Matrix metalloproteinases shape the oligodendrocyte (niche) during development and upon demyelination

Perineuronal nets as regulators of parvalbumin interneuron function: Factors implicated in their formation and degradation

The brain extracellular matrix (ECM) has garnered increasing attention as a fundamental component of brain function in a predominantly "neuron-centric" paradigm. Particularly, the perineuronal nets (PNNs), a specialized net-like structure formed by ECM aggregates, play significant roles in brain development and physiology. PNNs enwrap synaptic junctions in various brain regions, precisely balancing new synaptic formation and long-term stabilization, and are highly dynamic entities that change in response to environmental stimuli, especially during the neurodevelopmental period. They are found mainly surrounding parvalbumin (PV)-expressing GABAergic interneurons, being proposed to promote PV interneuron maturation and protect them against oxidative stress and neurotoxic agents. This structural and functional proximity underscores the crucial role of PNNs in modulating PV interneuron function, which is critical for the excitatory/inhibitory balance and, consequently, higher-level behaviours. This review delves into the molecular underpinnings governing PNNs formation and degradation, elucidating their functional interactions with PV interneurons. In the broader physiological context and brain-related disorders, we also explore their intricate relationship with other molecules, such as reactive oxygen species and metalloproteinases, as well as glial cells. Additionally, we discuss potential therapeutic strategies for modulating PNNs in brain disorders.

Exosome-specific loading Sox10 for the treatment of Cuprizone-induced demyelinating model

Demyelination is a pathological feature commonly observed in various central nervous system diseases. It is characterized by the aggregation of oligodendrocyte progenitor cells (OPCs) in the lesion area, which face difficulties in differentiating into mature oligodendrocytes (OLGs). The differentiation of OPCs requires the presence of Sox10, but its expression decreases under pathological conditions. Therefore, we propose a therapeutic strategy to regulate OPCs differentiation and achieve myelin repair by endogenously loading Sox10 into exosomes. To accomplish this, we generated a lentivirus-armed Sox10 that could anchor to the inner surface of the exosome membrane. We then infected HEK293 cells to obtain exosomes with high expression of Sox10 (exosomes-Sox10, ExoSs). In vitro, experiments confirmed that both Exos and ExoSs can be uptaken by OPCs, but only ExoSs exhibit a pro-differentiation effect on OPCs. In vivo, we administered PBS, Exos, and ExoSs to cuprizone-induced demyelinating mice. The results demonstrated that ExoSs can regulate the differentiation of PDGFRα+ OPCs into APC+ OLGs and reduce myelin damage in the corpus callosum region of the mouse brain compared to other groups. Further testing suggests that Sox10 may have a reparative effect on the myelin sheath by enhancing the expression of MBP, possibly facilitated by the exosome delivery of the protein into the lesion. This endogenously loaded technology holds promise as a strategy for protein-based drugs in the treatment of demyelinating diseases.

Collagen in the central nervous system: contributions to neurodegeneration and promise as a therapeutic target

The extracellular matrix is a richly bioactive composition of substrates that provides biophysical stability, facilitates intercellular signaling, and both reflects and governs the physiological status of the local microenvironment. The matrix in the central nervous system (CNS) is far from simply an inert scaffold for mechanical support, instead conducting an active role in homeostasis and providing broad capacity for adaptation and remodeling in response to stress that otherwise would challenge equilibrium between neuronal, glial, and vascular elements. A major constituent is collagen, whose characteristic triple helical structure renders mechanical and biochemical stability to enable bidirectional crosstalk between matrix and resident cells. Multiple members of the collagen superfamily are critical to neuronal maturation and circuit formation, axon guidance, and synaptogenesis in the brain. In mature tissue, collagen interacts with other fibrous proteins and glycoproteins to sustain a three-dimensional medium through which complex networks of cells can communicate. While critical for matrix scaffolding, collagen in the CNS is also highly dynamic, with multiple binding sites for partnering matrix proteins, cell-surface receptors, and other ligands. These interactions are emerging as critical mediators of CNS disease and injury, particularly regarding changes in matrix stiffness, astrocyte recruitment and reactivity, and pro-inflammatory signaling in local microenvironments. Changes in the structure and/or deposition of collagen impact cellular signaling and tissue biomechanics in the brain, which in turn can alter cellular responses including antigenicity, angiogenesis, gliosis, and recruitment of immune-related cells. These factors, each involving matrix collagen, contribute to the limited capacity for regeneration of CNS tissue. Emerging therapeutics that attempt to rebuild the matrix using peptide fragments, including collagen-enriched scaffolds and mimetics, hold great potential to promote neural repair and regeneration. Recent evidence from our group and others indicates that repairing protease-degraded collagen helices with mimetic peptides helps restore CNS tissue and promote neuronal survival in a broad spectrum of degenerative conditions. Restoration likely involves bolstering matrix stiffness to reduce the potential for astrocyte reactivity and local inflammation as well as repairing inhibitory binding sites for immune-signaling ligands. Facilitating repair rather than endogenous replacement of collagen degraded by disease or injury may represent the next frontier in developing therapies based on protection, repair, and regeneration of neurons in the central nervous system.

