TGFβ-1 and neurological function after hypoxia-ischemia in adult rats

SARS-CoV-2 Infection to Premature Neuronal Aging and Neurodegenerative Diseases: Is there any Connection with Hypoxia?

The pandemic of coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, has become a global concern as it leads to a spectrum of mild to severe symptoms and increases death tolls around the world. Severe COVID-19 results in acute respiratory distress syndrome, hypoxia, and multi- organ dysfunction. However, the long-term effects of post-COVID-19 infection are still unknown. Based on the emerging evidence, there is a high possibility that COVID-19 infection accelerates premature neuronal aging and increases the risk of age-related neurodegenerative diseases in mild to severely infected patients during the post-COVID period. Several studies correlate COVID-19 infection with neuronal effects, though the mechanism through which they contribute to the aggravation of neuroinflammation and neurodegeneration is still under investigation. SARS-CoV-2 predominantly targets pulmonary tissues and interferes with gas exchange, leading to systemic hypoxia. The neurons in the brain require a constant supply of oxygen for their proper functioning, suggesting that they are more vulnerable to any alteration in oxygen saturation level that results in neuronal injury with or without neuroinflammation. We hypothesize that hypoxia is one of the major clinical manifestations of severe SARS-CoV-2 infection; it directly or indirectly contributes to premature neuronal aging, neuroinflammation, and neurodegeneration by altering the expression of various genes responsible for the survival of the cells. This review focuses on the interplay between COVID-19 infection, hypoxia, premature neuronal aging, and neurodegenerative diseases and provides a novel insight into the molecular mechanisms of neurodegeneration.

LTBP1 Gene Expression in the Cerebral Cortex and its Neuroprotective Mechanism in Mice with Postischemic Stroke Epilepsy

OBJECTIVE

This study aimed at exploring the expression level of LTBP1 in the mouse model of epilepsy. The mechanism of LTBP1 in epileptic cerebral neural stem cells was deeply investigated to control the occurrence of epilepsy with neuroprotection.

METHODS

qRT-PCR was conducted for the expression levels of LTBP1 in clinical human epileptic tissues and neural stem cells, as well as normal cerebral tissues and neural stem cells. The mouse model of postischemic stroke epilepsy (PSE) was established by the middle cerebral artery occlusion (MCAO). Then, qRT-PCR was conducted again for the expression levels of LTBP1 in mouse epileptic tissues and neural stem cells as well as normal cerebral tissues and neural stem cells. The activation and inhibitory vectors of LTBP1 were constructed to detect the effects of LTBP1 on the proliferation of cerebral neural stem cells in the PSE model combined with CCK-8. Finally, Western blot was conducted for the specific mechanism of LTBP1 affecting the development of epileptic cells.

RESULTS

Racine score and epilepsy index of 15 mice showed epilepsy symptoms after the determination with MCAO, showing a successful establishment of the PSE model. LTBP1 expression in both diseased epileptic tissues and cells was higher than that in normal clinical epileptic tissues and cells. Meanwhile, qRT-PCR showed higher LTBP1 expression in both mouse epileptic tissues and their neural stem cells compared to that in normal tissues and cells. CCK-8 showed that the activation of LTBP1 stimulated the increased proliferative capacity of epileptic cells, while the inhibition of LTBP1 expression controlled the proliferation of epileptic cells. Western blot showed an elevated expression of TGFβ/SMAD signaling pathway-associated protein SMAD1/5/8 after activating LTBP1. The expression of molecular MMP-13 associated with the occurrence of inflammation was also activated.

CONCLUSION

LTBP1 can affect the changes in inflammation-related pathways by activating the TGFβ/SMAD signaling pathway and stimulate the development of epilepsy, and the inhibition of LTBP1 expression can control the occurrence of epilepsy with neuroprotection.

Transforming growth factor-β1 protects against LPC-induced cognitive deficit by attenuating pyroptosis of microglia via NF-κB/ERK1/2 pathways

Background

Demyelinating diseases in central nervous system (CNS) are a group of diseases characterized by myelin damage or myelin loss. Transforming growth factor beta1 (TGF-β1) is widely recognized as an anti-inflammatory cytokine, which can be produced by both glial and neuronal cells in CNS. However, the effects of TGF-β1 on demyelinating diseases and its underlying mechanisms have not been well investigated.

Methods

A demyelinating mouse model using two-point injection of lysophosphatidylcholine (LPC) to the corpus callosum in vivo was established. Exogenous TGF-β1 was delivered to the lesion via brain stereotactic injection. LFB staining, immunofluorescence, and Western blot were applied to examine the severity of demyelination and pyroptosis process in microglia. Morris water maze test was used to assess the cognitive abilities of experimental mice. Furthermore, lipopolysaccharide (LPS) was applied to induce pyroptosis in primary cultured microglia in vitro, to explore potential molecular mechanism.

