Deconvoluting Wavelengths Leading to Fluorescent Light Induced Inflammation and Cellular Stress in Zebrafish (Danio rerio)

Abstract

Fluorescent light (FL) has been shown to induce a cellular immune and inflammatory response that is conserved over 450 MY of evolutionary divergence and among vertebrates having drastically different lifestyles such as Mus musculus, Danio rerio, Oryzias latipes and Xiphophorus maculatus. This surprising finding of an inflammation and immune response to FL not only holds for direct light receiving organs (skin) but is also observed within internal organs (brain and liver). Light responsive genetic circuitry initiated by the IL1B regulator induces a highly conserved acute phase response in each organ assessed for all of biological models surveyed to date; however, the specific light wavelengths triggering this response have yet to be determined so investigation of mechanisms and/or light specific molecule(s) leading to this response are difficult to assess. To understand how specific light wavelengths are received in both external and internal organs, zebrafish were exposed to specific 50 nm light wavebands spanning the visible spectrum from 300-600 nm and the genetic responses to each waveband exposure were assessed. Surprisingly, the induced cellular stress response previously observed following FL exposure is not triggered by the lower "damaging" wavelengths of light (UVB and UVA from 300-400 nm) but instead is maximally induced by higher wavelengths ranging from 450-500 nm in skin to 500-600 nm in both brain and liver).

Figure 1

Spectral distribution of natural sunlight in San Marcos, TX at noon (top, A) and Phillips 4100 K cool white bulbs used for the FL exposures (bottom, B).

Figure 2

NanoString nCounter technology was used to confirm the fold changes determined using EdgeR in skin (blue), brain (orange) and liver (gray).

Figure 3

FL modulated pathways in zebrafish skin, brain and liver consistent with an up-regulation of the immune and inflammatory response. 50 nm regions were surveyed from 300–600 nm to determine which specific wavelengths were responsible for this response. Red indicates specific canonical pathways as determined by IPA that had a z-score of > 2 and green represent pathways with a z-score < 2. The numbers inside of each box represent the IPA determined z-score of modulation. Both 400–450 and 450–500 nm reflected the FL response in skin; 500–550 nm in brain and 550–600 nm in liver. The primary waveband mimicking the FL response is highlighted in blue for each organ. To see the number of genes represented in each pathway see Fig. S1.

Figure 4

Upstream regulators modulated by discrete 50 nm wavebands that are also modulated by FL. Genes with an * are oppositely modulated following 50 nm exposure compared to the complex FL exposure. We observed both light responsive gene expression (ie. genes modulated in response to all light stimuli; INSR and SREBF1) and waveband specific gene expression (ie. genes modulated in response to only discrete wavelengths).

Figure 5

Upstream regulators modulated in FL and the two primary shared wavebands within the FL spectrum. While both regions have significant gene identity sharing with the FL exposed brain samples, the 300–350 nm region oppositely modulated genes compared to FL and the 500–550 nm region modulated genes in the same direction as FL (Table 2).

Figure 6

Upstream regulators modulated in liver by both FL and 500–550 nm (left) or 550–600 nm (right). IL1B, TNF and NFkB complex are up modulated following both wavebands. The 500–550 nm region on the left is primarily responsible for the up-regulation of cell cycle progression and DNA repair and the 550–600 nm region is primarily responsible for the immune and inflammatory response. Both are regulated and controlled by the IL1B regulator which is the top modulated regulator in the liver FL response.