Project description:In the brain, a unique homeostatic equilibrium strictly controls immune reactions. In healthy conditions, the immune system poorly communicates with the central nervous system (CNS), immune cell migration across the blood brain barrier (BBB) is kept at a very low level and the unique CNS microenvironment strictly restricts immune reactions. Here, we identified the astroglial gap junction protein Connexin 43 has a new actor of this homeostasis. We showed that genetic inactivation of astroglial Cx43 in the mouse induces expression of a specific set of chemokines and endothelial adhesion molecules leading to neutrophils, macrophages, B and T lymphocytes and mature plasmocytes infiltration at the BBB, and to the development of antigen presentation-related mechanisms, in sterile conditions. Thus, astroglial Cx43 by decreasing the expression of leukocytes adhesion and migration mediators, promotes the immune quiescence of the BBB
Project description:Astrocytes, the most prominent glial cell type in the brain, send specialized processes called endfeet around blood vessels and express a large molecular repertoire regulating the cerebrovascular system physiology. One of the most striking properties of astrocyte endfeet is their enrichment in gap junction protein Connexin 43 and 30 (Cx43 and Cx30) allowing in particular for direct intercellular trafficking of ions and small signaling molecules through perivascular astroglial networks. In this study, we addressed the specific role of Cx30 at the gliovascular interface. Using an inactivation mouse model for Cx30 (Cx30M-NM-^T/M-NM-^T), we showed that absence of Cx30 does not affect blood-brain barrier (BBB) organization and permeability. However, it results in the cerebrovascular fraction, in a strong upregulation of Sgcg encoding g-Sarcoglycan (SG), a member of the Dystrophin-associated protein complex (DAPC) connecting cytoskeleton and the extracellular matrix. The same molecular event occurs in Cx30T5M/T5M mutated mice, where Cx30 channels are closed, demonstrating that Sgcg regulation relied on Cx30 channel functions. We further characterized the cerebrovascular Sarcoglycan complex (SGC) and showed the presence of M-NM-1-, M-NM-2-, M-NM-4-, M-NM-3-, M-NM-5- and M-NM-6- SG, as well as Sarcospan. Altogether, our results suggest that the Sarcoglycan complex is present in the cerebrovascular system, and that expression of one of its members, g-Sarcoglycan, depends on Cx30 channels. As described in skeletal muscles, the SGC may contribute to membrane stabilization and signal transduction in the cerebrovascular system, which may therefore be regulated by Cx30 channel-mediated functions. Comparison of 3-month-old Cx30 deleted mice against WT genetic background.
Project description:Brain postnatal development is characterized by critical periods of experience dependent remodeling. Maturation of local circuits inhibitory neurons terminate this period of enhanced plasticity. Astroglial cells are known to influence excitatory and inhibitory synaptic transmission as well as network activity through active signaling mechanisms. Although these can be developmentally regulated, the role of astrocytes in the timing of post-natal critical period is unknown. Here we show in the visual cortex that astrocytes con-trol the maturation of inhibitory neurons and thereby closure of the critical period. We uncover a novel underlying pathway involving regulation of the extracellular matrix that allows interneurons maturation via astroglial connexin signaling. We find that timing of the critical period closure is controlled by a marked upregulation of the astroglial protein connexin 30 that inhibits expression of the matrix degrading enzyme MMP9 through the RhoA-GTPase pathway. Our results thus demonstrate that astrocytes not only influ-ence neuronal activity but are also key elements in the experience–dependent wiring of brain circuits. Therefore, astrocytes represent a new cellular partner to consider in our understanding of the post-natal shaping of neuronal activities, hence providing a new target to alleviate malfunctions associated to im-paired closure of the critical period and settling of synaptic circuits.
Project description:Astrocytes, the most prominent glial cell type in the brain, send specialized processes called endfeet around blood vessels and express a large molecular repertoire regulating the cerebrovascular system physiology. One of the most striking properties of astrocyte endfeet is their enrichment in gap junction protein Connexin 43 and 30 (Cx43 and Cx30) allowing in particular for direct intercellular trafficking of ions and small signaling molecules through perivascular astroglial networks. In this study, we addressed the specific role of Cx30 at the gliovascular interface. Using an inactivation mouse model for Cx30 (Cx30Δ/Δ), we showed that absence of Cx30 does not affect blood-brain barrier (BBB) organization and permeability. However, it results in the cerebrovascular fraction, in a strong upregulation of Sgcg encoding g-Sarcoglycan (SG), a member of the Dystrophin-associated protein complex (DAPC) connecting cytoskeleton and the extracellular matrix. The same molecular event occurs in Cx30T5M/T5M mutated mice, where Cx30 channels are closed, demonstrating that Sgcg regulation relied on Cx30 channel functions. We further characterized the cerebrovascular Sarcoglycan complex (SGC) and showed the presence of α-, β-, δ-, γ-, ε- and ζ- SG, as well as Sarcospan. Altogether, our results suggest that the Sarcoglycan complex is present in the cerebrovascular system, and that expression of one of its members, g-Sarcoglycan, depends on Cx30 channels. As described in skeletal muscles, the SGC may contribute to membrane stabilization and signal transduction in the cerebrovascular system, which may therefore be regulated by Cx30 channel-mediated functions.