Results

The degree of demyelination in LPC-modeling mice was found improved with supplement of TGF-β1. Besides, TGF-β1 treatment evidently ameliorated the activated proinflammatory pyroptosis of microglia, with downregulated levels of the key pyroptosis effector Gasdermin D (GSDMD), inflammasomes, and cleaved-IL-1β, which effectively attenuated neuroinflammation in vivo. Evaluated by behavioral tests, the cognitive deficit in LPC-modeling mice was found mitigated with application of TGF-β1. Mechanistically, TGF-β1 could reverse pyroptosis-like morphology in LPS-stimulated primary cultured microglia observed by scanning electron microscopy, as well as decrease the protein levels of cleaved-GSDMD, inflammasomes, and cleaved-IL-1β. Activation of ERK1/2 and NF-κB pathways largely abolished the protective effects of TGF-β1, which indicated that TGF-β1 alleviated the pyroptosis possibly via regulating NF-κB/ERK1/2 signal pathways.

Conclusions

Our studies demonstrated TGF-β1 notably relieved the demyelinating injury and cognitive disorder in LPC-modeling mice, by attenuating the inflammatory pyroptosis of microglia via ERK1/2 and NF-κB pathways. Targeting TGF-β1 activity might serve as a promising therapeutic strategy in demyelinating diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02557-0.

A20 Ameliorates Intracerebral Hemorrhage-Induced Inflammatory Injury by Regulating TRAF6 Polyubiquitination

Reducing excessive inflammation is beneficial for the recovery from intracerebral hemorrhage (ICH). Here, the roles and mechanisms of A20 (TNFAIP3), an important endogenous anti-inflammatory factor, are examined in ICH. A20 expression in the PBMCs of ICH patients and an ICH mouse model was detected, and the correlation between A20 expression and neurologic deficits was analyzed. A20 expression was increased in PBMCs and was negatively related to the modified Rankin Scale score. A20 expression was also increased in mouse perihematomal tissues. A20^-/- and A20-overexpressing mice were generated to further analyze A20 function. Compared with wild-type (WT) mice, A20^-/- and A20-overexpressing mice showed significant increases and decreases, respectively, in hematoma volume, neurologic deficit score, mortality, neuronal degeneration, and proinflammatory factors. Moreover, WT-A20^-/- parabiosis was established to explore the role of A20 in peripheral blood in ICH injury. ICH-induced damage, including brain edema, neurologic deficit score, proinflammatory factors, and neuronal apoptosis, was reduced in A20^-/- parabionts compared with A20^-/- mice. Finally, the interactions between TRAF6 and Ubc13 and UbcH5c were increased in A20^-/- mice compared with WT mice; the opposite occurred in A20-overexpressing mice. Enhanced IκBα degradation and NF-κB activation were observed in A20^-/- mice, but the results were reversed in A20-overexpressing mice. These results suggested that A20 is involved in regulating ICH-induced inflammatory injury in both the central and peripheral system and that A20 reduces ICH-induced inflammation by regulating TRAF6 polyubiquitination. Targeting A20 may thus be a promising therapeutic strategy for ICH.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Neuronal and astroglial TGFβ-Smad3 signaling pathways differentially regulate dendrite growth and synaptogenesis

To address the role of the transforming growth factor beta (TGFβ)-Smad3 signaling pathway in dendrite growth and associated synaptogenesis, we used small inhibitory RNA to knockdown the Smad3 gene in either cultured neurons and or primary astrocytes. We found that TGFβ1 treatment of primary neurons increased dendrite extensions and the number of synapsin-1-positive synapses. When Smad3 was knockdown in primary neurons, dendrite growth was inhibited and the number of synapsin-1-positive synapses reduced even with TGFβ1 treatment. When astrocyte-conditioned medium (ACM), collected from TGFβ1-treated astrocytes (TGFβ1-stimulated ACM), was added to cultured neurons, dendritic growth was inhibited and the number of synapsin-1-positive puncta reduced. When TGFβ1-stimulated ACM was collected from astrocytes with Smad3 knocked down, this conditioned media promoted the growth of dendrites and the number of synapsin-1-positive puncta in cultured neurons. We further found that TGFβ1 signaling through Smad3 increased the expression of chondroitin sulfate proteoglycans, neurocan, and phosphacan in ACM. Application of chondroitinase ABC to the TGFβ1-stimulated ACM reversed its inhibitory effects on the dendrite growth and the number of synapsin-1-positive puncta. On the other hand, we found that TGFβ1 treatment caused a facilitation of Smad3 phosphorylation and translocation to the nucleus induced by status epilepticus (SE) in wild-type (Smad3(+/+)) mice, and this treatment also caused a promotion of γ-aminobutyric acid-ergic synaptogenesis impaired by SE in Smad3(+/+) as well as in Smad3(-/-) mice, but more dramatic promotion in Smad3(+/+) mice. Thus, we provide evidence for the first time that TGFβ-Smad3 signaling pathways within neuron and astrocyte differentially regulate dendrite growth and synaptogenesis, and this pathway may be involved in the pathogenesis of some central nervous system diseases, such as epilepsy.

