The expression of proinflammatory cytokine mRNA in the sciatic–tibial nerve of ischemia–reperfusion injury

We evaluated the proinflammatory cytokines, TNF-α and IL-1β, mRNA expression in the rat sciatic and tibial nerves following ischemia–reperfusion (IR) injury, using competitive RT–PCR, to explore the role of cytokines in IR injury. The expressions of both TNF-α and IL-1β mRNA were related to severity of ischemia and occurred with reperfusion rather than ischemia alone. TNF-α gene expression peaked at 24 h of reperfusion, while that of IL-1β peaked at 12 h. These data support the notion that the proinflammatory cytokines TNF-α and IL-1β are involved in the inflammatory response of IR injury to the peripheral nervous system and may be involved in the pathophysiology of ischemic fiber degeneration.     

Interferon-γ Induces Apoptosis and Augments the Expression of Fas and Fas Ligand by Microglia in Vitro

Activation of microglia by interferon-γ (IFN-γ) has been implicated in a number of central nervous system (CNS) inflammatory disease processes. Because IFN-γ has also been shown to play a role in programmed cell death, we investigated its cytotoxicity and its effect on the Fas apoptotic pathway in microglia. Flow cytometry was used to quantify the IFN-γ-mediated apoptotic response and Fas and Fas ligand (FasL) expression in two well-characterized murine microglia cell lines (BV-2 and N9). Nuclear fragmentation, suggestive of apoptosis, was noted within 24 h of incubation of microglia with IFN-γ (10 U/ml). After a 72-h incubation, almost every BV-2 and N9 microglia, but not GL261 glioma cells, underwent cell death and detached from the culture plates. This cytotoxicity occurred even at low IFN-γ concentrations (1 U/ml) and was inhibited by BAF, a pan-caspase inhibitor. Incubation of BV-2 and N9 microglia, but not GL261 glioma cells, with IFN-γ also potentiated the expression of Fas and FasL in a similar dose–response and time-course manner, as seen for the apoptotic response. Whereas Fas expression increased by 100% in both microglia cells, FasL upregulation was more pronounced and increased by as much as 200% in the N9 cells. These findings suggest that in addition to its role as a microglia activator, IFN-γ may also induce apoptosis of microglia, possibly through simultaneous upregulation of Fas and FasL. Interferon-γ modulation of the Fas pathway and apoptosis in microglia may be important in the pathogenesis of inflammatory CNS disease processes.     

TGFα and the Blood–Brain Barrier: Accumulation in Cerebral Vasculature

Transforming growth factor α (TGFα) is a cytokine that belongs to the epidermal growth factor (EGF) family of growth factors. EGF has a fast and saturable entry from blood to brain that is inhibitable by TGFα (18). In this report, we studied the passage of TGFα from blood to brain after an i.v. bolus injection. Using radioactively labeled peptide, we found that TGFα had an apparent rate of entry of 0.7 μl/g/min. However, most of the TGFα was trapped in the capillary endothelial cells of the cerebral vasculature rather than entering the brain parenchyma. No saturation was detected. TGFα was relatively stable in blood for 20 min after i.v. injection, but dissociation of the isotope ¹²⁵I was more evident in brain. The accumulation of TGFα in the cerebral vasculature was similar to that of amyloid-β protein_1–40. Therefore, we conclude that TGFα from the periphery interacts with the blood–brain barrier without substantial uptake into brain parenchyma. This raises the possibility that TGFα might be involved in intracranial vascular disorders such as angiopathy.     

Compartmentalization of antigen specific cytokine responses to the central nervous system in CNS borreliosis: secretion of IFN-γ predominates over IL-4 secretion in response to outer surface proteins of Lyme disease Borrelia spirochetes

The neurological manifestations of Lyme disease have been proposed to be partly due to cytokine-mediated immunopathological mechanisms. In this study, the number of Borrelia-specific cells secreting interferon-γ and interleukin-4 was determined in blood and cerebrospinal fluid from patients with CNS borreliosis (n=23), other neurological diseases (n=20), and in blood from healthy controls (n=10), utilizing an ELISPOT-assay. Elevated specific secretion of IFN-γ was found in CNS borreliosis, most pronounced in cerebrospinal fluid, whereas secretion of IL-4 was strikingly low. This may indicate that symptoms are due to side effects of the immune response, since IFN-γ secretion in the absence of corresponding levels of IL-4 may be associated with tissue destruction.     