Project description:Astrocytes are intimately linked with brain blood vessels, a relationship critical for neuronal function. However, astroglial factors driving these physical and functional associations during postnatal brain development have yet to be identified. By characterizing structural and transcriptional changes in mouse cortical astrocytes during the first two postnatal weeks, we find that high-mobility group box 1 (Hmgb1), normally upregulated with injury and involved in adult cerebrovascular repair, is highly expressed in astrocytes at birth and then decreases rapidly. Astrocyte-selective ablation of Hmgb1 at birth affects astrocyte morphology and endfoot placement, alters distribution of endfoot proteins connexin43 and aquaporin-4, induces transcriptional changes in astrocytes related to cytoskeleton remodeling, and profoundly disrupts endothelial ultrastructure. While lack of astroglial Hmgb1 does not affect the blood-brain barrier or angiogenesis postnatally, it impairs neurovascular coupling and behavior in adult mice. These findings identify astroglial Hmgb1 as a key player in postnatal gliovascular maturation.
Project description:Astrocytes are intimately linked with brain vessels, a relationship that is critical for neuronal health and function. However, key astroglial molecular factors that drive these physical and functional associations during postnatal brain development have not yet been identified. We characterized structural and transcriptional changes in mouse cortical astrocytes and microvessels during the first two postnatal weeks and found that high-mobility group box 1 (Hmgb1), normally upregulated with injury and involved in adult cerebrovascular repair, was highly expressed in astrocytes at birth to then decreased rapidly. Astrocyte-selective ablation of Hmgb1 in newborn mice affected astrocyte morphology and endfoot placement, induced disruption of endfoot proteins connexin43 and aquaporin-4, induced transcriptional changes in astrocytes, and profoundly altered endothelial cell ultrastructure. While lack of astroglial Hmgb1 did not affect the blood-brain barrier or angiogenesis postnatally, it impaired neurovascular coupling and behavior in adult mice. These findings identify astroglial Hmgb1 as a key player in postnatal gliovascular maturation.
Project description:TDP-43 is a DNA/RNA-binding protein that regulates gene expression and its malfunction in neurons has been causally associated with multiple neurodegenerative disorders. Although progress has been made in understanding the functions of TDP-43 in neurons, little is known about its role in endothelial cells (ECs), angiogenesis and vascular function. Using inducible EC-specific TDP-43 knockout mice, we show that TDP-43 is required for sprouting angiogenesis, vascular barrier integrity and blood vessel stability. Postnatal EC-specific deletion of TDP-43 leads to retinal hypovascularization due to defects in vessel sprouting associated with reduced EC proliferation and migration. In mature blood vessels, loss of TDP-43 disrupts the blood-brain barrier and triggers vascular degeneration. These vascular defects are associated with an inflammatory response in the central-nervous system with activation of microglia and astrocytes. Mechanistically, deletion of TDP-43 disrupts fibronectin matrix around sprouting vessels and reduces -catenin signaling in ECs. Together, our results indicate that TDP-43 is essential for the formation of a stable and mature vasculature.
Project description:Blood-brain barrier (BBB) function deteriorates during aging, contributing to cognitive impairment and neurodegeneration. It is unclear what drives BBB leakage in aging and how it can be prevented. Using single-nucleus transcriptomics, we identified decreased connexin 43 (CX43) expression in Cadherin-5+ (Cdh5+) cerebral vascular cells in naturally aging mice and confirmed it in human brain samples. Global or Cdh5+ cell-specific CX43 deletion in mice exacerbated BBB dysfunction during aging. The CX43-dependent effect was not due to its canonical gap junction function but was associated with reduced NAD+ levels and mitochondrial dysfunction through NAD+-dependent sirtuin 3. CX43 interacts with and negatively regulates poly (ADP-ribose) polymerase 1 (PARP1). Pharmacologic inhibition of PARP1 by olaparib or nicotinamide mononucleotide supplementation rescued NAD+ levels and alleviated aging-associated BBB leakage. These findings establish the endothelial CX43-PARP1-NAD+ pathway’s role in vascular aging and identify a potential therapeutic strategy to combat aging-associated BBB leakage with neuroprotective implications.
Project description:The majority of patients with amyotrophic lateral sclerosis (ALS) have abnormal TDP-43 aggregates in the nucleus and/or cytosol of their surviving neurons and glia. Although accumulating evidence indicates that astroglial dysfunctions contribute to motor neuron degeneration in ALS, the normal physiological functions of TDP-43 in astrocytes are largely unknown and whether the loss of astroglial TDP-43 contributes to ALS remains to be clarified. Here, we showed that TDP-43 deleted astrocytes showed cell-autonomously enhanced GFAP immunoreactivity without affecting astrocyte or microglia proliferation. At the transcriptomic level, TDP-43 deleted astrocytes resemble the A1-reactive astrocytes and induce microglia to increase C1q expression. These astrocytic changes do not cause the loss of motor neurons in spinal cords or denervation at the neuromuscular junctions. In contrast, there was a selective reduction of mature oligodendrocytes, but not oligodendrocyte precursor cells, suggesting a tri-glial dysfunction mediated by TDP-43-deleted astrocytes. Mice with astroglial TDP-43 deletion developed motor, but not sensory, deficits. Taken together, our results demonstrate that TDP-43 is required to maintain the protective functions of astrocytes relevant to the development of motor deficits in mice.