Neurexins control the strength and precise timing of glycinergic inhibition in the auditory brainstem.

Neurexins play diverse functions as presynaptic organizers in various glutamatergic and GABAergic synapses. However, it remains unknown whether and how neurexins are involved in shaping functional properties of the glycinergic synapses, which mediate prominent inhibition in the brainstem and spinal cord. To address these issues, we examined the role of neurexins in a model glycinergic synapse between the principal neuron in the medial nucleus of the trapezoid body (MNTB) and the principal neuron in the lateral superior olive (LSO) in the auditory brainstem. Combining RNAscope with stereotactic injection of AAV-Cre in the MNTB of neurexin1/2/3 conditional triple knockout mice, we showed that MNTB neurons highly express all isoforms of neurexins although their expression levels vary remarkably. Selective ablation of all neurexins in MNTB neurons not only reduced the amplitude but also altered the kinetics of the glycinergic synaptic transmission at LSO neurons. The synaptic dysfunctions primarily resulted from an impaired Ca2+ sensitivity of release and a loosened coupling between voltage-gated Ca2+ channels and synaptic vesicles. Together, our current findings demonstrate that neurexins are essential in controlling the strength and temporal precision of the glycinergic synapse, which therefore corroborates the role of neurexins as key presynaptic organizers in all major types of fast chemical synapses.

Reelin Regulates Developmental Desynchronization Transition of Neocortical Network Activity.

During the first and second stages of postnatal development, neocortical neurons exhibit a wide range of spontaneous synchronous activity (SSA). Towards the end of the second postnatal week, the SSA is replaced by a more sparse and desynchronized firing pattern. The developmental desynchronization of neocortical spontaneous neuronal activity is thought to be intrinsically generated, since sensory deprivation from the periphery does not affect the time course of this transition. The extracellular protein reelin controls various aspects of neuronal development through multimodular signaling. However, so far it is unclear whether reelin contributes to the developmental desynchronization transition of neocortical neurons. The present study aims to investigate the role of reelin in postnatal cortical developmental desynchronization using a conditional reelin knockout (RelncKO) mouse model. Conditional reelin deficiency was induced during early postnatal development, and Ca2+ recordings were conducted from organotypic cultures (OTCs) of the somatosensory cortex. Our results show that both wild type (wt) and RelncKO exhibited an SSA pattern during the early postnatal week. However, at the end of the second postnatal week, wt OTCs underwent a transition to a desynchronized network activity pattern, while RelncKO activity remained synchronous. This changing activity pattern suggests that reelin is involved in regulating the developmental desynchronization of cortical neuronal network activity. Moreover, the developmental desynchronization impairment observed in RelncKO was rescued when RelncKO OTCs were co-cultured with wt OTCs. Finally, we show that the developmental transition to a desynchronized state at the end of the second postnatal week is not dependent on glutamatergic signaling. Instead, the transition is dependent on GABAAR and GABABR signaling. The results suggest that reelin controls developmental desynchronization through GABAAR and GABABR signaling.

Safety of Anti-Reelin Therapeutic Approaches for Chronic Inflammatory Diseases.

Reelin, a large extracellular glycoprotein, plays critical roles in neuronal development and synaptic plasticity in the central nervous system (CNS). Recent studies have revealed non-neuronal functions of plasma Reelin in inflammation by promoting endothelial-leukocyte adhesion through its canonical pathway in endothelial cells (via ApoER2 acting on NF-κB), as well as in vascular tone regulation and thrombosis. In this study, we have investigated the safety and efficacy of selectively depleting plasma Reelin as a potential therapeutic strategy for chronic inflammatory diseases. We found that Reelin expression remains stable throughout adulthood and that peripheral anti-Reelin antibody treatment with CR-50 efficiently depletes plasma Reelin without affecting its levels or functionality within the CNS. Notably, this approach preserves essential neuronal functions and synaptic plasticity. Furthermore, in mice induced with experimental autoimmune encephalomyelitis (EAE), selective modulation of endothelial responses by anti-Reelin antibodies reduces pathological leukocyte infiltration without completely abolishing diapedesis. Finally, long-term Reelin depletion under metabolic stress induced by a Western diet did not negatively impact the heart, kidney, or liver, suggesting a favorable safety profile. These findings underscore the promising role of peripheral anti-Reelin therapeutic strategies for autoimmune diseases and conditions where endothelial function is compromised, offering a novel approach that may avoid the immunosuppressive side effects associated with conventional anti-inflammatory therapies.

