Glioblastoma (GBM) remains the most aggressive primary brain tumor in adults, with limited therapeutic options and inevitable recurrence despite maximal standard-of-care treatment. Photodynamic therapy (PDT) and oncolytic virotherapy have independently shown promise as alternative approaches, yet their combined potential in GBM remains incompletely explored. We engineered a highly neuroattenuated herpes simplex virus type 1–based oncolytic virus (oHSV1), genetically related to talimogene laherparepvec (T-VEC), to express the photosensitizer KillerRed (KR) targeted to the cell plasma membrane (memKR). The cytolytic activity of this recombinant virus was evaluated in multiple human and murine GBM cell lines, patient-derived GBM cells, and three-dimensional (3D) spheroid models. We further assessed whether photoactivation of virus-encoded memKR or of the chemical photosensitizer phthalocyanine could enhance oHSV1-mediated cytotoxicity, including in spheroids infected via monocyte-based viral delivery. The recombinant memKR-encoding virus (oHSV1-KR) efficiently infected and killed GBM cells across 2D and 3D culture systems. Photoactivation of memKR significantly enhanced virus-mediated cytotoxicity in patient-derived GBM spheroids, particularly at lower viral doses. Similarly, phthalocyanine photoactivation augmented oHSV1-induced cell death, accelerating loss of viability in both monolayer cultures and spheroids. Monocyte-mediated delivery of oHSV1-KR resulted in effective viral transfer to GBM spheroids and retained responsiveness to photodynamic activation. These findings demonstrate that combining oHSV1–based virotherapy with photodynamic activation enhances cytotoxic efficacy in advanced preclinical models of GBM. While limited to in vitro and ex vivo systems, this work establishes a modular and controllable therapeutic platform and provides a foundation for future in vivo and immunological studies aimed at translational development.

GPR37 has been recognized as a negative regulator of oligodendrocyte myelination. However, its role in demyelination recovery remains unclear. To examine the function of GPR37 in remyelination, we compared wild-type and GPR37-deficient mice of either sex after focal (lysolecithin) or global (cuprizone) toxin-induced demyelination, as well as immune-mediated demyelination (experimental autoimmune encephalomyelitis, EAE). We found that the absence of GPR37 resulted in enhanced recovery in all three models. In focal demyelination, we observed that, while the initial lesioned area was similar in size between genotypes, two weeks after induction of demyelination, the remyelinated area was markedly larger and lesion size was reduced in Gpr37 null mice compared to wild-type animals. Unlike local demyelination, which induced similar demyelination in both genotypes, cuprizone induced much faster and more severe demyelination in the mutant's corpus callosum. However, we observed a significant increase in remyelination in the mutant mice compared to their wild-type counterparts. After immune-mediated demyelination, the clinical scores of Gpr37 null mice were lower than those of wild-type animals from day 16 post-induction of EAE. Similar results were obtained in mice lacking GPR37 specifically in oligodendrocytes, indicating that faster recovery after EAE is cell autonomous. Our study suggests that GPR37 is both myelin-protective and negatively regulates remyelination in the adult brain. Furthermore, our findings demonstrate that GPR37 exhibits context-dependent functions across distinct demyelinating disease models.Significance Statement Myelination by oligodendrocytes is essential for the normal function of the central nervous system. However, in conditions where demyelination occurs, such as multiple sclerosis (MS) and other white matter disorders, the restoration of the myelin sheath through remyelination becomes essential for neurological recovery. In this study, we investigate the role of GPR37, a G protein-coupled receptor abundant in oligodendrocytes that negatively regulates myelination, during recovery following demyelination. By utilizing both toxin-induced and immune-mediated models of demyelination, we found that the absence of GPR37 enhances remyelination. This suggests that GPR37 could serve as a potential therapeutic target to promote remyelination in conditions such as MS, and other neurological and psychiatric disorders associated with white matter abnormalities.

