Production of nitric oxide and transforming growth factor-beta in developing and adult rat brain

Sex differences in effects of gestational polychlorinated biphenyl exposure on hypothalamic neuroimmune and neuromodulator systems in neonatal rats

Polychlorinated biphenyls (PCBs) are ubiquitous in the environment and exposure to them is associated with immune, endocrine and neural dysfunction. Effects of PCBs on inflammation and immunity are best described in spleen and blood, with fewer studies on neural tissues. This is an important gap in knowledge, as molecules typically associated with neuroinflammation also serve neuromodulatory roles and interact with hormones in normal brain development. The current study used Sprague-Dawley rats to assess whether gestational PCB exposure altered hypothalamic gene expression and serum cytokine concentration in neonatal animals given an immune challenge. Dams were fed wafers containing a mixture of PCBs at an environmentally relevant dose and composition (20 μg/kg, 1:1:1 Aroclor 1242:1248:1254) or oil vehicle control throughout their pregnancy. One day old male and female offspring were treated with an inflammatory challenge (lipopolysaccharide, LPS, 50 μg/kg, sc) or saline vehicle control approximately 3.5 h prior to tissue collection. Across both basal and activated inflammatory states, PCB exposure caused greater expression of a subset of inflammatory genes in the hypothalamus and lower expression of genes involved in dopamine, serotonin, and opioid systems compared to oil controls. PCB exposure also altered reactions to inflammatory challenge: it reversed the normal decrease in Esr2 hypothalamic expression and induced an abnormal increase in IL-1b and IL-6 serum concentration in response to LPS. Many of these effects were sex specific. Given the potential long-term consequences of neuroimmune disruption, our findings demonstrate the need for further research.

Role of cytokines in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma is one of the most frequent cancers and standard treatment has only marginally improved the 5-year survival rate of patients with this disease in the last few decades. It is supposed that cytokine alterations in immune, inflammatory and angiogenetic regulatory routes within the head and neck squamous cell carcinoma microenvironment play a critical role in tumor aggressiveness, its response to chemo- and radiation therapies, as well as the development of immune escape mechanisms.

Involvement of prostaglandin E2 released from leptomeningeal cells in increased expression of transforming growth factor-β in glial cells and cortical neurons during systemic inflammation

The leptomeninges play a central role in the antiinflammatory response through the glia-neuron interaction during systemic inflammation. In the present study, we examined the possible production of two potent antiinflammatory mediators, prostaglandin E(2) (PGE(2)) and transforming growth factor-beta1 (TGF-beta1) by leptomeningeal cells during systemic inflammation. After immunization with the complete Freund's adjuvant (CFA), cyclooxygenase (COX)-2 and membrane-bound PGE synthase-1 (mPGES-1) were induced in the leptomeninges. Primary cultured leptomeningeal cells secreted PGE(2) after treatment with lipopolysaccharide (LPS) or proinflammatory cytokines. The LPS-induced release of PGE(2) was depressed by a selective COX-2 inhibitor, NS-398. On the other hand, TGF-beta1 and TGF-beta receptor II (TGF-betaRII) both markedly increased in the leptomeninges and the parenchymal cells after the CFA injection. Double-staining immunohistochemistry demonstrated TGF-beta1 to be induced in both glial cells and cortical neurons, whereas TGF-betaRII was induced only in cortical neurons. Furthermore, the conditioned medium prepared from the leptomeningeal cells after LPS stimulation was able to induce an increased expression of TGF-beta1 and TGF-betaRII in the primary cultured glial cells and cortical neurons. This increased expression was suppressed by NS-398. PGE(2) was found to increase directly the production of TGF-beta1 and TGF-betaRII in the primary cultured cells. These observations strongly suggest that PGE(2), which is biosynthesized by the leptomeninges, mainly regulates the production of TGF-beta1 by glial cells and cortical neuron, thus playing a protective role in the cortical neurons during systemic inflammation. Furthermore, TGF-beta1 may also exert a protective effect directly on the cortical neurons.

