Piscine PTHrP regulation of calcium and phosphate transport in winter flounder renal proximal tubule primary cultures

Abstract

Multiple factors control calcium (Ca(2+)) and inorganic phosphate (P(i)) transport in the fish nephron, and the recently discovered members of the piscine parathyroid hormone-like protein family are likely participants in such regulatory mechanisms. The effects of an NH(2)-terminal peptide (amino acids 1-34) of Takifugu rubripes parathyroid hormone-related protein, (1-34)PTHrP, on Ca(2+) and P(i) transport were investigated in winter flounder (Pseudopleuronectes americanus) proximal tubule cells in primary culture (fPTCs). RT-PCR performed on RNA extracted from fPTCs and from intact kidney tissue indicated that expression of PTHrP and types 1 and 3 PTH/PTHrP receptors occurred both in vivo and in vitro and that circulating levels of PTHrP measured by specific radioimmunoassay averaged 2.5 +/- 0.13 ng/ml. fPTC monolayers were mounted in Ussing chambers, and under neutral electrochemical conditions, addition of 10 nM (1-34)PTHrP to the basolateral side induced a slight increase in Ca(2+) transport rate from luminal to peritubular side, significantly stimulating net Ca(2+) reabsorption. (1-34)PTHrP also significantly increased the P(i) secretory flux, and slightly reduced P(i) reabsorption, evoking a significant increase in P(i) net secretion. This stimulatory effect was partially inhibited by bisindolylmaleimide, an inhibitor of protein kinase C. Incubation of ex vivo flounder renal tubules with (1-34)PTHrP resulted in apparent reduction of Na(+)-P(i) cotransporter type II (NaP(i)-II) protein in tubule membranes. PTHrP seems therefore to participate in the modulation of Ca(2+) and P(i) homeostasis by fish kidney.

Pth4, an ancient parathyroid hormone lost in eutherian mammals, reveals a new brain‐to‐bone signaling pathway

“…We demonstrated that Pth4 can recognize the 3 zebrafish Pth receptors (i.e., Pth1ra, Pth1rb, and Pth2r) to activate cAMP/PKA signaling. In fish, previous analyses by real‐time PCR found that pth2r was expressed in the central nervous system, kidney and scales (23, 45, 50), and pth1rb in the kidney, intestine, and vertebral bone (51–53). In the current study, WISH revealed that pth1ra is expressed in the gills, intestinal epithelium, craniofacial bones, and spinal cord Fig.…”

“…Six peptides and 3 receptors had been identified previously, revealing a higher complexity of this gene family in noneutherian vertebrates than in eutherians. Pthlh (i.e., Pth3) has been reported to promote calcium uptake from surrounding water via branchial and intestinal epithelia (61), stimulating calcium reabsorption and phosphate secretion through Npt2a in the kidney (53) and promoting osteoclast activity in scales via Pthr (62). In addition to calcium uptake, Pth3 seems to affect Pi concentrationinthe serumoffishspecies (10).…”

PTH Reloaded: A New Evolutionary Perspective

“…Additionally, a study has demonstrated that intermittent administration of Pth3 in seabream caused a modification of the bone proteome suggesting an anabolic response on the skeleton (Anjos et al, 2013 ). Besides Pth3 also stimulates renal phosphate secretion in winter flounder (Guerreiro et al, 2010 ). Regarding to the involvement in embryonic development of the skeleton, zebrafish Pth3 seems to have a conserved role to that of mammals.…”

“…In fish, three receptors have been isolated Pth1r(Pth1ra), Pth2r and Pth3r(Pth1rb) (Rubin and Juppner, 1999 ) but the affinity, specificity, and the physiological roles are far from defined. Pth1ra is expressed in scales and vertebral bone of seabream (Rotllant et al, 2005 ; Anjos et al, 2013 ), in kidney of winter flounder (Guerreiro et al, 2010 ), and gills, scales, craniofacial bones, intestine, kidney, spine, brain and spinal cord in zebrafish (Kwong and Perry, 2015 ; Suarez-Bregua et al, 2017 ). Pth1rb is expressed in vertebral bone and intestine of seabream (Rotllant et al, 2005 ; Anjos et al, 2013 ), gills and bone of zebrafish (Kwong and Perry, 2015 ), and kidney in winter flounder (Guerreiro et al, 2010 ) suggesting, therefore, a potential role in calcium-phosphate balance in fish similar to Pth1ra.…”

“…Pth1ra is expressed in scales and vertebral bone of seabream (Rotllant et al, 2005 ; Anjos et al, 2013 ), in kidney of winter flounder (Guerreiro et al, 2010 ), and gills, scales, craniofacial bones, intestine, kidney, spine, brain and spinal cord in zebrafish (Kwong and Perry, 2015 ; Suarez-Bregua et al, 2017 ). Pth1rb is expressed in vertebral bone and intestine of seabream (Rotllant et al, 2005 ; Anjos et al, 2013 ), gills and bone of zebrafish (Kwong and Perry, 2015 ), and kidney in winter flounder (Guerreiro et al, 2010 ) suggesting, therefore, a potential role in calcium-phosphate balance in fish similar to Pth1ra. Finally, despite the expression of pth2r has been demonstrated in brain, eye, notochord, otic vesicle, pharyngeal arches, ovary and testis in zebrafish (Bhattacharya et al, 2011 ; Kwong and Perry, 2015 ), its function remains poorly understood.…”