Anti-inflammatory protein TNFα-stimulated gene-6 (TSG-6) reduces inflammatory response after brain injury in mice

Astrocyte-mediated inflammatory responses in traumatic brain injury: mechanisms and potential interventions

Astrocytes play a pivotal role in the inflammatory response triggered by traumatic brain injury (TBI). They are not only involved in the initial inflammatory response following injury but also significantly contribute to Astrocyte activation and inflammasome release are key processes in the pathophysiology of TBI, significantly affecting the progression of secondary injury and long-term outcomes. This comprehensive review explores the complex triggering mechanisms of astrocyte activation following TBI, the intricate pathways controlling the release of inflammasomes from activated astrocytes, and the subsequent neuroinflammatory cascade and its multifaceted roles after injury. The exploration of these processes not only deepens our understanding of the neuroinflammatory cascade but also highlights the potential of astrocytes as critical therapeutic targets for TBI interventions. We then evaluate cutting-edge research aimed at targeted therapeutic approaches to modulate pro-inflammatory astrocytes and discuss emerging pharmacological interventions and their efficacy in preclinical models. Given that there has yet to be a relevant review elucidating the specific intracellular mechanisms targeting astrocyte release of inflammatory substances, this review aims to provide a nuanced understanding of astrocyte-mediated neuroinflammation in TBI and elucidate promising avenues for therapeutic interventions that could fundamentally change TBI management and improve patient outcomes. The development of secondary brain injury and long-term neurological sequelae. By releasing a variety of cytokines and chemokines, astrocytes regulate neuroinflammation, thereby influencing the survival and function of surrounding cells. In recent years, researchers have concentrated their efforts on elucidating the signaling crosstalk between astrocytes and other cells under various conditions, while exploring potential therapeutic interventions targeting these cells. This paper highlights the specific mechanisms by which astrocytes produce inflammatory mediators during the acute phase post-TBI, including their roles in inflammatory signaling, blood-brain barrier integrity, and neuronal protection. Additionally, we discuss current preclinical and clinical intervention strategies targeting astrocytes and their potential to mitigate neurological damage and enhance recovery following TBI. Finally, we explore the feasibility of pharmacologically assessing astrocyte activity post-TBI as a biomarker for predicting acute-phase neuroinflammatory changes.

TSG-6 Protects Against Cerebral Ischemia-Reperfusion Injury via Upregulating Hsp70-1B in Astrocytes

AIMS

This study aimed to investigate the relationship between tumor necrosis factor alpha-induced protein (TNFAIP6/TSG-6) and astrocytes in cerebral ischemia/reperfusion (I/R) injury.

METHODS

Utilizing in vivo and in vitro cerebral I/R models, cerebral infarct volumes, neurobehavioral outcomes, blood-brain barrier (BBB) permeability, as well as indicators of astrocyte apoptosis, reactivity, and A1 phenotype were assessed to evaluate the effects of recombinant rattus TSG-6 (rrTSG-6) on astrocytes in acute cerebral I/R injury. Following mRNA sequencing of all astrocyte groups, astrocyte apoptosis and reactivity were analyzed through a combined intervention of rrTSG-6 and Apoptozole, a heat shock protein 70-1B (Hsp70-1B) inhibitor, in vitro.

RESULTS

The findings demonstrated that rrTSG-6 significantly reduced cerebral infarct volumes by nearly half, improved neurobehavioral outcomes, mitigated BBB damage, and suppressed the expressions of astrocyte apoptosis markers, reactivity indicators, and A1 phenotype markers. mRNA sequencing revealed that the Hsp70-1B protein level increased to approximately 1.6 times that of the rrTSG-6 non-intervention group. Furthermore, Apoptozole impeded the expressions of astrocyte apoptosis markers, reactivity indicators, and A1 phenotype markers.

CONCLUSION

TSG-6 inhibited nuclear factor kappa-B (NF-κB) phosphorylation by upregulating Hsp70-1B in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced astrocytes, thereby exerting a protective effect through anti-apoptotic mechanisms and the suppression of astrocyte reactivity and A1 transformation following cerebral I/R injury.