Structural and functional reorganization of inhibitory synapses by activity-dependent cleavage of neuroligin-2.

Recent evidence has demonstrated that the transsynaptic nanoscale organization of synaptic proteins plays a crucial role in regulating synaptic strength in excitatory synapses. However, the molecular mechanism underlying this transsynaptic nanostructure in inhibitory synapses still remains unclear and its impact on synapse function in physiological or pathological contexts has not been demonstrated. In this study, we utilized an engineered proteolysis technique to investigate the effects of acute cleavage of neuroligin-2 (NL2) on synaptic transmission. Our results show that the rapid cleavage of NL2 led to impaired synaptic transmission by reducing both neurotransmitter release probability and quantum size. These changes were attributed to the dispersion of RIM1/2 and GABAA receptors and a weakened spatial alignment between them at the subsynaptic scale, as observed through superresolution imaging and model simulations. Importantly, we found that endogenous NL2 undergoes rapid MMP9-dependent cleavage during epileptic activities, which further exacerbates the decrease in inhibitory transmission. Overall, our study demonstrates the significant impact of nanoscale structural reorganization on inhibitory transmission and unveils ongoing modulation of mature GABAergic synapses through active cleavage of NL2 in response to hyperactivity.

NINJ1 mediates plasma membrane rupture by cutting and releasing membrane disks.

The membrane protein NINJ1 mediates plasma membrane rupture in pyroptosis and other lytic cell death pathways. Here, we report the cryo-EM structure of a NINJ1 oligomer segmented from NINJ1 rings. Each NINJ1 subunit comprises amphipathic (⍺1, ⍺2) and transmembrane (TM) helices (⍺3, ⍺4) and forms a chain of subunits, mainly by the TM helices and ⍺1. ⍺3 and ⍺4 are kinked, and the Gly residues are important for function. The NINJ1 oligomer possesses a concave hydrophobic side that should face the membrane and a convex hydrophilic side formed by ⍺1 and ⍺2, presumably upon activation. This structural observation suggests that NINJ1 can form membrane disks, consistent with membrane fragmentation by recombinant NINJ1. Live-cell and super-resolution imaging uncover ring-like structures on the plasma membrane that are released into the culture supernatant. Released NINJ1 encircles a membrane inside, as shown by lipid staining. Therefore, NINJ1-mediated membrane disk formation is different from gasdermin-mediated pore formation, resulting in membrane loss and plasma membrane rupture.

Chronic corticosterone exposure in rats induces sex-specific alterations in hypothalamic reelin fragments, MeCP2, and DNMT3a protein levels.

Women are disproportionately affected by stress-related disorders like depression. In our prior research, we discovered that females exhibit lower basal hypothalamic reelin levels, and these levels are differentially influenced by chronic stress induced through repeated corticosterone (CORT) injections. Although epigenetic mechanisms involving DNA methylation and the formation of repressor complexes by DNA methyl-transferases (DNMTs) and Methyl-CpG binding protein 2 (MeCP2) have been recognized as regulators of reelin expression in vitro, there is limited understanding of the impact of stress on the epigenetic regulation of reelin in vivo and whether sex differences exist in these mechanisms. To address these questions, we conducted various biochemical analyses on hypothalamic brain samples obtained from male and female rats previously treated with either 21 days of CORT (40 mg/kg) or vehicle (0.9 % saline) subcutaneous injections. Upon chronic CORT treatment, a reduction in reelin fragment NR2 was noted in males, while the full-length molecule remained unaffected. This decrease paralleled with an elevation in MeCP2 and a reduction in DNMT3a protein levels only in males. Importantly, sex differences in baseline and CORT-induced reelin protein levels were not associated with changes in the methylation status of the Reln promoter. These findings suggest that CORT-induced reelin decreases in the hypothalamus may be a combination of alterations in downstream processes beyond gene transcription. This research brings novel insights into the sexually distinct consequences of chronic stress, an essential aspect to understand, particularly concerning its role in the development of depression.

