Acute exposure of 532 nm laser differentially regulates skin tissue transcription factors

Abstract

High energy laser, particularly 532 nm, is widely used in defense and medical applications and there is need to address its occupational safety. Thermal and non-thermal effects of 532 nm high energy laser on skin are cause of concern. This study indicates impact of 532 nm laser on rat skin and first of its kind of attempt to understand transcriptional activation of genes as an early response following laser exposure. Skin of experimental rats were exposed to 532 nm radiance at 0.1, 0.25 and 0.50 W/cm2 for 10 sec. Thermographic changes of skin exposed to 532 nm laser exhibited increased Tmax temperature in radiance dependent manner. After thermal imaging, skin of experimental rats was collected 1 h post laser exposure for studying differential gene expression. The skin exposed to lower power density (0.1 W/cm2) did not show significant changes in expression of gene pathways studied. At moderate radiance (0.25 W/cm2), predominantly canonical wnt/B-catenin pathway genes notch1, axin2, ccdn1, wnt5a and redox homeostasis genes; txn1, nqo1 and txnrd1 were expressed. At higher radiance (0.5 W/cm2), significant repression of genes related to wound healing process particularly notch/wnt pathway viz. hes5, wnt1, wn3b with higher expression of dab2 was recorded. The data obtained from these studies would help in drawing safety limits for skin exposure to 532 nm laser. Further, genes expressed at moderate and high level of radiance exposure to skin were distinct and differential and provide new avenue to configure pathway to counteract laser induced delay in tissue injury and hair follicular damage.

Fig 1. Dosimetry studies of rat skin exposed to 532 nm laser.

Fig 1A represent unexposed rat skin while Fig 1B–1F presents shows rat skin exposed to 532 nm laser at various fluences; 0.1 W/cm² (B), 0.25 W/cm² (C), 0.5 W/cm² (D), 1.0 W/cm² (E), 1.5 W/cm² (F) and 2.0 W/cm² (H).

Fig 2. Morphometric analysis and thermal imaging of rat skin exposed to 532 nm laser.

Thermogram of exposed rat skin to 532 nm laser at various fluences vs respective baseline thermogram is: 0.1 W/cm² (B1) vs A1, 0.25 W/cm² (B2) vs A2 and 0.5 W/cm² (B3) vs A3. Fig 1C shows Tmax data and temperature difference between exposed and unexposed rat skin.

Fig 3. Volcano plot of genes expressed following 532 nm laser exposure at low irradiance of 0.10 W/cm².

Fig 4. Volcano plot of genes expressed following 532 nm laser exposure at moderate irradiance of 0.25 W/cm².

Fig 5. Volcano plot of genes expressed following 532 nm laser exposure at high radiance of 0.5 W/cm².

Fig 6. Volcano plot of intergroup comparison of genes expressed following 532 nm laser exposure at low irradiance (0.10 W/cm²) and moderate irradiance (0.25 W/cm²).

Fig 7. Volcano plot of intergroup comparison of genes expressed following 532 nm laser exposure at low irradiance (0.10 W/cm²) and high irradiance (0.50 W/cm²).

Fig 8. Volcano plot of intergroup comparison of genes expressed following 532 nm laser exposure at moderate irradiance (0.25 W/cm²) and high irradiance (0.50 W/cm²).

Fig 9

Validation of genes; ho1 gene (A) and ppard gene (B) using q-PCR in rat skin exposure 532 nm laser. The fold change for 0.1 W/cm² exposure was negligible to unexposed group and hence not depicted on graph.

Fig 10

Effect of 532 nm laser exposure on total antioxidant status (A) and expression of hemeoxygenase 1 (B) and erythropoietin (C) in rat skin. *p<0.05.

Fig 11. Clustergram of genes expressed significantly following 532 nm laser exposure at moderate irradiance of 0.25 W/cm².

Fig 12. Clustergram of genes expressed significantly following 532 nm laser exposure at high irradiance of 0.50 W/cm².