Assessing Aβ-independent effects of Module 42 on immune function in vitro.

INTRODUCTION: A deep multi-omic analysis of post mortem human brains has identified a new co-expression protein network - Module 42 (M42), strongly corelated with Alzheimer's disease (AD) pathology. M42 comprises 32 transmembrane and extracellular matrix (ECM)-associated proteins, including the amyloid precursor protein (APP) and apolipoprotein E (apoE), and its members have been implicated in amyloid beta (Aβ) pathology. We systematically evaluated the Aβ-independent effects of M42 on immune function in vitro. METHODS: Recombinant M42 proteins were expressed and purified. Their effects on phagocytosis, intracellular signaling, and cell viability were assessed in human induced pluripotent stem cell-derived macrophages. RESULTS: Treatment with Midkine (MDK) reduced phagocytosis, while treatment with the ectodomain of Transmembrane protein with EGF-like and two follistatin-like domains 2 (TMEFF2) had the opposite effect. Both proteins promoted intracellular Ca(2+) signaling, and TMEFF2 also suppressed Syk kinase activity. No M42 proteins had an effect on viability. DISCUSSION: Our results suggest an additional role for M42 in AD via regulating immune functions. HIGHLIGHTS: We tested M42 proteins for their effects on immune functions in vitro. Five proteins altered phagocytosis, and seven altered Ca(2+) signaling. MDK and TMEFF2 ectodomain had an effect on both phagocytosis and Ca(2+) signaling.