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults and remains largely incurable because of diffuse invasion, cellular heterogeneity, therapy resistance, and recurrence. These traits depend not only on tumor-intrinsic programs but also on dynamic interactions between glioma cells and the tumor microenvironment. Connexins are extensively remodeled in GBM and are best known for forming gap junction channels, whose broad inhibition risks disrupting essential homeostatic functions in the healthy brain. By contrast, connexin hemichannels (HCs) are regulated plasma membrane conduits that can open under inflammatory, hypoxic, oxidative, and metabolic stress. Here, we review evidence that connexin HCs may act as conditionally activated amplifiers of tumor-microenvironment signaling in GBM. We discuss connexin expression in normal brain and GBM, with emphasis on Cx43, Cx46, Cx26, and Cx30, and examine how HC opening may influence glutamate and ATP release, macrophage/microglia-associated inflammation, neuronal hyperexcitability, vascular remodeling, metabolic adaptation, and redox signaling. We distinguish direct evidence from GBM models from mechanistic inferences derived from related systems. Emerging studies indicate that HC-targeting interventions can reduce GBM invasiveness, alter extracellular ATP and glutamate accumulation, modulate tumor-associated pathology, and attenuate network hyperexcitability in preclinical models. We conclude that connexin HCs are promising but incompletely validated therapeutic targets at the GBM tumor-microenvironment interface and highlight the need for biomarkers of pathological HC activation in human tumors.

BACKGROUND:Connexin (Cx) hemichannels (HCs) contribute to glioblastoma (GBM) progression by facilitating intercellular communication and releasing pro-tumorigenic molecules, including ATP and glutamate. METHODS:The efficacy of abEC1.1, a monoclonal antibody that inhibits Cx26, Cx30, and Cx32 HCs, was assessed in vitro by measuring invasion capability, dye and Ca2+ uptake, glutamate and ATP release in patient-derived GBM cultures or organoids. Adeno-associated virus (AAV)-mediated antibody gene delivery, or convection-enhanced delivery (CED) of the purified antibody, was used in vivo to test the effect on tumor growth and animal survival, using a syngeneic GBM mouse model. The ability of the antibody to affect glioma-related hyperexcitability was evaluated by patch-clamp recordings in a 2D co-culture model comprising astrocytes and neurons isolated from mouse hippocampi, seeded with GL261 cells. RESULTS:abEC1.1 suppressed GBM cell invasion, reducing gliotransmitter release, and impairing tumor progression. In patient-derived GBM cultures, abEC1.1 significantly decreased cell migration and ATP/glutamate release. In vivo, AAV-mediated antibody gene delivery or CED of the purified antibody reduced tumor burden and prolonged survival in the GL261 syngeneic mouse model of GBM. Furthermore, abEC1.1 mitigated glioma-induced excitatory synaptic activity in the 2D co-culture model, suggesting a dual role in tumor control and hyperexcitability suppression. CONCLUSIONS:Our findings establish Cx HC inhibition as a promising therapeutic avenue in GBM and highlight abEC1.1 as a potential candidate for clinical translation.

Glioblastoma (GBM) is among the most aggressive and lethal human tumors. The current standard of care, surgical resection followed by chemotherapy, offers limited efficacy, as recurrence remains frequent and severe, underscoring the urgent need for novel therapeutic strategies. Photodynamic therapy (PDT) and oncolytic virotherapy have emerged as promising alternatives. PDT utilizes light-sensitive molecules to generate reactive oxygen species (ROS), selectively inducing tumor cell death, while oncolytic virotherapy employs viruses to lyse tumor cells and activate anti-tumor immune responses. Notably, talimogene laherparepvec (T-VEC), an HSV-1-based oncolytic virus (oHSV1), is already approved for treating unresectable melanoma. To explore a combinatorial approach for GBM, we engineered highly neuroattenuated oHSV1 variants with a genetic background similar to T-VEC, expressing KillerRed (KR) a photosensitizing protein alone or in combination with immunotherapeutic factors. Our results demonstrate potent cytolytic effects of these recombinant viruses in multiple murine and human GBM cell lines, as well as in primary tumor cells. In a syngeneic C57BL/6J mouse model, oHSV1 administration induced extensive tumor necrosis, accompanied by infiltration of CD3+ immune cells. Additionally, we confirmed the feasibility of monocyte mediated systemic delivery of oHSV1, further supporting its therapeutic potential for GBM. ### Competing Interest Statement The authors have declared no competing interest.

