SMAlow/undetectable pericytes differentiate into microglia- and macrophage-like cells in ischemic brain

Dynamic changes in the structure and function of brain mural cells around chronically implanted microelectrodes

Integration of neural interfaces with minimal tissue disruption in the brain is ideal to develop robust tools that can address essential neuroscience questions and combat neurological disorders. However, implantation of intracortical devices provokes severe tissue inflammation within the brain, which requires a high metabolic demand to support a complex series of cellular events mediating tissue degeneration and wound healing. Pericytes, peri-vascular cells involved in blood-brain barrier maintenance, vascular permeability, waste clearance, and angiogenesis, have recently been implicated as potential perpetuators of neurodegeneration in brain injury and disease. While the intimate relationship between pericytes and the cortical microvasculature have been explored in other disease states, their behavior following microelectrode implantation, which is responsible for direct blood vessel disruption and dysfunction, is currently unknown. Using two-photon microscopy we observed dynamic changes in the structure and function of pericytes during implantation of a microelectrode array over a 4-week implantation period. Pericytes respond to electrode insertion through transient increases in intracellular calcium and underlying constriction of capillary vessels. Within days following the initial insertion, we observed an influx of new, proliferating pericytes which contribute to new blood vessel formation. Additionally, we discovered a potentially novel population of reactive immune cells in close proximity to the electrode-tissue interface actively engaging in encapsulation of the microelectrode array. Finally, we determined that intracellular pericyte calcium can be modulated by intracortical microstimulation in an amplitude- and frequency-dependent manner. This study provides a new perspective on the complex biological sequelae occurring at the electrode-tissue interface and will foster new avenues of potential research consideration and lead to development of more advanced therapeutic interventions towards improving the biocompatibility of neural electrode technology.

The Triad of Blood-Brain Barrier Integrity: Endothelial Cells, Astrocytes, and Pericytes in Perinatal Stroke Pathophysiology

Pediatric stroke, a significant cause of long-term neurological deficits in children, often arises from disruptions within neurovascular unit (NVU) components. The NVU, a dynamic ensemble of astrocytes, endothelial cells, pericytes, and microglia, is vital for maintaining cerebral homeostasis and regulating vascular brain development. Its structural integrity, particularly at the blood-brain barrier (BBB), depends on intercellular junctions and the basement membrane, which together restrict paracellular transport and shield the brain from systemic insults. Dysfunction in this intricate system is increasingly linked to pediatric stroke and related cerebrovascular conditions. Mutations disrupting endothelial cell adhesion or pericyte-endothelial interactions can compromise BBB stability, leading to pathological outcomes such as intraventricular hemorrhage in the germinal matrix, a hallmark of vascular brain immaturity. Additionally, inflammation, ferroptosis, necroptosis, and autophagy are key cellular processes influencing brain damage and repair. Excessive activation of these mechanisms can exacerbate NVU injury, whereas targeted therapeutic modulation offers potential pathways to mitigate damage and support recovery. This review explores the cellular and molecular mechanisms underlying NVU dysfunction, BBB disruption, and subsequent brain injury in pediatric stroke. Understanding the interplay between genetic mutations, environmental stressors, and NVU dynamics provides new insights into stroke pathogenesis. The susceptibility of the germinal matrix to vascular rupture further emphasizes the critical role of NVU integrity in early brain development. Targeting inflammatory pathways and cell death mechanisms presents promising strategies to preserve NVU function and improve outcomes for affected neonates.

NO-releasing double-crosslinked responsive hydrogels accelerate the treatment and repair of ischemic stroke

