title: Regulation of progranulin expression in human microglia and proteolysis of progranulin by matrix metalloproteinase-12 (MMP-12).
abstract: BACKGROUND
  The essential role of progranulin (PGRN) as a neurotrophic factor has been demonstrated by the discovery that haploinsufficiency due to GRN gene mutations causes frontotemporal lobar dementia. In addition to neurons, microglia in vivo express PGRN, but little is known about the regulation of PGRN expression by microglia.
  
  
  OBJECTIVE
  In the current study, we examined the regulation of expression and function of PGRN, its proteolytic enzyme macrophage elastase (MMP-12), as well as the inhibitor of PGRN proteolysis, secretory leukocyte protease inhibitor (SLPI), in human CNS cells.
  
  
  METHODS
  Cultures of primary human microglia and astrocytes were stimulated with the TLR ligands (LPS or poly IC), Th1 cytokines (IL-1/IFNγ), or Th2 cytokines (IL-4, IL-13). Results were analyzed by Q-PCR, immunoblotting or ELISA. The roles of MMP-12 and SLPI in PGRN cleavage were also examined.
  
  
  RESULTS
  Unstimulated microglia produced nanogram levels of PGRN, and PGRN release from microglia was suppressed by the TLR ligands or IL-1/IFNγ, but increased by IL-4 or IL-13. Unexpectedly, while astrocytes stimulated with proinflammatory factors released large amounts of SLPI, none were detected in microglial cultures. We also identified MMP-12 as a PGRN proteolytic enzyme, and SLPI as an inhibitor of MMP-12-induced PGRN proteolysis. Experiments employing PGRN siRNA demonstrated that microglial PGRN was involved in the cytokine and chemokine production following TLR3/4 activation, with its effect on TNFα being the most conspicuous.
  
  
  CONCLUSIONS
  Our study is the first detailed examination of PGRN in human microglia. Our results establish microglia as a significant source of PGRN, and MMP-12 and SLPI as modulators of PGRN proteolysis. Negative and positive regulation of microglial PGRN release by the proinflammatory/Th1 and the Th2 stimuli, respectively, suggests a fundamentally different aspect of PGRN regulation compared to other known microglial activation products. Microglial PGRN appears to function as an endogenous modulator of innate immune responses.
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, United States of America. hyeon-sook.suh@einstein.yu.edu
authors.forename: Hyeon-Sook
authors.initials: HS
authors.lastname: Suh
authors.forename: Namjong
authors.initials: N
authors.lastname: Choi
authors.forename: Leonid
authors.initials: L
authors.lastname: Tarassishin
authors.forename: Sunhee C
authors.initials: SC
authors.lastname: Lee
mesh_terms: D001253:Astrocytes / Q000201:enzymology / Q000378:metabolism; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D053508:Matrix Metalloproteinase 12 / Q000235:genetics / Q000378:metabolism*; D017628:Microglia / Q000201:enzymology / Q000378:metabolism; D000077153:Progranulins; D059748:Proteolysis; D034741:RNA, Small Interfering; D053481:Secretory Leukocyte Peptidase Inhibitor / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D016207:Cytokines; C492314:GRN protein, human; D036341:Intercellular Signaling Peptides and Proteins; D000077153:Progranulins; D034741:RNA, Small Interfering; D053481:Secretory Leukocyte Peptidase Inhibitor; D053508:Matrix Metalloproteinase 12