PLC\u03b32 regulates TREM2 signalling and integrin-mediated adhesion and migration of human iPSC-derived macrophages

Juliane Obst,Mira Kreuzer,Thomas B Smith,Emma Mead,Hazel L Hall-Roberts,Elena Di Daniel,John B Davis,Lorenza Magno

doi:10.1038/s41598-021-96144-7

Abstract

Human genetic studies have linked rare coding variants in microglial genes, such as TREM2, and more recently PLCG2 to Alzheimer’s disease (AD) pathology. The P522R variant in PLCG2 has been shown to confer protection for AD and to result in a subtle increase in enzymatic activity. PLCγ2 is a key component of intracellular signal transduction networks and induces Ca2+ signals downstream of many myeloid cell surface receptors, including TREM2. To explore the relationship between PLCγ2 and TREM2 and the role of PLCγ2 in regulating immune cell function, we generated human induced pluripotent stem cell (iPSC)- derived macrophages from isogenic lines with homozygous PLCG2 knockout (Ko). Stimulating TREM2 signalling using a polyclonal antibody revealed a complete lack of calcium flux and IP1 accumulation in PLCγ2 Ko cells, demonstrating a non-redundant role of PLCγ2 in calcium release downstream of TREM2. Loss of PLCγ2 led to broad changes in expression of several macrophage surface markers and phenotype, including reduced phagocytic activity and survival, while LPS-induced secretion of the inflammatory cytokines TNFα and IL-6 was unaffected. We identified additional deficits in PLCγ2- deficient cells that compromised cellular adhesion and migration. Thus, PLCγ2 is key in enabling divergent cellular functions and might be a promising target to increase beneficial microglial functions.

Highlights

Alzheimer’s disease (AD) is a chronic neurodegenerative disease and the most common cause of dementia
We aimed to investigate the role of Phospholipase Cγ2 (PLCγ2) within the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) pathway and its effect on macrophage phenotypes
The previous discovery of AD-related mutations in the microglial expressed genes TREM2 and PLCγ2 has marked them as promising new targets to manipulate microglial function in neurodegenerative disease

Summary

Introduction

Alzheimer’s disease (AD) is a chronic neurodegenerative disease and the most common cause of dementia. Recent large-scale genetic studies have identified an increasing number of susceptibility genes linked to conferring either risk or protection in developing LOAD. Many of these genes are predominantly expressed in myeloid cells such as microglia, the brain’s resident immune cells, emphasizing the role of the innate immune response in AD pathogenesis. Dominantly inherited immune disorders have been linked to germline mutations in PLCγ2 These mutations are enriched in affected families and localise to the autoinhibitory regulatory domains of the enzyme, resulting in constitutively increased activity of PLCγ2. Similar to the PLAID and APLAID mutations, this protective variant is located in the autoinhibitory regulatory region of PLCγ2, and has a slight hypermorphic effect on enzymatic function in recombinant cell lines[18]. In contrast to the previous observations in BMDMs, P522R led to reduced phagocytosis of fungal and bacterial particles in the cell models used in this study, while endocytosis of oligomeric Aβ42 was e nhanced[20]

Objectives

Methods

Results

Conclusion