Stroke is a global disease that seriously threatens human life. The pathological mechanisms of ischemic stroke include neuroinflammation, oxidative stress, and the destruction of blood vessels at the lesion site. Here, a biocompatible in situ hydrogel platform was designed to target multiple pathogenic mechanisms post-stroke, including anti-inflammation, anti-oxidant, and promotion of angiogenesis. Double-crosslinked responsive multifunctional hydrogels could quickly respond to the pathological microenvironment of the ischemic damage site and mediate the delivery of nitric oxide (NO) and ISO-1 (inhibitor of macrophage migration inhibitory factor, MIF). The hydrogel demonstrated good biocompatibility and could scavenge reactive oxygen species (ROS) and inflammatory cytokines, such as interleukin-6 (IL-6), interleukin-10 (IL-10), and MIF. In a mouse stroke model, hydrogels, when situated within the microenvironment of cerebral infarction characterized by weak acidity and elevated ROS release, would release anti-inflammatory nanoparticles rapidly that exert an anti-inflammatory effect. Concurrently, NO was sustained release to facilitate angiogenesis and provide neuroprotective effects. Neurological function was significantly improved in treated mice as assessed by the modified neurological severity score, rotarod test, and open field test. These findings indicate that the designed hydrogel held promise for sustained delivery of NO and ISO-1 to alleviate cerebral ischemic injury by responding to the brain's pathological microenvironment.

Screening and Identification of Brain Pericyte-Selective Markers

BACKGROUND

Pericytes, a type of mural cells, exert important functions in the CNS. One major challenge in pericyte research is the lack of pericyte-specific and subpopulation-specific markers.

METHODS

To address this knowledge gap, we first generated a novel transgenic mouse line in which vascular smooth muscle cells (vSMCs) are permanently labeled with tdTomato. Next, we isolated PDGFRβ+tdTomato- pericytes and PDGFRβ+tdTomato+ vSMCs from the brains of these mice and subsequently performed RNAseq analysis to identify pericyte-enriched genes.

RESULTS

Using this approach, we successfully identified 40 pericyte-enriched genes and 158 vSMC-enriched genes, which are involved in different biological processes and molecular functions. Using ISH/IHC analysis, we found that Pla1a and Cox4i2 were predominantly enriched in subpopulations of brain pericytes, although they also marked some non-vascular parenchymal cells.

CONCLUSIONS

These findings suggest that Pla1a and Cox4i2 preferably label subpopulations of pericytes in the brain compared to vSMCs, and thus, they may be useful in distinguishing these populations.

Expression of Lumican and Osteopontin in Perivascular Areas of the Glioblastoma Peritumoral Niche and Its Value for Prognosis

Glioblastoma (GB) is one of the most aggressive and treatment-resistant cancers due to its complex tumor microenvironment (TME). We previously showed that GB progression is dependent on the aberrant induction of chaperone-mediated autophagy (CMA) in pericytes (PCs), which promotes TME immunosuppression through the PC secretome. The secretion of extracellular matrix (ECM) proteins with anti-tumor (Lumican) and pro-tumoral (Osteopontin, OPN) properties was shown to be dependent on the regulation of GB-induced CMA in PCs. As biomarkers are rarely studied in TME, in this work, we aimed to validate Lumican and OPN as prognostic markers in the perivascular areas of the peritumoral niche of a cohort of GB patients. Previously, we had validated their expression in GB xenografted mice presenting GB infiltration (OPN) or GB elimination (Lumican) dependent on competent or deficient CMA PCs, respectively. Then, patient sample classification by GB infiltration into the peritumoral brain parenchyma was related to GB-induced CMA in microvasculature PCs, analyzing the expression of the lysosomal receptor, LAMP-2A. Our results revealed a correlation between GB-induced CMA activity in peritumoral PCs and GB patients' outcomes, identifying three degrees of severity. The perivascular expression of both immune activation markers, Iba1 and CD68, was related to CMA-dependent PC immune function and determined as useful for efficient GB prognosis. Lumican expression was identified in perivascular areas of patients with less severe outcome and partially co-localizing with PCs presenting low CMA activity, while OPN was primarily found in perivascular areas of patients with poor outcome and partially co-localizing with PCs presenting high CMA activity. Importantly, we found sex differences in the incidence of middle-aged patients, being significantly higher in men but with worse prognosis in women. Our results confirmed that Lumican and OPN in perivascular areas of the GB peritumoral niche are effective predictive biomarkers for evaluating prognosis and monitoring possible therapeutic immune responses dependent on PCs in tumor progression.

