HDAC inhibitors engage MITF and the disease-associated microglia signature to enhance amyloid β uptake

Abstract

Disease-associated microglia (DAM), initially described in mouse models of neurodegenerative diseases, have been classified into two related states; starting from a TREM2-independent DAM1 state to a TREM2dependent state termed DAM2, with each state being characterized by the expression of specific marker genes (Keren-Shaul, 2017). Recently, single-cell (sc)RNA-Seq studies have reported the existence of DAM in humans (Pettas, 2022; Jauregui, 2023; Friedman, 2018; Mathys, 2019; Tuddenham, 2024); however, whether DAM play beneficial or detrimental roles in the context of neurodegeneration is still under debate (Butovsky and Weiner, 2018; Wang and Colonna, 2019). Here, we present a pharmacological approach to mimic human DAM in vitro: we validated in silico predictions that two different histone deacetylase (HDAC) inhibitors, Entinostat and Vorinostat, recapitulate aspects of the DAM signature in two human microglia-like model systems. HDAC inhibition increases RNA expression of MITF, a transcription factor previously described as a regulator of the DAM signature (Dolan, 2023). This engagement of MITF appears to be associated with one part of the DAM signature, refining our understanding of the DAM signature as a combination of at least two transcriptional programs that appear to be correlated in vivo. Further, we functionally characterized our DAM-like model system, showing that the upregulation of this transcriptional program by HDAC inhibitors leads to an upregulation of amyloid β and pHrodo Dextran uptake - while E.coli uptake is reduced - and a specific reduction of MCP1 secretion in response to IFN-γ and TNF-α. Enhanced amyloid β uptake was confirmed in iPSC-derived microglia. Overall, our strategy for compound-driven microglial polarization offers potential for exploring the function of human DAM and for an immunomodulatory strategy around HDAC inhibition.

Keywords: Disease-associated microglia (DAM); Functional analysis; Human microglia; In vitro model systems; Pharmacological modelling.