Conditional Tnfaip6-Knockout in Inner Ear Hair Cells Does not Alter Auditory Function

Noise-induced hearing loss is a worldwide public health issue that is characterized by temporary or permanent changes in hearing sensitivity. This condition is closely linked to inflammatory responses, and interventions targeting the inflammatory gene tumor necrosis factor-alpha (TNFα) are known to mitigate cochlear noise damage. TNFα-induced proteins (TNFAIPs) are a family of translucent acidic proteins, and TNFAIP6 has a notable association with inflammatory responses. To date, there have been few reports on TNFAIP6 levels in the inner ear. To elucidate the precise mechanism, we generated transgenic mouse models with conditional knockout of Tnfaip6 (Tnfaip6 cKO). Evaluation of hair cell morphology and function revealed no significant differences in hair cell numbers or ribbon synapses between Tnfaip6 cKO and wild-type mice. Moreover, there were no notable variations in hair cell numbers or hearing function in noisy environments. Our results indicate that Tnfaip6 does not have a substantial impact on the auditory system.

Brain Ischemic Tolerance Triggered by Preconditioning Involves Modulation of Tumor Necrosis Factor-α-Stimulated Gene 6 (TSG-6) in Mice Subjected to Transient Middle Cerebral Artery Occlusion

Ischemic preconditioning (PC) induced by a sub-lethal cerebral insult triggers brain tolerance against a subsequent severe injury through diverse mechanisms, including the modulation of the immune system. Tumor necrosis factor (TNF)-α-stimulated gene 6 (TSG-6), a hyaluronate (HA)-binding protein, has recently been involved in the regulation of the neuroimmune response following ischemic stroke. Thus, we aimed at assessing whether the neuroprotective effects of ischemic PC involve the modulation of TSG-6 in a murine model of transient middle cerebral artery occlusion (MCAo). The expression of TSG-6 was significantly elevated in the ischemic cortex of mice subjected to 1 h MCAo followed by 24 h reperfusion, while this effect was further potentiated (p < 0.05 vs. MCAo) by pre-exposure to ischemic PC (i.e., 15 min MCAo) 72 h before. By immunofluorescence analysis, we detected TSG-6 expression mainly in astrocytes and myeloid cells populating the lesioned cerebral cortex, with a more intense signal in tissue from mice pre-exposed to ischemic PC. By contrast, levels of TSG-6 were reduced after 24 h of reperfusion in plasma (p < 0.05 vs. SHAM), but were dramatically elevated when severe ischemia (1 h MCAo) was preceded by ischemic PC (p < 0.001 vs. MCAo) that also resulted in significant neuroprotection. In conclusion, our data demonstrate that neuroprotection exerted by ischemic PC is associated with the elevation of TSG-6 protein levels both in the brain and in plasma, further underscoring the beneficial effects of this endogenous modulator of the immune system.

Tumor necrosis factor-stimulated gene-6 ameliorates early brain injury after subarachnoid hemorrhage by suppressing NLRC4 inflammasome-mediated astrocyte pyroptosis

Subarachnoid hemorrhage is associated with high morbidity and mortality and lacks effective treatment. Pyroptosis is a crucial mechanism underlying early brain injury after subarachnoid hemorrhage. Previous studies have confirmed that tumor necrosis factor-stimulated gene-6 (TSG-6) can exert a neuroprotective effect by suppressing oxidative stress and apoptosis. However, no study to date has explored whether TSG-6 can alleviate pyroptosis in early brain injury after subarachnoid hemorrhage. In this study, a C57BL/6J mouse model of subarachnoid hemorrhage was established using the endovascular perforation method. Our results indicated that TSG-6 expression was predominantly detected in astrocytes, along with NLRC4 and gasdermin-D (GSDMD). The expression of NLRC4, GSDMD and its N-terminal domain (GSDMD-N), and cleaved caspase-1 was significantly enhanced after subarachnoid hemorrhage and accompanied by brain edema and neurological impairment. To explore how TSG-6 affects pyroptosis during early brain injury after subarachnoid hemorrhage, recombinant human TSG-6 or a siRNA targeting TSG-6 was injected into the cerebral ventricles. Exogenous TSG-6 administration downregulated the expression of NLRC4 and pyroptosis-associated proteins and alleviated brain edema and neurological deficits. Moreover, TSG-6 knockdown further increased the expression of NLRC4, which was accompanied by more severe astrocyte pyroptosis. In summary, our study revealed that TSG-6 provides neuroprotection against early brain injury after subarachnoid hemorrhage by suppressing NLRC4 inflammasome activation-induced astrocyte pyroptosis.

