Biology subjects

Garner, C.

Publications and source records attributed to Garner, C..

5 recordsLinked to original sources

bioRxiv2025

Piccolo Regulates Secretion of the Extracellular Matrix Components Brevican and Tenascin R from Astrocytes to Drive Synapse Formation: Implications for Pontocerebellar Hypoplasia Type 3 (PCH3)

BackgroundAstrocytes are crucial for CNS health, for instance via the secretion of extracellular matrix (ECM) components that are vital for synapse formation and maturation. While the scaffolding protein Piccolo is known for its role at synapses, its function in astrocytes and contribution to neurodegenerative disorders like Pontocerebellar Hypoplasia Type 3 (PCH3) are largely unknown. Understanding these mechanisms is key to elucidating PCH3 pathology. MethodsWe used a multi-faceted approach with a Pclogt/gtrat model. Methods included RNA-sequencing for gene expression and GO analysis. Immunohistochemistry and immunocytochemistry assessed Piccolo localization, ECM component (Brevican [Bcan], Tenascin-R [TNR]) levels, distribution, and secretion in brain sections and primary astrocytes. Golgi morphology was evaluated via GM130 staining. Neuronal network formation and function were investigated by co-culturing wild-type neurons with Pclowt/wt or Pclogt/gt astrocytes in a Banker setup, assessing synapse density (immunostaining, RRP electrophysiology) and spontaneous activity (mEPSCs, mIPSCs). Astrocyte-conditioned media (ACM) experiments determined secreted factor roles. ResultsRNA-seq showed significant DEG increases in older versus young Pclogt/gt rats (P25 vs. P5), which were strongly enriched in cell communication, signaling, and ECM GO terms. We identified a novel astrocyte-specific Piccolo isoform that partially localizes at the Golgi. Piccolo gene trap transposon mutation led to impaired ECM secretion (reduced extracellular Bcan, altered TNR) from astrocytes, correlating with a fragmented Golgi in Pclogt/gt astrocytes. Functionally, Pclogt/gt astrocytes significantly reduced synapse density and altered intrinsic activity (increased mEPSC frequency) in neuronal networks. This synaptic deficit was substantially rescued by Pclowt/wtastrocyte conditioned media (ACM). ConclusionOur findings reveal a critical, unrecognized role for Piccolo in regulating astrocytic ECM secretion, essential for proper neuronal network formation and activity. Astrocytic Piccolo dysfunction disrupts this process, causing impaired synaptogenesis and altered intrinsic network activity, providing a novel cellular and molecular mechanism for neurodegenerative diseases like PCH3 and highlights astrocytes as potential therapeutic targets.

neuroscience↗

bioRxiv2020

Temporal dynamics of functional networks in long-term infant scalp EEG

Human functional connectivity networks are modulated on time scales ranging from milliseconds to days. Rapid changes in connectivity over short time scales are a feature of healthy cognitive function, and variability over long time scales can impact the likelihood of seizure occurrence. However, relatively little is known about modulation of healthy functional networks over long time scales. To address this, we analyzed functional connectivity networks calculated from long-term EEG recordings from 19 healthy infants. Networks were subject-specific, as inter-subject correlations between weighted adjacency matrices were low. However, within individual subjects, both sleep and wake networks were stable over time, with stronger functional connectivity during sleep than wakefulness. This enabled automatic separation of wakefulness and sleep states via principle components analysis of the functional network time series, with median classification accuracy of 91%. Lastly, we found that network strength, degree, clustering coefficient, and path length significantly varied with time of day, when measured in both wakefulness and sleep. Together, these results suggest that modulation of healthy functional networks occurs over long timescales and is robust and repeatable. Accounting for such temporal periodicities may improve the physiological interpretation and use of functional connectivity analysis to investigate brain function in health and disease.

neuroscience↗

bioRxiv2020

Automated Detection of Ripple Oscillations in Long-Term Scalp EEG from Patients with Infantile Spasms

