Cyclin-dependent kinase inhibitor p21 dysregulation induces oligodendrocyte differentiation impairment in multiple sclerosis cerebral organoids

Multiple sclerosis (MS) is an auto-immune neurological disorder characterized by inflammation, demyelination, and neural degeneration. The origin and evolution of MS are still poorly understood because of lack of animal models and relative inaccessibility to human brain tissue. Cerebral organoids represent an interesting tool to study neurological disorders as they recapitulate early human neurodevelopment, including the generation, proliferation and differentiation of neural progenitors into glial cell and neurons.

Members of the Cip/Kip family of cyclin-dependent kinases inhibitors (CDKi), such as p21, p27 and p57, are well characterized for their role as negative regulators of the cell cycle. Recent studies have shown that they play additional roles unrelated to cell cycle regulation, such as control of oligodendrocyte differentiation and maturation and thus, myelination. However, their importance in MS hasn’t been thoroughly described.

The purpose of this work was to use patient with MS induced pluripotent stem cells derived cerebral organoids to study the importance of CDKi in MS pathogenesis. We used this model to analyze the expression of CDKi in control and MS organoids, and study their effect on cell proliferation and differentiation capacity, after 42 days in vitro.

We first analyzed p21, p27 and p57 expression in cerebral organoids derived from healthy controls and from patients with PPMS, RRMS and SPMS. P21⁺ and P57⁺ cells were localized in the lower layers and colocalized with PAX6⁺ neural stem cells. P27⁺ cells were mostly expressed in the outer layers, and colocalized with CTIP2⁺ neurons. No ectopic cell location was found in the different types of MS compared to control organoids. Quantification revealed no difference for p27 and p57 expression in MS organoids compared to control, while a significant decrease was observed for p21 in every type of MS, particularly PPMS. Analysis of the cleavage plane angle revealed a transition from symmetric proliferative to asymmetric neurogenic division in MS samples, which was associated with p21 downregulation. We then analyzed Olig2⁺ oligodendrocyte population in organoids, a significant decrease of Olig2⁺ cell expression was detected in MS organoids, particularly PPMS.

In conclusion this work is a proof of principle, showing the c-organoids derived from patients with MS can be used as an innovative tool to better understand the genetic basis for phenotypic differences seen in MS. Using this model, we identified p21 as a new protein of interest in progressive MS pathogenesis.