Investigating the In Vitro Effects of Human-Derived Platelet Lysate on Microglia Polarization: Implications for Myelin Repair
Year: 2025
Type: article
Abstract: Myelin is essential for proper axonal function in the central nervous system (CNS) and in peripheral nerves. In the CNS, myelin sheaths are formed by oligodendrocytes, and their loss - also known as demyelination - prompts a robust repair process known as remyelination. During CNS remyelination, new myelin-forming cells are generated from oligodendrocyte progenitor cells (OPCs). Microglia, the resident immune cells of the CNS, play a critical role through their ability to adopt diverse activation states, timely regulating OPC function during remyelination. Indeed, a switch from a pro-inflammatory to an anti-inflammatory polarization state is essential for proper remyelination (Miron et al., 2013). Although remyelination represents a strong regenerative response to myelin damage, during multiple sclerosis (MS), remyelination ultimately fails, resulting in chronically demyelinated lesions. Why does remyelination fail in MS? During MS, platelets and platelet-derived molecules accumulate in chronic lesions. Our recent study has demonstrated a bimodal action of platelets and platelet-derived molecules on OPC function (Philp et al., 2024). While transient exposure to platelets or platelet lysate (PL) enhances OPC differentiation, sustained exposure fails to do so. Besides OPCs, does PL also regulate microglia polarization during remyelination? As a first approach to this question, this study aimed to investigate the ability of PL to influence microglial polarization on BV2 microglial cell line. Three experimental paradigms were employed to determine whether human-derived PL: (1) induces a pro-inflammatory or anti-inflammatory phenotypic polarization in microglia, (2) modulates microglia polarization, and (3) influences a phenotypic switch from a pro-inflammatory to an anti-inflammatory state. To address these specific aims, ELISA and RT-qPCR were used to evaluate the presence of different polarization markers. First, treatment with PL at concentrations of 0.1%, 1%, or 10% did not induce significant changes in TNF-α (a pro-inflammatory marker) or IGF-1 (an anti-inflammatory marker) secretion when assessed via ELISA. Second, RT-qPCR revealed that PL treatment failed to upregulate Tnf-α or Ym1 (an anti-inflammatory marker) expression at the mRNA level. Furthermore, PL did not modulate microglia polarization or alter IL-4-driven switching from a pro-inflammatory to an anti-inflammatory state. Thus, PL did not significantly alter BV2 microglial phenotype under any experimental condition. These results indicate that, under the defined in vitro conditions, PL is insufficient to induce or modulate microglial polarization. This might be explained due to loss of bioactive factors in the lysate, the inherent limitations of the BV2 model, human individuals PL’ variability, or species mismatch. While platelets show regenerative potential in peripheral systems and in vivo CNS studies, their effects on microglia in simplified in vitro systems are overlooked. Future studies may benefit from beyond BV2 cells and lysate-based approaches. Primary or iPSC-derived microglia, brain slice cultures, and in vivo demyelination models—combined with refined platelet characterization—will be essential to uncover the reparative role of platelets in remyelination.
Source: Työväentutkimus Vuosikirja
Author: Shrestha, Gautam Lal
Language: English
Subfield: Clinical Neurology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7200538361