Novel potent liposome agonists of triggering receptor expressed on myeloid cells 2 phenocopy antibody treatment in cells

Abstract

The receptor Triggering Receptor Expressed on Myeloid cells 2 (TREM2) is associated with several neurodegenerative diseases including Alzheimer's Disease and TREM2 stimulation represents a novel therapeutic opportunity. TREM2 can be activated by antibodies targeting the stalk region, most likely through receptor dimerization.Endogenous ligands of TREM2 are suggested to be negatively charged apoptotic bodies, mimicked by phosphatidylserine incorporated in liposomes and other polyanionic molecules likely binding to TREM2 IgV fold. However, there has been much discrepancy in the literature on the nature of phospholipids (PLs) that can activate TREM2 and on the stability of the corresponding liposomes over time. We describe optimized liposomes as robust agonists selective for TREM2 over TREM1 in cellular system.The detailed structure/activity relationship studies of lipid polar heads indicate that

Alzheimer's disease‐associated R47H TREM2 increases, but wild‐type TREM2 decreases, microglial phagocytosis of synaptosomes and neuronal loss

“…Whereas when a relatively low phosphatidylserine concentration is distributed among a physiological mix of neutral phospholipids and cholesterol, then the specific binding of TREM2 might be enhanced. This is supported by the recent report that these physiological liposomes are better ligands for TREM2 and that R47H TREM2 is preferentially activated by phosphatidylserine in these liposomes (Boudesco et al, 2022).…”

“…As R47H‐expressing iPS‐Mg had increased uptake of synaptosomes, we tested whether R47H TREM2 expression affected activation of TREM2 by phosphatidylserine. Common variant/WT TREM2 and homozygous R47H TREM2‐expressing iPS‐Mg were activated with phosphatidylserine liposomes, containing a physiological mixture of cell membrane lipids (Boudesco et al, 2022 ), and the level of phospho‐SYK was measured by AlphaLISA. SYK tyrosine kinase is immediately downstream of TREM2 and mediates TREM2‐induced phagocytosis (Olufunmilayo & Holsinger, 2022 ).…”

“…Liposomes were prepared as described in (Boudesco et al, 2022 ) in a 50/32/18 molar ratio of cholesterol/ 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine/phospholipid respectively, where the phospholipid was either 1,2‐dioleoyl‐sn‐glycero‐3‐phospho‐L‐serine (phosphatidylserine liposomes) or 1,2‐dioleoyl‐sn‐glycero‐3‐ phosphocholine (phosphatidylcholine liposomes). Chloroform‐dissolved lipids (purchased from Avanti) were mixed in 0.5 ml of absolute ethanol, and solvents removed by rotary evaporation at 45°C under gradually lowered pressure exposure (from 999 mbar to 0).…”

The hypermorphic PLCγ2 S707Y variant dysregulates microglial cell function – insight into PLCγ2 activation in brain health and disease, and opportunities for therapeutic modulation

“…The PLCγ2 S707Y variant is strongly hypermorphic in hiPSC-derived microglia Standard PLC functional assays using heterologous cell lines show the PLCγ2 S707Y disease-linked variant to be hypermorphic under both basal and stimulated conditions, due to the disruption that the mutation causes on the autoinhibitory interface [3,7,34]. To achieve selective activation of PLCγ2 in microglia, a commercial antibody against TREM2 was used to stimulate signalling [35,36]. The accumulation of inositol monophosphate (IP1), a stable downstream metabolite of IP3 induced by activation of the phospholipase C (PLC) cascade, was quantified using a homogeneous time resolved fluorescence (HTRF) assay.…”