The neuroprotective properties of NLX-112 in MPTP treated mice are mediated by reactive gliosis and astrocytic GDNF

Abstract

Introduction: Preventing dopaminergic (DA) neuronal death is key to halting the progression of Parkinson’s Disease (PD). There is evidence for serotonin 5-HT1A agonists having neuroprotective effects on DA neurons. NLX-112 is a potent and selective 5-HT1A agonist which is currently undergoing clinical development for L-DOPA-induced dyskinesia in PD. Therefore, we examined the neuroprotective potential of NLX-112 in a mouse MPTP model of PD. Method: Mice were divided into four groups and received either saline, MPTP, NLX-112 or MPTP+NLX-112 (s.c). Immunoreactivity (-ir) for tyrosine-hydroxylase (TH, expressed in DA neurons), glial fibrillary associated protein (GFAP, an astrocytic filament protein), ionized calcium-binding adapter molecule 1 (Iba1, a microglial phagocytotic protein) and glial derived neurotrophic factor (GDNF, promotes neuronal survival) was investigated in the substantia- nigra (SN) and striatum. Cell number, co-localisation and optical-density was used to determine the extent of -ir. All experiments complied with ARRIVE guidelines. Approach for statistical analysis: Group comparisons were carried out using one-way ANOVA followed by Fishers LSD and performed on the statistical software package GraphPad Prism 9.0. Results and conclusions: Compared to saline treated mice, MPTP caused a loss of TH+ve neurons in the SN (-29%) and TH+ve fibre density in the striatum (-55%), with both effects attenuated by NLX-112 (-3% in the SN and -30% in the striatum). In the striatum, MPTP increased GFAP-ir, an effect which was reduced by NLX-112. Co-localisation of GFAP-GDNF in the striatum was increased by MPTP (110%), and was increased even further by NLX-112+MPTP (333%). In the SN, GFAP-GDNF co-localisation was unchanged by MPTP, but was increased by NLX-112+MPTP (173%). Furthermore, MPTP increased Iba1-ir (117%) in the SN, an effect almost abolished by NLX-112. These data show that NLX-112 exhibits neuroprotective properties in MPTP treated mice. In this model, NLX-112’s protective effects are likely mediated through reversal of MPTP induced inflammation as shown by attenuation of astrogliosis and inhibition of microgliosis but also by upregulation of the neurotrophic factor, GDNF in astrocytes.