title: Novel pathway of adipogenesis through cross-talk between adipose tissue macrophages, adipose stem cells and adipocytes: evidence of cell plasticity.
abstract: BACKGROUND
  Previous studies highlight a complex relationship between lineage and phenotype for adipose tissue macrophages (ATMs), adipose stem cells (ASCs), and adipocytes, suggesting a high degree of plasticity of these cells. In the present study, using a novel co-culture system, we further characterized the interaction between ATMs, ASCs and adipocytes.
  
  
  METHODS
  Human adipocytes and the stromal vascular fraction containing ATMs and ASCs were isolated from human adipose tissue and co-cultured for 24 hours. FACS was used to characterize ATMs and ASCs before and after co-culture. Preadipocytes generated after co-culture were characterized by immunostaining for DLK (preadipocytes), CD14 and CD68 (ATMs), CD34 (ASCs), and Nile Red staining for lipid drops. qRT-PCR was used to quantify adipogenic markers such as C/EBPα and PPARγ. A novel fluorescent nanobead lineage tracing method was utilized before co-culture where fluorescent nanobeads were internalized by CD68 (+) ATMs.
  
  
  RESULTS
  Co-culture of adipocytes with ATMs and ASCs increased the formation of new preadipocytes, thereby increasing lipid accumulation and C/EBPα and PPARγ gene expression. Preadipocytes originating after co-culture were positive for markers of preadipocytes, ATMs and ASCs. Moreover, fluorescent nanobeads were internalized by ATMs before co-culture and the new preadipocytes formed after co-culture also contained fluorescent nanobeads, suggesting that new preadipocytes originated in part from ATMs. The formation of CD34(+)/CD68(+)/DLK (+) cell spheres supported the interaction of ATMs, ASCs and preadipocytes.
  
  
  CONCLUSIONS
  Cross-talk between adipocytes, ATMs and ASCs promotes preadipocyte formation. The regulation of this novel adipogenic pathway involves differentiation of ATMs to preadipocytes. The presence of CD34(+)/CD68(+)/DLK(+) cells grouped in spheres suggest that paracrine interactions between these cell types plays an important role in the generation and proliferation of new preadipocytes. This phenomenon may reflect the in vivo plasticity of adipose tissue in which ATMs play an additional role during inflammation and other disease states. Understanding this novel pathway could influence adipogenesis, leading to new treatments for obesity, inflammation, and type 2 diabetes.
authors.affiliation: Department of Obstetrics and Gynecology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America. gchazenbalk@mednet.ucla.edu
authors.forename: Gregorio
authors.initials: G
authors.lastname: Chazenbalk
authors.forename: Cristina
authors.initials: C
authors.lastname: Bertolotto
authors.forename: Saleh
authors.initials: S
authors.lastname: Heneidi
authors.forename: Medet
authors.initials: M
authors.lastname: Jumabay
authors.forename: Bradley
authors.initials: B
authors.lastname: Trivax
authors.forename: Joel
authors.initials: J
authors.lastname: Aronowitz
authors.forename: Kotaro
authors.initials: K
authors.lastname: Yoshimura
authors.forename: Charles F
authors.initials: CF
authors.lastname: Simmons
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Dumesic
authors.forename: Ricardo
authors.initials: R
authors.lastname: Azziz
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D050156:Adipogenesis / Q000235:genetics / Q000502:physiology*; D000273:Adipose Tissue / Q000166:cytology* / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D066298:In Vitro Techniques; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*