Biology subjects

Flaherty, D.

Publications and source records attributed to Flaherty, D..

5 recordsLinked to original sources

bioRxiv2024

A domain-swapped CaMKII conformation facilitates linker-mediated allosteric regulation

Memory formation, fertilization, and cardiac function rely on precise Ca2+ signaling and subsequent Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation. Ca2+ sensitivity of the four CaMKII paralogs in mammals has been linked to the length of the variable linker region that is a hot spot for alternative splicing. In this study, we determined that the position of charged residues within the linker modulates the Ca2+/CaM sensitivity. We present an X-ray crystal structure of the full-length CaMKII{delta} holoenzyme consisting of domain-swapped dimers within a dodecameric complex. In this structure, the kinase domain of one subunit is docked onto the hub domain of an adjacent subunit, providing an additional interface within the holoenzyme. Mutations at the hub equatorial and lateral interfaces led to alterations in the stoichiometry of CaMKII holoenzyme as well as Ca2+/CaM sensitivity. Using molecular dynamics (MD) to compare domain-swapped to non-domain-swapped CaMKIIs, we demonstrate that the domain-swapped conformation facilitates an interaction between the calmodulin binding region and the linker region. Based on MD simulations and small-angle X-ray scattering (SAXS) measurements, we propose a model where the position of charges on the linker region drives an interaction with the regulatory segment that modulates the degree of autoinhibition. Finally, we use live-cell imaging to show that the activation profiles we observe in vitro are recapitulated in cells. Our findings provide a new framework for understanding allosteric regulation of CaMKII by the linker region in Ca2+-sensitive cells.

biochemistry↗

bioRxiv2024

ABCA7-dependent Neuropeptide-Y signalling is a resilience mechanism required for synaptic integrity in Alzheimer's disease

Alzheimers disease (AD) remains a complex challenge characterized by cognitive decline and memory loss. Genetic variations have emerged as crucial players in the etiology of AD, enabling hope for a better understanding of the disease mechanisms; yet the specific mechanism of action for those genetic variants remain uncertain. Animal models with reminiscent disease pathology could uncover previously uncharacterized roles of these genes. Using CRISPR/Cas9 gene editing, we generated a knockout model for abca7, orthologous to human ABCA7 - an established AD-risk gene. The abca7+/- zebrafish showed reduced astroglial proliferation, synaptic density, and microglial abundance in response to amyloid beta 42 (A{beta}42). Single-cell transcriptomics revealed abca7-dependent neuronal and glial cellular crosstalk through neuropeptide Y (NPY) signaling. The abca7 knockout reduced the expression of npy, bdnf and ngfra, which are required for synaptic integrity and astroglial proliferation. With clinical data in humans, we showed reduced NPY in AD correlates with elevated Braak stage, predicted regulatory interaction between NPY and BDNF, identified genetic variants in NPY associated with AD, found segregation of variants in ABCA7, BDNF and NGFR in AD families, and discovered epigenetic changes in the promoter regions of NPY, NGFR and BDNF in humans with specific single nucleotide polymorphisms in ABCA7. These results suggest that ABCA7-dependent NPY signaling is required for synaptic integrity, the impairment of which generates a risk factor for AD through compromised brain resilience. O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/573893v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@eecf7forg.highwire.dtl.DTLVardef@78d8e0org.highwire.dtl.DTLVardef@1e65d71org.highwire.dtl.DTLVardef@100db01_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

neuroscience↗

bioRxiv2024

Rare genetic variation in Fibronectin 1 (FN1) protects against APOEe4 in Alzheimer's disease

The risk of developing Alzheimers disease (AD) significantly increases in individuals carrying the APOE{varepsilon}4 allele. Elderly cognitively healthy individuals with APOE{varepsilon}4 also exist, suggesting the presence of cellular mechanisms that counteract the pathological effects of APOE{varepsilon}4; however, these mechanisms are unknown. We hypothesized that APOE{varepsilon}4 carriers without dementia might carry genetic variations that could protect them from developing APOE{varepsilon}4-mediated AD pathology. To test this, we leveraged whole genome sequencing (WGS) data in National Institute on Aging Alzheimers Disease Family Based Study (NIA-AD FBS), Washington Heights/Inwood Columbia Aging Project (WHICAP), and Estudio Familiar de Influencia Genetica en Alzheimer (EFIGA) cohorts and identified potentially protective variants segregating exclusively among unaffected APOE{varepsilon}4 carriers. In homozygous unaffected carriers above 70 years old, we identified 510 rare coding variants. Pathway analysis of the genes harboring these variants showed significant enrichment in extracellular matrix (ECM)-related processes, suggesting protective effects of functional modifications in ECM proteins. We prioritized two genes that were highly represented in the ECM-related gene ontology terms, (FN1) and collagen type VI alpha 2 chain (COL6A2) and are known to be expressed at the blood-brain barrier (BBB), for postmortem validation and in vivo functional studies. The FN1 and COL6A2 protein levels were increased at the BBB in APOE{varepsilon}4 carriers with AD. Brain expression of cognitively unaffected homozygous APOE{varepsilon}4 carriers had significantly lower FN1 deposition and less reactive gliosis compared to homozygous APOE{varepsilon}4 carriers with AD, suggesting that FN1 might be a downstream driver of APOE{varepsilon}4-mediated AD-related pathology and cognitive decline. To validate our findings, we used zebrafish models with loss-of-function (LOF) mutations in fn1b - the ortholog for human FN1. We found that fibronectin LOF reduced gliosis, enhanced gliovascular remodeling and potentiated the microglial response, suggesting that pathological accumulation of FN1 could impair toxic protein clearance, which is ameliorated with FN1 LOF. Our study suggests vascular deposition of FN1 is related to the pathogenicity of APOE{varepsilon}4, LOF variants in FN1 may reduce APOE{varepsilon}4-related AD risk, providing novel clues to potential therapeutic interventions targeting the ECM to mitigate AD risk.

