The Role of Pericytes in Regulation of Innate and Adaptive Immunity

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.

Immune response recalibration using immune therapy and biomimetic nano-therapy against high-grade gliomas and brain metastases

Although with aggressive standards of care like surgical resection, chemotherapy, and radiation, high-grade gliomas (HGGs) and brain metastases (BM) treatment has remained challenging for more than two decades. However, technological advances in this field and immunotherapeutic strategies have revolutionized the treatment of HGGs and BM. Immunotherapies like immune checkpoint inhibitors, CAR-T targeting, oncolytic virus-based therapy, bispecific antibody treatment, and vaccination approaches, etc., are emerging as promising avenues offering new hope in refining patient's survival benefits. However, selective trafficking across the blood-brain barrier (BBB), immunosuppressive tumor microenvironment (TME), metabolic alteration, and tumor heterogeneity limit the therapeutic efficacy of immunotherapy for HGGs and BM. Furthermore, to address this concern, the NanoBioTechnology-based bioinspired delivery system has been gaining tremendous attention in recent years. With technological advances such as Trojan horse targeting and infusing/camouflaging nanoparticles surface with biological molecules/cells like immunocytes, erythrocytes, platelets, glioma cell lysate and/or integrating these strategies to get hybrid membrane for homotypic recognition. These biomimetic nanotherapy offers advantages over conventional nanoparticles, focusing on greater target specificity, increased circulation stability, higher active loading capacity, BBB permeability (inherent inflammatory chemotaxis of neutrophils), decreased immunogenicity, efficient metabolism-based combinatorial effects, and prevention of tumor recurrence by induction of immunological memory, etc. provide new age of improved immunotherapies outcomes against HGGs and BM. In this review, we emphasize on neuro-immunotherapy and the versatility of these biomimetic nano-delivery strategies for precise targeting of hard-to-treat and most lethal HGGs and BM. Moreover, the challenges impeding the clinical translatability of these approaches were addressed to unmet medical needs of brain cancers.

Contribution of brain pericytes to neuroinflammation following repetitive head trauma

BACKGROUND

Neuroinflammation is a prominent pathological hallmark of traumatic brain injury (TBI) and glia cells have been widely characterized in the onset or progression of brain inflammation. While an effect of inflammation on cerebrovascular breakdown has been observed, little is known about the specific contribution of brain pericytes to the inflammatory response in TBI. Here, we focused on studying the pericyte response to inflammatory stimuli commonly found in the brain following TBI.

METHODS

Mouse brain vascular pericytes were exposed to IL-1β, TNF-α and IFN-γ for 2 h and 24 h and probed for markers of pericyte health and a panel of inflammatory mediators. As the platelet-derived growth factor (PDGF) pathway is critical to pericyte function, we also assessed the effect of PDGF-BB stimulation on the inflammatory response in pericytes. Cultured pericytes were treated with PDGF-BB (10 ng/mL) prior to, simultaneously, and following inflammatory insult. To further investigate their role in brain immunosurveillance, we analyzed the cytokine secretome in mouse pericyte cultures treated with PDGF-BB, as well as in brain vascular pericytes isolated from repetitive mild TBI (r-mTBI) mice that were fed phenytoin-enriched chow, an inducer of PDGF-BB secretion.

RESULTS

Cytokine stimulation with TNF-α, IL-1β, and IFN-γ for 2 and 24 h led to significant upregulation of PDGFRβ in cultured pericytes, with an 8-fold increase after 24 h. MTT assays showed no significant change in cell viability, indicating that cytokine treatment did not induce cytotoxicity. Further, elevated levels of pro-inflammatory markers STAT1 and p-NFkB were observed in response to cytokine exposure, with a concurrent increase in VCAM1 and MMP9 expression. PDGF-BB treatment significantly attenuated the inflammatory response in pericytes, reducing PDGFRβ levels and the activation of inflammatory pathways, including STAT1 and NFkB. Cytokine secretion profiles also revealed that PDGF-BB, when administered post-inflammatory insult, selectively reduced pro-inflammatory cytokines such as IL-1β and IFN-γ. Additionally, phenytoin treatment in r-mTBI mice decreased IL-1β, TNF-α, IL-5, and KC/GRO levels in isolated brain pericytes, while IL-2, IL-4, and IL-6 levels were unchanged compared to untreated r-mTBI animals.

