Interleukin‐1β regulates proenkephalin gene expression in astrocytes cultured from rat cortex

Abstract

Glial cells execute essential functions in central nervous system (CNS) development and are also believed to play important roles during gliosis in response to trauma or disease. These developmental and pathological states have also been associated with elevated expression of opioid genes. Because levels of the cytokine interleukin-1 beta (IL-1 beta) increase following CNS lesions, we examined the possible influence of IL-1 beta on the expression of opioid genes in astrocytes cultured from rat cortex. Proenkephalin mRNA expression was stimulated by IL-1 beta in a time- and concentration-dependent manner, being maximal with 5 U/ml IL-1 beta at 4 h. Although the beta-adrenergic agonist isoproterenol was also active, interferon, glutamate, and carbachol were not. Unlike isoproterenol, the actions of IL-1 beta were not associated with a cyclic adenosine monophosphate (AMP)-dependent pathway. Interleukin-1 beta also regulated a proenkephalin-chloramphenicol acetyltransferase fusion gene transiently transfected into astrocytes, with a dose-response similar to that active in proenkephalin mRNA. These effects of IL-1 beta were region-specific, not being observed with either cerebellar or hippocampal astrocytes; however, isoproterenol was active in the latter cell populations. Proenkephalin mRNA in cortical astrocytes was stimulated following a temperature stress. These results suggest that enhanced proenkephalin gene expression in astrocytes by IL-1 beta may be important in neuroimmune interactions and in trauma-induced CNS injury or stress.

The interleukin-1β-mediated regulation of proenkephalin and opioid receptor messenger RNA in primary astrocyte-enriched cultures

“…Our finding that proenkephalin expression in cortical cultures was not altered by IL-1 is at variance with observations reported by Low et al 19 and Negro et al 20 These groups reported an IL-1 -mediated increase in proenkephalin mRNA in cortical astrocyte-enriched cultures. However, the discrepancy between our findings and those described in the above studies may be due to differences in the nature and treatment of the glial cell cultures.…”

“…a subculture). Moreover, Low et al 19 treated the cultures with a 10-fold greater IL-1 concentration than was employed in our study, whereas Negro et al 20 used a cytokine concentration comparable to our own, but for a substantially shorter treatment period (4 h versus 24 h). Thus, the manner of the establishment, maintenance and treatment of astrocyteenriched cultures may impact significantly on their responsiveness to the cytokine.…”

“…Like those immune cells in inflamed tissue, astrocytes also appear to respond to IL-1 with an altered opioid peptide expression: IL-1 has been found to modulate the proenkephalin mRNA expression level in cultured astrocytes. 19,20 We have recently described the differential expression by primary astrocyte-enriched cultures of the mRNA species for the three opioid receptor types, µ, and . 23 The observation that astrocytes synthesize proenkephalin, together with the findings that µ, and mRNA species were expressed at different levels within a particular culture, and were also characterized by distinct distribution profiles across different astrocyte-enriched cultures, raised the question of the functional significance of these molecules within the astrocytes.…”

Distinct mRNA expression of the highly homologous convertases PC5 and PACE4 in the rat brain and pituitary

“…The cleavage of pro-enkephalin by PACE4 has not been tested but will be the object of future studies. Such limited proteolysis is all the more important since intermediate pro-enkephalin molecules have been implicated in trophic functions, neuroimmune interactions, or trauma-induced CNS injury or stress (Low et al, 1992;Negro et al, 1992).…”

Interleukin-1 Enhances the ATP-Evoked Release of Arachidonic Acid from Mouse Astrocytes

“…One such cytokine, IL-1␤, which is primarily present in activated microglia or invading macrophages (Giulian et al, 1986;Hertier et al, 1988;Woodroofe et al, 1991) binds to high-affinity interleukin-1 (IL-1) receptors and induces a large variety of cellular responses (Dinarello, 1994). At low concentrations (in the pM range), IL-1␤ binds to receptors present on astrocytes (Ban et al, 1993) and induces the expression of various genes (Benveniste et al, 1990;Negro et al, 1992;Théry et al, 1992;Das and Potter, 1995). In particular, IL-1␤ has been shown to enhance the amounts of both secreted and cytosolic phospholipase A2 isoenzymes (sPLA 2 and cPLA 2 ) (Oka and Arita, 1991;Ozaki et al, 1994).…”