strongly implicate the STAT3 pathway in astrocytes as a broadly triggered signaling pathway for astrogliosis. We also observed, however, that the acute neuroinflammatory response to the known inflammogen, LPS, can activate STAT3 in CNS tissue without inducing classical signs of astrogliosis. Thus, acute phase neuroinflammatory responses and neurotoxicity-induced astrogliosis both signal through STAT3 but appear to do so through different modules, perhaps localized to different cell types.

Genetic correlational analysis reveals no association between MPP+ and the severity of striatal dopaminergic damage following MPTP treatment in BXD mouse strains

“…Furthermore, this dopaminergic damage was accompanied by elevation in glial fibrillary acidic protein (GFAP), a hallmark of the astroglial response to underlying neural injury (e.g. see O'Callaghan et al, 2014). Nearly all of these indicators of striatal dopaminergic neurotoxicity were affected in our inbred mouse strains, especially striatal DA content, as measured by HPLC in tissue homogenates and reported in Jones et al (2013).…”

“…We determined the degree of association between the amount of MPP + produced in this study and MPTP-related striatal dopaminergic neurotoxicity as well as the associated astrogliosis reported in the Jones et al (2013) study. GFAP is an astrogliosis marker (see O'Callaghan et al, 2014;O'Callaghan and Sriram, 2005). The associations were estimated by Pearson correlation using the BXD strain means for the principal component (PC) analysis-derived composite of MPTP-based reductions in striatal DA, DOPAC, HVA and TH protein from Jones et al (2013).…”

“…MPP + is taken up preferentially by the dopamine (DA) transporter resulting in striatal DA terminal degeneration and, at higher dosages, loss of DA neurons in the substantia nigra (SN) (Muthane et al, 1994;O'Callaghan et al, 1990). Treatment of mice with a single low dosage of MPTP serves as an experimental tool for studying factors that may impact striatal dopaminergic nerve terminal degeneration (Jones et al, 2013;Sriram et al, 2004;O'Callaghan et al, 1990O'Callaghan et al, , 2014.…”

MPTP neurotoxicity is highly concordant between the sexes among BXD recombinant inbred mouse strains

“…Following the same procedures (see Jones et al, 2013) we measured striatal monoamines by HPLC with electrochemical detection from the left striatum and TH and GFAP by sandwich ELISA in the right side (O’Callaghan, 1991, 2002; Sriram et al, 2004; O’Callaghan et al, 2014). Values for the monoamines were normalized by tissue weight and the TH and GFAP values were normalized to total homogenate protein assayed by BCA (Smith et al, 1985).…”

“…The mice were injected with 12.5 mg/kg MPTP (vs. saline) and tissue harvested 48 h later. GFAP content was determined by sandwich ELISA (O’Callaghan, 1991; O’Callaghan et al, 2014). GFAP concentrations were normalized to total protein and expressed as mean ± s.e.m.…”