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“Lighten-Up to Relax”: Photo-mediated human uterine smooth muscle relaxation as a novel tocolytic strategy.
Abstract Number: BP-4
Abstract Type: Original Research
Preterm labor is major risk factor for perinatal morbidity and mortality. The issue is further magnified by a lack of efficacious treatment options. Recent studies demonstrate light-induced relaxation of pre-contracted vascular smooth muscle occurs via an opsin 4 G-protein coupled receptor pathway (1). We questioned if uterine smooth muscle (USM) demonstrates similar photo-mediated relaxation via an OPSIN-family GPCR signaling pathway.
Human USM tissue was collected and screened for Opsin 3,4 and 5 mRNA expression utilizing 2 step RT/PCR. Ex vivo functional organ bath studies were performed with late gestation human USM. All USM strips were pre-contracted with 0.5 μM oxytocin and allowed to equilibrate for 1hour in the dark. Pretreatment with 9cis retinal (5.7 mM) and G protein receptor kinase (GRK) inhibitor (Methyl 5-[(E)-2-(5-nitrofuran-2-yl)ethenyl]furan-2-carboxylate, 20μM) was used to prevent ambient light desensitization. USM strips were then exposed to increasing intensity of white light (11.6-17.8 Log2 [lux]) or specific wavelengths (no light, 630nm (red), 532nm (green) or 405nm (blue). Changes in digital recordings of muscle force were recorded with Acknowledge software. Statistical analysis utilized ANOVA comparison with Bonferroni’s correction to assess differences between groups (p<0.05 taken as significant).
mRNA encoding opsin 3 and 4 were detected in human USM (Figure 1A).Pre-contracted human USM photo-mediated relaxation to white light (full visible spectrum) is dose/intensity dependent with significant relaxation seen at 11.7 Log2 [lux] and an IC50 of 14.69 Log2 [lux](Figure 1B,***p<0.001).Compiled results of percent change in Integral Force (g*sec) following treatment with specific wavelengths of light revealed significant relaxation in the treatment group receiving GRK inhibitor, 9cis retinal and 405nm blue light compared to changes in force measured in no light control (Figure 1C,***p<0.001).There was no significant change in force measured in human USM strips receiving GRK inhibitor, 9cis retinal and red (630nm) or green (532nm) light treatments, respectively (Figure 1C).
Human USM expresses mRNA for the Opsin 3 and 4 receptors.Photo-relaxation occurs in human USM in an intensity dependent and wavelength specific fashion.Focused light treatment may represent a novel non-invasive tocolytic approach.
(1) Sikka G et al. Proc Natl Acad Sci USA. 2014 Dec 16;111(50):17977-82.