Human glial cell culture models of inflammation in the central nervous system

HIV-1 CNS in vitro infectivity models based on clinical CSF samples

BACKGROUND

The concentration of antiretrovirals in CSF is often utilized as a surrogate for CNS drug exposure. This measurement does not consider pharmacodynamic or combinative effects of ART. We have developed a novel endpoint measurement to assess antiretroviral activity of CSF from subjects on ART.

METHODS

CSF samples were obtained from patients receiving tenofovir/emtricitabine (245/200 mg once daily) with either rilpivirine (25 mg once daily) or lopinavir/ritonavir/maraviroc (400/100/150 mg twice daily) and HIV-uninfected controls. Antiviral activity of ART-containing CSF was assessed in cell cultures using PBMCs and neuro-derived glial (U87) and astrocyte (373) cell lines. Infectivity model half-maximal inhibitory concentration (IMIC50) values were calculated and expressed as -log2IMIC50. Results were correlated with CSF antiretroviral concentrations.

RESULTS

Compared with controls, CSF from both ART studies demonstrated in vitro antiretroviral activity in all models. CSF antiretroviral activity of patients on lopinavir/ritonavir/maraviroc was significantly greater than that of patients on rilpivirine [-log2IMIC50 (95% CI) 4.82 (4.74-4.89) versus 3.43 (3.33-3.54) in PBMCs, 3.06 (2.98-3.15) versus 2.56 (2.46-2.65) in U87 cells and 6.00 (6.11-5.88) versus 4.90 (5.09-4.72) in 373 cells, respectively]. Positive correlations were observed for individual CSF antiretroviral activity in different cellular models with CSF concentrations of rilpivirine (P = 0.040 in 373 cells) and lopinavir (P = 0.048 in 373 cells), but not maraviroc.

CONCLUSIONS

Antiviral activity of CSF from patients on ART was successfully calculated and was greater with a regimen containing four active drugs compared with three active drugs. The use of neuro-derived cell lines alongside PBMCs to assess the effect of ART on CSF may act as a useful future clinical research tool.

miR-206 modulates lipopolysaccharide-mediated inflammatory cytokine production in human astrocytes

Astrocyte-derived inflammation is a common component of acute or chronic injury in the central nervous system. MicroRNAs (miRNAs) are small non-coding RNAs that play important regulatory roles in the inflammatory response. In this study, we found that miR-206 is induced upon stimulation with lipopolysaccharide. Overexpression of miR-206 in astrocytes led to increased expression of inflammatory cytokines (interleukin-6, interleukin-1β, CCL5) upon exposure to lipopolysaccharide, whereas knockdown of miR-206 had completely opposite effects. We used a combination of bioinformatics and experimental techniques to demonstrate that NR4A2, which belongs to the nuclear receptor (NR) 4 family of orphan nuclear receptors, is a direct target of miR-206. Overexpression of miR-206 mimics decreased the activity of a luciferase reporter containing the NR4A2 3'-untranslated region and led to decreased NR4A2 mRNA and protein levels. In contrast, ectopic expression of an miR-206 inhibitor led to elevated NR4A2 expression. We also found that miR-206 modulated the lipopolysaccharide-induced proinflammatory response by targeting NR4A2 and activating nuclear factor-kappa B activity. Finally, we demonstrated that the transcription factor AP-1 plays a critical role in lipopolysaccharide-induced expression of miR-206 and that the extracellular signal-regulated kinase signaling pathway contributes to the regulation of miR-206 level in astrocytes. These data demonstrate that miR-206 positively regulates the lipopolysaccharide-induced inflammatory response in human astrocytes.

