Candidate genes of the transcellular and paracellular calcium absorption pathways in the small intestine of laying hens

Abstract

To meet the high calcium (Ca) demand during eggshell biomineralization (2 g of Ca per egg), laying hens develop specific metabolic regulations to maintain Ca homeostasis. The intake of Ca, its solubilization, and absorption capacity are enhanced at sexual maturity (SM). A better knowledge of the intestinal Ca transporters involved in their variations at this stage could indicate new nutritional strategies to enhance Ca digestive utilization. Transcellular Ca absorption pathway and its major player calbindin-D 28 K (CALB1) mediate a saturable transport, which has been extensively described in this model. Conversely, a contribution by the paracellular pathway involving non-saturable Ca transport through intercellular tight junction has also been suggested. The aim of the present study was to identify candidate genes of these two pathways and their patterns of expression, in immature pullets (12, 15, and 17 wk old) and mature laying hens (23 wk old) in the duodenum, jejunum, and ileum. Using RT-qPCR, this study identifies 3 new candidate genes for transcellular, and 9 for paracellular Ca transport. A total of 5 candidates of the transcellular pathway, transient receptor potential cation channels subfamily C member 1 (TRPC1) and M member 7 (TRPM7); CALB1 and ATPase plasma membrane Ca2+ transporting 1 (ATP2B1) and ATPase plasma membrane Ca2+ transporting 2 (ATP2B2) were enhanced with age or after SM in the duodenum, the jejunum or all 3 segments. A total of 4 candidates of the paracellular pathway Claudin 2 (CLDN2) and tight junction proteins 1, 2, and 3 (TJP1, TJP2 and TJP3) increased in the small intestine after SM. Additionally, CALB1, ATP2B2, and CLDN2 were overexpressed in the duodenum or the jejunum or both segments after SM. The enhanced expression of candidate genes of the paracellular Ca pathway after SM, supports that the non-saturable transport could be a mechanism of great importance when high concentrations of soluble Ca are observed in the intestinal content during eggshell formation. Both pathways may work cooperatively in the duodenum and jejunum, the main sites of Ca absorption in laying hens.

Phytate Degradation, Transcellular Mineral Transporters, and Mineral Utilization by Two Strains of Laying Hens as Affected by Dietary Phosphorus and Calcium

“…In laying hens, SLC34A2 showed a remarkable mRNA copy number in the ileum, suggesting that it is a relevant transcellular P transporter in the intestine of poultry. Correspondingly, SLC20A1 has been reported to be expressed in the mid and posterior intestine, including the ileum, underlining its contribution to P absorption in this segment [ 25 ]. In view of the strain-specific intestinal capacity of phytate degradation in LB and LSL laying hens, the results of the ileal mineral P transporters suggest compensatory mechanisms in LB hens to balance P absorption.…”

Avian eggshell biomineralization: an update on its structure, mineralogy and protein tool kit

“…Uterine Ca 2+ secretion is quantitatively associated with calbindin levels and the regulation of uterine calcium transfer in conjunction with its synthesis has been studied in detail [ 20 , 29 ]. The regulation of molecular actors involved in the supply of calcium in intestine, are dependent on the active metabolite of vitamin D [ 96 ]. However, this regulation is poorly documented for the avian uterus.…”

A new model for vertebrate mineralization via stabilized amorphous calcium carbonate for avian eggshell formation

“…A paracellular Ca 2+ uptake pathway was recently described in intestine that acts to replenish calcium stores from dietary sources during eggshell biomineralization. The paracellular pathway involves claudins (CLDN), occludins (OCN), junctional adhesion molecules (JAM) and tight junction proteins (TJP) (45). Our uterine RNA-Seq analysis reveals elevated expression of several genes of this paracellular pathway (Tjp1, Cldn1, Cldn10, Ocln, Jam2) (https://anr.fr/Projet-ANR-13-BSV6-0007).…”

“…Mechanisms of transepithelial transfer of calcium and bicarbonates have been widely studied and represent the current accepted model for eggshell mineralization (23,26,27). Recently, intestinal paracellular transfer of calcium during eggshell formation was demonstrated (45), raising the possibility of paracellular transfer of calcium in uterus as well; however, no experimental data addressing this possibility is yet available. The vesicular transport of calcium is a third complementary pathway to transfer stabilized ACC to the calcification site.…”