New knowledge on anti-IgLON5 disease.

PURPOSE OF REVIEW: Anti-IgLON5 disease is characterized by a distinctive sleep disorder, associated with a heterogeneous spectrum of neurological symptoms. Initial autopsies showed a novel neuronal tauopathy predominantly located in the tegmentum of the brainstem. Recently, new diagnostic red flags, biomarkers predictors of response to immunotherapy, and novel insights into the autoimmune pathogenesis of the disease have been reported. RECENT FINDINGS: Patients with diagnosis of neurodegenerative dementia, progressive supranuclear palsy (PSP) or with motor-neuron disease (MND)-like syndrome have been reported to have IgLON5 antibodies, which are the hallmark of anti-IgLON5 disease. Second, low levels of neurofilament light chain in serum and cerebrospinal fluid of patients at disease onset could be a predictor of immunotherapy response. Recent neuropathological studies indicate that the neuronal tau deposits occur late in the course of the disease. Moreover, IgLON5 antibodies induce cytoskeletal changes in cultured hippocampal neurons suggesting that the tauopathy could be secondary of the IgLON5 antibody effects. SUMMARY: Anti-IgLON5 disease can mimic and should be considered in atypical presentations of MND, neurodegenerative dementia and PSP. Neurofilament light chain levels seem promising biomarker for disease prognosis. Finally, the neuropathological and in vitro experimental studies strengthen the autoimmune hypothesis of the disease.

Fas2EB112: a tale of two chromosomes.

The cell-cell adhesion molecule Fasciclin II (Fas2) has long been studied for its evolutionarily conserved role in axon guidance. It is also expressed in the follicular epithelium, where together with a similar protein, Neuroglian (Nrg), it helps to drive the reintegration of cells born out of the tissue plane. Remarkably, one Fas2 protein null allele, Fas2G0336, demonstrates a mild reintegration phenotype, whereas work with the classic null allele Fas2EB112 showed more severe epithelial disorganization. These observations raise the question of which allele (if either) causes a bona fide loss of Fas2 protein function. The problem is not only relevant to reintegration but fundamentally important to understanding what this protein does and how it works: Fas2EB112 has been used in at least 37 research articles, and Fas2G0336 in at least three. An obvious solution is that one of the two chromosomes carries a modifier that either suppresses (Fas2G0336) or enhances (Fas2EB112) phenotypic severity. We find not only the latter to be the case, but identify the enhancing mutation as Nrg14, also a classic null allele.

The CHD Protein Kismet Restricts the Synaptic Localization of Cell Adhesion Molecules at the Drosophila Neuromuscular Junction.

The appropriate expression and localization of cell surface cell adhesion molecules must be tightly regulated for optimal synaptic growth and function. How neuronal plasma membrane proteins, including cell adhesion molecules, cycle between early endosomes and the plasma membrane is poorly understood. Here we show that the Drosophila homolog of the chromatin remodeling enzymes CHD7 and CHD8, Kismet, represses the synaptic levels of several cell adhesion molecules. Neuroligins 1 and 3 and the integrins αPS2 and ßPS are increased at kismet mutant synapses but Kismet only directly regulates transcription of neuroligin 2. Kismet may therefore regulate synaptic CAMs indirectly by activating transcription of gene products that promote intracellular vesicle trafficking including endophilin B (endoB) and/or rab11. Knock down of EndoB in all tissues or neurons increases synaptic FasII while knock down of EndoB in kis mutants does not produce an additive increase in FasII. In contrast, neuronal expression of Rab11, which is deficient in kis mutants, leads to a further increase in synaptic FasII in kis mutants. These data support the hypothesis that Kis influences the synaptic localization of FasII by promoting intracellular vesicle trafficking through the early endosome.

