title: Secreted protein acidic and rich in cysteine (SPARC)-null mice exhibit more uniform outflow.
abstract: OBJECTIVE
  Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein known to regulate extracellular matrix (ECM) in many tissues and is highly expressed in trabecular meshwork (TM). SPARC-null mice have a 15% to 20% decrease in intraocular pressure (IOP) compared to wild-type (WT) mice. We hypothesized that mouse aqueous outflow is segmental, and that transgenic deletion of SPARC causes a more uniform pattern that correlates with IOP and TM morphology.
  
  
  METHODS
  Eyes of C57BL6-SV129 WT and SPARC-null mice were injected with fluorescent microbeads, which were also passively exposed to freshly enucleated eyes. Confocal and electron microscopy were performed. Percentage effective filtration length (PEFL) was calculated as PEFL = FL/TL × 100%, where TL = total length and FL = filtration length. IOP was measured by rebound tonometry.
  
  
  RESULTS
  Passive microbead affinity for WT and SPARC-null ECM did not differ. Segmental flow was observed in the mouse eye. SPARC-null mice had a 23% decrease in IOP. PEFL increased in SPARC-null (70.61 ± 11.36%) versus WT mice (54.68 ± 9.95%, P < 0.005; n = 11 pairs), and PEFL and IOP were negatively correlated (R(2) = 0.72, n = 10 pairs). Morphologically, TM of high-tracer regions had increased separation between beams compared to low-tracer regions. Collagen fibril diameter decreased in SPARC-null (28.272 nm) versus WT tissue (34.961 nm, P < 0.0005; n = 3 pairs).
  
  
  CONCLUSIONS
  Aqueous outflow in mice is segmental. SPARC-null mice demonstrated a more uniform outflow pattern and decreased collagen fibril diameter. Areas of high flow had less compact juxtacanalicular connective tissue ECM, and IOP was inversely correlated with PEFL. Our data show a correlation between morphology, aqueous outflow, and IOP, indicating a modulatory role of SPARC in IOP regulation.
authors: Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA 02114, USA.
authors: Swarup S
authors: SS
authors: Swaminathan
authors: Dong-Jin
authors: DJ
authors: Oh
authors: Min Hyung
authors: MH
authors: Kang
authors: Ruiyi
authors: R
authors: Ren
authors: Rui
authors: R
authors: Jin
authors: Haiyan
authors: H
authors: Gong
authors: Douglas J
authors: DJ
authors: Rhee
mesh_terms: D000818:Animals; D001082:Aqueous Humor / Q000502:physiology*; D005109:Extracellular Matrix / Q000502:physiology*; D024021:Fibril-Associated Collagens / Q000502:physiology; D006023:Glycoproteins / Q000172:deficiency*; D007429:Intraocular Pressure / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008863:Microspheres; D015676:Osteonectin; D014065:Tonometry, Ocular; D014129:Trabecular Meshwork / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000172:deficiency*
chemical_list: D024021:Fibril-Associated Collagens; D006023:Glycoproteins; D015676:Osteonectin; C578250:SPARC protein, mouse; D025521:Tumor Suppressor Proteins