Abstract Connexins (Cxs) are fundamental in cell–cell communication, functioning as gap junction channels (GJCs) that facilitate solute exchange between adjacent cells and as hemichannels (HCs) that mediate solute exchange between the cytoplasm and the extracellular environment. Mutations in the GJB1 gene, which encodes Cx32, lead to X-linked Charcot-Marie-Tooth type 1 (CMTX1), a rare hereditary demyelinating disorder of the peripheral nervous system (PNS) without an effective cure or treatment. In Schwann cells, Cx32 HCs are thought to play a role in myelination by enhancing intracellular and intercellular Ca2+ signaling, which is crucial for proper PNS myelination. Single-point mutations (p.S85C, p.D178Y, p.F235C) generate pathological Cx32 HCs characterized by increased permeability (“leaky”) or excessive activity (“hyperactive”). We investigated the effects of abEC1.1-hIgG1, a fully human immunoglobulin G1 (hIgG1) monoclonal antibody, on wild-type (WT) and mutant Cx32D178Y HCs. Using HeLa DH cells conditionally co-expressing Cx and a genetically encoded Ca2+ biosensor (GCaMP6s), we demonstrated that mutant HCs facilitated 58% greater Ca2+ uptake in response to elevated extracellular Ca2+ concentrations ([Ca2+]ex) compared to WT HCs. abEC1.1-hIgG1 dose-dependently inhibited Ca2+ uptake, achieving a 50% inhibitory concentration (EC50) of ~ 10 nM for WT HCs and ~ 80 nM for mutant HCs. Additionally, the antibody suppressed DAPI uptake and ATP release. An atomistic computational model revealed that serine 56 (S56) of the antibody interacts with aspartate 178 (D178) of WT Cx32 HCs, contributing to binding affinity. Despite the p.D178Y mutation weakening this interaction, the antibody maintained binding to the mutant HC epitope at sub-micromolar concentrations. In conclusion, our study shows that abEC1.1-hIgG1 effectively inhibits both WT and mutant Cx32 HCs, highlighting its potential as a therapeutic approach for CMTX1. These findings expand the antibody’s applicability for treating diseases associated with Cx HCs and inform the rational design of next-generation antibodies with enhanced affinity and efficacy against mutant HCs.

Ataxia-telangiectasia (A-T) is a rare disorder caused by genetic defects of A-T mutated (ATM) kinase, a key regulator of stress response, and characterized by neurodegeneration, immunodeficiency, and high incidence of cancer. Here we investigated NK cells in a mouse model of A-T (Atm-/-) showing that they are strongly impaired at killing tumor cells due to a block of early signaling events. On the other hand, in Atm-/- littermates with thymic lymphoma NK cell cytotoxicity is enhanced as compared with ATM-proficient mice, possibly via tumor-produced TNF-α. Results also suggest that expansion of exhausted NKG2D+ NK cells in Atm-/- mice is driven by low-level expression of stress-inducible NKG2D ligands, whereas development of thymoma expressing the high-affinity MULT1 ligand is associated with NKG2D down-regulation on NK cells. These results expand our understanding of immunodeficiency in A-T and encourage exploring NK cell biology in A-T patients in the attempt to identify cancer predictive biomarkers and novel therapeutic targets.

Stable cell pools have the advantage of providing a definite, consistent, and reproducible transmission of a transgene of interest, compared to transient expression from a plasmid transfection. Stably expressing a transgene of interest in cells under induction is a powerful way to (switch on and) study a gene function in both in vitro and in vivo assays. Taking advantage of the ability of lentivirus (LV) to promote transgene delivery, and genomic integration and expression in both dividing and nondividing cells, a doxycycline-inducible transfer vector expressing a bicistronic transgene was developed to study the function of connexins in HeLa DH cells. Here, delving on connexin 32 (Cx32), we report how to use the backbone of this vector as a tool to generate stable pools to study the function of a gene of interest (GOI), especially with assays involving Ca2+ imaging, employing the GCaMP6s indicator. We describe a step-by-step protocol to produce the LV particle by transient transfection and the direct use of the harvested LV stock to generate stable cell pools. We further present step-by-step immunolabeling protocols to characterize the transgene protein expression by confocal microscopy using an antibody that targets an extracellular domain epitope of Cx32 in living cells, and in fixed permeabilized cells using high affinity anti-Cx32 antibodies. Using common molecular biology laboratory techniques, this protocol can be adapted to generate stable pools expressing any transgene of interest, for both in vitro and in vivo functional assays, including molecular, immune, and optical assays.

