Potential mechanisms for astrocyte-TIMP-1 downregulation in chronic inflammatory diseases.
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.
Laboratory of Cellular Neuroimmunology, Center for Neurovirology and Neurodegenerative Disorders, Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198-5215, USA.
Jessica
J
Gardner
Kathleen
K
Borgmann
Muralidhar S
MS
Deshpande
Alok
A
Dhar
Li
L
Wu
Raisa
R
Persidsky
Anuja
A
Ghorpade
D001253:Astrocytes / Q000378:metabolism*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D004660:Encephalitis / Q000378:metabolism* / Q000503:physiopathology; D005109:Extracellular Matrix / Q000378:metabolism*; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D020871:RNA Stability / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D017472:Receptors, Interleukin-1 / Q000378:metabolism; D050436:Regulatory Elements, Transcriptional / Q000187:drug effects / Q000235:genetics; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology; D019014:fas Receptor / Q000187:drug effects / Q000378:metabolism
D007375:Interleukin-1; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1; D019715:Tissue Inhibitor of Metalloproteinase-1; D019014:fas Receptor