All transcripts were created with artificial intelligence software and modified with manual review by a third party. Although we make every effort to ensure accuracy with the manual review, some may contain computer-generated mistranslations resulting in inaccurate or nonsensical word combinations, or unintentional language. FASEB and the presenting speakers did not review the transcripts and are not responsible and will not be held liable for damages, financial or otherwise, that occur as a result of transcript inaccuracies.
Ciliary Gene Variants Are Associated with Diabetes Phenotypes in the General Population and Modulate Insulin Signaling in Cell Models of Disease
Rare monogenic disorders of the primary cilium, termed ciliopathies, are characterized by extreme presentations of otherwise-common diseases, such as liver disease, obesity, and kidney failure. Intriguingly, many ciliopathies exhibit the later development of impaired glucose handling and type 2 diabetes mellitus (T2DM), which many studies show holds true even when adjusting for differences in BMI and diet. In fact, even patients with nonsyndromic ciliary disorders, such as autosomal dominant polycystic kidney disease, exhibit an unexplained predisposition to diabetes and insulin resistance. However, despite a revolution in our understanding of the cilium’s role in rare disease pathogenesis, the organelle’s contribution to common diseases, such as T2DM, remains largely unknown. We hypothesized that common genetic variants in Mendelian ciliopathy genes might contribute to the risk for T2DM and common complex diseases more broadly in the general population. We performed association studies of >17,000 common genetic variants across 122 well-characterized ciliary genes with 12 quantitative traits characteristic of ciliopathy syndromes (serum creatinine, serum glucose, etc.) and identified >100 significant ciliary gene-trait associations. Interestingly, certain classes of ciliary genes were more likely to be associated with specific disease traits; genes involved in intraflagellar transport (IFT) and receptor transport, for example, were found to be enriched for associations with diabetes-related traits but depleted for associations with kidneyrelated traits. These findings suggested that the cilium and ciliary genes involved in receptor transport might be contributing to the pathogenesis of T2DM in the general population.
To test this hypothesis, we assayed the effect of pharmacologic deciliation on insulin signaling in cell models of disease. Deciliation with either chloral hydrate or dibucaine significantly increase AKT phosphorylation in response to physiologic insulin doses compared to untreated, ciliated cells. In deciliated cells, insulin receptor itself showed exaggerated phosphorylation and activation in response to insulin, suggesting a specific role for the cilium in either the location, dynamics, or magnitude of insulin receptor activation. We next generated a library of CRISPR/Cas9-engineered cell lines heterozygous or homozygous for loss of function variants in the ciliary genes we identified as being significantly associated with diabetes-related phenotypes in our populationlevel informatic analysis. AKT activation in response to insulin is significantly perturbed in many of these cell lines, but with gene-specific differences in the magnitude and directionality of this effect. Homozygous knockout of IFT172 leads to a complete loss of cilia in cultured cells, and a 2-fold increase in AKT signaling in response to insulin; heterozygous loss of IFT172 does not result in any appreciable change in ciliation or cilium length, but results in a nearly 2-fold increase in AKT phosphorylation in response to physiologic insulin doses, similar to what is observed in the homozygous IFT172 knockout. On the other hand, while neither heterozygous nor homozygous loss of BBS4 leads to loss of cilia in cell models, homozygous null BBS4 cells have a 40% decrease in AKT phosphorylation in response to insulin dosing, while heterozygous loss of BBS4 has only a very minimal effect.
We are currently characterizing the role of additional ciliary genes in insulin receptor signaling and developing methods to specifically interrogate the mechanisms underlying the cilium’s contribution to this cellular process. We are implemented an AKT biosensor platform for use in live cells for the high throughput screening of compounds and genes that modulate ciliary phenotypes in insulin signaling, with the goal of identifying potentially druggable targets that could treat or prevent the development of diabetes both in ciliopathy patients in in diabetes patients more broadly.
Speakers
Theodore G. Drivas