Niemann-Pick type C1 (NPC1) disease is a lysosomal lipid storage disorder due to mutations in the NPC1 gene resulting in the accumulation of cholesterol within the endosomal/lysosomal compartments. The prominent feature of the disorder is the progressive Purkinje cell degeneration leading to ataxia.In a mouse model of NPC1 disease, we have previously demonstrated that impaired Sonic hedgehog signaling causes defective proliferation of granule cells (GCs) and abnormal cerebellar morphogenesis. Studies conducted on cortical and hippocampal neurons indicate a functional interaction between Sonic hedgehog and brain-derived neurotrophic factor (BDNF) expression, leading us to hypothesize that BDNF signaling may be altered in Npc1 mutant mice, contributing to the onset of cerebellar alterations present in NPC1 disease before the appearance of signs of ataxia.We characterized the expression/localization patterns of the BDNF and its receptor, tropomyosin-related kinase B (TrkB), in the early postnatal and young adult cerebellum of the Npc1nmf164 mutant mouse strain.In Npc1nmf164 mice, our results show (i) a reduced expression of cerebellar BDNF and pTrkB in the first 2 weeks postpartum, phases in which most GCs complete the proliferative/migrative program and begin differentiation; (ii) an altered subcellular localization of the pTrkB receptor in GCs, both in vivo and in vitro; (iii) reduced chemotactic response to BDNF in GCs cultured in vitro, associated with impaired internalization of the activated TrkB receptor; (iv) an overall increase in dendritic branching in mature GCs, resulting in impaired differentiation of the cerebellar glomeruli, the major synaptic complex between GCs and mossy fibers.

BACKGROUND:Keratitis ichthyosis deafness (KID) syndrome is a rare disorder caused by hemichannel (HC) activating gain-of-function mutations in the GJB2 gene encoding connexin (Cx) 26, for which there is no cure, or current treatments based upon the mechanism of disease causation. METHODS:We applied Adeno Associated Virus (AAV) mediated mAb gene transfer (AAVmAb) to treat the epidermal features of KID syndrome with a well-characterized HC blocking antibody using male mice of a murine model that replicates the skin pathology of the human disease. FINDINGS:We demonstrate that in vivo AAVmAb treatment significantly reduced the size and thickness of KID lesions, in addition to blocking activity of mutant HCs in the epidermis in vivo. We also show that AAVmAb treatment eliminated abnormal keratinocyte proliferation and enlarged cell size, decreased apoptosis, and restored the normal distribution of keratin expression. INTERPRETATION:Our findings reinforce the critical role played by increased HC activity in the skin pathology associated with KID syndrome. They also underscore the clinical potential of anti-HC mAbs coupled with genetic based delivery systems for treating the underlying mechanistic basis of this disorder. Inhibition of HC activity is an ideal therapeutic target in KID syndrome, and the genetic delivery of mAbs targeted against mutant HCs could form the basis of new therapeutic interventions to treat this incurable disease. FUNDING:Fondazione Telethon grant GGP19148 and University of Padova grant Prot. BIRD187130 to FM; Foundation for Ichthyosis and Related Skin Types (FIRST) and National Institutes of Health grant EY 026911 to TWW.

The vertebrate G protein-coupled receptors 37 and 37-like 1 (GPR37 and GPR37L1) were discovered more than two decades ago, and they have been implicated in various neurological and neurodegenerative diseases, as well as in inflammatory pain and tumorigenesis [...].