Progressive changes in regulation of apolipoproteins E and J in glial cultures during postnatal development and aging

Apolipoprotein (Apo) E and ApoJ are lipid- and cholesterol-carriers in the central nervous system and are implicated in age-related neurodegenerative diseases. The primary source of secreted ApoE and ApoJ (clusterin) in the brain is glia. Regulation of these apolipoproteins in mixed glial cultures from rat cerebral cortex differed most strongly between neonatal- and adult-derived glia. Basal secretion of ApoJ was two-fold greater in neonatal than adult glia. Responses to cytokines also differed by donor age. In adult glia, IL-6 increased ApoE secretion, but slightly decreased ApoJ. Both IL-1 beta and TNFalpha treatments increased ApoJ secretion from adult glia, with little effect on ApoE. In contrast to adult glia, neonatal ApoJ secretion did not respond to IL-1 beta, IL-6, or TNFalpha, and ApoE secretion from neonatal glia was slightly increased by IL-6. These differences may contribute to age-related neuroinflammatory processes, and are pertinent to the general use of neonatal-derived primary glia in models for neurodegenerative disease.

Increased interleukin-6 expression by microglia from brain of aged mice

Over expression of inflammatory cytokines in the brain may establish a state that is permissive to the onset of neurodegenerative disease. Because the occurrence of certain neurodegenerative diseases increases with age, in the present study we examined the expression of the inflammatory cytokine, interleukin-6 (IL-6), in the brain of aged mice. In an initial experiment, IL-6 was measured in crude protein extracts from brains of juvenile (1-month-old), adult (3-month-old), and aged (24-month-old) male BALB/c mice. The concentration of IL-6 in crude protein extracts from the cerebellum, cerebral cortex, and hippocampus increased with age. The increase in IL-6 was discrete, as levels in the hypothalamus were not age-dependent. To begin evaluating spontaneous IL-6 production in aging, glial cells were cultured from brains of neonate, adult, and aged mice. An age-associated increase in IL-6 mRNA and supernatant IL-6 concentration was evident, indicating glia from aged mice spontaneously express high levels of IL-6 relative to glia from adult and neonate mice. Flow cytometric analysis revealed that cultures established from aged brain compared to either adult or neonate brain comprised more microglia (i.e., MAC-1-positive cells). Furthermore, the proportion of microglia that was positive for IL-6 increased with age, whereas the proportion of astrocytes that were positive for IL-6 was not age-dependent. The present results suggest that IL-6 increases in the mouse brain with age, and that microglia cultured from aged mice spontaneously produce more IL-6 than those from neonate or adult mice. Therefore, microglia may contribute to the increased level of IL-6 present in aged brain.

Age-related activation of microglia and astrocytes: in vitro studies show persistent phenotypes of aging, increased proliferation, and resistance to down-regulation

Astrocytes and microglia from cerebral cortex of 3-, 6-, 12-, and 24-month-old F344 male rat donors showed progressively greater proliferation during primary culture. Microglia from aging donor brains exhibited an amoeboid-like morphology and express antigens characteristic of an activated state (e.g., major histocompatibility complex class II). Moreover, microglia from aging donors were less sensitive to several types of regulators. Granulocyte-macrophage colony stimulating factor stimulated proliferation in microglia from young, but not aging brains. Transforming growth factor (TGF)-beta1 inhibited astrocytic and microglial proliferation in cultures from young, but not aging donors. Similarly, the inhibition of lipopolysaccharide-induced NO production by TGF-beta1 in microglia was impaired in cultures from 12-month (middle-age) brains. Another aging change detected by middle age, increased glial fibrillary acidic protein (GFAP) expression, also persisted in astrocytes from 12- to 24-month-old brains, as evaluated by increased activity of a 5'-upstream GFAP promoter construct. Thus, both microglia and astrocytes originated from aging cerebral cortex maintain in vitro at least some of the activated phenotypes of aging glia that are observed in vivo. This new in vitro cell model may allow efficient analysis of glial age changes.

