Modulation of renal calcium and phosphate transporting proteins by dietary nitrogen and/or calcium in young goats1

Abstract

In young goats, a reduction in dietary nitrogen (N) had an impact on mineral homeostasis although ruminants are able to recycle N effectively due to rumino-hepatic circulation. A solitary calcium (Ca) reduction stimulated calcitriol synthesis and Ca concentrations remained unchanged, whereas a dietary N reduction led to a decrease in calcitriol, which could not be prevented by a simultaneous reduction of N and Ca. In a previous study, it was shown that a reduced dietary N intake caused a decrease in intestinal Ca absorption due to a reduction of intestinal Ca transporting proteins. As no data on the potential role of the kidneys are available, it was the aim of the present study to evaluate whether an N- and/or Ca-reduced diet had an impact on renal Ca and phosphate (Pi) transporting protein expression in young goats. The animals were divided into 4 feeding groups, each receiving an adequate N and Ca supply, a reduced N supply, a reduced Ca supply, or a combined N and Ca reduction for 6 to 9 wk. The protein expression of the renal Ca channel transient receptor potential cation channel subfamily V member 5 (TRPV5) was diminished in N-reduced fed goats (P = 0.03), whereas in Ca restricted animals, the expression remained unaltered. The mRNA and protein expression of the Ca-binding protein calbindin-D28K (CaBPD28K) and the sodium-Ca exchanger 1 (NCX1) were significantly decreased due to the N-reduced feeding (mRNA, P = 0.003; P < 0.0001; protein, P = 0.002; P = 0.02), whereas dietary Ca reduction increased the CaBPD28K and NCX1 mRNA expression (P = 0.05; P = 0.01). The mRNA and protein expression of the parathyroid hormone receptor (PTHR) decreased due to the N-reduced feeding (P = 0.02; P = 0.03). These results confirm that a reduced dietary N intake led to decreased TRPV5, CaBPD28K, PTHR, and NCX1 expression levels, contributing to low levels of calcitriol and plasma Ca. In contrast to this, sodium-phosphate cotransporter type IIa expression and plasma Pi concentration were increased during dietary N reduction, thus indicating that Pi homeostasis is modulated in a calcitriol-independent manner. In conclusion, the modulation of Ca transporting proteins expression in the kidney is not able to prevent changes in mineral homeostasis in young goats receiving an N-reduced diet.

Review: Regulation of gastrointestinal and renal transport of calcium and phosphorus in ruminants

“…This is in line with data from balance studies conducted with goat kids (Table 1). A concomitant decrease in dietary Ca and protein in these young animals caused a decrease in 1,25-(OH) 2 D 3 concentrations, resulting in a downregulation of TRPV5, CaBP D28K and NCX1 protein expressions (Firmenich et al, 2018).…”

“…A significant increase in NaPi IIa expression and a concomitant decrease in PTH receptor expression were observed in young goats (4 to 5 months) when dietary protein was diminished. The concentration of 1,25-(OH) 2 D 3 was reduced while PTH levels were not affected (Starke et al, 2013;Starke and Huber, 2014;Firmenich et al, 2018). The stimulation of NaPi IIa expression during a protein-reduced diet is not obvious.…”

Effects of dietary nitrogen and/or phosphorus reduction on mineral homeostasis and regulatory mechanisms in young goats

“…The protein sequences were verified for their homology with NCBI Blast (see text footnote 1). Immunoblot assays detecting the expression of ERK1/2, NaPi IIa and Na + /K + ATPase proteins in caprine tissue were performed as described elsewhere (5,37). Membranes were incubated solely with the secondary antibody to ensure exclusive detection of specific signals.…”

“…Previous studies have shown that goats fed reduced N diets had lower blood calcium (Ca) levels (4,5). In a study by Muscher and Huber (4), N-reduction also resulted in alterations in vitamin D metabolism.…”

Expression of Phosphatonin-Related Genes in Sheep, Dog and Horse Kidneys Using Quantitative Reverse Transcriptase PCR

“…The opposite appears to be the case in humans [ 15 , 16 ]. However, while the expression of phosphatonin-related proteins is relatively well described in the kidneys of goats [ 17 , 18 , 19 ] and in the intestines of horses, goats and cattle [ 20 , 21 , 22 , 23 ], knowledge on the expression of phosphatonin-related proteins in the kidneys of most domestic species is lacking.…”