Connexin (Cx) hemichannels (HCs) are large pore hexameric structures that allow the exchange of ions, metabolites and a variety of other molecules between the cell cytoplasm and extracellular milieu. HC inhibitors are attracting growing interest as drug candidates because deregulated fluxes through HCs have been implicated in a plethora of genetic conditions and other diseases. HC activity has been mainly investigated by electrophysiological methods and/or using HC-permeable dye uptake measurements. Here, we present an all-optical assay based on fluorometric measurements of ionized calcium (Ca2+) uptake with a Ca2+-selective genetically encoded indicator (GCaMP6s) that permits the optical tracking of cytosolic Ca2+ concentration ([Ca2+]cyt) changes with high sensitivity. We exemplify use of the assay in stable pools of HaCaT cells overexpressing human Cx26, Cx46, or the pathological mutant Cx26G45E, under control of a tetracycline (Tet) responsive element (TRE) promoter (Tet-on). We demonstrate the usefulness of the assay for the characterization of new monoclonal antibodies (mAbs) targeting the extracellular domain of the HCs. Although we developed the assay on a spinning disk confocal fluorescence microscope, the same methodology can be extended seamlessly to high-throughput high-content platforms to screen other kinds of inhibitors and/or to probe HCs expressed in primary cells and microtissues.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare type of vacuolating leukodystrophy (white matter disorder), which is mainly caused by defects in MLC1 or glial cell adhesion molecule (GlialCAM) proteins. In addition, autoantibodies to GlialCAM are involved in the pathology of multiple sclerosis. MLC1 and GLIALCAM genes encode for membrane proteins of unknown function, which has been linked to the regulation of different ion channels and transporters, such as the chloride channel VRAC (volume regulated anion channel), ClC-2 (chloride channel 2), and connexin 43 or the Na+/K+-ATPase pump. However, the mechanisms by which MLC proteins regulate these ion channels and transporters, as well as the exact function of MLC proteins remain obscure. It has been suggested that MLC proteins might regulate signalling pathways, but the mechanisms involved are, at present, unknown. With the aim of answering these questions, we have recently described the brain GlialCAM interactome. Within the identified proteins, we could validate the interaction with several G protein-coupled receptors (GPCRs), including the orphan GPRC5B and the proposed prosaposin receptors GPR37L1 and GPR37. In this review, we summarize new aspects of the pathophysiology of MLC disease and key aspects of the interaction between GPR37 receptors and MLC proteins.

Glioblastomas (GBM) are the most aggressive tumors originating in the brain. Histopathologic features include circuitous, disorganized, and highly permeable blood vessels with intermittent blood flow. These features contribute to the inability to direct therapeutic agents to tumor cells. Known targets for anti-angiogenic therapies provide minimal or no effect in overall survival of 12–15 months following diagnosis. Identification of novel targets therefore remains an important goal for effective treatment of highly vascularized tumors such as GBM. We previously demonstrated in zebrafish that a balanced level of expression of the transmembrane protein TMEM230/C20ORF30 was required to maintain normal blood vessel structural integrity and promote proper vessel network formation. To investigate whether TMEM230 has a role in the pathogenesis of GBM, we analyzed its prognostic value in patient tumor gene expression datasets and performed cell functional analysis. TMEM230 was found necessary for growth of U87-MG cells, a model of human GBM. Downregulation of TMEM230 resulted in loss of U87 migration, substratum adhesion, and re-passaging capacity. Conditioned media from U87 expressing endogenous TMEM230 induced sprouting and tubule-like structure formation of HUVECs. Moreover, TMEM230 promoted vascular mimicry-like behavior of U87 cells. Gene expression analysis of 702 patients identified that TMEM230 expression levels distinguished high from low grade gliomas. Transcriptomic analysis of patients with gliomas revealed molecular pathways consistent with properties observed in U87 cell assays. Within low grade gliomas, elevated TMEM230 expression levels correlated with reduced overall survival independent from tumor subtype. Highest level of TMEM230 correlated with glioblastoma and ATP-dependent microtubule kinesin motor activity, providing a direction for future therapeutic intervention. Our studies support that TMEM230 has both glial tumor and endothelial cell intracellular and extracellular functions. Elevated levels of TMEM230 promote glial tumor cell migration, extracellular scaffold remodeling, and hypervascularization and abnormal formation of blood vessels. Downregulation of TMEM230 expression may inhibit both low grade glioma and glioblastoma tumor progression and promote normalization of abnormally formed blood vessels. TMEM230 therefore is both a promising anticancer and antiangiogenic therapeutic target for inhibiting GBM tumor cells and tumor-driven angiogenesis.

