Potential mechanisms for astrocyte‐TIMP‐1 downregulation in chronic inflammatory diseases

Abstract

The pathogenesis of many neurodegenerative disorders, including human immunodeficiency virus (HIV)-1 associated dementia, is exacerbated by an imbalance between matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of metalloproteinases (TIMPs). In the context of disease, TIMP-1 has emerged as an important multifunctional protein capable of regulating inflammation. We previously reported differential TIMP-1 expression in acute versus chronic activation of astrocytes. This study investigates possible mechanisms underlying TIMP-1 downregulation in chronic neuroinflammation. We used interleukin (IL)-1beta as a model pro-inflammatory stimulus and measured TIMP-1 binding to extracellular matrix, cell death, receptor downregulation, TIMP-1 mRNA stability and transcriptional regulation in activated astrocytes. TIMP-1 remained localized to the cell body or was secreted into the cell supernatant. DNA fragmentation ELISA and MTT assay showed that prolonged IL-1beta activation of astrocytes induced significant astrocyte death. In acute and chronic IL-1beta-activated astrocytes, IL-1 receptor levels were not significantly different. TIMP-1 mRNA stability was measured in astrocytes and U87 astroglioma cells by real-time PCR, and TIMP-1 promoter activation was studied using TIMP-1-luciferase reporter constructs in transfected astrocytes. Our results indicated that TIMP-1 expression is regulated through multiple mechanisms. Transcriptional control and loss of mRNA stabilization are, however, the most likely primary contributors to chronic downregulation of TIMP-1. These data are important for unraveling the mechanisms underlying astrocyte responses during chronic neuroinflammation and have broader implications in other inflammatory diseases that involve MMP/TIMP imbalance.

Immunohistochemical analysis of MMP-9, MMP-2 and TIMP-1, TIMP-2 expression in the central nervous system following infection with viral and bacterial meningitis.

“…These findings may indicate that MMP-TIMP complexes form during inflammation. Astrocytes are an important source of TIMP activity [15,16], and a net balance between MMPs and TIMPs may be involved in the pathogenesis of CNS disease [17]. In addition to inhibiting MMPs, TIMPs are multifunctional molecules that have distinct biological roles [18].…”

Astrocyte Elevated Gene-1 Is a Novel Modulator of HIV-1-associated Neuroinflammation via Regulation of Nuclear Factor-κB Signaling and Excitatory Amino Acid Transporter-2 Repression

“…The Birth Defects Laboratory obtained written consent from all tissue donors. Human astrocytes were isolated as previously described (30). Briefly, brain tissues were dissected and mechanically dissociated.…”

Production and Roles of Glial Tissue Inhibitor of Metalloproteinases-1 in Human Immunodeficiency Virus-1-Associated Dementia Neuroinflammation: A Review

“…When stimulated with IL-1beta, astrocyte expression of MMP-2 peaked between 6-20 days [3] and MMP-1 level rose significantly after 20 days [16] . MMP-7 production by astrocytes, on the other hand, was drastically increased by IL-1beta stimulation after 24 h, but decreased over time to no significant difference to unstimulated cells by day 14 [16] . As for within the first 24 h of stimulation, IL-1beta did not increase astrocyte secretion of MMP-2 unless simultaneously stimulated with TGF-beta1 or TGFbeta2, while the two TGF-beta isoforms significantly downregulated the IL-1beta-stimulated increase of proMMP-1 [5] .…”

“…Infection with CNS isolates HIV-1 DJV , HIV-1 JR-FL , or Cerebrospinal Fluid (CSF) HIV-1 isolates HIV-1 SF162 and HIV-1 MSCSF all downregulated MDM expression of MMP-9 [2] . Among the HIV-1 strains tested, only the CNS isolate HIV-1 YU-culture without any cytokine stimulation [3] and MMP-1 after 14 days [16] . When stimulated with IL-1beta, astrocyte expression of MMP-2 peaked between 6-20 days [3] and MMP-1 level rose significantly after 20 days [16] .…”

“…Among the HIV-1 strains tested, only the CNS isolate HIV-1 YU-culture without any cytokine stimulation [3] and MMP-1 after 14 days [16] . When stimulated with IL-1beta, astrocyte expression of MMP-2 peaked between 6-20 days [3] and MMP-1 level rose significantly after 20 days [16] . MMP-7 production by astrocytes, on the other hand, was drastically increased by IL-1beta stimulation after 24 h, but decreased over time to no significant difference to unstimulated cells by day 14 [16] .…”