Multiple sclerosis (MS) stands as a prevalent cause of progressive disability in young adults, impacting 50–300 per 100,000 individuals and affecting an estimated 2.3 million people worldwide (Thompson et al., 2018). Most patients experience initial relapsing-remitting episodes, but approximately 50 % of patients undergo sustained and irreversible disability after 10–15 years. Additionally, 15 % of patients suffer progressive disease from onset. While effective treatments are available for the early stages of MS, the progressive stage currently lacks viable therapeutic options. This is partly due to an incomplete understanding of the mechanisms underlying disease progression (Correale et al., 2017; Ontaneda et al., 2015; Shirani et al., 2016). Emerging research has revealed that the progressive phase of MS entails early axonal damage and neuronal loss driven by a convergence of inflammatory mediators, demyelination, and the loss of axonal trophic support. Although clinical manifestations may become apparent at later stages, early axonal injury coincides with a central nervous system (CNS)-confined inflammatory process mediated by astrocytes (AST) and microglial cells (MG; Correale et al., 2017; Reich et al., 2018). MG, the sole resident immune cells of the CNS, do not only maintain CNS homeostasis but also serve as the initial defense against neurological disorders, including demyelinating diseases (Lenz and Nelson, 2018; Sarlus and Heneka, 2017; Wake et al., 2011). In response to pathological conditions, MG rapidly activate, proliferate, and migrate toward lesions (Colonna and Butovsky, 2017; Fu et al., 2012). The role of activated MG in influencing disease is two-fold: first, they facilitate the removal of damaged tissues by engulfing cellular debris, and second, they aid tissue regeneration by secreting cytokines, chemokines, and growth factors (Fu et al., 2012; Li and Barres, 2018). Specifically, in demyelinating diseases, MG clear myelin debris through phagocytosis, allowing the maturation of oligodendrocyte progenitor cells (OPCs) and subsequent remyelination (Lampron et al., 2015; Natrajan et al., 2015; Neumann et al., 2009). However, dysregulated MG contribute to disease severity in various neurological pathologies (Han et al., 2019). AST, on the other hand, can adopt a proinflammatory phenotype via a mechanism involving activated neuroinflammatory MG, which may further mediate neurodegeneration. This proinflammatory phenotype inhibits OPC proliferation and differentiation and is toxic to both oligodendrocytes (OLGs) and neurons (Liddelow et al., 2017). Nevertheless, astroglial activation can also occur in response to neurodegeneration, acting as a protective mechanism (Haindl et al., 2019).

A plethora of animal models that replicate the specific characteristics and pathophysiological processes of MS have been instrumental in unraveling disease mechanisms and developing therapeutic interventions (Kipp et al., 2012; Ransohoff, 2012). Experimental models of demyelination are induced by immunity, viruses and toxins. For instance, experimental autoimmune encephalomyelitis (EAE), the most commonly employed animal model of CNS demyelination, is triggered by immunization with myelin proteins and is particularly useful in the study of MS autoimmunity, while also replicating some of its motor features (Traugott et al., 1985; Walton, 2015). Unfortunately, many therapeutic strategies that showed promise in the EAE model have yielded limited or no benefits in MS pathology (Klinkert et al., 1997; Martino et al., 1997; Arnett et al., 2001; Clarner et al., 2011; Miron et al., 2009; Schmidt et al., 2009; Trebst et al., 2007). In contrast, toxin-based models are particularly valuable for assessing the effects of therapeutic agents on demyelination and remyelination processes. These models encompass (1) focal demyelination by agents like lysolecithin (LPC) or ethidium bromide, and (2) systemic toxin administration. Among the latter, cuprizone (CPZ) administration has gained popularity as a demyelination model, as it lacks the T cell infiltration of autoimmune response-mediated models. CPZ-induced demyelination is characterized by the loss of mature OLGs and concurrent MG and AST activation (Lampron et al., 2015; McMahon et al., 2002; Mildner et al., 2007; Plemel et al., 2018; Woodruff and Franklin, 1999; Ghasemlou et al., 2007).

In vivo models offer a more faithful representation of the intricate cellular and molecular processes leading to pathology within the human CNS. However, these models can be costly and require extended treatment periods. In vitro models offer numerous advantages, including cost-effectiveness and precise control over experimental conditions, thus rendering more reproducible outcomes. We have developed a pioneering in vitro model encompassing all CNS cell types to investigate oligodendroglial maturation and myelin deposition in demyelinating and remyelinating conditions. This model is also helpful in evaluating MG behavior through their potential elimination and subsequent repopulation. Given the critical reliance of MG development and survival on colony-stimulating factor-1 receptor (CSF-1R) signaling, we have employed BLZ945-induced CSF-1R inhibition to effectively deplete MG. This model holds promise for assessing candidate therapies promoting oligodendroglial differentiation to preserve and restore myelin and prevent neurodegeneration.