No abstract

Variants identified in genome‐wide association studies have implicated immune pathways in the development of Alzheimer’s disease (AD). Here, we investigated the mechanistic basis for protection from AD associated with PLCγ2 R522, a rare coding variant of the PLCG2 gene. We studied the variant's role in macrophages and microglia of newly generated PLCG2‐R522‐expressing human induced pluripotent cell lines (hiPSC) and knockin mice, which exhibit normal endogenous PLCG2 expression. In all models, cells expressing the R522 mutation show a consistent non‐redundant hyperfunctionality in the context of normal expression of other PLC isoforms. This manifests as enhanced release of cellular calcium ion stores in response to physiologically relevant stimuli like Fc‐receptor ligation or exposure to Aβ oligomers. Expression of the PLCγ2‐R522 variant resulted in increased stimulus‐dependent PIP2 depletion and reduced basal PIP2 levels in vivo. Furthermore, it was associated with impaired phagocytosis and enhanced endocytosis. PLCγ2 acts downstream of other AD‐related factors, such as TREM2 and CSF1R, and alterations in its activity directly impact cell function. The inherent druggability of enzymes such as PLCγ2 raises the prospect of PLCγ2 manipulation as a future therapeutic approach in AD.

No abstract

Ca 2þ signaling is vital for various cellular processes including synaptic vesicle exocytosis, muscle contraction, regulation of secretion, gene transcription, and cellular proliferation. The endoplasmic reticulum (ER) is the largest intracellular Ca 2þ store, and dysregulation of ER Ca 2þ signaling and homeostasis contributes to the pathogenesis of various complex disorders and Mendelian disease traits. We describe four unrelated individuals with a complex multisystem disorder characterized by woolly hair, liver dysfunction, pruritus, dysmorphic features, hypotonia, and global developmental delay. Through whole-exome sequencing and family-based genomics, we identified bi-allelic variants in CCDC47 that encodes the Ca 2þ-binding ER transmembrane protein CCDC47. CCDC47, also known as calumin, has been shown to bind Ca 2þ with low affinity and high capacity. In mice, loss of Ccdc47 leads to embryonic lethality, suggesting that Ccdc47 is essential for early development. Characterization of cells from individuals with predicted likely damaging alleles showed decreased CCDC47 mRNA expression and protein levels. In vitro cellular experiments showed decreased total ER Ca 2þ storage, impaired Ca 2þ signaling mediated by the IP 3 R Ca 2þ release channel, and reduced ER Ca 2þ refilling via store-operated Ca 2þ entry. These results, together with the previously described role of CCDC47 in Ca 2þ signaling and development, suggest that bi-allelic loss-offunction variants in CCDC47 underlie the pathogenesis of this multisystem disorder. Ca 2þ signaling is a multipurpose intracellular signaling system that regulates a number of cellular processes including synaptic vesicle exocytosis, muscle contraction, regulation of secretion, transcription, and cellular proliferation. 1 The endoplasmic reticulum (ER), or the sarcoplasmic reticulum (SR) in muscle cells, is the largest store of intracellular Ca 2þ. 2 ER Ca 2þ depletion is also observed in a number of genetic disorders due to variants in Ca 2þ channels and sensors. For example, Brody myopathy (MIM: 601003) is caused by recessive variants in ATP2A1 (MIM: 611974), which encodes the fast-twitch skeletal muscle sarcoplasmic reticulum Ca 2þ ATPase (SERCA1), 3 while Darier disease (MIM: 124200) occurs due to variants in ATP2A2 (MIM: 108740), which encodes another sarcoplasmic reticulum Ca 2þ ATPase, SERCA2. 4 Minicore myopathy (MIM: 255320) and central core disease (MIM: 117000) result from variants in RYR1 (MIM: 180901), which encodes a major Ca 2þ release channel, 5 and autosomal centronuclear myopathy (MIM: 160150) is associated with variants in MTMR14 (MIM: 611089), which encodes a muscle-specific inositol phosphatase. 6 Stormorken syndrome (MIM: 185070), tubular aggregate myopathy 1 (MIM: 160565), and immunodeficiency 10 (MIM: 612783) are caused by variants in STIM1 (MIM: 605921), 7-9 which encodes a Ca 2þ sensor. Tubular aggregate myopathy 2 (MIM: 615883) and immunodeficiency 9 (MIM: 612782) are caused by variants in ORAI1 (MIM: 610277), 10,11 which encodes a Ca 2þ channel that...

Microglia are increasingly recognized as vital players in the pathology of a variety of neurodegenerative conditions including Alzheimer’s (AD) and Parkinson’s (PD) disease. While microglia have a protective role in the brain, their dysfunction can lead to neuroinflammation and contributes to disease progression. Also, a growing body of literature highlights the seven phosphoinositides, or PIPs, as key players in the regulation of microglial-mediated neuroinflammation. These small signaling lipids are phosphorylated derivates of phosphatidylinositol, are enriched in the brain, and have well-established roles in both homeostasis and disease.Disrupted PIP levels and signaling has been detected in a variety of dementias. Moreover, many known AD disease modifiers identified via genetic studies are expressed in microglia and are involved in phospholipid metabolism. One of these, the enzyme PLCγ2 that hydrolyzes the PIP species PI(4,5)P2, displays altered expression in AD and PD and is currently being investigated as a potential therapeutic target.Perhaps unsurprisingly, neurodegenerative conditions exhibiting PIP dyshomeostasis also tend to show alterations in aspects of microglial function regulated by these lipids. In particular, phosphoinositides regulate the activities of proteins and enzymes required for endocytosis, toll-like receptor signaling, purinergic signaling, chemotaxis, and migration, all of which are affected in a variety of neurodegenerative conditions. These functions are crucial to allow microglia to adequately survey the brain and respond appropriately to invading pathogens and other abnormalities, including misfolded proteins. AD and PD therapies are being developed to target many of the above pathways, and although not yet investigated, simultaneous PIP manipulation might enhance the beneficial effects observed. Currently, only limited therapeutics are available for dementia, and although these show some benefits for symptom severity and progression, they are far from curative. Given the importance of microglia and PIPs in dementia development, this review summarizes current research and asks whether we can exploit this information to design more targeted, or perhaps combined, dementia therapeutics. More work is needed to fully characterize the pathways discussed in this review, but given the strength of the current literature, insights in this area could be invaluable for the future of neurodegenerative disease research.