Endogenous TSG-6 modulates corneal inflammation following chemical injury

PURPOSE

Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) is upregulated in various pathophysiological contexts, where it has a diverse repertoire of immunoregulatory functions. Herein, we investigated the expression and function of TSG-6 during corneal homeostasis and after injury.

METHODS

Human corneas, eyeballs from BALB/c (TSG-6+/+), TSG-6+/- and TSG-6-/- mice, human immortalized corneal epithelial cells and murine corneal epithelial progenitor cells were prepared for immunostaining and real time PCR analysis of endogenous expression of TSG-6. Mice were subjected to unilateral corneal debridement or alkali burn (AB) injuries and wound healing assessed over time using fluorescein stain, in vivo confocal microscopy and histology.

RESULTS

TSG-6 is endogenously expressed in the human and mouse cornea and established corneal epithelial cell lines and is upregulated after injury. A loss of TSG-6 has no structural and functional effect in the cornea during homeostasis. No differences were noted in the rate of corneal epithelial wound closure between BALB/c, TSG-6+/- and TSG-6-/- mice. TSG-6-/- mice presented decreased inflammatory response within the first 24 h of injury and accelerated corneal wound healing following AB when compared to control mice.

CONCLUSION

TSG-6 is endogenously expressed in the cornea and upregulated after injury where it propagates the inflammatory response following chemical injury.

Repeated mild traumatic brain injury in mice elicits long term innate immune cell alterations in blood, spleen, and brain

Mild traumatic brain injury is an insidious event whereby the initial injury leads to ongoing secondary neuro- and systemic inflammation through various cellular pathways lasting days to months after injury. Here, we investigated the impact of repeated mild traumatic brain injury (rmTBI) and the resultant systemic immune response in male C57B6 mice using flow cytometric methodology on white blood cells (WBCs) derived from the blood and spleen. Isolated mRNA derived from spleens and brains of rmTBI mice was assayed for changes in gene expression at one day, one week, and one month following the injury paradigm. We observed increases in Ly6C+, Ly6C-, and total monocyte percentages in both blood and spleen at one month after rmTBI. Differential gene expression analysis for the brain and spleen tissues uncovered significant changes in many genes, including csf1r, itgam, cd99, jak1,cd3ε, tnfaip6, and nfil3. Additional analysis revealed alterations in several immune signaling pathways over the course of one month in the brain and spleen of rmTBI mice. Together, these results indicate that rmTBI produces pronounced gene expression changes in the brain and spleen. Furthermore, our data suggest that monocyte populations may reprogram towards the proinflammatory phenotype over extended periods of time after rmTBI.

Tumor Necrosis Factor (TNF)-α-Stimulated Gene 6 (TSG-6): A Promising Immunomodulatory Target in Acute Neurodegenerative Diseases

Tumor necrosis factor (TNF)-α-stimulated gene 6 (TSG-6), the first soluble chemokine-binding protein to be identified in mammals, inhibits chemotaxis and transendothelial migration of neutrophils and attenuates the inflammatory response of dendritic cells, macrophages, monocytes, and T cells. This immunoregulatory protein is a pivotal mediator of the therapeutic efficacy of mesenchymal stem/stromal cells (MSC) in diverse pathological conditions, including neuroinflammation. However, TSG-6 is also constitutively expressed in some tissues, such as the brain and spinal cord, and is generally upregulated in response to inflammation in monocytes/macrophages, dendritic cells, astrocytes, vascular smooth muscle cells and fibroblasts. Due to its ability to modulate sterile inflammation, TSG-6 exerts protective effects in diverse degenerative and inflammatory diseases, including brain disorders. Emerging evidence provides insights into the potential use of TSG-6 as a peripheral diagnostic and/or prognostic biomarker, especially in the context of ischemic stroke, whereby the pathobiological relevance of this protein has also been demonstrated in patients. Thus, in this review, we will discuss the most recent data on the involvement of TSG-6 in neurodegenerative diseases, particularly focusing on relevant anti-inflammatory and immunomodulatory functions. Furthermore, we will examine evidence suggesting novel therapeutic opportunities that can be afforded by modulating TSG-6-related pathways in neuropathological contexts and, most notably, in stroke.