Uncovering Novel Extracellular Matrix Transcriptome Alterations in Lesions of Multiple Sclerosis

The extracellular matrix (ECM) of the central nervous system (CNS) is an interconnected network of proteins and sugars with critical roles in both homeostasis and disease. In neurological diseases, excessive ECM deposition and remodeling impact both injury and repair. CNS lesions of multiple sclerosis (MS), a chronic inflammatory and degenerative disease, cause prominent alterations of the ECM. However, there are a lack of data investigating how the multitude of ECM members change in relation to each other and how this affects the MS disease course. Here, we evaluated ECM changes in MS lesions compared to a control brain using databases generated in-house through spatial mRNA-sequencing and through a public resource of single-nucleus RNA sequencing previously published by Absinta and colleagues. These results underline the importance of publicly available datasets to find new targets of interest, such as the ECM. Both spatial and public datasets demonstrated widespread changes in ECM molecules and their interacting proteins, including alterations to proteoglycans and glycoproteins within MS lesions. Some of the altered ECM members have been described in MS, but other highly upregulated members, including the SPARC family of proteins, have not previously been highlighted. SPARC family members are upregulated in other conditions by reactive astrocytes and may influence immune cell activation and MS disease course. The profound changes to the ECM in MS lesions deserve more scrutiny as they impact neuroinflammation, injury, and repair.

Hypoxic oligodendrocyte precursor cell-derived VEGFA is associated with blood-brain barrier impairment

Cerebral small vessel disease is characterised by decreased cerebral blood flow and blood-brain barrier impairments which play a key role in the development of white matter lesions. We hypothesised that cerebral hypoperfusion causes local hypoxia, affecting oligodendrocyte precursor cell-endothelial cell signalling leading to blood-brain barrier dysfunction as an early mechanism for the development of white matter lesions. Bilateral carotid artery stenosis was used as a mouse model for cerebral hypoperfusion. Pimonidazole, a hypoxic cell marker, was injected prior to humane sacrifice at day 7. Myelin content, vascular density, blood-brain barrier leakages, and hypoxic cell density were quantified. Primary mouse oligodendrocyte precursor cells were exposed to hypoxia and RNA sequencing was performed. Vegfa gene expression and protein secretion was examined in an oligodendrocyte precursor cell line exposed to hypoxia. Additionally, human blood plasma VEGFA levels were measured and correlated to blood-brain barrier permeability in normal-appearing white matter and white matter lesions of cerebral small vessel disease patients and controls. Cerebral blood flow was reduced in the stenosis mice, with an increase in hypoxic cell number and blood-brain barrier leakages in the cortical areas but no changes in myelin content or vascular density. Vegfa upregulation was identified in hypoxic oligodendrocyte precursor cells, which was mediated via Hif1α and Epas1. In humans, VEGFA plasma levels were increased in patients versus controls. VEGFA plasma levels were associated with increased blood-brain barrier permeability in normal appearing white matter of patients. Cerebral hypoperfusion mediates hypoxia induced VEGFA expression in oligodendrocyte precursor cells through Hif1α/Epas1 signalling. VEGFA could in turn increase BBB permeability. In humans, increased VEGFA plasma levels in cerebral small vessel disease patients were associated with increased blood-brain barrier permeability in the normal appearing white matter. Our results support a role of VEGFA expression in cerebral hypoperfusion as seen in cerebral small vessel disease.

CD147 and MMPs as key factors in physiological and pathological processes

Cluster of differentiation 147 (CD147) or extracellular matrix metalloproteinase inducer (EMMPRIN) is a transmembrane glycoprotein that induces the synthesis of matrix metalloproteinases (MMPs). MMPs, as zinc-dependent proteases and versatile enzymes, play critical roles in the degradation of the extracellular matrix (ECM) components, cleaving of the receptors of cellular surfaces, signaling molecules, and other precursor proteins, which may lead to attenuation or activation of such targets. CD147 and MMPs play essential roles in physiological and pathological conditions and any disorder in the expression, synthesis, or function of CD147 and MMPs may be associated with various types of disease. In this review, we have focused on the roles of CD147 and MMPs in some major physiological and pathological processes.