Differential contribution of canonical and noncanonical NLGN3 pathways to early social development and memory performance.

Neuroligin (NLGN) 3 is a postsynaptic cell adhesion protein organizing synapse formation through two different types of transsynaptic interactions, canonical interaction with neurexins (NRXNs) and a recently identified noncanonical interaction with protein tyrosine phosphatase (PTP) δ. Although, NLGN3 gene is known as a risk gene for neurodevelopmental disorders such as autism spectrum disorder (ASD) and intellectual disability (ID), the pathogenic contribution of the canonical NLGN3-NRXN and noncanonical NLGN3-PTPδ pathways to these disorders remains elusive. In this study, we utilized Nlgn3 mutant mice selectively lacking the interaction with either NRXNs or PTPδ and investigated their social and memory performance. Neither Nlgn3 mutants showed any social cognitive deficiency in the social novelty recognition test. However, the Nlgn3 mutant mice lacking the PTPδ pathway exhibited significant decline in the social conditioned place preference (sCPP) at the juvenile stage, suggesting the involvement of the NLGN3-PTPδ pathway in the regulation of social motivation and reward. In terms of learning and memory, disrupting the canonical NRXN pathway attenuated contextual fear conditioning while disrupting the noncanonical NLGN3-PTPδ pathway enhanced it. Furthermore, disruption of the NLGN3-PTPδ pathway negatively affected the remote spatial reference memory in the Barnes maze test. These findings highlight the differential contributions of the canonical NLGN3-NRXN and noncanonical NLGN3-PTPδ synaptogenic pathways to the regulation of higher order brain functions associated with ASD and ID.

Targeting the intracellular neurexin interactome by in vivo proximity ligation.

In a recent study, Profes, Tiroumalechetty, and colleagues used the in vivo proximity ligation technique TurboID to scrupulously characterize the interactome of the intracellular domain (ICD) of neurexin, revealing that this domain may be involved in presynaptic actin assembly by interacting with actin-associated proteins.

Caudally pronounced deficiencies in preplate splitting and migration underly a rostro-caudal progression of cortical lamination defects in the reeler brain.

In mammalian neocortex development, every cohort of newborn neurons is guided toward the marginal zone, leading to an "inside-out" organization of the 6 neocortical layers. This migratory pattern is regulated by the extracellular glycoprotein Reelin. The reeler mouse shows a homozygous mutation of the reelin gene. Using RNA in situ hybridization we could demonstrate that the Reelin-deficient mouse cortex (male and female) displays an increasing lamination defect along the rostro-caudal axis that is characterized by strong cellular intermingling, but roughly reproduces the "inside-out" pattern in rostral cortex, while caudal cortex shows a relative inversion of neuronal positioning ("outside-in"). We found that in development of the reeler cortex, preplate-splitting is also defective with an increasing severity along the rostro-caudal axis. This leads to a misplacement of subplate neurons that are crucial for a switch in migration mode within the cortical plate. Using Flash Tag labeling and nucleoside analog pulse-chasing, we found an according migration defect within the cortical plate, again with a progressive severity along the rostro-caudal axis. Thus, loss of one key player in neocortical development leads to highly area-specific (caudally pronounced) developmental deficiencies that result in multiple roughly opposite rostral versus caudal adult neocortical phenotypes.

NINJ1 induces plasma membrane rupture and release of damage-associated molecular pattern molecules during ferroptosis.

