Scientists use in vitro models to investigate multiple sclerosis (MS). By growing individual or mixed brain cells in the lab, researchers can simulate simplified versions of cell interactions in the central nervous system (CNS). These advanced models offer a controlled environment to explore some of the underlying mechanisms of MS [1]. Recently, the introduction of induced pluripotent stem cells (iPSCs) technology has marked a breakthrough in MS research. iPSCs can self-organise and develop into different cell types when cultured in 2D or 3D structures [2]. Neural cultures, also called brain organoids when grown in three dimensions, can model key features of human brain architecture and function [3].
MS in a dish: exploring the mechanism of cell dysfunction
In 2006, Kazutoshi Takahashi and Shinya Yamanaka directly reverted mouse somatic cells to an embryonic-like state, generating the induced pluripotent stem cells [4]. In recognition of this groundbreaking discovery, Professor Yamanaka was awarded the 2012 Nobel Prize in Physiology or Medicine. Since then, iPSC technology has become a promising strategy to model cellular dysfunctions of many diseases, including MS [5]. Today, pluripotent stem cells can be derived from both healthy individuals and patients and can be differentiated into neural progenitor cells [5]. One of the first successful attempts to derive pluripotent stem cells from individuals with MS was made using a skin biopsy [6]. The researchers were able to reprogram skin fibroblasts and obtained differentiated astrocytes, oligodendrocytes, and neurons [6].
In the context of MS, there is a particular interest in studying oligodendrocytes in vitro to uncover the mechanisms of myelination and pave the way for potential remyelinating therapies (See also our Spotlight on Neuroregeneration). Oligodendrocytes are the myelinating cells in the central nervous system, responsible for forming the protective sheath around axons [7].
Dr Valentina Fossati, from the New York Stem Cell Foundation Research Institute, and her group have pioneered an automated method to generate in short time oligodendrocyte progenitor cells from iPSC of individuals with MS [8]. Dr Fossati shares with us, “At first, it felt like science fiction but now we have over 114 MS lines. Oligodendrocytes are among the most challenging cells to recreate in vitro because they mature late in neural development, after other glial cells and neurons have formed. As a result, it takes around 75 days to observe oligodendrocytes formation, with the process beginning around day 50. This also means that the culture will contain a mixture of different cell types, making it a co-culture rather than a pure oligodendrocyte culture – just as it happens in the organoids”.
Glial-enriched cultures derived from individuals with progressive MS differ from those of healthy individuals. They contain fewer oligodendrocytes, which express more immune and inflammatory genes [9]. “It may be that these oligodendrocytes are particularly vulnerable to ferroptosis,” Dr Fossati continues. “It is crucial to conduct large-scale studies on human cells to better understand their mechanisms of function and dysfunction. This would enable us to explore the complexities of MS, potentially leading to a more precise stratification of this condition. Studying a disease in humans provides insight into its full heterogeneity. In contrast, mice are kept in highly controlled environments throughout their lives and typically represent only a single strain of the condition.”
Dysregulation of cellular metabolism
Neural progenitor cells (NPCs) can influence the maturation of oligodendrocyte progenitor cells [10]. In individuals with MS, NPCs exhibit a reduced ability to provide neuroprotection when myelin is injured and offer less support for the differentiation of OPCs in vitro compared to healthy individuals [10]. This altered progenitor cell function may be associated to cellular senescence, a key aspect of the aging process [11]. Cellular senescence has been observed in the neural progenitor cells of individuals with MS, as evidenced by both post-mortem brain tissue analyses and in vitro studies [11]. In the brain, senescent progenitor cells have been found within white matter lesions in post-mortem tissue from individuals with MS. Moreover, NPCs derived from induced pluripotent stem cells from individuals with MS show higher levels of cellular senescence markers compared to controls [11].
Professor Stefano Pluchino, from the University of Cambridge, tells us, “These findings mark a new chapter in stem cell research for MS, leading to the exploration of mechanisms of intrinsic cell dysfunction in human cells derived from individuals with the condition. In Cambridge, we have begun investigating mechanisms of pathology potentially linked to intrinsic cell dysfunctions. In a recent study, we focused on mechanisms of senescence, hypothesising that senescent neural progenitor cells could play a role in MS progression [12]. We did not use iPSC technology for individuals with MS, as iPSC reprogramming would rejuvenate the cells and reset their epigenetic memory. Instead, we established induced neural stem/progenitor cell (iNSC) lines from fibroblast of individuals with progressive MS. This direct reprogramming technology preserved the epigenetic memory and aging-related markers [12]. We observed that in 59.8% of cases, iNSC from individuals with MS were senescent, compared to 22.5% of cases from healthy individuals of the same age. At this point, we delved deeper into this senescence and noticed that the cellular metabolism was dysregulated. These cells were hypermetabolic, exhibiting enhanced glucose utilisation, increased oxidative phosphorylation, and higher cholesterol synthesis. The glucose was mainly used for cholesterol synthesis, leading to lipid droplets accumulation and the secretion of a neurotoxic secretory phenotype associated with senescence (SASP) [12]. Finally, we showed that the oral medication simvastatin inhibits the enzyme HMGCR, thereby reducing neurotoxicity.”
As these technologies evolve, they hold the promise of deepening our understanding of the complexity of MS, while also facilitating the identification of potential therapeutical targets [13].
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Written by Stefania de Vito
Special thanks to Dr Valentina Fossati (New York Stem Cell Foundation Research Institute) and to Professor Stefano Pluchino (Cambridge University) for their insights.
References
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[13] Simões-Abade MBC et al. Frontiers Cell. Neurosci. 2024; 18: 1488691.