IL‐1β induces hypomyelination in the periventricular white matter through inhibition of oligodendrocyte progenitor cell maturation via FYN/MEK/ERK signaling pathway in septic neonatal rats

Neuroinflammation elicited by microglia plays a key role in periventricular white matter (PWM) damage (PWMD) induced by infectious exposure. This study aimed to determine if microglia‐derived interleukin‐1β (IL‐1β) would induce hypomyelination through suppression of maturation of oligodendrocyte progenitor cells (OPCs) in the developing PWM. Sprague‐Dawley rats (1‐day old) were injected with lipopolysaccharide (LPS) (1 mg/kg) intraperitoneally, following which upregulated expression of IL‐1β and IL‐1 receptor 1 (IL‐1R₁) was observed. This was coupled with enhanced apoptosis and suppressed proliferation of OPCs in the PWM. The number of PDGFR‐α and NG2‐positive OPCs was significantly decreased in the PWM at 24 h and 3 days after injection of LPS, whereas it was increased at 14 days and 28 days. The protein expression of Olig1, Olig2, and Nkx2.2 was significantly reduced, and mRNA expression of Tcf4 and Axin2 was upregulated in the developing PWM after LPS injection. The expression of myelin basic protein (MBP) and 2',3'‐cyclic‐nucleotide 3"‐phosphodiesterase (CNPase) was downregulated in the PWM at 14 days and 28 days after LPS injection; this was linked to reduction of the proportion of myelinated axons and thinner myelin sheath as revealed by electron microscopy. Primary cultured OPCs treated with IL‐1β showed the failure of maturation and proliferation. Furthermore, FYN/MEK/ERK signaling pathway was involved in suppression of maturation of primary OPCs induced by IL‐1β administration. Our results suggest that following LPS injection, microglia are activated and produce IL‐1β in the PWM in the neonatal rats. Excess IL‐1β inhibits the maturation of OPCs via suppression of FYN/MEK/ERK phosphorylation thereby leading to axonal hypomyelination. GLIA 2016;64:583–602     

Neuronal–Glial Differential Expression of TGF-α and Its Receptor in the Dorsal Root Ganglia in Response to Sciatic Nerve Lesion

Injury to peripheral nerves often results in structural and functional changes in the dorsal root ganglia (DRG). Although the mechanisms underlying these changes remain largely unknown, satellite cell activation and up-regulation of several neurotrophic factors in the DRG occur in response to the nerve lesion, modulating the plasticity of affected neurons. To investigate potential roles of transforming growth factor α (TGF-α) in these plastic changes in the DRG following a sciatic nerve transection, here we examined the expression in DRGs of TGF-α and its receptor (EGF receptor), molecules known to be mitogenic to glia and Schwann cells and to be neurotrophic for some differentiated neurons. In the normal DRGs, TGF-α and its receptor are expressed mainly in small neurons and satellite cells surrounding some large or medium-sized neurons as determined by immunohistochemistry and in situ hybridization. In response to sciatic nerve lesion, there was a marked and differential up-regulation of TGF-α and EGF receptor expression within DRG, evident as early as 24 h after lesion and lasting for at least 14 days. While the up-regulated TGF-α was localized mainly on satellite cells in the ipsilateral and contralateral DRGs, EGF receptor up-regulation was mainly neuronal (with the expression expanding to include all neurons) in the ipsilateral DRGs, but mainly glial in the contralateral DRGs. These changes in TGF-α and its receptor expression suggest that TGF-α may play a role in the satellite cell proliferation and/or activation as well as in neuronal survival after nerve lesion.     

Androgenic–anabolic steroids blunt morphine-induced c-fos expression in the rat striatum: possible role of β-endorphin

Self-administration of large doses of androgenic–anabolic steroids (AAS) in a significant portion of the population suggests that these agents are drugs of abuse. However, acute administration of AAS did not induce striatal immediate-early genes (IEG) expression in male rats, indicating that AAS do not share a common mechanism of action with other drugs of abuse. Surveys have indicated that people who abuse AAS are more likely to self-administer other drugs of abuse than do people who do not take AAS. In the present study, chronic administration of AAS blunted the striatal c-fos response to morphine, indicating that AAS can alter the molecular responses to at least one drug of abuse. Chronic administration of AAS also increased the content of β-endorphin in the midline thalamus, suggesting a possible mechanism by which AAS may modulate the response to morphine through regulation of thalamo-striatal neurons.     