Ferroptosis is a regulated form of necrotic cell death caused by iron-dependent accumulation of oxidized phospholipids in cellular membranes, culminating in plasma membrane rupture (PMR) and cell lysis. PMR is also a hallmark of other types of programmed necrosis, such as pyroptosis and necroptosis, where it is initiated by dedicated pore-forming cell death-executing factors. However, whether ferroptosis-associated PMR is also actively executed by proteins or driven by osmotic pressure remains unknown. Here, we investigate a potential ferroptosis role of ninjurin-1 (NINJ1), a recently identified executor of pyroptosis-associated PMR. We report that NINJ1 oligomerizes during ferroptosis, and that Ninj1-deficiency protects macrophages and fibroblasts from ferroptosis-associated PMR. Mechanistically, we find that NINJ1 is dispensable for the initial steps of ferroptosis, such as lipid peroxidation, channel-mediated calcium influx, and cell swelling. In contrast, NINJ1 is required for early loss of plasma membrane integrity, which precedes complete PMR. Furthermore, NINJ1 mediates the release of cytosolic proteins and danger-associated molecular pattern (DAMP) molecules from ferroptotic cells, suggesting that targeting NINJ1 could be a therapeutic option to reduce ferroptosis-associated inflammation.

Caspase cleavage of gasdermin E causes neuronal pyroptosis in HIV-associated neurocognitive disorder.

Despite effective antiretroviral therapies, 20-30% of persons with treated HIV infection develop a neurodegenerative syndrome termed HIV-associated neurocognitive disorder (HAND). HAND is driven by HIV expression coupled with inflammation in the brain but the mechanisms underlying neuronal damage and death are uncertain. The inflammasome-pyroptosis axis coordinates an inflammatory type of regulated lytic cell death that is underpinned by the caspase-activated pore-forming gasdermin proteins. The mechanisms driving neuronal pyroptosis were investigated herein in models of HAND, using multi-platform molecular and morphological approaches that included brain tissues from persons with HAND and simian immunodeficiency virus (SIV)-infected non-human primates as well as cultured human neurons. Neurons in the frontal cortices from persons with HAND showed increased cleaved gasdermin E (GSDME), which was associated with ß-III tubulin degradation and increased HIV levels. Exposure of cultured human neurons to the HIV-encoded viral protein R (Vpr) elicited time-dependent cleavage of GSDME and Ninjurin-1 (NINJ1) induction with associated cell lysis that was inhibited by siRNA suppression of both proteins. Upstream of GSDME cleavage, Vpr exposure resulted in activation of caspases-1 and 3. Pretreatment of Vpr-exposed neurons with the caspase-1 inhibitor, VX-765, reduced cleavage of both caspase-3 and GSDME, resulting in diminished cell death. To validate these findings, we examined frontal cortical tissues from SIV-infected macaques, disclosing increased expression of GSDME and NINJ1 in cortical neurons, which was co-localized with caspase-3 detection in animals with neurological disease. Thus, HIV infection of the brain triggers the convergent activation of caspases-1 and -3, which results in GSDME-mediated neuronal pyroptosis in persons with HAND. These findings demonstrate a novel mechanism by which a viral infection causes pyroptotic death in neurons while also offering new diagnostic and therapeutic strategies for HAND and other neurodegenerative disorders.

Plasma Neuronal Growth Regulator 1 May Link Physical Activity to Reduced Risk of Type 2 Diabetes: A Proteome-Wide Study of ARIC Participants.

Habitual physical activity (PA) impacts the plasma proteome and reduces the risk of developing type 2 diabetes (T2D). Using a large-scale proteome-wide approach in Atherosclerosis Risk in Communities study participants, we aimed to identify plasma proteins associated with PA and determine which of these may be causally related to lower T2D risk. PA was associated with 92 plasma proteins in discovery (P < 1.01 × 10-5), and 40 remained significant in replication (P < 5.43 × 10-4). Eighteen of these proteins were independently associated with incident T2D (P < 1.25 × 10-3), including neuronal growth regulator 1 (NeGR1; hazard ratio per SD 0.85; P = 7.5 × 10-11). Two-sample Mendelian randomization (MR) inverse variance weighted analysis indicated that higher NeGR1 reduces T2D risk (odds ratio [OR] per SD 0.92; P = 0.03) and was consistent with MR-Egger, weighted median, and weighted mode sensitivity analyses. A stronger association was observed for the single cis-acting NeGR1 genetic variant (OR per SD 0.80; P = 6.3 × 10-5). Coupled with previous evidence that low circulating NeGR1 levels promote adiposity, its association with PA and potential causal role in T2D shown here suggest that NeGR1 may link PA exposure with metabolic outcomes. Further research is warranted to confirm our findings and examine the interplay of PA, NeGR1, adiposity, and metabolic health.

