Effects of glutaminase 1 inhibitor on rotator cuff derived cells: a preliminary report in 12 patients.

BACKGROUND: Glutaminase 1 (GLS1) degrades glutamate into glutamine and ammonia, and is required for the survival of senescent human cells. GLS1 inhibitors contribute to the improvement of various pathological conditions associated with aging. Rotator cuff tears (RCT) increase with age, and recently the Stump classification has been proposed to evaluate the fragility of the torn rotator cuff site, with Type 3 being the most fragile and a high risk of re-tear after rotator cuff repair surgery. We hypothesized that GLS1 expression is upregulated in the degenerated rotator cuff and that GLS1 inhibitors would improve rotator cuff degeneration. In this study, we evaluated the effects of GLS1 inhibitors on human rotator cuff-derived cells. METHODS: Twelve patients who underwent surgery for RCT were included in this study. Rotator cuff tissue was harvested during arthroscopic repair for tissue and cell evaluation. Tissue evaluation involved quantitative assessment of mRNA expression of GLS1 using real-time PCR (qPCR) and immunostaining. Rotator cuff-derived cells were isolated and cultured, divided into four groups: (1) Control group (without IL-1β and GLS1 inhibitor), (2) IL-1β(-)/GLS1 inhibitor(+), (3) IL-1β(+)/GLS1 inhibitor(-), (4) IL-1β(+)/GLS1 inhibitor(+). Cell viability was evaluated by WST assay and mRNA expression was evaluated by qPCR at 48 h after treatment. The expression of p16 and Scleraxis (SCX) was also evaluated by fluorescent immunostaining. RESULTS: Tissue evaluation showed significantly higher expression of GLS1 in Stump classification Type 3. Cell viability was significantly decreased by IL-1β loading and increased by the GLS1 inhibitor. The mRNA expression levels of GLS1, IL-6, p16 and p21 were decreased by the GLS1 inhibitor. The mRNA expression of the tendon markers, type 1 collagen, Mohawk and SCX were increased by the GLS1 inhibitor. Immunostaining revealed that the GLS1 inhibitor decreased p16 expression and increased SCX expression. CONCLUSIONS: This study showed that GLS1 was upregulated in the degenerated rotator cuff, and that the administration of a GLS1 inhibitor decreased inflammation and aging markers while increasing cell viability and tendon markers in rotator cuff-derived cells. These results indicate that GLS1 inhibitors exert anti-inflammatory effects in rotator cuff tears, prevent age-related degeneration of the rotator cuff, and promote tendon repair.