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Compensatory regulation of Na+ absorption by Na+/H+ exchanger and Na+-Cl- cotransporter in zebrafish (Danio rerio).

Chang WJ, Wang YF, Hu HJ, Wang JH, Lee TH, Hwang PP - Front. Zool. (2013)

Bottom Line: Environmental acid stress suppressed nhe3b expression in HR cells and decreased Na+ content, which was followed by up-regulation of NCC cells accompanied by recovery of Na+ content.Moreover, knockdown of ncc resulted in a significant decrease of Na+ content in acid-acclimated zebrafish.These results provide evidence that HR and NCC cells exhibit functional redundancy in Na+ absorption, similar to the regulatory mechanisms in mammalian kidney, and suggest this functional redundancy is a critical strategy used by zebrafish to survive in a harsh environment that disturbs body fluid Na+ homeostasis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan. pphwang@gate.sinica.edu.tw.

ABSTRACT

Introduction: In mammals, internal Na+ homeostasis is maintained through Na+ reabsorption via a variety of Na+ transport proteins with mutually compensating functions, which are expressed in different segments of the nephrons. In zebrafish, Na+ homeostasis is achieved mainly through the skin/gill ionocytes, namely Na+/H+ exchanger (NHE3b)-expressing H+-ATPase rich (HR) cells and Na+-Cl- cotransporter (NCC)-expressing NCC cells, which are functionally homologous to mammalian proximal and distal convoluted tubular cells, respectively. The present study aimed to investigate whether or not the functions of HR and NCC ionocytes are differentially regulated to compensate for disruptions of internal Na+ homeostasis and if the cell differentiation of the ionocytes is involved in this regulation pathway.

Results: Translational knockdown of ncc caused an increase in HR cell number and a resulting augmentation of Na+ uptake in zebrafish larvae, while NHE3b loss-of-function caused an increase in NCC cell number with a concomitant recovery of Na+ absorption. Environmental acid stress suppressed nhe3b expression in HR cells and decreased Na+ content, which was followed by up-regulation of NCC cells accompanied by recovery of Na+ content. Moreover, knockdown of ncc resulted in a significant decrease of Na+ content in acid-acclimated zebrafish.

Conclusions: These results provide evidence that HR and NCC cells exhibit functional redundancy in Na+ absorption, similar to the regulatory mechanisms in mammalian kidney, and suggest this functional redundancy is a critical strategy used by zebrafish to survive in a harsh environment that disturbs body fluid Na+ homeostasis.

No MeSH data available.


Related in: MedlinePlus

Loss of HR cells by gcm2 knockdown increases NCC cell number and Na+ absorption ability. (A, B): Immunostaining images of NCC cells (arrow) in 4-dpf wild type larvae (WT) and gcm2 morphants. Scale bar = 100 μm. (C): Comparison of NCC cell density between wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 8). (D): Na+ influx in 4-dpf wild types, gcm2 morphants, and foxi3a/3b morphants (n = 6). (E): Whole body Na+ content in wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 6). Mean ± SD. *p < 0.05 (Student’s t-test).
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Figure 2: Loss of HR cells by gcm2 knockdown increases NCC cell number and Na+ absorption ability. (A, B): Immunostaining images of NCC cells (arrow) in 4-dpf wild type larvae (WT) and gcm2 morphants. Scale bar = 100 μm. (C): Comparison of NCC cell density between wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 8). (D): Na+ influx in 4-dpf wild types, gcm2 morphants, and foxi3a/3b morphants (n = 6). (E): Whole body Na+ content in wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 6). Mean ± SD. *p < 0.05 (Student’s t-test).

Mentions: The transcription factor Gcm2 is known to control the differentiation of HR cells, which express NHE3b [23,32,33]. Blocking HR cell differentiation with gcm2 MOs resulted in an increase of NCC cells (Figure 2A-C). This increase in NCC cells may be related to an increase in the ability of morphants to absorb Na+. Compared to 4 dpf wild type larvae, Na+ influx was significantly increased in gcm2 morphants, but was dramatically decreased in foxi3a/3b morphants (Figure 2D). The transcription factors Foxi3a and Foxi3b control the differentiation of NaR and HR cells [34,35], and were also found to be required for the differentiation of NCC cells (Additional file 1: Figure S1). Closer inspection of the gcm2 morphants revealed an initial decrease of Na+ content at 3 dpf, which was restored to wild type levels at 4 dpf; by 5 dpf, the Na+ content of the morphants had exceeded that of the wild type (Figure 2E). Taken together, it appears that loss of HR cells impairs the Na+ uptake function, and subsequently stimulates NCC cell differentiation resulting in a compensatory increase in Na+ accumulation.