CONCLUSIONS

Our results indicate an immunoreactive role for brain pericytes in the propagation of neuroinflammation. Moreover, following brain insults, we found PDGF-BB stimulation can normalize pericyte function and reduce cerebrovascular inflammation, a key factor in secondary brain injury. Targeting brain pericytes may provide novel therapeutic opportunities to improve cerebrovascular health and reduce brain inflammation in the aftermath of TBI.

Development of Engineered Microparticles for Investigating Enzymatic Degradation of Proteins and Peptides within Phagosomes

Phagocytosis involves the engulfment and enzymatic degradation of particulate objects by phagocytes in a compartment called a phagosome. The degradation mechanisms for natural phagocytic objects such as proteins and peptides are not well understood. To explore this, we developed a novel method using microparticles made of proteins and/or peptides and poly(N-isopropylacrylamide) (PNIPAM) via microfabrication. These microparticles were fed to phagocytes, and the presence of fluorescently labeled fragments in phagosome-derived vesicles (PDVs) was characterized. Using ovalbumin (OVA) and poly-l-lysine as test proteins and peptides, we found that RAW264.7 macrophages engulfed these microparticles, leading to fluorescent PDVs, indicating enzymatic degradation of OVA. We extended this approach to other proteins such as histone and immunoglobulin G and to different phagocytes such as BV2 microglial cells and mouse bone marrow-derived macrophages. Our method also allows for induction of phagosomal rupture and membrane labeling of PDVs.

Advancing Immunotherapy in Pancreatic Cancer: A Brief Review of Emerging Adoptive Cell Therapies

Pancreatic cancer has the lowest 5-year survival rate (13%) among major cancers and is the third leading cause of cancer-related deaths in the United States. The high lethality of this cancer is attributed to its insidious onset, late-stage diagnosis, rapid progression, and limited treatment options. Addressing these challenges requires a deeper understanding of the complex tumor microenvironment to identify novel therapeutic targets. Newer approaches like adoptive cell therapy have shown remarkable success in treating hematological malignancies, but their application in solid tumors, particularly pancreatic cancer, is still in the early stages of development. ACT broadly involves isolating immune cells (T lymphocytes, Natural Killer cells, and macrophages) from the patient, followed by genetic engineering to enhance and mount a specific anti-tumor response. Various ACT modalities are under investigation for pancreatic cancer, including chimeric antigen receptor T cells (CAR-T), chimeric antigen receptor NK cells (CAR-NK), tumor-infiltrating lymphocytes (TIL), T-cell receptor (TCR)-engineered T cells, and cytokine-induced killer cells (CIK). Major hurdles have been identifying actionable tumor antigens and delivering focused cellular therapies to overcome the immunosuppressive and dense fibrotic stroma surrounding the pancreatic cancer. Further studies are needed to explore the limitations faced by cellular therapy in pancreatic cancer and identify novel combination treatment approaches in order to improve clinical outcomes.

Multiscale computational model predicts how environmental changes and treatments affect microvascular remodeling in fibrotic disease