A dispensable role of mural cell-derived laminin-5 in intracerebral hemorrhage

Although most laminin isoforms are neuroprotective in stroke, mural cell-derived laminin-α5 plays a detrimental role in an ischemia-reperfusion model. To determine whether this deleterious effect is an intrinsic feature of mural cell-derived laminin-α5 or unique to ischemic stroke, we performed loss-of-function studies using middle-aged mice with laminin-α5 deficiency in mural cells (α5-PKO) in an intracerebral hemorrhage (ICH) model. Control and α5-PKO mice exhibited comparable changes in all parameters examined, including hematoma size, neuronal death, neurological function, blood-brain barrier integrity, and reactive gliosis. These findings highlight a minimal role of mural cell-derived laminin-α5 in ICH. Together with the detrimental role of mural cell-derived laminin-α5 in ischemic stroke, these negative results in ICH model suggest that mural cell-derived laminin-α5 may exert distinct functions in different diseases.

Signaling Role of Pericytes in Vascular Health and Tissue Homeostasis

Pericytes are multipotent cells embedded within the vascular system, primarily surrounding capillaries and microvessels where they closely interact with endothelial cells. These cells are known for their intriguing properties due to their heterogeneity in tissue distribution, origin, and multifunctional capabilities. Specifically, pericytes are essential in regulating blood flow, promoting angiogenesis, and supporting tissue homeostasis and regeneration. These multifaceted roles draw on pericytes' remarkable ability to respond to biochemical cues, interact with neighboring cells, and adapt to changing environmental conditions. This review aims to summarize existing knowledge on pericytes, emphasizing their versatility and involvement in vascular integrity and tissue health. In particular, a comprehensive view of the major signaling pathways, such as PDGFβ/ PDGFRβ, TGF-β, FOXO and VEGF, along with their downstream targets, which coordinate the behavior of pericytes in preserving vascular integrity and promoting tissue regeneration, will be discussed. In this light, a deeper understanding of the complex signaling networks defining the phenotype of pericytes in healthy tissues is crucial for the development of targeted therapies in vascular and degenerative diseases.

A new insight into the role of pericytes in ischemic stroke

The functional structure of the blood-brain barrier (BBB) deteriorates after stroke by developing diffuse microvascular and neurovascular dysfunction and loss of white matter integrity. This causes nervous tissue injury and causes sensory and motor disabilities in stroke patients. Improving the integrity of the BBB and neurovascular remodeling after stroke can promote post-stroke injury conditions. Pericytes are contractile cells abundant in the BBB and sandwiched between astrocytes and endothelial cells of the microvessels. Stroke could lead to the degeneration of pericytes in the BBB. However, recent evidence shows that promoting pericytes enhances BBB integrity and neurovascular remodeling. Furthermore, pericytes achieve multipotent properties under hypoxic conditions, allowing them to transdifferentiate into the brain resident cells such as microglia. Microglia regulate immunity and inflammatory response after stroke. The current review studies recent findings in the intervening mechanisms underlying the regulatory effect of pericytes in BBB recovery after stroke.

A dispensable role of oligodendrocyte-derived laminin-α5 in brain homeostasis and intracerebral hemorrhage

Laminin, a major component of the basal lamina in the CNS, is also expressed in oligodendrocytes (OLs). However, the function of OL-derived laminin remains largely unknown. Here, we performed loss-of-function studies using two OL-specific laminin-α5 conditional knockout mouse lines. Both mutants were grossly normal and displayed intact blood-brain barrier (BBB) integrity. In a mouse model of intracerebral hemorrhage (ICH), control mice and both mutants exhibited comparable hematoma size and neurological dysfunction. In addition, similar levels of hemoglobin and IgG leakage were detected in the mutant brains compared to the controls, indicating comparable BBB damage. Consistent with this finding, subsequent studies revealed no differences in tight junction protein (TJP) and caveolin-1 expression among control and knockout mice, suggesting that neither paracellular nor transcellular mechanism was affected in the mutants. Furthermore, compared to the controls, both mutant lines showed comparable oligodendrocyte number, oligodendrocyte proliferation rate, MBP/MAG levels, and SMI-32 expression, highlighting a minimal role of OL-derived laminin-α5 in OL biology. Together, these findings highlight a dispensable role of OL-derived laminin-α5 in both brain homeostasis and ICH pathogenesis.