Effect of lomeguatrib-temozolomide combination on MGMT promoter methylation and expression in primary glioblastoma tumor cells

Temozolomide (TMZ) is commonly used in the treatment of glioblastoma (GBM). The MGMT repair enzyme (O (6)-methylguanine-DNA methyltransferase) is an important factor causing chemotherapeutic resistance. MGMT prevents the formation of toxic effects of alkyl adducts by removing them from the DNA. Therefore, MGMT inhibition is an interesting therapeutic approach to circumvent TMZ resistance. The aim of the study was to investigate the effect of the combination of lomeguatrib (an MGMT inactivator) with TMZ, on MGMT expression and methylation. Primary cell cultures were obtained from GBM tumor tissues. The sensitivity of primary GBM cell cultures and GBM cell lines to TMZ, and to the combination of TMZ and lomeguatrib, was determined by a cytotoxicity assay (MTT). MGMT and p53 expression, and MGMT methylation were investigated after drug application. In addition, the proportion of apoptotic cells and DNA fragmentation was analyzed. The combination of TMZ and lomeguatrib in primary GBM cell cultures and glioma cell lines decreased MGMT expression, increased p53 expression, and did not change MGMT methylation. Moreover, apoptosis was induced and DNA fragmentation was increased in cells. In addition, we also showed that lomeguatrib-TMZ combination did not have any effect on the cell cycle. Finally, we determined that the sensitivity of each primary GBM cells and glioma cell lines to the lomeguatrib-TMZ combination was different and significantly associated with the structure of MGMT methylation. Our study suggests that lomeguatrib can be used with TMZ for GBM treatment, although further clinical studies will be needed so as to determine the feasibility of this therapeutic approach.

The Aicardi-Goutières syndrome. Molecular and clinical features of RNAse deficiency and microRNA overload

Intracellular RNAses are involved in various functions, including microRNA maturation and turnover. Mutations occurring in genes encoding RNAses cause Aicardi-Goutiéres syndrome (AGS). AGS mutations silence RNAse activity, thus inducing accumulation of endogenous RNAs, mainly consisting of short RNAs and microRNAs. Overload of intracellular RNA triggers Toll like receptor-dependent interferon-alpha production in the brain, which in turn activates neurotoxic lymphocytes and inhibits angiogenesis thus inducing the typical clinical phenotype of AGS. However, these pathogenic mechanisms are attenuated after three years of age by the endogenous production of DNAJP58IPK and Cystatin F, which arrest AGS progression. Because RNAses are involved in microRNA turnover, we evaluated the expression of 957 microRNAs in lymphocytes from AGS patients and control patients. Our results indicate that microRNA overload occurs in AGS patients. This upregulation inhibits microRNA turnover impeding the synthesis of the novel microRNAs required for the differentiation and myelination of the brain during the initial period of postnatal life. These pathogenic mechanisms result in AGS, a neurological syndrome characterized by irritability, mild hyperpyrexia, pyramidal and extrapyramidal signs, and spastic-dystonic tetraplegia. Typical cerebrospinal fluid alterations include lymphocytosis and elevated interferon-alpha levels. Brain imaging demonstrates cerebral calcifications, white matter abnormalities, and progressive cerebral atrophy.Thus, evidence exists that mutations silencing intracellular RNases affect microRNA turnover resulting in the severe clinical consequences in the brain characterizing the clinical feature of AGS.

Brain-region-specific astroglial responses in vitro after LPS exposure

Astroglia is well-known to be integrated in the complex regulation of neuroinflammation in the central nervous system. Astrocytes become activated and synthesize cytokines, chemokines, and prostanoids during degenerative and vulnerable processes and interact with other immune-competent cells. Degenerative disorders often occur in a brain-region-specific fashion suggesting differences in the activity and reactivity of innate immune cells. We have investigated the potency of lipopolysaccharides (LPS) to differently stimulate astrocytes from the cortex and midbrain. Astroglial cultures were prepared from Bagg albino/c mice and exposed to LPS. Astrocytes from both brain areas already differed in their capacity and profile of cytokine expression under basal unstimulated conditions. In response to LPS, we observed both a region-specific pattern of up-regulation of distinct cytokines and differences in the extent and time-course of activation. Our data demonstrate that astrocytes reveal a region-specific basal profile of cytokine expression and a selective area-specific regulation of cytokines upon LPS-induced inflammation. This makes astrocytes likely candidates to be responsible for region-specific incidence rates of neurological and neurodegenerative disorders.