The Role of SPARC in Maintaining Periodontal Ligament Integrity

Objective: We have previously reported periodontal ligament (PDL) abnormalities in SPARC-null mice. Specifically, the PDL of SPARC-null mice had significantly less total and thick collagen as compared to age matched wild-type (WT) mice. Periostin is also expressed in the PDL and periostin-null mice have disrupted PDL architecture as defined by histological analysis. Here, we sought to determine whether the combined loss of SPARC and periostin expression in the periodontal ligament differentially affects normal PDL.

Methods: Mandibles and maxillas from age-matched wild type and periostin-SPARC double null mice (PSP-null) at 1-month, 4-months, 8-months, and >18-months were characterized. At least four mice of each genotype were analyzed per age group. Hemotoxylin and eosin stain was used to examine overall PDL tissue morphology. Picro Sirius red stain was used to stain collagen fibers and was viewed under polarized light. Total collagen and proportions of thick and thin collagen were quantified from picro sirius red stained sections.  

Results: The PDL of PSP-null is disorganized as compared to WT mice. PSP-null PDL have altered fibroblast orientation, distorted ratios of mature to immature collagen, disorganization of collagen fibers, and changes in collagen morphology when compared to WT age-matched controls. The changes in PSP-null PDL morphology were most distinct in mice >4-months of age.

Conclusions: These results implicate SPARC and periostin as essential for the maintenance of the PDL, and provide impetus for further examination of overlapping mechanisms of SPARC and periostin.