In the past two decades, mounting evidence has modified the classical view of the cerebellum as a brain region specifically involved in the modulation of motor functions. Indeed, clinical studies and engineered mouse models have highlighted cerebellar circuits implicated in cognitive functions and behavior. Furthermore, it is now clear that insults occurring in specific time windows of cerebellar development can affect cognitive performance later in life and are associated with neurological syndromes, such as Autism Spectrum Disorder. Despite its almost homogenous cytoarchitecture, how cerebellar circuits form and function is not completely elucidated yet. Notably, the apparently simple neuronal organization of the cerebellum, in which Purkinje cells represent the only output, hides an elevated functional diversity even within the same neuronal population. Such complexity is the result of the integration of intrinsic morphogenetic programs and extracellular cues from the surrounding environment, which impact on the regulation of the transcriptome of cerebellar neurons. In this review, we briefly summarize key features of the development and structure of the cerebellum before focusing on the pathways involved in the acquisition of the cerebellar neuron identity. We focus on gene expression and mRNA processing programs, including mRNA methylation, trafficking and splicing, that are set in motion during cerebellar development and participate to its physiology. These programs are likely to add new layers of complexity and versatility that are fundamental for the adaptability of cerebellar neurons.

Megalencephalic Leukoencephalopathy with subcortical Cysts (MLC) is a type of vacuolating leukodystrophy, which is mainly caused by mutations in MLC1 or GLIALCAM. The two MLC-causing genes encode for membrane proteins of yet unknown function that have been linked to the regulation of different chloride channels such as the ClC-2 and VRAC. To gain insight into the role of MLC proteins, we have determined the brain GlialCAM interacting proteome. The proteome includes different transporters and ion channels known to be involved in the regulation of brain homeostasis, proteins related to adhesion or signaling as several G protein-coupled receptors (GPCRs), including the orphan GPRC5B and the proposed prosaposin receptor GPR37L1. Focusing on these two GPCRs, we could validate that they interact directly with MLC proteins. The inactivation of Gpr37l1 in mice upregulated MLC proteins without altering their localization. Conversely, a reduction of GPRC5B levels in primary astrocytes downregulated MLC proteins, leading to an impaired activation of ClC-2 and VRAC. The interaction between the GPCRs and MLC1 was dynamically regulated upon changes in the osmolarity or potassium concentration. We propose that GlialCAM and MLC1 associate with different integral membrane proteins modulating their functions and acting as a recruitment site for various signaling components as the GPCRs identified here. We hypothesized that the GlialCAM/MLC1 complex is working as an adhesion molecule coupled to a tetraspanin-like molecule performing regulatory effects through direct binding or influencing signal transduction events.

Mammalian cerebellar astrocytes critically regulate the differentiation and maturation of neuronal Purkinje cells and granule precursors. The G protein-coupled receptor 37-like 1 (Gpr37l1) is expressed by Bergmann astrocytes and interacts with patched 1 (Ptch1) at peri-ciliary membranes. Cerebellar primary astrocyte cultures from wild-type and Gpr37l1 null mutant mouse pups were established and studied. Primary cilia were produced by cultures of both genotypes, as well as Ptch1 and smoothened (Smo) components of the sonic hedgehog (Shh) mitogenic pathway. Compared to wild-type cells, Gpr37l1(-/-) astrocytes displayed striking increases in proliferative activity, Ptch1 protein expression and internalization, intracellular cholesterol content, ciliary localization of Smo, as well as a marked production of active Shh. Similar effects were reproduced by treating wild-type astrocytes with a putative prosaptide ligand of Gpr37l1. These findings indicate that Gpr37l1-Ptch1 interactions specifically regulate Ptch1 internalization and trafficking, with consequent stimulation of Shh production and activation of proliferative signaling.

Tight coordination of gene expression in the developing cerebellum is crucial for establishment of neuronal circuits governing motor and cognitive function, However, transcriptional changes alone do not explain all of the switches underlying neuronal differentiation. Here we unveiled a widespread and highly dynamic splicing program that affects synaptic genes in cerebellar neurons. The motifs enriched in modulated exons implicated the splicing factor Sam68 as a regulator of this program. Sam68 controls splicing of exons with weak branchpoints by directly binding near the 3' splice site and competing with U2AF recruitment. Ablation of Sam68 disrupts splicing regulation of synaptic genes associated with neurodevelopmental diseases and impairs synaptic connections and firing of Purkinje cells, resulting in motor coordination defects, ataxia, and abnormal social behavior. These findings uncover an unexpectedly dynamic splicing regulatory network that shapes the synapse in early life and establishes motor and cognitive circuitry in the developing cerebellum.