Matrix metalloprotease 9 promotes liver recovery from ischemia and reperfusion injury

BACKGROUND

Matrix metalloprotease (MMP) 9 has been always considered as a destructor of extracellular matrix, promoting liver injury and metastasis of carcinoma. In this study, we investigated the role of MMP-9 in liver wound healing from ischemia and reperfusion injury (IRI).

METHODS

MMP9-/- mice were used to establish partial hepatic IRI model. Serum alanine aminotransferase and hepatic cytokines (tumor necrosis factor alpha, interleukin [IL]-1β, IL-10, and transforming growth factor beta [TGF-β]) levels were analyzed after IRI. Hepatic stellate cells were isolated from wild-type mice to determine the effect of MMP-9 on TGF-β activation. In addition, the effect of TGF-β on liver wound healing from IRI was determined.

RESULTS

Liver recovery from IRI was impaired in MMP9-/- mice, which was described as elevated serum alanine aminotransferase, hepatic tumor necrosis factor alpha, and IL-1β levels. Meanwhile, TGF-β-active protein level was decreased in the liver of MMP9-/- mice. In vitro test, the activation of TGF-β was suppressed in the presence of anti-MMP-9 monoclonal antibody. TGF-β treatment promoted liver recovery from IRI in MMP9-/- mice.

CONCLUSIONS

MMP-9 promoted liver recovery from IRI by activating TGF-β. Thus, MMP-9 plays dual roles (bad and good) in liver IRI, depending on the timing.

Cytokines and perinatal brain damage

Perinatal brain damage has been implicated in the pathogenesis of neurodevelopmental impairments and psychiatric illnesses. This article reviews evidence that infection outside of the brain can damage the brain, and discusses specific cytokines and pathomechanisms that probably mediate the putative effect of remote infection on the developing brain. Events associated with increased circulating inflammatory cytokines, chemokines, and immune cells are described. Finally, studies of genetic variation in susceptibility to cytokine-related brain damage are reviewed.

Protection of ischemic brain cells is dependent on astrocyte-derived growth factors and their receptors

An in vitro ischemia model (oxygen, glucose, and serum deprivation) is used to investigate the possible cellular and molecular mechanisms responsible for cerebral ischemia. We have previously demonstrated that supernatants derived from ischemic microglia can protect ischemic brain cells by releasing GDNF and TGF-beta1. In the present study, we investigate whether products of ischemic astrocytes can also protect ischemic microglia, astrocytes, and neurons in a similar manner. Supernatants from ischemic astrocytes were collected after various periods of ischemia and incubated with microglia, astrocytes, or neurons individually, under in vitro ischemic conditions. The components responsible for the protective effects of astrocyte-derived supernatants were then identified by Western blot, ELISA, trypan blue dye exclusion, and immunoblocking assays. Results showed that under conditions of in vitro ischemia the number of surviving microglia, astrocytes, and neurons was significantly increased by the incorporation of the astrocyte-derived supernatants. Astrocyte supernatant-mediated protection of ischemic microglia was dependent on TGF-beta1 and NT-3, ischemic astrocytes were protected by GDNF, and ischemic neurons were protected by NT-3. In addition, protein expression of TGF-beta1 and NT-3 receptors in microglia, GDNF receptors in astrocytes, and NT-3 receptors in neurons was increased by in vitro ischemia. These results suggest that astrocyte-derived protection of ischemic brain cells is dependent not only on factors released from the ischemic astrocytes, but also on the type of receptor present on the responding cells. Therapeutic potential of TGF-beta1, GDNF, and NT-3 in the control of cerebral ischemia is further suggested.