Constitutive cell proliferation and neurogenesis in the organum vasculosum lamina terminalis and subfornical organ of adult rats

Neurogenesis continues throughout adulthood in the subventricular zone, hippocampal subgranular zone, and the hypothalamic median eminence (ME) and the adjacent medio-basal hypothalamus. The ME is one of the circumventricular organs (CVO), which are specialized brain areas characterized by an incomplete blood-brain barrier and, thus, are involved in mediating communication between the central nervous system and the periphery. Additional CVOs include the organum vasculosum laminae terminalis (OVLT) and the subfornical organs (SFO). Previous studies have demonstrated that the ME contains neural stem cells (NSCs) capable of generating new neurons and glia in the adult brain. However, it remains unclear whether the OVLT and SFO also contain proliferating cells, the identity of these cells, and their ability to differentiate into mature neurons. Here we show that glial and mural subtypes exhibit NSC characteristics, expressing the endogenous mitotic maker Ki67, and incorporating the exogenous mitotic marker BrdU in the OVLT and SFO of adult rats. Glial cells constitutively proliferating in the SFO comprise NG2 glia, while in the OVLT, both NG2 glia and tanycytes appear to constitute the NSC pool. Furthermore, pericytes, which are mural cells associated with capillaries, also contribute to the pool of cells constitutively proliferating in the OVLT and SFO of adult rats. In addition to these glial and mural cells, a fraction of NSCs containing proliferation markers Ki67 and BrdU also expresses the early postmitotic neuronal marker doublecortin, suggesting that these CVOs comprise newborn neurons. Notably, these neurons can differentiate and express the mature neuronal marker NeuN. These findings establish the sensory CVOs OVLT and SFO as additional neurogenic niches, where the generation of new neurons and glia persists in the adult brain.

Endothelial and mural laminin-α5 contributes to neurovascular integrity maintenance

BACKGROUND

Laminin-α5, a major component of the basal lamina, is predominantly synthesized by endothelial and mural cells (pericytes and vascular smooth muscle cells) in the CNS. Loss of laminin-α5 in either population fails to induce any abnormalities due to functional redundancy. Thus, the functional significance of laminin-α5 in neurovascular integrity remains unknown. Here, we hypothesize that ablation of laminin-α5 in both endothelial and mural cells increases neurovascular permeability.

METHODS

The compound knockout mice were generated by crossing laminin-α5 floxed mice with Tie2-Cre and PDGFRβ-Cre, which target endothelial cells and mural cells, respectively. Neurovascular permeability in these mutants was determined with both exogenous and endogenous tracers. Endothelial paracellular and transcellular permeability was assessed by examining the expression of tight junction proteins and transcytosis-associated proteins. In addition, transmission electron microscopy (TEM) was used to visualize tight junction ultrastructure and endothelial caveolae vesicles. Defects in pericytes and astrocytes were investigated by examining pericyte coverage/contact and astrocyte polarity.

RESULTS

Elevated neurovascular permeability was observed in the mutants. Subsequent studies found increased Caveolin-1 and decreased major facilitator superfamily domain-containing protein 2a (MFSD2A) expression, but unaltered Claudin-5 or zonula occludens-1 (ZO-1) expression. Consistent with these results, mutant mice exhibited increased endothelial caveolae vesicle number with intact tight junction structure under TEM. Additionally, pericyte coverage and contact were also decreased in the mutant mice, while astrocyte polarity was unaffected.

CONCLUSIONS

These results strongly indicate that endothelial and mural cell-derived laminin-α5 actively maintains neurovascular integrity via the transcellular rather than paracellular mechanism.