genetics↗

bioRxiv2023

Model-based inference of a plant-specific dual role for HOPS in regulating guard cell vacuole fusion

Stomata are the pores on a leaf surface that regulate gas exchange. Each stoma consists of two guard cells whose movements regulate pore opening and thereby control CO2 fixation and water loss. Guard cell movements depend in part on the remodeling of vacuoles, which have been observed to change from a highly fragmented state to a fused morphology during stomata opening. This change in morphology requires a membrane fusion mechanism that responds rapidly to environmental signals, allowing plants to respond to diurnal and stress cues. With guard cell vacuoles being both large and responsive to external signals, stomata represent a unique system in which to delineate mechanisms of membrane fusion. Fusion of vacuole membranes is a highly conserved process in eukaryotes, with key roles played by two multi-subunit complexes: HOPS (homotypic fusion and vacuolar protein sorting) and SNARE (soluble NSF attachment protein receptor). HOPS is a vacuole tethering factor that is thought to chaperone SNAREs from apposing vacuole membranes into a fusion-competent complex capable of rearranging membranes. To resolve a counter-intuitive observation regarding the role of HOPS in regulating plant vacuole morphology, we derived a quantitative model of vacuole fusion dynamics and used it to generate testable predictions about HOPS-SNARE interactions. We derived our model by applying simulation-based inference to integrate prior knowledge about molecular interactions with limited, qualitative observations of emergent vacuole phenotypes. By constraining the model parameters to yield the emergent outcomes observed for stoma opening - as induced by two distinct chemical treatments - we predicted a dual role for HOPS and identified a stalled form of the SNARE complex that differs from phenomena reported in yeast. We predict that HOPS has contradictory actions at different points in the fusion signaling pathway, promoting the formation of SNARE complexes, but limiting their activity. Author summaryPlants "breathe" through pores in their leaves where each pore is formed by two specialized cells called guard cells. To open these pores, guard cells change in volume. This volume change is controlled by water-filled organelles called vacuoles that morph from multiple small entities to a few large ones capable of taking up more water to reshape the cell. Specialized proteins in vacuole membranes make this change happen by pulling vacuoles together until they fuse. Some of these proteins reside in membranes, but others must be drawn to the membrane from the cells cytoplasm. Specific lipid molecules in the membrane play an important role in recruiting those proteins to the vacuole membrane. We previously made an unexpected finding that removing this lipid induces plant vacuole fusion. To make sense of this observation, we used a mathematical model to piece together our knowledge of the proteins involved in this process and what we know about the chemical treatments that cause vacuoles to morph. Using computer simulations, we uncovered new rules about how molecules interact in membranes to accomplish the task of vacuole fusion in plants. We think the rules uncovered through mathematical modeling allow plants to respond quickly to environmental cues.

systems biology↗

bioRxiv2023

Clonal CD8 T cells in the leptomeninges are locally controlled and influence microglia in human neurodegeneration

Recent murine studies have highlighted a crucial role for the meninges in surveilling the central nervous system (CNS) and influencing CNS inflammation. However, how meningeal immunity is altered in human neurodegeneration and its potential effects on neuroinflammation is understudied. In the present study, we performed single-cell analysis of the transcriptomes and T cell receptor repertoire of 72,576 immune cells from 36 postmortem human brain and leptomeninges tissues from donors with neurodegenerative diseases including amyotrophic lateral sclerosis, Alzheimers disease, and Parkinsons disease. We identified the meninges as an important site of antigen presentation and CD8 T cell activation and clonal expansion and found that T cell activation in the meninges is a requirement for infiltration into the CNS. We further found that natural killer cells have the potential to negatively regulate T cell activation locally in the meninges through direct killing and are one of many regulatory mechanisms that work to control excessive neuroinflammation.

neuroscience↗