Biology subjects

Kuulasmaa, T.

Publications and source records attributed to Kuulasmaa, T..

5 recordsLinked to original sources

bioRxiv2024

Protective variant in PLCgamma2 mitigates Alzheimer's disease associated pathology via enhancing beneficial microglia functions

BackgroundPLC{gamma}2-P522R (phospholipase C gamma 2, proline 522 to arginine) is a protective variant that reduces the risk for late onset Alzheimers disease. Recently, it was shown to decrease {beta}-amyloid pathology in 5XFAD mouse model of AD. In this study, our goal was to investigate the protective functions of PLC{gamma}2-P522R variant in a less aggressive mouse model of AD as well as to assess the underlying mechanisms at the molecular and cellular level using mouse and human microglia models. MethodsThe effects of the protective PLC{gamma}2-P522R variant on microglia activation, AD-related {beta}-amyloid and neuronal pathologies, as well as behavioral changes were investigated in PLC{gamma}2-P522R knock-in mice crossbred with APP/PS1 AD model mice. Transcriptomic, proteomic, and functional studies were carried out in cultured and acutely isolated adult PLC{gamma}2-P522R mouse microglia to study molecular mechanisms. Finally, microglia-like cell models generated from blood and skin biopsy samples of the PLC{gamma}2-P522R variant carriers were employed to translate the key findings to human cells. ResultsOur results demonstrate that the PLC{gamma}2-P522R variant reduced brain {beta}-amyloid plaque burden of APP/PS1 mice. Simultaneously, PLC{gamma}2-P522R variant increased non-proinflammatory microglia activation and microglia clustering around {beta}-amyloid plaques, leading to reduced {beta}-amyloid plaque-associated neuronal dystrophy. In cultured mouse primary microglia, PLC{gamma}2-P522R variant decreased accumulation of large lipid droplets, reduced cell stress, and increased acute response to strong inflammatory stimuli. Transcriptomic and proteomic analyses in acutely isolated adult mouse microglia as well as in human monocyte-derived microglial cells showed that PLC{gamma}2-P522R upregulates mitochondrial fatty acid oxidation and downregulates inflammatory/interferon signaling pathways. Accordingly, PLC{gamma}2-P522R increased mitochondrial respiration in iPSC-derived microglial cells. ConclusionsTogether, these findings suggest that PLC{gamma}2-P522R variant exerts protection against AD-associated {beta}-amyloid and neuronal pathologies via enhancing microglial barrier formation around {beta}-amyloid plaques and suppressing pro-inflammatory activation. Observed changes in fatty acid metabolism and mitochondrial flexibility as well as the downregulation of genes involved in inflammatory signaling pathways suggest that these protective effects of the PLC{gamma}2-P522R variant are mediated through an anti-ageing mechanism.

neuroscience↗

bioRxiv2024

C9orf72 repeat expansion-carrying iPSC-microglia from FTD patients show increased phagocytic activity concomitantly with decreased number of autophagosomal-lysosomal vesicles

C9orf72 hexanucleotide repeat expansion (HRE) is a major genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. The role of microglia in these C9orf72 HRE-associated diseases is understudied. To elucidate effects of C9orf72 HRE on microglia, we have characterized human induced pluripotent stem cell-derived microglia (iMG) from behavioral variant frontotemporal dementia (bvFTD) patients carrying the C9orf72 HRE. C9orf72 HRE iMG were compared to iMG from healthy controls and sporadic bvFTD patients. The phenotypes of iMG were analyzed using bulk RNA sequencing, biochemical and immunofluorescence analyses, and live cell imaging. C9orf72 HRE-carrying iMG showed nuclear RNA foci and poly-GP dipeptide repeat proteins but no decreased C9orf72 mRNA or protein expression. TDP-43 pathology was absent from all bvFTD iMG. As compared to healthy control iMG, quantitative immunofluorescence analyses indicated that all bvFTD iMG had reduced number, size, and intensity of LAMP2-A-positive vesicles. C9orf72 HRE-carrying iMG additionally showed decreased number, size, and intensity of p62/SQSTM1-positive vesicles. These changes were accompanied by increased phagocytic activity of the C9orf72 HRE-carrying iMG. Serum starvation increased phagocytic activity also in the iMG of sporadic bvFTD patients. RNA sequencing revealed that iMG of C9orf72 HRE-carrying bvFTD patients as compared to the iMG of sporadic bvFTD patients showed differential gene expression in pathways related to RNA and protein regulation and mitochondrial metabolism. Our data suggest potential alterations in the autophagosomal/lysosomal pathways in bvFTD patient iMG, which are further reinforced by the C9orf72 HRE and functionally manifest as increased phagocytic activity.

