Profiling Microglia in a Mouse Model of Machado–Joseph Disease

Abstract

Microglia have been increasingly implicated in neurodegenerative diseases (NDs), and specific disease associated microglia (DAM) profiles have been defined for several of these NDs. Yet, the microglial profile in Machado–Joseph disease (MJD) remains unexplored. Here, we characterized the profile of microglia in the CMVMJD135 mouse model of MJD. This characterization was performed using primary microglial cultures and microglial cells obtained from disease-relevant brain regions of neonatal and adult CMVMJD135 mice, respectively. Machine learning models were implemented to identify potential clusters of microglia based on their morphological features, and an RNA-sequencing analysis was performed to identify molecular perturbations and potential therapeutic targets. Our findings reveal morphological alterations that point to an increased activation state of microglia in CMVMJD135 mice and a disease-specific transcriptional profile of MJD microglia, encompassing a total of 101 differentially expressed genes, with enrichment in molecular pathways related to oxidative stress, immune response, cell proliferation, cell death, and lipid metabolism. Overall, these results allowed us to define the cellular and molecular profile of MJD-associated microglia and to identify genes and pathways that might represent potential therapeutic targets for this disorder.

Microglial Depletion Has No Impact on Disease Progression in a Mouse Model of Machado–Joseph Disease

“…In accordance to our previous observations [29], at 21 weeks of age, a significant decrease in the number of microglial cells was found in the cerebellar lobules (1593 ± 536 microglia per mm 3 ; p = 0.047085) (Figure 1e,f,n) and in the PN (2743 ± 748 microglia per mm 3 ; p = 0.019112) (Figure 1i,j,o) but not in the DCN (Figure 1a,b,m) of vehicle-treated CMVMJD135 mice when compared with vehicle-treated WT mice. This suggests the possibility of mutant ATXN3 causing glia toxicity or/and a consequence of their interaction with neurons and/or other cells, which can eventually lead to microglial death processes.…”

“…In fact, reactive microgliosis was observed in MJD patients' brains [9,26,27] and in a mouse model of MJD [28]. Additionally, we have recently shown morphological alterations that point to an increased activation state, as well as molecular perturbations related with oxidative stress, immune response, and lipid metabolism being seen significantly altered in microglial cells derived from CMVMJD135 mice [29], an MJD mouse model that replicates the motor symptoms and neuropathology of the human condition [30]. Because most brain cells express ATXN3, microglial dysfunction may contribute to the disease process, due to the effects of mutant ATXN3 in microglia itself or as a consequence of their interaction with neurons.…”

“…We have previously demonstrated morphological, phenotypic, and transcriptomic alterations that point to an increased activation state of microglial cells during the late stages of disease in CMVMJD135 mice [29]. Here, we aimed to understand if these alterations are, or not, actively contributing to disease onset and progression in MJD.…”

“…These alterations, typically found in different situations of brain disease and pathology [13][14][15]63,64], suggest that microglia from CMVMJD135 + vehicle and CMVMJD135 + PLX3397 mice are similar and showed an activation profile, which was not dependent on CSF1R signaling. Because mutant ATXN3 is expressed in microglia [29], we hypothesize that this activation profile may be induced by mutant ATXN3 in microglial cells themselves or/and emerge as a consequence of their interaction with neurons undergoing degenerative processes. This, however, remains to be explored.…”

“…We have recently shown morphological alterations that point to an increased activation state, and pinpointed molecular pathways involved with oxidative stress, immune response, and lipid metabolism as significantly altered in microglia from CMVMJD135 mice [29]. However, it is unknown if and how these cells actively contribute to the disease process and symptoms progression of MJD.…”