Effect of lipopolysaccharide on global gene expression in the immature rat brain

To improve the understanding of the molecular mechanisms whereby lipopolysaccharide (LPS) affects the immature brain, global gene expression following LPS exposure was investigated in neonatal rats. Brains (n = 5/time point) were sampled 2, 6, and 72 h after LPS and compared with age-matched controls. The mRNA from each brain was analyzed separately on Affymextrix GeneChip Rat Expression Set 230. The number of genes regulated after LPS were 847 at 2 h, 1564 at 6 h, and 1546 genes at 72 h. Gene ontology analysis demonstrated that, at both 2 and 6 h after LPS, genes associated with protein metabolism, response to external stimuli and stress (immune and inflammatory response, chemotaxis) and cell death were overrepresented. At 72 h, the most strongly regulated genes belonged to secretion of neurotransmitters, transport, synaptic transmission, cell migration, and neurogenesis. Several pathways associated with cell death/survival were identified (caspase-tumor necrosis factor alpha [TNF-alpha]-, p53-, and Akt/phosphatidylinositol-3-kinase (PI3 K)-dependent mechanisms). Caspase-3 activity increased and phosphorylation of Akt decreased 8 h after peripheral LPS exposure. These results show a complex cerebral response to peripheral LPS exposure. In addition to the inflammatory response, a significant number of cell death-associated genes were identified, which may contribute to increased vulnerability of the immature brain to hypoxia-ischemia (HI) following LPS exposure.

Histophysiological effects of fluid resuscitation on heart, lung and brain tissues in rats with hypovolemia

The efficacy of using colloids and crystalloids in the treatment of hypovolemia still remains controversial. An important aspect in treating hypovolemia is to re-establish normal tissue hemodynamics after fluid resuscitation. Production of nitric oxide (NO) or growth factors such as transforming growth factor beta (TGF-beta) has been identified as a key mechanism in physiological and pathological processes in the different systems. This study was designed to investigate the histophysiological effects of resuscitation with different plasma substitutes on the heart, lung and brain tissues following acute blood loss in male Sprague-Dawley rats weighing 250-280g (n=30). After anesthesia with sodium pentobarbital, the left femoral vein and artery were cannulated for the administration of volume expanders and for direct measurement of arterial pressure and heart rate. Twenty rats were bled (5ml/10min) and infused (5ml/10min) with one of four randomly selected solutions, (a) human albumin, (b) gelatin (Gelofusine), (c) dextran-70 (Macrodex); or (d) physiological saline (0.9% isotonic saline). Five control rats were bled without infusion. Tissue samples were taken and fixed in 10% formalin solution, then processed for embedding in paraffin wax. Sections were cut and stained with hematoxylin and eosin. Indirect immunohistochemical labelling was performed to reveal binding of primary antibodies against endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and TGF-beta. Mild immunoreactivity of eNOS was observed in endothelial cells of vessels in brain, heart and lung tissues. Increased immunoreactivities of eNOS, iNOS and TGF-beta were observed in the non-fluid resuscitated group in these organs; mild, moderate, moderate and strong immunoreactivities were seen in the albumin, gelatin, physiological saline and dextran-70 treated groups, respectively. Immunoreactivities of iNOS and TGF-beta in the non-fluid resuscitated group were increased significantly, in comparison to the other groups, apart from the dextran-70 treated group. The results of this study show that gelatin solution and physiological saline may be of use after acute blood loss, and dextran-70 is not the preferred resuscitation fluid in the early stages of acute blood loss. It was concluded that albumin solution is the preferred fluid for resuscitation.

Central penetration and stability of N-terminal tripeptide of insulin-like growth factor-I, glycine-proline-glutamate in adult rat

Insulin-like growth factor-I is a neurotrophic factor and can prevent neurons from ischemic brain injury. However, the large molecular weight and metabolic effects can be problematic in its central delivery. Glycine-proline-glutamate (GPE) is the N-terminal tripeptide of insulin-like growth factor-I, which is naturally cleaved in the plasma and brain tissues. GPE reduces neuronal loss from hypoxic-ischemic brain injury following central administration. Central penetration and the stability of GPE in the plasma and central nervous system were examined in rats using radioimmunoassay and HPLC. GPE was rapidly metabolised in the plasma (8 min) after intraperitoneal administration. Despite having a short half-life in plasma, GPE was detected in the cerebrospinal fluid up to 40 min after intraperitoneal administration. With present of peptidase inhibitors, GPE existed in the brain tissue up to 3 h after intracerebroventricular administration, suggesting a role for peptolysis in its stability. The endopeptidase inhibitors 4- (2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) reduced GPE metabolism in the brain tissue while acid peptidase inhibitor pepstatin-A decreased GPE metabolism in the plasma. GPE reduced neuronal loss in the CA1-2 sub-region of the hippocampus given (intraperitoneally) after 30 min of hypoxic-ischemic injury in adult rats, further suggested the effectiveness of GPE central uptake. These results indicated that GPE crosses the blood-CSF and the functional CSF-brain barriers. The longer half-life of GPE in the CNS may be due to its unique enzymatic stability.