title: Spine degeneration in a murine model of chronic human tobacco smokers.
abstract: OBJECTIVE
  To investigate the mechanisms by which chronic tobacco smoking promotes intervertebral disc degeneration (IDD) and vertebral degeneration in mice.
  
  
  METHODS
  Three month old C57BL/6 mice were exposed to tobacco smoke by direct inhalation (4 cigarettes/day, 5 days/week for 6 months) to model long-term smoking in humans. Total disc proteoglycan (PG) content [1,9-dimethylmethylene blue (DMMB) assay], aggrecan proteolysis (immunobloting analysis), and cellular senescence (p16INK4a immunohistochemistry) were analyzed. PG and collagen syntheses ((35)S-sulfate and (3)H-proline incorporation, respectively) were measured using disc organotypic culture. Vertebral osteoporosity was measured by micro-computed tomography.
  
  
  RESULTS
  Disc PG content of smoke-exposed mice was 63% of unexposed control, while new PG and collagen syntheses were 59% and 41% of those of untreated mice, respectively. Exposure to tobacco smoke dramatically increased metalloproteinase-mediated proteolysis of disc aggrecan within its interglobular domain (IGD). Cellular senescence was elevated two-fold in discs of smoke-exposed mice. Smoke exposure increased vertebral endplate porosity, which closely correlates with IDD in humans.
  
  
  CONCLUSIONS
  These findings further support tobacco smoke as a contributor to spinal degeneration. Furthermore, the data provide a novel mechanistic insight, indicating that smoking-induced IDD is a result of both reduced PG synthesis and increased degradation of a key disc extracellular matrix protein, aggrecan. Cleavage of aggrecan IGD is extremely detrimental as this results in the loss of the entire glycosaminoglycan-attachment region of aggrecan, which is vital for attracting water necessary to counteract compressive forces. Our results suggest identification and inhibition of specific metalloproteinases responsible for smoke-induced aggrecanolysis as a potential therapeutic strategy to treat IDD.
authors.affiliation: Beijing Haidian Hospital, Department of Orthopaedics, 29 Zhong-Guan-Cun Street, Beijing 100080, China.
authors.forename: D
authors.initials: D
authors.lastname: Wang
authors.forename: L A
authors.initials: LA
authors.lastname: Nasto
authors.forename: P
authors.initials: P
authors.lastname: Roughley
authors.forename: A S
authors.initials: AS
authors.lastname: Leme
authors.forename: A M
authors.initials: AM
authors.lastname: Houghton
authors.forename: A
authors.initials: A
authors.lastname: Usas
authors.forename: G
authors.initials: G
authors.lastname: Sowa
authors.forename: J
authors.initials: J
authors.lastname: Lee
authors.forename: L
authors.initials: L
authors.lastname: Niedernhofer
authors.forename: S
authors.initials: S
authors.lastname: Shapiro
authors.forename: J
authors.initials: J
authors.lastname: Kang
authors.forename: N
authors.initials: N
authors.lastname: Vo
mesh_terms: D053674:Aggrecans / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D016922:Cellular Senescence / Q000187:drug effects; D003094:Collagen / Q000378:metabolism; D004195:Disease Models, Animal; D055959:Intervertebral Disc Degeneration / Q000139:chemically induced* / Q000000981:diagnostic imaging / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010024:Osteoporosis / Q000139:chemically induced* / Q000000981:diagnostic imaging / Q000378:metabolism; D011509:Proteoglycans / Q000187:drug effects / Q000378:metabolism; D059748:Proteolysis / Q000187:drug effects; D012907:Smoking / Q000009:adverse effects*; D055114:X-Ray Microtomography
chemical_list: D053674:Aggrecans; D011509:Proteoglycans; D003094:Collagen