Lubricin Restoration in a Mouse Model of Congenital Deficiency

Abstract

Objective Congenital deficiency of the principal boundary lubricant in cartilage (lubricin, encoded by the gene PRG4) increases joint friction and causes progressive joint failure. This study was undertaken to determine whether restoring lubricin expression would prevent, delay, or reverse the disease process caused by congenital deficiency. Methods Using genetically engineered lubricin deficient mice, we restored gene function before conception or at 3 weeks, 2 months, or 6 months after birth. We evaluated the effect of restoring gene function (i.e., expressing lubricin) on the tibial-femoral-patellar joints of mice, histologically and by ex vivo biomechanical testing. Results Restoring gene function prior to conception prevented disease. Restoring gene function at 3 weeks of age improved, but did not normalize, joint histology and whole joint friction; cyclic loading produced fewer activated caspase-3 containing chondrocytes when lubricin expression was restored at three weeks of age compared to non-restored littermates. Restoring lubricin expression in 2-month-old or 6-month-old mice had no beneficial effect on histology, whole joint friction, or activation of caspase-3 compared to non-restored littermates. Conclusions When boundary lubrication is congenitally deficient and cartilage becomes damaged, the window of opportunity for restoring lubrication and slowing disease progression is limited.

Arthroscopic irrigation of the bovine stifle joint increases cartilage surface friction and decreases superficial zone lubricin

“…However, other studies are teaching us about how long a joint can withstand temporary elevated friction. Hill et al found that restoring PRG4 gene function in a gene trap mouse at 3 weeks improved of friction and chondrocyte viability compared to restoration at 2 and 6 months after birth (Hill et al, 2015). Adding purified human synoviocyte lubricin to CACP synovial fluid and testing this as a lubricant in bovine cartilage friction experiments produced similar static and dynamic COF values as wild-type human synovial fluid (Waller et al, 2013).…”

Early genetic restoration of lubricin expression in transgenic mice mitigates chondrocyte peroxynitrite release and caspase-3 activation

“…Details describing this mouse been reported previously. [21] To excise the gene trap, the cre allele, ROSA26 CreERT2 (Jax strain 008423), was used which allows widespread excision of the gene trap following intraperitoneal injections of tamoxifen. Colonies of Prg4 GT/GT ; ROSA26 CreERt 2/+ ( Prg4 GT/GT ) mouse genotype (Jax strain 025740), lubricin knockout mice Prg4 −/− (Jax strain 025737), and lubricin wild type mice Prg4 +/+ (Jax strain 000664) were used for this study.…”

“…Three separate groups of mice from various genotypes were assessed for different experiments. Power analysis for the first group of mice was supported by the effect size in Hill et al[21] The first group of mice (N=39 total mice) was used for biomechanical analysis and assessment of joint damage, caspase-3, and hyaluronic acid content. Scientists were blinded for all studies completed with the first group of mice.…”

“…[17–20] Recently, it was shown in 8-week-old, lubricin-null gene trap mice that recombination at 21 days produced less activation of caspase-3 in chondrocytes and displayed improved, but not normalized, histological features and whole joint coefficient of friction (COF) compared to their lubricin-null, non-recombined counterparts. [21] The aforementioned study also showed that restoring lubricin gene function prior to conception prevented arthrosis and joint disease. [21]…”

“…[21] The aforementioned study also showed that restoring lubricin gene function prior to conception prevented arthrosis and joint disease. [21]…”