Inhibition of endotoxin-induced nitric oxide synthase production in microglial cells by the presence of astroglial cells: a role for transforming growth factor beta

In mixed glial cell cultures from cerebral cortices of newborn rats, endotoxin induces inducible nitric oxide (iNOS), nitric oxide (NO), and interleukin-1 beta (IL-1 beta) production in microglial cells. Earlier we demonstrated that endotoxin induced iNOS but not IL-1 beta expression in microglial cells is inhibited by the presence of astroglial cells. In the present paper we describe studies on the mechanism by which astroglial cells exert selective suppressive action on iNOS expression by microglial cells. Expression of iNOS and IL-1 beta was studied by single or double label immunocytochemical techniques and cell identification was performed with GSA-I-B4-isolectin and an antibody against GFAP. Production of IL-1 beta and NO was determined by measurement of IL-1 beta and nitrite concentrations in cell lysates and the culture medium, respectively. TGF beta, a cytokine known to inhibit NO production by endotoxin challenged macrophages, was measured in culture medium of mixed glial cell cultures using a bioassay. Microglial, astroglial, and mixed glial cell cultures produced similar concentrations of TGF beta. The potential effect of TGF beta was studied by using immunoneutralizing antibodies against TGF beta 1 and TGF beta 2 on the induction of iNOS in microglial cells in the presence of astroglial cells. Incubation of the mixed glial cell culture with these TGF beta antibodies (3 micrograms/ml) markedly increased endotoxin-induced NO production and iNOS expression in microglial cells, whereas the production of IL-1 beta was not affected. The antibodies against TGF beta 1 and TGF beta 2 marginally increased NO production in pure microglial cell cultures, nonetheless in cultures of purified microglial cells recombinant TGF beta 1 and TGF beta 2 together with endotoxin inhibited NO production. We conclude that the presence of astroglial cells is essential for the inhibitory effect of TGF beta on NO production by microglial cells (possibly) by activation of TGF beta or by increasing the sensitivity of microglial cells for TGF beta.

Control of nitric oxide production by transforming growth factor-beta1: mechanistic insights and potential relevance to human disease

Studies on the multifunctional nature of the transforming growth factor-beta (TGF-beta) family of cytokines and the enzyme nitric oxide synthase (NOS) have suggested that they mediate a wide variety of vital processes in evolutionarily divergent organisms. Numerous mechanistic studies have investigated the consequences of the regulation of NO by the TGF-beta's for mammalian physiology. Studies with several cell types in vitro indicate that TGF-beta1 negatively controls the expression of the enzyme responsible for the prolonged production of large amounts NO, the inducible nitric oxide synthase (NOS2; iNOS), by reducing the expression and activity of NOS2 at multiple levels. Recent studies with TGF-beta1 null mice or mice which overexpress TGF-beta1 suggest that this cytokine may be a primary negative regulator of NOS2 in vivo. The interaction between NOS2 and TGF-beta1 may represent a central homeostatic mechanism in mammalian physiology with implications for a variety of human diseases.

Inducible nitric oxide synthase in tangle-bearing neurons of patients with Alzheimer's disease

In Alzheimer's disease (AD), affected neurons accumulate beta amyloid protein, components of which can induce mouse microglia to express the high-output isoform of nitric oxide synthase (NOS2) in vitro. Products of NOS2 can be neurotoxic. In mice, NOS2 is normally suppressed by transforming growth factor beta 1 (TGF-beta 1). Expression of TGF-beta 1 is decreased in brains from AD patients, a situation that might be permissive for accumulation of NOS2. Accordingly, we investigated the expression of NOS2 in patients with AD, using three monospecific antibodies: a previously described polyclonal and two new monoclonal antibodies. Neurofibrillary tangle-bearing neurons and neuropil threads contained NOS2 in brains from each of 11 AD patients ranging in age from 47 to 81 years. NOS2 was undetectable in brains from 6 control subjects aged 23-72 years, but was expressed in small amounts in 3 control subjects aged 77-87 years. Thus, human neurons can express NOS2 in vivo. The high-output pathway of NO production may contribute to pathogenesis in AD.