Age- and region-specific expressions of the messenger RNAs encoding for steroidogenic enzymes P450scc, P450c17 and 3β-HSD in the postnatal rat brain

Neurosteroids are now known to be synthesized de novo in the nervous system through mechanisms at least partly independent of peripheral steroidogenic glands. In mammals, the presence of the cholesterol side-chain cleavage enzyme (cytochrome P450scc) and the enzyme 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴-isomerase (3β-HSD) has been well established in the brain, whereas limited information has been available on the enzyme 17α-hydroxylase/c17, 20-lyase (cytochrome P450c17), which converts pregnenolone to dehydroepiandrosterone, one of the most abundant neurosteroids. In addition, little is known regarding developmental changes in these steroidogenic enzymes during postnatal life. Thus, the pathway of neurosteroid formation in the brain is still incomplete. Therefore, we examined expressions of the messenger RNAs (mRNAs) encoding for three key enzymes, P450scc, P450c17 and 3β-HSD, in the rat brain at different postnatal ages using RT-PCR analysis. The expression of P450scc mRNA was found throughout the brain at the same level, while the 3β-HSD mRNA expression was higher in the cerebellum and cerebrum than in other brain regions. The P450c17 mRNA was highly expressed in the mesencephalon. On the other hand, higher expressions of the cerebellar and cerebral 3β-HSD mRNAs were observed only in neonatal life. In contrast, the expression of P450scc mRNA was relatively constant during neonatal life and in adulthood. A similar constant expression of the P450c17 mRNA was evident in the mesencephalon. Serial Southern hybridization in this study confirmed the specific mRNA expression corresponding to each enzyme. These results suggest that in the postnatal rat the expression of 3β-HSD or P450c17 mRNA may be age- or region-dependent, unlike the P450scc mRNA expression.     

The role of brain cytokines in mediating the behavioral and neuroendocrine effects of intracerebral Mycoplasma fermentans

Intracerebral administration of Mycoplasma fermentans (MF), a small microorganism that has been found in the brain of some AIDS patients, induces behavioral and neuroendocrine alterations in rats. To examine the role of tumor necrosis factor-α (TNFα) and interleukin-1 (IL-1) in mediating these effects we measured MF-induced expression of TNFα and IL-1β mRNA in various brain regions, and the effects of TNFα synthesis blockers and IL-1 receptor antagonist (IL-1ra) on MF-induced sickness behavior and adrenocortical activation. Intracerebroventricular (i.c.v.) administration of heat-inactivated MF induced the expression of both TNFα and IL-1β mRNA in the cortex, dorsal hippocampus, amygdala, and hypothalamus. Pre-treatment of rats with either TNFα synthesis blockers, pentoxifylline or rolipram, or with IL-1ra did not attenuate MF-induced anorexia, body weight loss, and suppression of social behavior. However, simultaneous administration of both pentoxifylline and IL-1ra markedly attenuated MF-induced anorexia and body weight loss, but had no effect on the suppression of social behavior. Pre-treatment with pentoxifylline, but not with IL-1ra, significantly attenuated MF-induced corticosterone (CS) secretion. Together, these findings indicate that both TNFα and IL-1 participate, in a complementary manner, in mediating some of the behavioral effects of MF, whereas only TNFα, but not IL-1, is involved in mediating MF-induced adrenocortical activation. We suggest that cytokines within the brain are involved in mediating at least some of the neurobehavioral and neuroendocrine abnormalities that may be produced by MF in AIDS patients.     

A novel GLP‐1/GIP/Gcg triagonist reduces cognitive deficits and pathology in the 3xTg mouse model of Alzheimer's disease

Type 2 diabetes mellitus (T2DM) is an important risk factor for Alzheimer's disease (AD). Glucagon‐like peptide‐1 (GLP‐1) and glucose‐dependent insulinotropic polypeptide (GIP) have been identified to be effective in T2DM treatment and neuroprotection. In this study, we further explored the effects of a novel unimolecular GLP‐1/GIP/Gcg triagonist on the cognitive behavior and cerebral pathology in the 7‐month‐old triple transgenic mouse model of AD (3xTg‐AD), and investigated its possible electrophysiological and molecular mechanisms. After chronic administration of the GLP‐1/GIP/Gcg triagonist (10 nmol/kg bodyweight, once daily, i.p.) for 30 days, open field, Y maze and Morris water maze tests were performed, followed by in vivo electrophysiological recording, immunofluorescence and Western blotting experiments. We found that the chronic treatment with the triagonist could improve long‐term spatial memory of 3xTg‐AD mice in Morris water maze, as well as the working memory in Y maze task. The triagonist also alleviated the suppression of long‐term potentiation (LTP) in the CA1 region of hippocampus. In addition, the triagonist significantly reduced hippocampal pathological damages, including amyloid‐β (Aβ) and phosphorylated tau aggregates, and upregulated the expression levels of ^S133p‐CREB, ^T286p‐CAMKII and ^S9p‐GSK3β in the hippocampus of the 3xTg‐AD mice. These results demonstrate for the first time that the novel GLP‐1/GIP/Gcg triagonist is efficacious in ameliorating cognitive deficits and pathological damages of 3xTg‐AD mice, suggesting that the triagonist might be potentially beneficial in the treatment of AD.