ApoER2-Dab1 disruption as the origin of pTau-associated neurodegeneration in sporadic Alzheimer's disease.

In sporadic Alzheimer's disease (sAD) specific regions, layers and neurons accumulate hyperphosphorylated Tau (pTau) and degenerate early while others remain unaffected even in advanced disease. ApoER2-Dab1 signaling suppresses Tau phosphorylation as part of a four-arm pathway that regulates lipoprotein internalization and the integrity of actin, microtubules, and synapses; however, the role of this pathway in sAD pathogenesis is not fully understood. We previously showed that multiple ApoER2-Dab1 pathway components including ApoE, Reelin, ApoER2, Dab1, pP85αTyr607, pLIMK1Thr508, pTauSer202/Thr205 and pPSD95Thr19 accumulate together within entorhinal-hippocampal terminal zones in sAD, and proposed a unifying hypothesis wherein disruption of this pathway underlies multiple aspects of sAD pathogenesis. However, it is not yet known whether ApoER2-Dab1 disruption can help explain the origin(s) and early progression of pTau pathology in sAD. In the present study, we applied in situ hybridization and immunohistochemistry (IHC) to characterize ApoER2 expression and accumulation of ApoER2-Dab1 pathway components in five regions known to develop early pTau pathology in 64 rapidly autopsied cases spanning the clinicopathological spectrum of sAD. We found that (1) these selectively vulnerable neuron populations strongly express ApoER2; and (2) multiple ApoER2-Dab1 components representing all four arms of this pathway accumulate in abnormal neurons and neuritic plaques in mild cognitive impairment (MCI) and sAD cases and correlate with histological progression and cognitive deficits. Multiplex-IHC revealed that Dab1, pP85αTyr607, pLIMK1Thr508, pTauSer202/Thr205 and pPSD95Thr19 accumulate together within many of the same ApoER2-expressing neurons and in the immediate vicinity of ApoE/ApoJ-enriched extracellular plaques. Collective findings reveal that pTau is only one of many ApoER2-Dab1 pathway components that accumulate in multiple neuroanatomical sites in the earliest stages of sAD and provide support for the concept that ApoER2-Dab1 disruption drives pTau-associated neurodegeneration in human sAD.

SCO-spondin knockout mice exhibit small brain ventricles and mild spine deformation.

Reissner's fiber (RF) is an extracellular polymer comprising the large monomeric protein SCO-spondin (SSPO) secreted by the subcommissural organ (SCO) that extends through cerebrospinal fluid (CSF)-filled ventricles into the central canal of the spinal cord. In zebrafish, RF and CSF-contacting neurons (CSF-cNs) form an axial sensory system that detects spinal curvature, instructs morphogenesis of the body axis, and enables proper alignment of the spine. In mammalian models, RF has been implicated in CSF circulation. However, challenges in manipulating Sspo, an exceptionally large gene of 15,719 nucleotides, with traditional approaches has limited progress. Here, we generated a Sspo knockout mouse model using CRISPR/Cas9-mediated genome-editing. Sspo knockout mice lacked RF-positive material in the SCO and fibrillar condensates in the brain ventricles. Remarkably, Sspo knockout brain ventricle sizes were reduced compared to littermate controls. Minor defects in thoracic spine curvature were detected in Sspo knockouts, which did not alter basic motor behaviors tested. Altogether, our work in mouse demonstrates that SSPO and RF regulate ventricle size during development but only moderately impact spine geometry.

