Phosphorus Restriction Changes the Expression of Fibroblast Growth Factor 23 and Its Receptors in Laying Hens

Abstract

Dietary phosphorus oversupply wastes non-renewable natural resources and raises environmental concerns in animal agriculture. We hypothesized that laying hens do not need large safety margins for dietary phosphorus because of the existence of fibroblast growth factor 23 (FGF23). In experiment 1, a total of 504 Hy-Line Brown laying hens (40-week-old) were randomly assigned to seven diets (for each diet, six replicates of 12 hens), containing 0.12, 0.17, 0.22, 0.27, 0.32, 0.37, and 0.42% non-phytate phosphorus, respectively, for 15 weeks. In experiment 2, a total of 14 Hy-Line Brown laying hens (40-week-old) were randomly assigned to two diets: (1) phosphorus restricted (n = 7) diet containing 0.14% non-phytate phosphorus, and (2) regular phosphorus (n = 7) diet containing 0.32% non-phytate phosphorus, for 21 days. Laying performance and egg quality were investigated in experiments 1 and 2. Phosphorus excretion and physiological changes were determined in experiment 2. It was found that dietary non-phytate phosphorus levels had no effects (P > 0.05) on laying performance and egg quality in either experiment. In experiment 2, laying hens fed 0.14% non-phytate phosphorus had decreased phosphorus excretion (by 52.6%, P < 0.001) when compared to those fed 0.32% non-phytate phosphorus. In response to the 0.14% non-phytate phosphorus diet, laying hens in experiment 2 exhibited: (1) suppressed calvaria mRNA expressions of FGF23 (by 57.8%, P < 0.001) and fibroblast growth factor receptor 1 (FGFR1, by 52.8%, P = 0.012), (2) decreased serum levels of FGF23 (by 41.7%, P = 0.011) and phosphorus (by 40.3%, P < 0.001), (3) decreased kidney mRNA expressions of FGFR1 (by 66.0%, P = 0.040) and FGFR4 (by 63.3%, P = 0.012) and decreased kidney protein expression of type 2a sodium-phosphorus co-transporter (NPt2a, by 51%, P = 0.025), (4) increased duodenum protein expression of NPt2b (by 45%, P = 0.032), and (5) increased excretion of calcium (by 22.9%, P ≤ 0.024). Collectively, decreasing dietary non-phytate phosphorus by up to 0.12% had no negative effects on egg-production performance but significantly decreased phosphorus excretion in laying hens. The laying hens adjusted to low-phosphorus diets by increasing intestinal NPt2b protein production, which was associated with decreased serum FGF23 concentration. Decreasing dietary non-phytate phosphorus is suggested to laying-hen nutritionists.

The adaptability of Hy-Line Brown laying hens to low-phosphorus diets supplemented with phytase

“…In addition, phytase, the most widely used dietary exogenous enzyme in animal production ( Adeola, 2011 ), breaks down phytate-phosphate from plant feed ingredients and dramatically reduces the animals' requirement for inorganic phosphorus ( Fernández et al., 2019 ). Interestingly, while the aforementioned technologies have repeatedly been documented in the literature, it still remains unclear in the field that how much inorganic phosphate rock will need be supplemented into poultry diets when those technologies are applied ( Li et al., 2015 , Adhikari et al., 2020 , Ren et al., 2020 ).…”

Dietary vitamin D3 deprivation suppresses fibroblast growth factor 23 signals by reducing serum phosphorus levels in laying hens

“…Our results showed that dietary vitamin D 3 deficiency reduces the mRNA expression of FGFR (including FGFR1 , FGFR2 , FGFR3 and FGFR4 ) and VDR in the calvaria, but has no effect on the liver. Hepatic FGF23 mRNA expression is not sensitive to dietary phosphorus, nicotinamide and vitamin D 3 levels ( Ren et al., 2020b , 2020c ), suggesting that FGF23 may be related to other physiological functions in laying hens. Calvaria FGFR1 can sense changes in extracellular phosphorus levels and regulate the production of FGF23 ( Takashi et al., 2019 ).…”

“…Calvaria FGFR1 can sense changes in extracellular phosphorus levels and regulate the production of FGF23 ( Takashi et al., 2019 ). Similarly, serum phosphorus could change FGFR1 expression in the calvaria, which is an important factor in regulating the secretion of FGF23 ( Ren et al., 2020b ). It cannot be ignored that these receptors play an important role in osteogenic development, cartilage proliferation and bone loss, thereby regulating the calcium and phosphorus homeostasis of bones ( Arnold et al, 2021 ; Starczak et al., 2018 ; Xie et al., 2020 ).…”

“…Briefly, eggshell thickness was measured using a dial pipe gauge (ETG-1061; Robotmation, Co., Ltd., Tokyo, Japan); eggshell strength was measured using a texture analyzer (EFG-0503; Robotmation, Co., Ltd., Tokyo, Japan); egg yolk color, albumen height, and Haugh units were tested using a multifunction egg quality analyzer (EMT-5200; Robotmation, Co., Ltd., Tokyo, Japan); specific gravity was measured using a flotation method in saline solutions; shell index was calculated as shell weight of whole egg; 2) 24-h total excreta from each laying hen was collected for the determination of phosphorus and calcium excretion; 3) calvaria, liver, intestinal mucosa (duodenum, jejunum and ileum) and kidney samples were collected after euthanasia, frozen in liquid nitrogen, and then transferred to a −80 °C freezer until further analysis. All experimental analysis methods were performed as previously described ( Liu et al., 2018 ; Ren et al., 2020b , 2020c ).…”

“…Obviously, such big differences on dietary vitamin D 3 levels would affect phosphorus metabolism physiology and FGF23 secretion status in poultry ( Jiang et al., 2015 ). Excessive FGF23 secretion has been considered as the major reason for low phosphorus utilization and high phosphorus excretion ( Ren et al., 2017 , 2020b ). Investigating the effects of dietary vitamin D 3 levels on FGF23 signals in avian species would help to broaden our understandings in phosphorus metabolism mechanisms and provide a guide for proper dietary vitamin D 3 addition in poultry.…”