Integration of O-GlcNAc into Stress Response Pathways

The modification of nuclear, mitochondrial, and cytosolic proteins by O-linked βN-acetylglucosamine (O-GlcNAc) has emerged as a dynamic and essential post-translational modification of mammalian proteins. O-GlcNAc is cycled on and off over 5000 proteins in response to diverse stimuli impacting protein function and, in turn, epigenetics and transcription, translation and proteostasis, metabolism, cell structure, and signal transduction. Environmental and physiological injury lead to complex changes in O-GlcNAcylation that impact cell and tissue survival in models of heat shock, osmotic stress, oxidative stress, and hypoxia/reoxygenation injury, as well as ischemic reperfusion injury. Numerous mechanisms that appear to underpin O-GlcNAc-mediated survival include changes in chaperone levels, impacts on the unfolded protein response and integrated stress response, improvements in mitochondrial function, and reduced protein aggregation. Here, we discuss the points at which O-GlcNAc is integrated into the cellular stress response, focusing on the roles it plays in the cardiovascular system and in neurodegeneration.

Targeting Fibronectin to Overcome Remyelination Failure in Multiple Sclerosis: The Need for Brain- and Lesion-Targeted Drug Delivery

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease with unknown etiology that can be characterized by the presence of demyelinated lesions. Prevailing treatment protocols in MS rely on the modulation of the inflammatory process but do not impact disease progression. Remyelination is an essential factor for both axonal survival and functional neurological recovery but is often insufficient. The extracellular matrix protein fibronectin contributes to the inhibitory environment created in MS lesions and likely plays a causative role in remyelination failure. The presence of the blood–brain barrier (BBB) hinders the delivery of remyelination therapeutics to lesions. Therefore, therapeutic interventions to normalize the pathogenic MS lesion environment need to be able to cross the BBB. In this review, we outline the multifaceted roles of fibronectin in MS pathogenesis and discuss promising therapeutic targets and agents to overcome fibronectin-mediated inhibition of remyelination. In addition, to pave the way for clinical use, we reflect on opportunities to deliver MS therapeutics to lesions through the utilization of nanomedicine and discuss strategies to deliver fibronectin-directed therapeutics across the BBB. The use of well-designed nanocarriers with appropriate surface functionalization to cross the BBB and target the lesion sites is recommended.

Single-nucleus transcriptome analysis reveals disease- and regeneration-associated endothelial cells in white matter vascular dementia

BACKGROUND

Vascular dementia (VaD) is the accumulation of vascular lesions in the subcortical white matter of the brain. These lesions progress and there is no direct medical therapy.

AIMS

To determine the specific cellular responses in VaD so as to provide molecular targets for therapeutic development.

MATERIALS AND METHODS

Single-nucleus transcriptome analysis was performed in human periventricular white matter (PVWM) samples of VaD and normal control (NC) subjects.

RESULTS

Differential analysis shows that cell type-specific transcriptomic changes in VaD are associated with the disruption of specific biological processes, including angiogenesis, immune activation, axonal injury and myelination. Each cell type in the neurovascular unit within white matter has a specific alteration in gene expression in VaD. In a central cell type for this disease, subcluster analysis of endothelial cells (EC) indicates that VaD contains a disease-associated EC subcluster that expresses genes associated with programmed cell death and a response to protein folding. Two other subpopulations of EC in VaD express molecular systems associated with regenerative processes in angiogenesis, and in axonal sprouting and oligodendrocyte progenitor cell maturation.

CONCLUSION

This comprehensive molecular profiling of brain samples from patients with VaD reveals previously unknown molecular changes in cells of the neurovascular niche, and an attempt at regeneration in injured white matter.

Matrix Metalloproteinase-9 as an Important Contributor to the Pathophysiology of Depression

Matrix metalloproteinases (MMPs) are physiologically expressed in the central nervous system in neurons, astrocytes and microglia, and their aberrant elevation contributes to a number of diseases. Amongst the MMP members, MMP−9 has generated considerable attention because of its possible involvement in inflammatory responses, blood-brain barrier permeability, the regulation of perineuronal nets, demyelination, and synaptic long-term potentiation. Emerging evidence indicate an association between MMP−9 and the syndrome of depression. This review provides an updated and comprehensive summary of the probable roles of MMP−9 in depression with an emphasis on the mechanisms and potential of MMP−9 as a biomarker of depression.

Is Oxidative Stress the Link Between Cerebral Small Vessel Disease, Sleep Disruption, and Oligodendrocyte Dysfunction in the Onset of Alzheimer's Disease?