Compensatory regulation of Na+ absorption by Na+/H+ exchanger and Na+-Cl- cotransporter in zebrafish (Danio rerio).

Chang WJ, Wang YF, Hu HJ, Wang JH, Lee TH, Hwang PP - Front. Zool. (2013)

Loss of HR cells by gcm2 knockdown increases NCC cell number and Na+ absorption ability. (A, B): Immunostaining images of NCC cells (arrow) in 4-dpf wild type larvae (WT) and gcm2 morphants. Scale bar = 100 μm. (C): Comparison of NCC cell density between wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 8). (D): Na+ influx in 4-dpf wild types, gcm2 morphants, and foxi3a/3b morphants (n = 6). (E): Whole body Na+ content in wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 6). Mean ± SD. *p < 0.05 (Student’s t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750650&req=5

Figure 2: Loss of HR cells by gcm2 knockdown increases NCC cell number and Na+ absorption ability. (A, B): Immunostaining images of NCC cells (arrow) in 4-dpf wild type larvae (WT) and gcm2 morphants. Scale bar = 100 μm. (C): Comparison of NCC cell density between wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 8). (D): Na+ influx in 4-dpf wild types, gcm2 morphants, and foxi3a/3b morphants (n = 6). (E): Whole body Na+ content in wild type larvae (white bars) and gcm2 morphants (gray bars) at different developmental stages (n = 6). Mean ± SD. *p < 0.05 (Student’s t-test).
Mentions: The transcription factor Gcm2 is known to control the differentiation of HR cells, which express NHE3b [23,32,33]. Blocking HR cell differentiation with gcm2 MOs resulted in an increase of NCC cells (Figure 2A-C). This increase in NCC cells may be related to an increase in the ability of morphants to absorb Na+. Compared to 4 dpf wild type larvae, Na+ influx was significantly increased in gcm2 morphants, but was dramatically decreased in foxi3a/3b morphants (Figure 2D). The transcription factors Foxi3a and Foxi3b control the differentiation of NaR and HR cells [34,35], and were also found to be required for the differentiation of NCC cells (Additional file 1: Figure S1). Closer inspection of the gcm2 morphants revealed an initial decrease of Na+ content at 3 dpf, which was restored to wild type levels at 4 dpf; by 5 dpf, the Na+ content of the morphants had exceeded that of the wild type (Figure 2E). Taken together, it appears that loss of HR cells impairs the Na+ uptake function, and subsequently stimulates NCC cell differentiation resulting in a compensatory increase in Na+ accumulation.

Bottom Line: Environmental acid stress suppressed nhe3b expression in HR cells and decreased Na+ content, which was followed by up-regulation of NCC cells accompanied by recovery of Na+ content.Moreover, knockdown of ncc resulted in a significant decrease of Na+ content in acid-acclimated zebrafish.These results provide evidence that HR and NCC cells exhibit functional redundancy in Na+ absorption, similar to the regulatory mechanisms in mammalian kidney, and suggest this functional redundancy is a critical strategy used by zebrafish to survive in a harsh environment that disturbs body fluid Na+ homeostasis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan. pphwang@gate.sinica.edu.tw.

ABSTRACT

Introduction: In mammals, internal Na+ homeostasis is maintained through Na+ reabsorption via a variety of Na+ transport proteins with mutually compensating functions, which are expressed in different segments of the nephrons. In zebrafish, Na+ homeostasis is achieved mainly through the skin/gill ionocytes, namely Na+/H+ exchanger (NHE3b)-expressing H+-ATPase rich (HR) cells and Na+-Cl- cotransporter (NCC)-expressing NCC cells, which are functionally homologous to mammalian proximal and distal convoluted tubular cells, respectively. The present study aimed to investigate whether or not the functions of HR and NCC ionocytes are differentially regulated to compensate for disruptions of internal Na+ homeostasis and if the cell differentiation of the ionocytes is involved in this regulation pathway.

Results: Translational knockdown of ncc caused an increase in HR cell number and a resulting augmentation of Na+ uptake in zebrafish larvae, while NHE3b loss-of-function caused an increase in NCC cell number with a concomitant recovery of Na+ absorption. Environmental acid stress suppressed nhe3b expression in HR cells and decreased Na+ content, which was followed by up-regulation of NCC cells accompanied by recovery of Na+ content. Moreover, knockdown of ncc resulted in a significant decrease of Na+ content in acid-acclimated zebrafish.

Conclusions: These results provide evidence that HR and NCC cells exhibit functional redundancy in Na+ absorption, similar to the regulatory mechanisms in mammalian kidney, and suggest this functional redundancy is a critical strategy used by zebrafish to survive in a harsh environment that disturbs body fluid Na+ homeostasis.

No MeSH data available.


Related in: MedlinePlus