Liver sinusoidal endothelial cells show reduced scavenger function and downregulation of Fc gamma receptor IIb, yet maintain a preserved fenestration in the Glmpgt/gt mouse model of slowly progressing liver fibrosis.

Liver sinusoidal endothelial cells (LSECs) are fenestrated endothelial cells with a unique, high endocytic clearance capacity for blood-borne waste macromolecules and colloids. This LSEC scavenger function has been insufficiently characterized in liver disease. The Glmpgt/gt mouse lacks expression of a subunit of the MFSD1/GLMP lysosomal membrane protein transporter complex, is born normal, but soon develops chronic, mild hepatocyte injury, leading to slowly progressing periportal liver fibrosis, and splenomegaly. This study examined how LSEC scavenger function and morphology are affected in the Glmpgt/gt model. FITC-labelled formaldehyde-treated serum albumin (FITC-FSA), a model ligand for LSEC scavenger receptors was administered intravenously into Glmpgt/gt mice, aged 4 months (peak of liver inflammation), 9-10 month, and age-matched Glmpwt/wt mice. Organs were harvested for light and electron microscopy, quantitative image analysis of ligand uptake, collagen accumulation, LSEC ultrastructure, and endocytosis receptor expression (also examined by qPCR and western blot). In both age groups, the Glmpgt/gt mice showed multifocal liver injury and fibrosis. The uptake of FITC-FSA in LSECs was significantly reduced in Glmpgt/gt compared to wild-type mice. Expression of LSEC receptors stabilin-1 (Stab1), and mannose receptor (Mcr1) was almost similar in liver of Glmpgt/gt mice and age-matched controls. At the same time, immunostaining revealed differences in the stabilin-1 expression pattern in sinusoids and accumulation of stabilin-1-positive macrophages in Glmpgt/gt liver. FcγRIIb (Fcgr2b), which mediates LSEC endocytosis of soluble immune complexes was widely and significantly downregulated in Glmpgt/gt liver. Despite increased collagen in space of Disse, LSECs of Glmpgt/gt mice showed well-preserved fenestrae organized in sieve plates but the frequency of holes >400 nm in diameter was increased, especially in areas with hepatocyte damage. In both genotypes, FITC-FSA also distributed to endothelial cells of spleen and bone marrow sinusoids, suggesting that these locations may function as possible compensatory sites of clearance of blood-borne scavenger receptor ligands in liver fibrosis.

Distinct neurexin isoforms cooperate to initiate and maintain foraging activity.

Neurexins are synaptic adhesion molecules that play diverse roles in synaptic development, function, maintenance, and plasticity. Neurexin genes have been associated with changes in human behavior, where variants in NRXN1 are associated with autism, schizophrenia, and Tourette syndrome. While NRXN1, NRXN2, and NRXN3 all encode major α and ß isoforms, NRXN1 uniquely encodes a γ isoform, for which mechanistic roles in behavior have yet to be defined. Here, we show that both α and γ isoforms of neurexin/nrx-1 are required for the C. elegans behavioral response to food deprivation, a sustained period of hyperactivity upon food loss. We find that the γ isoform regulates initiation and the α isoform regulates maintenance of the behavioral response to food deprivation, demonstrating cooperative function of multiple nrx-1 isoforms in regulating a sustained behavior. The γ isoform alters monoamine signaling via octopamine, relies on specific expression of NRX-1 isoforms throughout the relevant circuit, and is independent of neuroligin/nlg-1, the canonical trans-synaptic partner of nrx-1. The α isoform regulates the pre-synaptic structure of the octopamine producing RIC neuron and its maintenance role is conditional on neuroligin/nlg-1. Collectively, these results demonstrate that neurexin isoforms can have separate behavioral roles and act cooperatively across neuronal circuits to modify behavior, highlighting the need to directly analyze and consider all isoforms when defining the contribution of neurexins to behavior.