Comparative study of the expression of cholinergic system components in the CNS of experimental autoimmune encephalomyelitis mice: Acute vs remitting phase

Abstract

Acetylcholine (ACh) is involved in the modulation of the inflammatory response. ACh levels are regulated by its synthesizing enzyme, choline acetyltransferase (ChAT), and by its hydrolyzing enzymes, mainly acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A more comprehensive understanding of the cholinergic system in experimental autoimmune encephalomyelitis (EAE) disease progression could pave the path for the development of therapies to ameliorate multiple sclerosis (MS). In this work, we analyzed possible alterations of the CNS cholinergic system in the neuroinflammation process by using a MOG-induced EAE mice model. MOG- and vehicle-treated animals were studied at acute and remitting phases. We examined neuropathology and analyzed mRNA expression of ChAT, AChE and the α7 subunit of the nicotinic acetylcholine receptor (α7nAChR), as well as AChE and BuChE enzyme activities, in brain and spinal cord sections during disease progression. The mRNA expression and enzyme activities of these cholinergic markers were up- or down-regulated in many cholinergic areas and other brain areas of EAE mice in the acute and remitting phases of the disease. BuChE was present in a higher proportion of astroglia and microglia/macrophage cells in the EAE remitting group. The observed changes in cholinergic markers expression and cellular localization in the CNS during EAE disease progression suggests their potential involvement in the development of the neuroinflammatory process and may lay the ground to consider cholinergic system components as putative anti-inflammatory therapeutic targets for MS.

Possible Correlation between Cholinergic System Alterations and Neuro/Inflammation in Multiple Sclerosis

“…BChE activity is detected in both glial cell populations and presents a significant increment in EAE animals in the chronic phase compared to the peak phase or control brains. The high ratio of BChE to AChE found in astrocytes of EAE mice in peak phase [63] may suggest this ratio as a potential marker for brain areas selectively vulnerable to this neuropathology as it was described for Alzheimer's disease brains [64]. However, the treatment of EAE mice with a BChE/AChE inhibitor (rivastigmine) resulted in an amelioration of the clinical symptoms associated also with a reduction in the demyelination [24], supporting the role of BChE in neuroinflammation and demyelination ( Figure 3).…”

“…The BChE activity, a non-selective cholinesterase enzyme that catalyzes the ACh hydrolysis, is altered in the habenula and solitary nucleus in both disease phases of EAE mice and in higher proportion in astroglia and microglia/macrophage cells in the chronic group [63]. BChE activity is detected in both glial cell populations and presents a significant increment in EAE animals in the chronic phase compared to the peak phase or control brains.…”

“…ACh may play a role in the development or in the remission of MS. Recent analyses of cholinergic markers in the brain and spinal cord of EAE mice revealed specific alterations in their expression in different brain areas and cellular populations associated to the different phases of the disease [63]. The mRNA coding for ChAT, the enzyme responsible for the synthesis of ACh from choline and acetyl-CoA that serves as a marker of cholinergic cells, presents alterations in the expression levels in different brain regions and spinal cord and in different disease phases of EAE mice [63].…”

“…Recent analyses of cholinergic markers in the brain and spinal cord of EAE mice revealed specific alterations in their expression in different brain areas and cellular populations associated to the different phases of the disease [63]. The mRNA coding for ChAT, the enzyme responsible for the synthesis of ACh from choline and acetyl-CoA that serves as a marker of cholinergic cells, presents alterations in the expression levels in different brain regions and spinal cord and in different disease phases of EAE mice [63]. Several cholinergic nuclei of EAE mice in the chronic phase present an increment in ChAT expression levels and an increase of the AChE activity and mRNA expression at peak of disease, suggesting that the balance of ACh levels may contribute to the chronicity of the disease.…”

“…α7 nAChR mRNA expression in the EAE chronic group is increased in habenula and decreased in the dorsal tegmental nucleus. Conversely, the mRNA levels of this receptor are increased in the dorsal tegmental nucleus of animals in the peak phase [63]. The altered expression of this receptor subunit in EAE mice during the chronic phase compared to the peak phase of the disease may sustain its role in the neuro-inflammation regulation also in the brain (Figure 3).…”