Modelling Parkinson’s Disease pathology using MITF mutant mice

Abstract

Background: In Parkinson’s disease (PD), dysfunctions in the autophagy-lysosomal system are well known and indeed, several genes related to familial PD also regulate lysosomal function. The MiT/TFE transcription factor family, which includes MITF, TFEB, TFE3, and TFEC, has been shown to play a significant downstream role in this regulation of lysosomal biogenesis and the autophagy-lysosomal system. However, only TFEB has been studied in the context of PD. This study investigates whether neuropathology in MITF mutant mouse models Parkinson’s pathology. Methods: Cryosections of post-fixed brain from male wildtype and MITF mutant mice aged 3 months and 12 months were examined (Mitf mi-enu22(398)/Mitf mi-enu22(398); Mitf Mi wh/+; N=3-8 per group). Fluorescence intensity of tyrosine hydroxylase (TH) in striatum, and density of dopaminergic (TH-positive) neurons in substantia nigra (SN) was analyzed, based upon immunostaining. Immunostaining for glial fibrillary acidic protein (GFAP, a marker of astrocytosis) and for ionized calcium-binding adaptor molecule 1 (IBA1, a marker of microglia) was also completed in several brain regions, including striatum and substantia nigra. Morphology of astrocytes and microglia in these regions was also completed using standardised analyses with software, including ImageJ. Results: Although there was no change in density of TH-positive neurons in substantia nigra, TH content was significantly reduced in both Enu and Mi-wh mutant mice in striatum at both 3 and 12 months of age. GFAP expression was increased in SN, nucleus accumbens and hippocampus by 12 months, in particular in Mi-wh mice, with strong trends observed in Enu mice. Size of individual astrocytes was also increased in Mi-wh mice, suggesting a change in morphology to a more activated state. The size of individual microglia was also increased in SN in Mi-wh mice. Conclusions: MITF mutant mice show neuropathology reminiscent of early PD, including a significant loss in striatal TH, with evidence of astrocytosis, and microgliosis in SN. However, we did not observe a loss in dopaminergic neurons of the SN. We note that many mouse models that carry mutations that lead to familial PD in humans similarly show striatal pathology with no evidence of TH loss in SN. Findings of this study indicate that mutant, dysfunctional MITF may be associated with early dopaminergic impairment and pro- Page 3 of 51inflammatory alterations, supporting further investigation of the role of the MITF transcription factor in PD.