Abstract
Purpose: :
Thrombospondins-1 (TSP1) and -2 (TSP2) are matricellular proteins which have been shown to regulate cytoskeleton, cell adhesion, and extracellular matrix remodeling.1 Both TSP1 and TSP2 are found in the trabecular meshwork (TM); TSP1 is expressed throughout the TM with a predominance in the juxtacanalicular region whereas TSP2 is more concentrated in the uveal meshwork.2 We hypothesized that TSP1 and TSP2 participate in the regulation of intraocular pressure (IOP). We tested our hypothesis by comparing the IOPs of TSP1-null, TSP2-null, and their corresponding wild-type (WT) mice.
Methods: :
TSP1- and TSP2-null as well as the corresponding C57BL/6 and C57BL6x129SvJ, respectively, WT mice were obtained from Jackson Laboratory. The mice were bred independently, fed ad lib, and housed under identical 12/12-hour light-dark cycles (on 7:00, off 19:00). Wild-type and TSP1- and TSP2-null 5-6 week-old mice were anesthetized by intraperitoneal injection of a ketamine (100 mg/kg) and xylazine (9 mg/kg) mixture and the IOP was measured between 11:00 and 15:00. A commercial rebound tonometer (TonoLab) was used to take six IOP measurements in each eye between 4 and 7 minutes after anesthestic was injected, as prior studies have shown this to be a period with stable IOP. Toluidine blue staining was used for morphological evaluation.
Results: :
TSP1-null mice have a 10% lower IOP than their corresponding C57BL/6 WT mice (14.2 ± 1.9 mmHg, n=70 versus 15.8 ± 1.5 mmHg, n=54) (p<10-6). TSP2-null mice have a 7% lower IOP than their corresponding C57BL6x129SvJ WT mice (16.8 ± 2.0 mmHg, n=56 versus 18.1 ± 1.6 mmHg, n=54) (p=0.002). Light microscopy did not reveal evidence of gross morphological differences of the iridocorneal angles between knockout and WT mice.
Conclusions: :
TSPs-1 and -2 have functional significance to the regulation of IOP. In other organs, TSP is generally associated with extracellular matrix deposition and TSP-1-null mice have a phenotype functionally consistent with diminished transforming growth factor-beta1 (TGF-β1).3 TSP1 is a potent activator of TGF-β1. TSP1 is found in greater amounts within the TM from patients with glaucoma. The greater functional impact of the TSP1 deletion may be a consequence of its greater concentration in the juxtacanalicular region.
Keywords: intraocular pressure • extracellular matrix • trabecular meshwork