neuroscience↗

bioRxiv2024

Neuronal downregulation of PLCG2 impairs synaptic function and elicits Alzheimer disease hallmarks

We developed a high content screening to investigate how Alzheimer disease (AD) genetic risk factors may affect synaptic mechanisms in rat primary neuronal cultures. Out of the target genes identified, we found that Plcg2 downregulation in mouse dentate gyrus neurons consistently disrupted dendritic morphology and synaptic function. In human neuronal cultures (hNCs), PLCG2 downregulation also impaired synaptic function and increased A{beta} levels and Tau phosphorylation. Very rare PLCG2 loss-of-function (LoF) variants were associated with a 10-fold increased AD risk. PLCG2 LoF carriers exhibit low mRNA/protein PLCG2/PLC{gamma}2 levels and the R953* LoF mutation compromised synaptic function and increased AD hallmarks in hNCs. Single nuclei RNAseq analyses confirmed that the downregulation of PLCG2 impacted pathways related to synaptic and neuronal functions, potentially through neurexin in neurons. In conclusion, PLC{gamma}2 downregulation could increase AD risk by impairing synaptic functions and increasing the A{beta} levels and Tau phosphorylation in neurons.

neuroscience↗

bioRxiv2020

The Alzheimer's disease-associated protective Plcγ2-P522R variant promotes beneficial microglial functions

BackgroundMicroglia-specific genetic variants are enriched in several neurodegenerative diseases, including Alzheimers disease (AD), implicating a central role for alterations of the innate immune system in the disease etiology. A rare coding variant in the PLCG2 gene (rs72824905, p.P522R) selectively expressed in microglia and macrophages was recently identified and shown to reduce the risk for AD. MethodsTo assess the role of this variant in the context of immune cell functions, we generated a Plc{gamma}2-P522R knock-in (KI) mouse model using CRISPR/Cas9 gene editing. ResultsFunctional analyses of macrophages derived from homozygous KI mice and wild type (WT) littermates revealed that the P522R variant potentiates the primary function of Plc{gamma}2 as a Pip2-metabolizing enzyme. This was associated with improved survival, enhanced phagocytic activity, and increased acute inflammatory response of the KI cells. Enhanced phagocytosis was also observed in mouse BV2 microglia-like cells overexpressing human PLC{gamma}2-P522R, but not in PLC{gamma}2-WT expressing cells. Furthermore, the brain mRNA signature together with microglia-specific PET imaging indicated microglia activation in Plc{gamma}2-P522R KI mice. ConclusionThus, we have delineated cellular mechanisms of the protective Plc{gamma}2-P522R variant, which provide further support for the emerging idea that activated microglia exert protective functions in AD.

neuroscience↗

bioRxiv2020

Diabetic phenotype in mouse and humans with β-amyloid pathology reduces the number of microglia around β-amyloid plaques

Type 2 diabetes (T2D) increases the risk of Alzheimers disease (AD). Even though these two diseases share common molecular pathways, the mechanisms remain elusive. To shed light into these mechanisms, mice with different AD- and/or tauopathy-linked genetic backgrounds were utilized; APPswe/PS1dE9 (A+Tw), Tau P301L (AwT+), and APPswe/PS1dE9/Tau P301L (A+T+). Feeding these mice with typical Western diet (TWD) led to obesity and diabetic phenotype as compared to respective mice with a standard diet. TWD also exacerbated memory and learning impairment in A+Tw and AwT+, but not in A+T+ mice. Furthermore, RNA sequencing of mouse hippocampal samples revealed altered responses to AD-related pathologies in A+Tw and A+T+ mice upon TWD, pointing specifically towards aberrant microglial functionality and PI3K-Akt signaling. Accordingly, fewer microglia alongside an increased number of dystrophic neurites around {beta}-amyloid plaques, and impaired PI3K-Akt signaling, were discovered in the hippocampus of TWD mice. Mechanistic elucidation revealed that disruption of the PI3K-Akt signaling pathway by pharmacological or genetic approaches significantly decreased the phagocytic uptake and proinflammatory response as well as increased the activity of Syk-kinase upon ligand-induced activation of Trem2/Dap12 signaling in mouse microglia. Finally, characterization of microglial pathology in cortical biopsies of idiopathic normal pressure hydrocephalus (iNPH) patients harboring {beta}-amyloid plaques revealed a significant decrease in the number of microglia per {beta}-amyloid plaque in obese iNPH patients with T2D as compared to both normal weight and obese iNPH patients without T2D. Collectively, these results suggest that the peripheral diabetic phenotype in mice and humans associates with reduced microglial response to {beta}-amyloid pathology.

neuroscience↗