Regional differences in the inflammatory and heat shock response in glia: implications for ALS

Abstract

Preferential neuronal vulnerability is characteristic of several neurodegenerative diseases including the motor neuron disease amyotrophic lateral sclerosis (ALS). It is well established that glia play a critical role in ALS, but it is unknown whether regional differences in the ability of glia to support motor neurons contribute to the specific pattern of neuronal degeneration. In this study, using primary mixed glial cultures from different mouse CNS regions (spinal cord and cortex), we examined whether regional differences exist in key glial pathways that contribute to, or protect against, motor neuron degeneration. Specifically, we examined the NF-κB-mediated inflammatory pathway and the cytoprotective heat shock response (HSR). Glial cultures were treated with pro-inflammatory stimuli, tumour necrosis factor-ɑ/lipopolysaccharide or heat stressed to stimulate the inflammatory and HSR respectively. We found that spinal cord glia expressed more iNOS and produced more NO compared to cortical glia in response to inflammatory stimuli. Intriguingly, we found that expression of ALS-causing SOD1 G93A did not elevate the levels of NO in spinal cord glia. However, activation of the stress-responsive HSR was attenuated in SOD1 G93A cultures, with a reduced Hsp70 induction in response to stressful stimuli. Exposure of spinal cord glia to heat shock in combination with inflammatory stimuli reduced the activation of the inflammatory response. The results of this study suggest that impaired heat shock response in SOD1 G93A glia may contribute to the exacerbated inflammatory reactions observed in ALS mice. Graphical abstract Mixed primary glial cultures were established from cortical and spinal cord regions of wild-type mice and mice expressing ALS–causing mutant human SOD1 and the inflammatory and heat shock responses were investigated in these cultures. In the absence of stress, all cultures appeared to have similar cellular composition, levels of inflammatory mediators and similar expression level of heat shock proteins. When stimulated, spinal cord glia were more reactive and activated the inflammatory pathway more readily than cortical glia; this response was similar in wild-type and SOD1 G93A glial cultures. Although the heat shock response was similar in spinal cord and cortical glial, in SOD1 G93A expressing glia from both the spinal cord and cortex, the induction of heat shock response was diminished. This impaired heat shock response in SOD1 G93A glia may therefore contribute to the exacerbated inflammatory reactions observed in ALS mice.

The microglial component of amyotrophic lateral sclerosis

“…This temporal transformation of microglial activation states has also been observed in other models of neurodegenerative conditions using single cell analysis, including models of Alzheimer’s disease ( Mathys et al , 2017 ), the EAE model of multiple sclerosis and a model of Huntington’s disease ( Ajami et al , 2018 ), with heterogeneity in activation states likely to be due to the chronicity and type of stimulus. Furthermore, microglia may elicit region-specific differences in response to either inflammatory cues or in disease states ( Beers et al , 2011 b ; Nikodemova et al , 2014 ; Clarke et al , 2019 ). To add further complexity, certain factors may be protective or toxic in a stimulus-dependent manner.…”

Regional Differences in Heat Shock Protein 25 Expression in Brain and Spinal Cord Astrocytes of Wild-Type and SOD1 G93A Mice

“…Both the loss of the supportive functions of glia [10,11] and gain of toxic immune phenotypes [12][13][14] are thought to contribute to motor neuron death in ALS. Existing regional differences in glia may further contribute to these mechanisms [11,15].…”

“…Since glia contribute to motor neuron death in ALS, it has been suggested that restoration of the lost supportive functions of glia or a reduction in the release of toxic factors from glia may be viable therapeutic strategies [16]. Targeting of heat shock proteins (Hsps), a family of cytoprotective protein chaperones, has been examined as a possible therapeutic approach in ALS, as some Hsps have both anti-aggregation and anti-inflammatory effects [15,17]. Indeed, amplification of the heat shock response (HSR) has shown promise in both pre-clinical and clinical ALS studies [18][19][20].…”

Histamine Is an Inducer of the Heat Shock Response in SOD1-G93A Models of ALS

“…Thus, in the present work, we investigated if the histaminergic challenge could increase the HSR in both neurons and glia, thus constituting an attractive therapeutic strategy for ALS [7,10]. Indeed, Hsp70 expression was reduced in the post-mortem tissues of ALS patients, while in the spinal cord Hsp70 protein accumulates and aggregates, thus leading to a deficit in cytosolic Hsps [18]. In addition to Hsp70, Hsp40 and HSF1 protein levels decreased in post-mortem tissue from patients with sporadic ALS, and in a mouse model of TDP-43-linked ALS [30].…”

“…HSR, and particularly Hsp70, plays an important role in the cellular processes implicated in ALS including stress granule formation, autophagy, proteasomal degradation and inflammatory signaling [18]. As an attractive therapeutic strategy for diseases, such as ALS, consists of boosting the Hsp levels in neurons and glial cells [10,19], in the present work we investigate if histamine signaling exerts its neuroprotective action through the HSR triggered in vitro in motor neurons and microglia cultures, and in vivo in spinal cord and cortex from symptomatic SOD1-G93A mice.…”