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Teele Palumaa, Lewis Taylor, Marzhan Nurlankyzy, Betül Yücel, Stuart Neil Peirson, Russell Foster, Aarti Jagannath; The role of salt-inducible kinase 1 in retinal physiology and light responses. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5256.
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© ARVO (1962-2015); The Authors (2016-present)
Salt-inducible kinase 1 (SIK1) is an important regulator of the core circadian clock. Being induced by light in the organism’s master clock, located in the suprachiasmatic nuclei (SCN), it acts to limit the magnitude of clock shifts. Indeed, mice with an inactive SIK1 are able to rapidly adjust their activity in response to a change in the environmental light cycle, i.e. overcome an experimental jetlag. This is hypothesised to be mediated by SIK1 inhibiting the induction of clock genes in the SCN. Alternatively, this effect could be explained by changes in retinal function. We therefore aimed to characterise the retinal gene expression, morphology and pupil constriction dynamics in mice expressing an inactive form of SIK1.
SIK1 knock-in (KI) mice, expressing a catalytically inactive form of SIK1, and their wild-type (WT) littermate controls were used. Retinal gene expression was measured with qPCR following a sham or a 30-minute light pulse. The retinas were also subjected to standard immunohistochemical analysis. Pupil constriction was measured both at day and night.
Gene expression analysis revealed no differences in the amount of retinal opsins (S and M opsins, rhodopsin and melanopsin) in the SIK1 WT and KI retinas. The expression of clock components Clock, Bmal1, Per1, Per2, Cry1 and Cry2, and the induction of light-regulated genes Fos and Dio2 were similar between the genotypes (p>0.05, n=3-8). Immunohistochemical analysis showed no morphological differences of pRGCs, S and M cones, horizontal and bipolar cells between the genotypes (n=3). Maximum pupil constriction of SIK1 WT and KI animals did not differ at day or at night (day WT 9.8% vs KI 7.6% of initial pupil area, night WT 35.0% vs KI 35.2%, p>0.05, n=5-6). Intriguingly, however, the light intensity required to reach 50% pupil constriction was 0.3 log units higher for SIK1 KI animals than for WT (logEC50 WT 12.50 vs KI 12.79 log quanta, p=0.037, n=5-6).
Here we show that absence of catalytically active SIK1 in the retina does not alter the morphology of main retinal cell types, or the expression of opsins, clock or light-induced genes. The circadian rhythm of pupil constriction is also maintained in SIK1 KI animals. Interestingly, the absence of functional SIK1 leads to an attenuated pupillary light response. The magnitude of this effect is not, however, sufficient to explain the circadian phenotype of the SIK1 KI mice.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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