Evaluation of neuroprotective and immunomodulatory properties of mesenchymal stem cells in an ex vivo retinal explant model

BACKGROUND

Glaucoma is a blinding degenerative neuropathy in which the death of retinal ganglion cells (RGCs) causes progressive loss of visual field and eventually vision. Neuroinflammation appears to be a key event in the progression and spread of this disease. Thus, microglial immunomodulation represents a promising therapeutic approach in which mesenchymal stem cells (MSCs) might play a crucial role. Their neuroprotective and regenerative potentials have already raised hope in animal models. Yet no definitive treatment has been developed, and some safety concerns have been reported in human trials. In the present study, we investigated the neuroprotective and immunomodulatory properties as well as the safety of MSCs in an ex vivo neuroretina explant model.

METHODS

Labeled rat bone marrow MSCs were placed in coculture with rat retinal explants after optic nerve axotomy. We analyzed the neuroprotective effect of MSCs on RGC survival by immunofluorescence using RBPMS, Brn3a, and NeuN markers. Gliosis and retinal microglial activation were measured by using GFAP, CD68, and ITGAM mRNA quantification and GFAP, CD68, and Iba1 immunofluorescence stainings. We also analyzed the mRNA expression of both 'M1' or classically activated state inflammatory cytokines (TNFα, IL1β, and IL6), and 'M2' or alternatively activated state microglial markers (Arginase 1, IL10, CD163, and TNFAIP6).

RESULTS

The number of RGCs was significantly higher in retinal explants cultured with MSCs compared to the control group at Day 7 following the optic nerve axotomy. Retinal explants cultured with MSCs showed a decrease in mRNA markers of gliosis and microglial activations, and immunostainings revealed that GFAP, Iba1, and CD68 were limited to the inner layers of the retina compared to controls in which microglial activation was observed throughout the retina. In addition, MSCs inhibited the M1 phenotype of the microglia. However, edema of the explants was observed in presence of MSCs, with an increase in fibronectin labeling at the surface of the explant corresponding to an epiretinal membrane-like phenotype.

CONCLUSION

Using an ex vivo neuroretina model, we demonstrated a neuroprotective and immunomodulatory effect of MSCs on RGCs. Unfortunately, the presence of MSCs also led to explant edema and epiretinal membrane formation, as described in human trials. Using the MSC secretome might offer the beneficial effects of MSCs without their potential adverse effects, through paracrine signaling.

Endogenously-Produced Hyaluronan and Its Potential to Regulate the Development of Peritoneal Adhesions

Formation of peritoneal adhesions (PA) is one of the major complications following intra-abdominal surgery. It is primarily caused by activation of the mesothelial layer and underlying tissues in the peritoneal membrane resulting in the transition of mesothelial cells (MCs) and fibroblasts to a pro-fibrotic phenotype. Pro-fibrotic transition of MCs—mesothelial-to-mesenchymal transition (MMT), and fibroblasts activation to myofibroblasts are interconnected to changes in cellular metabolism and culminate in the deposition of extracellular matrix (ECM) in the form of fibrotic tissue between injured sides in the abdominal cavity. However, ECM is not only a mechanical scaffold of the newly synthetized tissue but reciprocally affects fibrosis development. Hyaluronan (HA), an important component of ECM, is a non-sulfated glycosaminoglycan consisting of N-acetyl-D-glucosamine (GlcNAc) and D-glucuronic acid (GlcUA) that can affect the majority of processes involved in PA formation. This review considers the role of endogenously produced HA in the context of different fibrosis-related pathologies and its overlap in the development of PA.