Brain perivascular macrophages: current understanding and future prospects

Brain perivascular macrophages are specialized populations of macrophages that reside in the space around cerebral vessels, such as penetrating arteries and venules. With the help of cutting-edge technologies, such as cell fate mapping and single-cell multi-omics, their multifaceted, pivotal roles in phagocytosis, antigen presentation, vascular integrity maintenance and metabolic regulation have more recently been further revealed under physiological conditions. Accumulating evidence also implies that perivascular macrophages are involved in the pathogenesis of neurodegenerative disease, cerebrovascular dysfunction, autoimmune disease, traumatic brain injury and epilepsy. They can act in either protective or detrimental ways depending on the disease course and stage. However, the underlying mechanisms of perivascular macrophages remain largely unknown. Therefore, we highlight potential future directions in research on perivascular macrophages, including the utilization of genetic mice and novel therapeutic strategies that target these unique immune cells for neuroprotective purposes. In conclusion, this review provides a comprehensive update on the current knowledge of brain perivascular macrophages, shedding light on their pivotal roles in central nervous system health and disease.

Targeting Pericytes for Functional Recovery in Ischemic Stroke

Pericytes surrounding endothelial cells in the capillaries are emerging as an attractive cell resource, which can show a large variety of functions in ischemic stroke, including preservation of the blood-brain barrier, regulation of immune function, and support for cerebral vasculature. These functions have been fully elucidated in previous studies. However, in recent years, increasing evidence has shown that pericytes play an important role in neurological recovery after ischemic stroke due to their regenerative function which can be summarized in two aspects according to current discoveries, one is that pericytes are thought to be multipotential themselves, and the other is that pericytes can promote the differentiation of oligodendrocyte progenitor cells (OPCs). Considering the neuroprotective treatment for stroke has not been much progressed in recent years, new therapies targeting pericytes may be a future direction. Here, we will review the beneficial effects of pericytes in ischemic stroke from two directions: the barrier and vascular functions and the regenerative functions of pericytes.

Experimental procedures for flow cytometry of wild-type mouse brain: a systematic review

Objective

The aim of this study was to systematically review the neuroimmunology literature to determine the average immune cell counts reported by flow cytometry in wild-type (WT) homogenized mouse brains.

Background

Mouse models of gene dysfunction are widely used to study age-associated neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. The importance of the neuroimmune system in these multifactorial disorders has become increasingly evident, and methods to quantify resident and infiltrating immune cells in the brain, including flow cytometry, are necessary. However, there appears to be no consensus on the best approach to perform flow cytometry or quantify/report immune cell counts. The development of more standardized methods would accelerate neuroimmune discovery and validation by meta-analysis.

Methods

There has not yet been a systematic review of 'neuroimmunology' by 'flow cytometry' via examination of the PROSPERO registry. A protocol for a systematic review was subsequently based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using the Studies, Data, Methods, and Outcomes (SDMO) criteria. Literature searches were conducted in the Google Scholar and PubMed databases. From that search, 900 candidate studies were identified, and 437 studies were assessed for eligibility based on formal exclusion criteria.

Results

Out of the 437 studies reviewed, 58 were eligible for inclusion and comparative analysis. Each study assessed immune cell subsets within homogenized mouse brains and used flow cytometry. Nonetheless, there was considerable variability in the methods, data analysis, reporting, and results. Descriptive statistics have been presented on the study designs and results, including medians with interquartile ranges (IQRs) and overall means with standard deviations (SD) for specific immune cell counts and their relative proportions, within and between studies. A total of 58 studies reported the most abundant immune cells within the brains were TMEM119+ microglia, bulk CD4+ T cells, and bulk CD8+ T cells.

Conclusion

Experiments to conduct and report flow cytometry data, derived from WT homogenized mouse brains, would benefit from a more standardized approach. While within-study comparisons are valid, the variability in methods of counting of immune cell populations is too broad for meta-analysis. The inclusion of a minimal protocol with more detailed methods, controls, and standards could enable this nascent field to compare results across studies.

Tackling the glial scar in spinal cord regeneration: new discoveries and future directions

Axonal regeneration and functional recovery are poor after spinal cord injury (SCI), typified by the formation of an injury scar. While this scar was traditionally believed to be primarily responsible for axonal regeneration failure, current knowledge takes a more holistic approach that considers the intrinsic growth capacity of axons. Targeting the SCI scar has also not reproducibly yielded nearly the same efficacy in animal models compared to these neuron-directed approaches. These results suggest that the major reason behind central nervous system (CNS) regeneration failure is not the injury scar but a failure to stimulate axon growth adequately. These findings raise questions about whether targeting neuroinflammation and glial scarring still constitute viable translational avenues. We provide a comprehensive review of the dual role of neuroinflammation and scarring after SCI and how future research can produce therapeutic strategies targeting the hurdles to axonal regeneration posed by these processes without compromising neuroprotection.