ObjectiveScalp high frequency oscillations (HFOs) are a promising biomarker of epileptogenicity in infantile spasms (IS) and many other epilepsy syndromes, but prior studies have relied on visual analysis of short segments of data due to the prevalence of artifacts in EEG. Therefore, we set out to develop a fully automated method of HFO detection that can be applied to large datasets, and we sought to robustly characterize the rate and spatial distribution of HFOs in IS. MethodsWe prospectively collected long-term scalp EEG data from 13 subjects with IS and 18 healthy controls. For patients with IS, recording began prior to diagnosis and continued through initiation of treatment with adenocorticotropic hormone (ACTH). The median analyzable EEG duration was 18.2 hours for controls and 83.9 hours for IS subjects ([~]1300 hours total). Ripples (80-250 Hz) were detected in all EEG data using an automated algorithm. ResultsHFO rates were substantially higher in patients with IS compared to controls. In IS patients, HFO rates were higher during sleep compared to wakefulness (median 5.5/min and 2.9/min, respectively; p =0.002); controls did not exhibit a difference in HFO rate between sleep and wakefulness (median 0.98/min and 0.82/min, respectively). Spatially, the difference between IS patients and controls was most salient in the central/posterior parasaggital region, where very few HFOs were detected in controls. In IS subjects, ACTH therapy significantly decreased the rate of HFOs. DiscussionHere we show for the first time that a fully automated algorithm can be used to detect HFOs in long-term scalp EEG, and the results are accurate enough to clearly discriminate healthy subjects from those with IS. We also provide a detailed characterization of the spatial distribution and rates of HFOs associated with infantile spasms, which may have relevance for diagnosis and assessment of treatment response.

neuroscience↗

bioRxiv2019

Loss of Piccolo function in rats induces Pontocerebellar Hypoplasia type 3-like phenotypes

Piccolo, a presynaptic active zone protein, is best known for its role in the regulated assembly and function of vertebrate synapses. Genetic studies suggest a further link to several psychiatric disorders as well as Pontocerebellar Hypoplasia type 3 (PCH3), although a causal relationship is lacking. We have characterized recently generated knockout (Pclogt/gt) rats. Analysis revealed a dramatic reduction in brain size compared to wildtype (Pclowt/wt) animals, attributed to a decrease in the size of the cerebral cortical, cerebellar and pontine regions. Analysis of the cerebellum and brainstem revealed a reduced granule cell (GC) layer and a reduction in size of pontine nuclei. Moreover, the maturation of mossy fiber (MF) afferents from pontine neurons and the expression of the 6 GABAA receptor subunit at the MF-GC synapse are perturbed, as well as the innervation of Purkinje cells by cerebellar climbing fibers (CFs). Ultrastructural and functional studies revealed a reduced size of MF boutons, with fewer synaptic vesicles and altered synaptic transmission. These data imply that Piccolo is required for the normal development, maturation and function of neuronal networks formed between the brainstem and cerebellum. Consistently, behavioral studies demonstrated that adult Pclogt/gt rats display impaired motor coordination, despite adequate performance in tasks that reflect muscle strength and locomotion. Together these data suggest that loss of Piccolo function in patients with PCH3 could be causal for many of the observed anatomical and behavioral symptoms, and that the further analysis of these animals could provide fundamental mechanistic insights into this devastating disorder.\n\nSignificance StatementPontocerebellar Hypoplasia type 3 is a devastating developmental disorder associated with severe developmental delay, progressive microcephaly with brachycephaly, optic atrophy, seizures and hypertonia with hyperreflexia. Recent genetic studies have identified non-sense mutations in the coding region of the Piccolo gene, suggesting a functional link between this disorder and the presynaptic active zone. Our analysis of Piccolo knockout rats supports this hypothesis, formally demonstrating that anatomical and behavioral phenotypes seen in patients with PCH3 are also exhibited by these Piccolo deficient animals.

neuroscience↗

bioRxiv2018

Identification of an immune gene expression signature associated with favorable clinical features in Treg-enriched patient tumor samples

Immune heterogeneity within the tumor microenvironment undoubtedly adds several layers of complexity to our understanding of drug sensitivity and patient prognosis across various cancer types. Within the tumor microenvironment, immunogenicity is a favorable clinical feature in part driven by the antitumor activity of CD8+ T cells. However, tumors often inhibit this antitumor activity by exploiting the suppressive function of Regulatory T cells (Tregs), thus suppressing the adaptive immune response. Despite the seemingly intuitive immunosuppressive biology of Tregs, prognostic studies have produced contradictory results regarding the relationship between Treg enrichment and survival. We therefore analyzed RNA-seq data of Treg-enriched tumor samples to derive a pan-cancer gene signature able to help reconcile the inconsistent results of Treg studies, by better understanding the variable clinical association of Tregs across alternative tumor contexts. We show that increased expression of a 32-gene signature in Treg-enriched tumor samples (n=135) is able to distinguish a cohort of patients associated with chemosensitivity and overall survival This cohort is also enriched for CD8+ T cell abundance, as well as the antitumor M1 macrophage subtype. With a subsequent validation in a larger TCGA pool of Treg-enriched patients (n = 626), our results reveal a gene signature able to produce unsupervised clusters of Treg-enriched patients, with one cluster of patients uniquely representative of an immunogenic tumor microenvironment. Ultimately, these results support the proposed gene signature as a putative biomarker to identify certain Treg-enriched patients with immunogenic tumors that are more likely to be associated with features of favorable clinical outcome.

cancer biology↗