title: Downregulation of the tumour suppressor p16INK4A contributes to the polarisation of human macrophages toward an adipose tissue macrophage (ATM)-like phenotype.
abstract: OBJECTIVE
  Human adipose tissue macrophages (ATMs) display an alternatively activated (M2) phenotype, but are still able to produce excessive inflammatory mediators. However, the processes driving this particular ATM phenotype are not understood. Genome-wide association studies associated the CDKN2A locus, encoding the tumour suppressor p16(INK4A), with the development of type 2 diabetes. In the present study, p16(INK4A) levels in human ATMs and the role of p16(INK4A) in acquiring the ATM phenotype were assessed.
  
  
  METHODS
  Gene expression of p16                            (                               INK4A                            ) in ATMs was analysed and compared with that in monocyte-derived macrophages (MDMs) from obese patients or with macrophages from human atherosclerotic plaques (AMs). Additionally, p16(INK4A) levels were studied during macrophage differentiation and polarisation of monocytes isolated from healthy donors. The role of p16(INK4A) in MDMs from healthy donors was investigated by small interfering (si)RNA-mediated silencing or adenovirus-mediated overproduction of p16(INK4A).
  
  
  RESULTS
  Compared with MDMs and AMs, ATMs from obese patients expressed lower levels of p16                            (                               INK4A                            ). In vitro, IL-4-induced M2 polarisation resulted in lower p16(INK4A) protein levels after differentiation of monocytes from healthy donors in macrophages. Silencing of p16(INK4A) in MDMs mediated by siRNA increased the expression of M2 marker genes and enhanced the response to lipopolysaccharide (LPS), to give a phenotype resembling that of ATM. By contrast, adenovirus-mediated overproduction of p16(INK4A) in MDMs diminished M2 marker gene expression and the response to LPS. Western blot analysis revealed that p16(INK4A) overproduction inhibits LPS- and palmitate-induced Toll-like receptor 4 (TLR4)-nuclear factor of κ light polypeptide gene enhancer in B cells (NF-κB) signalling.
  
  
  CONCLUSIONS
  These results show that p16(INK4A) inhibits the acquisition of the ATM phenotype. The age-related increase in p16(INK4A) level may thus influence normal ATM function and contribute to type 2 diabetes risk.
authors.affiliation: Université Lille Nord de France, F-59000 Lille, France.
authors.forename: L
authors.initials: L
authors.lastname: Fuentes
authors.forename: K
authors.initials: K
authors.lastname: Wouters
authors.forename: S A
authors.initials: SA
authors.lastname: Hannou
authors.forename: C
authors.initials: C
authors.lastname: Cudejko
authors.forename: E
authors.initials: E
authors.lastname: Rigamonti
authors.forename: T H
authors.initials: TH
authors.lastname: Mayi
authors.forename: B
authors.initials: B
authors.lastname: Derudas
authors.forename: F
authors.initials: F
authors.lastname: Pattou
authors.forename: G
authors.initials: G
authors.lastname: Chinetti-Gbaguidi
authors.forename: B
authors.initials: B
authors.lastname: Staels
authors.forename: R
authors.initials: R
authors.lastname: Paumelle
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D016764:Cell Polarity; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis* / Q000235:genetics; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism; D015536:Down-Regulation; D005260:Female; D020868:Gene Silencing; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D016328:NF-kappa B / Q000378:metabolism; D009765:Obesity / Q000378:metabolism; D058226:Plaque, Atherosclerotic / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D016328:NF-kappa B; D034741:RNA, Small Interfering; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4