The Multiple Roles of Pericytes in Vascular Formation and Microglial Functions in the Brain

In the capillary walls, vascular endothelial cells are covered with mural cells, such as smooth muscle cells and pericytes. Although pericytes had been thought to play simply a structural role, emerging evidence has highlighted their multiple functions in the embryonic, postnatal, and adult brain. As the central nervous system (CNS) develops, the brain's vascular structure gradually matures into a hierarchical network, which is crucial for the proper development of neural lineage cells by providing oxygen and nutrients. Pericytes play an essential role in vascular formation and regulate blood‒brain barrier (BBB) integrity as a component of the neurovascular unit (NVU), in collaboration with other cells, such as vascular endothelial cells, astrocytes, neurons, and microglia. Microglia, the resident immune cells of the CNS, colonize the brain at embryonic day (E) 9.5 in mice. These cells not only support the development and maturation of neural lineage cells but also help in vascular formation through their extensive migration. Recent studies have demonstrated that pericytes directly contact microglia in the CNS, and their interactions have a profound effect on physiological and pathological aspects. This review summarizes the function of pericytes, focusing on the interplay between pericytes and microglia.

In Vitro Modeling of the Blood–Brain Barrier for the Study of Physiological Conditions and Alzheimer’s Disease

The blood–brain barrier (BBB) is an essential structure for the maintenance of brain homeostasis. Alterations to the BBB are linked with a myriad of pathological conditions and play a significant role in the onset and evolution of neurodegenerative diseases, including Alzheimer’s disease. Thus, a deeper understanding of the BBB’s structure and function is mandatory for a better knowledge of neurodegenerative disorders and the development of effective therapies. Because studying the BBB in vivo imposes overwhelming difficulties, the in vitro approach remains the main possible way of research. With many in vitro BBB models having been developed over the last years, the main aim of this review is to systematically present the most relevant designs used in neurological research. In the first part of the article, the physiological and structural–functional parameters of the human BBB are detailed. Subsequently, available BBB models are presented in a comparative approach, highlighting their advantages and limitations. Finally, the new perspectives related to the study of Alzheimer’s disease with the help of novel devices that mimic the in vivo human BBB milieu gives the paper significant originality.

Identification of novel multipotent stem cells in mouse spinal cord following traumatic injury

We showed that injury-induced multipotent stem cells (iSCs) emerge in the brain after stroke. These brain-derived iSCs (B-iSCs) can differentiate into various lineages, including neurons. This study aimed to determine whether similar stem cells can be induced even after non-ischemic injuries, such as trauma to the spinal cord. We characterized these cells, mainly focusing on their stemness, multipotency, and neuronal differentiation activities. Spinal cord injury was produced using forceps in adult mice. On day 3 after spinal cord injury, samples were obtained from the injured areas. Spinal cord sections were subjected to histological analyses. Cells were isolated and assessed for proliferative activities, immunohistochemistry, RT-PCR, FACS, and microarray analysis. Although nerve cell morphology was disrupted within the injured spinal cord, our histological observations revealed the presence of cells expressing stem cells, such as nestin and Sox2 in these areas. In addition, cells extracted from injured areas exhibited high proliferative abilities. These cells also expressed markers of both neural stem cells (e.g., nestin, Sox2) and multipotent stem cells (e.g., Sox2, c-myc, Klf4). They differentiated into adipocytes, osteocytes and chondrocytes, as well as neuronal cells. Microarray analysis further identified similar properties between spinal cord (SC)-derived iSCs and B-iSCs. However, SC-iSCs revealed specific genes related to the regulation of stemness and neurogenesis. We identified similar features related to multipotency in SC-iSCs compared to B-iSCs, including neuronal differentiation potential. Although the differences between SC-iSCs and B-iSCs remain largely undetermined, the present study shows that iSCs can develop even after non-ischemic injuries such as trauma. This phenomenon can occur outside the brain within the CNS.