Oxidative stress is an early occurrence in the development of Alzheimer’s disease (AD) and one of its proposed etiologic hypotheses. There is sufficient experimental evidence supporting the theory that impaired antioxidant enzymatic activity and increased formation of reactive oxygen species (ROS) take place in this disease. However, the antioxidant treatments fail to stop its advancement. Its multifactorial condition and the diverse toxicological cascades that can be initiated by ROS could possibly explain this failure. Recently, it has been suggested that cerebral small vessel disease (CSVD) contributes to the onset of AD. Oxidative stress is a central hallmark of CSVD and is depicted as an early causative factor. Moreover, data from various epidemiological and clinicopathological studies have indicated a relationship between CSVD and AD where endothelial cells are a source of oxidative stress. These cells are also closely related to oligodendrocytes, which are, in particular, sensitive to oxidation and lead to myelination being compromised. The sleep/wake cycle is another important control in the proliferation, migration, and differentiation of oligodendrocytes, and sleep loss reduces myelin thickness. Moreover, sleep plays a crucial role in resistance against CSVD, and poor sleep quality increases the silent markers of this vascular disease. Sleep disruption is another early occurrence in AD and is related to an increase in oxidative stress. In this study, the relationship between CSVD, oligodendrocyte dysfunction, and sleep disorders is discussed while focusing on oxidative stress as a common occurrence and its possible role in the onset of AD.

The extracellular matrix as modifier of neuroinflammation and remyelination in multiple sclerosis

Remyelination failure contributes to axonal loss and progression of disability in multiple sclerosis. The failed repair process could be due to ongoing toxic neuroinflammation and to an inhibitory lesion microenvironment that prevents recruitment and/or differentiation of oligodendrocyte progenitor cells into myelin-forming oligodendrocytes. The extracellular matrix molecules deposited into lesions provide both an altered microenvironment that inhibits oligodendrocyte progenitor cells, and a fuel that exacerbates inflammatory responses within lesions. In this review, we discuss the extracellular matrix and where its molecules are normally distributed in an uninjured adult brain, specifically at the basement membranes of cerebral vessels, in perineuronal nets that surround the soma of certain populations of neurons, and in interstitial matrix between neural cells. We then highlight the deposition of different extracellular matrix members in multiple sclerosis lesions, including chondroitin sulphate proteoglycans, collagens, laminins, fibronectin, fibrinogen, thrombospondin and others. We consider reasons behind changes in extracellular matrix components in multiple sclerosis lesions, mainly due to deposition by cells such as reactive astrocytes and microglia/macrophages. We next discuss the consequences of an altered extracellular matrix in multiple sclerosis lesions. Besides impairing oligodendrocyte recruitment, many of the extracellular matrix components elevated in multiple sclerosis lesions are pro-inflammatory and they enhance inflammatory processes through several mechanisms. However, molecules such as thrombospondin-1 may counter inflammatory processes, and laminins appear to favour repair. Overall, we emphasize the crosstalk between the extracellular matrix, immune responses and remyelination in modulating lesions for recovery or worsening. Finally, we review potential therapeutic approaches to target extracellular matrix components to reduce detrimental neuroinflammation and to promote recruitment and maturation of oligodendrocyte lineage cells to enhance remyelination.

Hypermethylation of EFEMP1 in the Hippocampus May Be Related to the Deficit in Spatial Memory of Rat Neonates Triggered by Repeated Administration of Propofol

It has been confirmed that repeated application of propofol, as an intravenous and short-fast-acting anesthetic, in neonatal animals or humans may produce long-term deficits in cognitive functions. With the aim of explaining the neurotoxic effects of repeated administration of propofol on neonatal rat pups from P7 to P9 especially from an epigenetic perspective, the present study used the Morris water maze to detect cognitive deficits in spatial learning and memory, Sequenom methylation on the CpG island located in the promoter region of epidermal growth factor-containing fibulin-like extracellular matrix protein 1 (EFEMP1) to assess the methylation level of this region, and Western blot to measure the expression of EFEMP1, TIMP-3, and MMP-9. As the results have shown, repeated propofol administration on neonatal rats caused significant systemic growth retardation, impairment of spatial learning and memory, and hypermethylation of the CpG sites in the promoter region of EFEMP1 accompanied by lower expression of EFEMP1 and TIMP-3 and enhanced expression of MMP-9. These data suggest that repeated propofol administration in neonatal rats may generate hypermethylation in the promoter region of EFEMP1 which results in downregulation of the expression of EFEMP1 and tissue inhibitor of metalloproteinase-3 (TIMP-3) but upregulation of the expression of matrix metalloproteinase-9 (MMP-9), which together may affect the stability of ECM to hamper the development of the central nervous system and therefore lead to deficits in cognitive functions.