Investigating the molecular, cellular, and tissue-level changes caused by disease, and the effects of pharmacological treatments across these biological scales, necessitates the use of multiscale computational modeling in combination with experimentation. Many diseases dynamically alter the tissue microenvironment in ways that trigger microvascular network remodeling, which leads to the expansion or regression of microvessel networks. When microvessels undergo remodeling in idiopathic pulmonary fibrosis (IPF), functional gas exchange is impaired and lung function declines. We integrated a multiscale computational model with independent experiments to investigate how combinations of biomechanical and biochemical cues in IPF alter cell fate decisions leading to microvascular remodeling. Our computational model predicted that extracellular matrix (ECM) stiffening reduced microvessel area, which was accompanied by physical uncoupling of endothelial cell (EC) and pericytes, the cells that comprise microvessels. Nintedanib, an Food and Drug Administration-approved drug for treating IPF, was predicted to further potentiate microvessel regression by decreasing the percentage of quiescent pericytes while increasing the percentage of pericytes undergoing pericyte-myofibroblast transition in high ECM stiffnesses. Importantly, the model suggested that YAP/TAZ inhibition may overcome the deleterious effects of nintedanib by promoting EC-pericyte coupling and maintaining microvessel homeostasis. Overall, our combination of computational and experimental modeling can predict and explain how cell decisions affect tissue changes during disease and in response to treatments.

Convergent inducers and effectors of T cell paralysis in the tumour microenvironment

Tumorigenesis embodies the formation of a heterotypic tumour microenvironment (TME) that, among its many functions, enables the evasion of T cell-mediated immune responses. Remarkably, most TME cell types, including cancer cells, fibroblasts, myeloid cells, vascular endothelial cells and pericytes, can be stimulated to deploy immunoregulatory programmes. These programmes involve regulatory inducers (signals-in) and functional effectors (signals-out) that impair CD8+ and CD4+ T cell activity through cytokines, growth factors, immune checkpoints and metabolites. Some signals target specific cell types, whereas others, such as transforming growth factor-β (TGFβ) and prostaglandin E2 (PGE2), exert broad, pleiotropic effects; as signals-in, they trigger immunosuppressive programmes in most TME cell types, and as signals-out, they directly inhibit T cells and also modulate other cells to reinforce immunosuppression. This functional diversity and redundancy pose a challenge for therapeutic targeting of the immune-evasive TME. Fundamentally, the commonality of regulatory programmes aimed at abrogating T cell activity, along with paracrine signalling between cells of the TME, suggests that many normal cell types are hard-wired with latent functions that can be triggered to prevent inappropriate immune attack. This intrinsic capability is evidently co-opted throughout the TME, enabling tumours to evade immune destruction.

RAGE mediates hippocampal pericyte responses and neurovascular unit lesions after TBI

Traumatic brain injury impairs brain function through various mechanisms. Recent studies have shown that alterations in pericytes in various diseases affect neurovascular function, but the effects of TBI on hippocampal pericytes remain unclear. Here, we investigated the effects of RAGE activation on pericytes after TBI using male C57BL/6 J mice. Hippocampal samples were collected at different time points within 7 days after TBI, the expression of PDGFR-β, NG2 and the HMGB1-S100B/RAGE signaling pathway was assessed by Western blotting, and the integrity of the hippocampal BBB at different time points was measured by immunofluorescence. RAGE-associated BBB damage in hippocampal pericytes occurred early after cortical impact. By culturing primary mouse brain microvascular pericytes, we determined the different effects of HMGB1-S100B on pericyte RAGE. To investigate whether RAGE blockade could protect neurological function after TBI, we reproduced the process of CCI by administering FPS-ZM1 to RAGE-/- mice. TEM images and BBB damage-related assays showed that inhibition of RAGE resulted in a significant improvement in the number of hippocampal vascular basement membranes and tight junctions and a reduction in perivascular oedema compared with those in the untreated group. In contrast, mouse behavioural testing and doublecortin staining indicated that targeting the HMGB1-S100B/RAGE axis after CCI could protect neurological function by reducing pericyte-associated BBB damage. In conclusion, the present study provides experimental evidence for the strong correlation between the pericyte HMGB1-S100B/RAGE axis and NVU damage in the hippocampus at the early stage of TBI and further demonstrates that pericyte RAGE serves as an important target for the protection of neurological function after TBI.

