Biology subjects

Ackermann, F.

Publications and source records attributed to Ackermann, F..

6 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↗

bioRxiv2022

Piccolino regulates the architecture of the ribbon at cochlear inner hair cell synapses

Cochlear inner hair cells (IHCs) form specialized ribbon synapses with spiral ganglion neurons that tireless-ly transmit sound information at high rates over long time periods with extreme temporal precision. This functional specialization is essential for precise sound encoding and is attributed to a distinct molecular machinery with unique players or splice variants compared to conventional neuronal synapses. Among these is the active zone (AZ) scaffold protein piccolo/aczonin, which is represented by its short splice variant piccolino at cochlear and retinal ribbon synapses. While the function of piccolo at synapses of the central nervous system has been intensively investigated, the role of piccolino at IHC synapses remains unclear. In this study, we characterized the structure and function of IHC-synapses in piccolo gene-trap mutant rats (Pclogt/gt). We found a mild hearing deficit with elevated thresholds and reduced amplitudes of auditory brainstem responses. Ca2+ channel distribution and ribbon morphology were altered in apical IHCs, while their presynaptic function seemed unchanged. We conclude that piccolino contributes to the AZ organization in IHCs and is essential for normal synaptic transmission.

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

Light induced synaptic vesicle autophagy

The regulated turnover of synaptic vesicle (SV) proteins is thought to involve the ubiquitin dependent tagging and degradation through endo-lysosomal and autophagy pathways. Yet, it remains unclear which of these pathways are used, when they become activated and whether SVs are cleared en-mass together with SV proteins or whether both are degraded selectively. Equally puzzling is how quickly these systems can be activated and whether they function in real time to support synaptic health. To address these questions, we have developed an imaging based system that simultaneously tags presynaptic proteins while monitoring autophagy. Moreover, by tagging SV proteins with a light activated reactive oxygen species (ROS) generator, Supernova, it was possible to temporally control the damage to specific SV proteins and assess their consequence to autophagy mediated clearance mechanisms and synaptic function. Our results show that, in mouse hippocampal neurons, presynaptic autophagy can be induced in as little as 5-10 minutes and eliminates primarily the damaged protein rather than the SV en-mass. Importantly, we also find that autophagy is essential for synaptic function, as light-induced damage to e.g. Synaptophysin only compromises synaptic function when autophagy is simultaneously blocked. These data support the concept that presynaptic boutons have a robust highly regulated clearance system to maintain not only synapse integrity, but also synaptic function.

neuroscience↗

bioRxiv2018

Mutant Screen Reveals the Piccolo’s Control over Depression and Brain-Gonad Crosstalk

Successful sexual reproduction involves complex, genetically encoded interplay between animal physiology and behavior. The rat provides a highly fecund mammalian model for studying how the brain impacts reproduction. Here, we report a forward genetics screen in rats to identify genes that affect reproduction. A panel of 18 distinct rat strains harboring Sleeping Beauty gene trap mutations were analyzed for the ability to reproduce. As expected, our mutant screen identified genes where reproductive failure was connected to gametogenesis (Btrc, Pan3, Spaca6, Ube2k) and embryogenesis (Alk3, Exoc6b, Slc1a3, Tmx4, Zmynd8). In addition, we identified Ata13 (longevity) and Pclo (neuronal disorders), previously not associated with an inability to conceive. Neurologically, Pclo is known to regulate the size of presynaptic vesicle pools. Here, dominant traits in Pclo mutant rats caused epileptiform activity and affected genes supporting GABAergic synaptic transmission (Gabra6, Gabrg3). Recessive traits in Pclo mutant rats transmitted altered reproductive behavior, as homozygous Pclo mutant rats produced gametes but neither sex would mate with wildtype rats. Pclo mutant rat behavior was linked to endophenotypes signifying compromised brain-gonad crosstalk via disturbed GnRH signaling and allelic markers for major depressive disorder in humans (Grm5, Htr2a, Sorcs3, Negr1, Drd2). Thus, by rat genetics, we identified Pclo as a candidate presynaptic factor required for reproduction. Author SummaryPiccolo gene mutations have previously been identified in human cohorts diagnosed with behavioral syndromes that impact ones emotions, including depression and bipolar disorder. Although studies in human populations implicate changes to Piccolos DNA sequence to enhanced susceptibility for behavioral disorders, studies in mouse models have yet to link Piccolo mutations to altered behavior. Here, by a novel genetics approach, we report Piccolo mutation-dependent effects on reproductive behavior in rats, a finding that may turn out to be relevant to the behavioral effects that are associated with human Piccolo gene mutations. Thus, research aimed at understanding how Piccolo functions to regulate reproduction in rats could prove pivotal in our ability to understand neurological mechanisms that influence human emotions.

genetics↗

bioRxiv2018

Critical role for Piccolo in Synaptic Vesicle Retrieval

Loss of function of the presynaptic active zone protein Piccolo has recently been linked to a devastating disease causing brain atrophy. Here, we address how Piccolo inactivation adversely affects synaptic function and thus may contributes to neuronal loss. Our analysis shows that Piccolo is critical for the activity dependent recycling and maintenance of synaptic vesicles (SVs). Specifically, we find that boutons lacking Piccolo have deficits in the Rab5/EEA1 dependent formation of early endosomes and thus the recycling of SVs. Mechanistically, impaired Rab5 function was caused by the reduced synaptic recruitment of Pra1, known to interact selectively with the zinc fingers of Piccolo. Importantly, over-expression of GTPase deficient Rab5 or the Znf1 domain of Piccolo restores the size and recycling of SV pools. These data provide a molecular link between the active zone and endosome sorting at synapses providing hints to how Piccolo contributes to both developmental and psychiatric disorders.\n\nImpact StatementThe efficient recycling of synaptic vesicle proteins is critical for the integrity and reliability of synaptic transmission. Increasingly genetic and environmental insults have been shown to affect this recycling pathway, resulting in both cognitive impairment in humans and neurodegenerative diseases, yet the underlying mechanisms are poorly understood. Here we could show that the presynaptic active zone protein Piccolo regulates efficient recycling of synaptic vesicles via Pra1 and Rab5, perhaps explaining why Piccolo loss of function contributes to Pontocerebellar Hypoplasia and major depressive disorders.

neuroscience↗