Chronobiologic study of the GH-IGF1 axis and the ageing immune system

SINE Insertion in the Intron of Pig GHR May Decrease Its Expression by Acting as a Repressor

Simple Summary

GH/IGF axis genes play a central role in the regulation of skeletal accretion during development and growth, and thus represent candidate genes for growth traits. Retrotransposon insertion polymorphisms are major contributors to structural variations. They tend to generate large effect mutations resulting in variations in target gene activity and phenotype due to the fact that they carry functional elements, such as enhancers, insulators, or promoters. In the present study, RIPs in four GH/IGF axis genes (GH, GHR, IGF1, and IGF1R) were investigated by comparative genomics and PCR. Four RIPs in the GHR gene and one RIP in the IGF1 gene were identified. Further analysis revealed that one RIP in the first intron of GHR might play a role in the regulation of GHR expression by acting as a repressor. These findings contribute to the understanding of the role of RIPs in the genetic variation of GH/IGF axis genes and phenotypic variation in pigs.

Abstract

The genetic diversity of the GH/IGF axis genes and their association with the variation of gene expression and phenotypic traits, principally represented by SNPs, have been extensively reported. Nevertheless, the impact of retrotransposon insertion polymorphisms (RIPs) on the GH/IGF axis gene activity has not been reported. In the present study, bioinformatic prediction and PCR verification were performed to screen RIPs in four GH/IGF axis genes (GH, GHR, IGF1 and IGF1R). In total, five RIPs, including one SINE RIP in intron 3 of IGF1, one L1 RIP in intron 7 of GHR, and three SINE RIPs in intron 1, intron 5 and intron 9 of GHR, were confirmed by PCR, displaying polymorphisms in diverse breeds. Dual luciferase reporter assay revealed that the SINE insertion in intron 1 of GHR significantly repressed the GHR promoter activity in PK15, Hela, C2C12 and 3T3-L1 cells. Furthermore, qPCR results confirmed that this SINE insertion was associated with a decreased expression of GHR in the leg muscle and longissimus dorsi, indicating that it may act as a repressor involved in the regulation of GHR expression. In summary, our data revealed that RIPs contribute to the genetic variation of GH/IGF axis genes, whereby one SINE RIP in the intron 1 of GHR may decrease the expression of GHR by acting as a repressor.

Rheumatoid arthritis and the biological clock

Rheumatoid arthritis (RA) is an autoimmune disease of unknown cause and a chronic and progressive inflammatory disorder ensuing in genetically predisposed subjects, characterized by synovitis causing joint destruction, as well as inflammation in body organ systems, leading to anatomical alteration and functional disability. Immune competent cells, deregulated synoviocytes and cytokines play a key role in the pathophysiological mechanisms. The immune system function shows time-related variations related to the influence of the neuroendocrine system and driven by the circadian clock circuitry. Immune processes and symptom intensity in RA are characterized by oscillations during the day following a pattern of circadian rhythmicity. A cross-talk between inflammatory and circadian pathways is involved in RA pathogenesis and underlies the mutual actions of disruption of the circadian clock circuitry on immune system function as well as of inflammation on the function of the biological clock. Modulation of molecular processes and humoral factors mediating in RA the interplay between the biological clock and the immune response and underlying the rhythmic fluctuations of pathogenic processes and symptomatology could represent a promising therapeutic strategy in the future.

Crosstalk between the circadian clock circuitry and the immune system

Various features, components, and functions of the immune system present daily variations. Immunocompetent cell counts and cytokine levels present variations according to the time of day and the sleep-wake cycle. Moreover, different immune cell types, such as macrophages, natural killer cells, and lymphocytes, contain a circadian molecular clockwork. The biological clocks intrinsic to immune cells and lymphoid organs, together with inputs from the central pacemaker of the suprachiasmatic nuclei via humoral and neural pathways, regulate the function of cells of the immune system, including their response to signals and their effector functions. Consequences of this include, for example, the daily variation in the response to an immune challenge (e.g., bacterial endotoxin injection) and the circadian control of allergic reactions. The circadian-immune connection is bidirectional, because in addition to this circadian control of immune functions, immune challenges and immune mediators (e.g., cytokines) were shown to have strong effects on circadian rhythms at the molecular, cellular, and behavioral levels. This tight crosstalk between the circadian and immune systems has wide-ranging implications for disease, as shown by the higher incidence of cancer and the exacerbation of autoimmune symptoms upon circadian disruption.