From Immunity to Neurogenesis: Toll-like Receptors as Versatile Regulators in the Nervous System

Toll-like receptors (TLRs) are among the main components of the innate immune system. They can detect conserved structures in microorganisms and molecules associated with stress and cellular damage. TLRs are expressed in resident immune cells and both neurons and glial cells of the nervous system. Increasing evidence is emerging on the participation of TLRs not only in the immune response but also in processes of the nervous system, such as neurogenesis and cognition. Below, we present a review of the literature that evaluates the expression and role of TLRs in processes such as neurodevelopment, behavior, cognition, infection, neuroinflammation, and neurodegeneration.

Multiscale computational model predicts how environmental changes and drug treatments affect microvascular remodeling in fibrotic disease

Investigating the molecular, cellular, and tissue-level changes caused by disease, and the effects of pharmacological treatments across these biological scales, necessitates the use of multiscale computational modeling in combination with experimentation. Many diseases dynamically alter the tissue microenvironment in ways that trigger microvascular network remodeling, which leads to the expansion or regression of microvessel networks. When microvessels undergo remodeling in idiopathic pulmonary fibrosis (IPF), functional gas exchange is impaired due to loss of alveolar structures and lung function declines. Here, we integrated a multiscale computational model with independent experiments to investigate how combinations of biomechanical and biochemical cues in IPF alter cell fate decisions leading to microvascular remodeling. Our computational model predicted that extracellular matrix (ECM) stiffening reduced microvessel area, which was accompanied by physical uncoupling of endothelial cell (ECs) and pericytes, the cells that comprise microvessels. Nintedanib, an FDA-approved drug for treating IPF, was predicted to further potentiate microvessel regression by decreasing the percentage of quiescent pericytes while increasing the percentage of pericytes undergoing pericyte-myofibroblast transition (PMT) in high ECM stiffnesses. Importantly, the model suggested that YAP/TAZ inhibition may overcome the deleterious effects of nintedanib by promoting EC-pericyte coupling and maintaining microvessel homeostasis. Overall, our combination of computational and experimental modeling can explain how cell decisions affect tissue changes during disease and in response to treatments.

Listeria-based vaccination against the pericyte antigen RGS5 elicits anti-vascular effects and colon cancer protection

Colorectal cancer (CRC) remains a leading cause of cancer-related mortality despite efforts to improve standard interventions. As CRC patients can benefit from immunotherapeutic strategies that incite effector T cell action, cancer vaccines represent a safe and promising therapeutic approach to elicit protective and durable immune responses against components of the tumor microenvironment (TME). In this study, we investigate the pre-clinical potential of a Listeria monocytogenes (Lm)-based vaccine targeting the CRC-associated vasculature. CRC survival and progression are reliant on functioning blood vessels to effectively mediate various metabolic processes and oxygenate underlying tissues. We, therefore, advance the strategy of initiating immunity in syngeneic mouse models against the endogenous pericyte antigen RGS5, which is a critical mediator of pathological vascularization. Overall, Lm-based vaccination safely induced potent anti-tumor effects that consisted of recruiting functional Type-1-associated T cells into the TME and reducing tumor blood vessel content. This study underscores the promising clinical potential of targeting RGS5 against vascularized tumors like CRC.

The diverse effects of transforming growth factor-β and SMAD signaling pathways during the CTL response

Cytotoxic T lymphocytes (CTLs) play an important role in defense against infections with intracellular pathogens and anti-tumor immunity. Efficient migration is required to locate and destroy infected cells in different regions of the body. CTLs accomplish this task by differentiating into specialized subsets of effector and memory CD8 T cells that traffic to different tissues. Transforming growth factor-beta (TGFβ) belongs to a large family of growth factors that elicit diverse cellular responses via canonical and non-canonical signaling pathways. Canonical SMAD-dependent signaling pathways are required to coordinate changes in homing receptor expression as CTLs traffic between different tissues. In this review, we discuss the various ways that TGFβ and SMAD-dependent signaling pathways shape the cellular immune response and transcriptional programming of newly activated CTLs. As protective immunity requires access to the circulation, emphasis is placed on cellular processes that are required for cell-migration through the vasculature.