Alimentary myo-inositol and low phosphate in two contrasting high-yielding laying hen strains: role of alpha-Klotho/fibroblast growth factor 23 (FGF23)

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FGF23 (fibroblast growth factor 23) was discovered in mammals and is mainly produced in bone. As a hormone, it regulates renal reabsorption of phosphate and formation of 1,25(OH)2D3, biologically active vitamin D. These endocrine effects are mediated by a membrane receptor requiring transmembrane protein Klotho as a co-receptor. While FGF23 is of high relevance in clinical medicine as a disease biomarker due to kidney and cardiovascular diseases being associated with early surges in plasma FGF23, Klotho is a powerful anti-aging factor. Also in laying hens, both proteins were detected with FGF23 being expressed in liver and Klotho in kidney. Similar to mammals, they are involved in the regulation of phosphate homeostasis. However, the details are far less characterized than in mammals. The project seeks to characterize (i) the impact of myo-inositol supplementation at high egg production performance on regulators of phosphate metabolism, Klotho and FGF23 in laying hens, (ii) the role of Klotho and FGF23 in laying hens forced to enhance phytic acid (InsP6) utilization due to mineral P deficiency, (iii) the significance of the genetic background of laying hens for Klotho and FGF23 in phosphorus deficiency, and (iv) the dependence of Klotho and FGF23 expression in laying hens on parathyroid hormone, 1,25(OH)2D3, plasma Ca2+/phosphate levels (project 3), inflammation (project 7), AMPK and insulin (project 5) as well as mitochondrial heteroplasmy (project 8). The investigations will contribute to a better understanding of the regulation of phosphate homeostasis in laying hens. This will likely result in better welfare of animals as well as lower phosphate exposure of the environment.