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The regulation of troponins I, C and ANP by GATA4 and Nkx2-5 in heart of hibernating thirteen-lined ground squirrels, Ictidomys tridecemlineatus.

Luu BE, Tessier SN, Duford DL, Storey KB - PLoS ONE (2015)

Bottom Line: Unlike its binding partner, the relative mRNA/protein expression and DNA binding of Nkx2-5 did not change during hibernation.This suggests that either Nkx2-5 does not play a substantial role or other regulatory mechanisms not presently studied (e.g. posttranslational modifications) are important during hibernation.The data suggest a significant role for GATA4-mediated gene transcription in the differential regulation of genes which aid cardiac-specific challenges associated with torpor-arousal.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada.

ABSTRACT
Hibernation is an adaptive strategy used by various mammals to survive the winter under situations of low ambient temperatures and limited or no food availability. The heart of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) has the remarkable ability to descend to low, near 0°C temperatures without falling into cardiac arrest. We hypothesized that the transcription factors GATA4 and Nkx2-5 may play a role in cardioprotection by facilitating the expression of key downstream targets such as troponin I, troponin C, and ANP (atrial natriuretic peptide). This study measured relative changes in transcript levels, protein levels, protein post-translational modifications, and transcription factor binding over six stages: euthermic control (EC), entrance into torpor (EN), early torpor (ET), late torpor (LT), early arousal (EA), and interbout arousal (IA). We found differential regulation of GATA4 whereby transcript/protein expression, post-translational modification (phosphorylation of serine 261), and DNA binding were enhanced during the transitory phases (entrance and arousal) of hibernation. Activation of GATA4 was paired with increases in cardiac troponin I, troponin C and ANP protein levels during entrance, while increases in p-GATA4 DNA binding during early arousal was paired with decreases in troponin I and no changes in troponin C and ANP protein levels. Unlike its binding partner, the relative mRNA/protein expression and DNA binding of Nkx2-5 did not change during hibernation. This suggests that either Nkx2-5 does not play a substantial role or other regulatory mechanisms not presently studied (e.g. posttranslational modifications) are important during hibernation. The data suggest a significant role for GATA4-mediated gene transcription in the differential regulation of genes which aid cardiac-specific challenges associated with torpor-arousal.

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Relative changes in the protein levels of the transcription factors GATA4 and Nkx2–5 as well as the phosphorylation state of GATA4 (Ser 261) in the heart of I. tridecemlineatus over the torpor-arousal cycle.Representative Western blots are shown for selected pairs of sampling points that are labeled to the left (lanes 1–4) and right (lanes 5–8) of the gel. Histograms show mean standardized band densities (± S.E.M., n = 4 independent protein isolations from different animals). Other information as in Fig. 1.
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pone.0117747.g002: Relative changes in the protein levels of the transcription factors GATA4 and Nkx2–5 as well as the phosphorylation state of GATA4 (Ser 261) in the heart of I. tridecemlineatus over the torpor-arousal cycle.Representative Western blots are shown for selected pairs of sampling points that are labeled to the left (lanes 1–4) and right (lanes 5–8) of the gel. Histograms show mean standardized band densities (± S.E.M., n = 4 independent protein isolations from different animals). Other information as in Fig. 1.

Mentions: Immunoblotting was use to assess changes in the relative protein levels of GATA4 and Nkx2–5 in ground squirrel heart over the torpor-arousal cycle as well as the phosphorylation state of GATA4 at Ser 261 (Fig. 2). Phosphorylation of GATA4 at Ser 261 has been previously established as a marker of transcription factor activity [30–31]. As compared to EC, total protein levels of GATA4 increased significantly by 1.7-fold in EN (P = 0.005), before returning to EC levels during ET, LT, and EA. During interbout arousal, however, total GATA4 protein levels decreased significantly to just 40% of EC values (P = 0.012). Similar to the GATA4 protein expression pattern, phosphorylation of GATA4 at Ser 261 also increased significantly in EN, rising strongly to levels that were 5.7-fold higher than EC (P<0.001). Phosphorylation state was reduced during torpor but peaked again during EA to 2.4-fold higher than EC (P = 0.023). Total protein levels of Nkx2–5 did not change significantly over the torpor-arousal cycle.


The regulation of troponins I, C and ANP by GATA4 and Nkx2-5 in heart of hibernating thirteen-lined ground squirrels, Ictidomys tridecemlineatus.

Luu BE, Tessier SN, Duford DL, Storey KB - PLoS ONE (2015)

Relative changes in the protein levels of the transcription factors GATA4 and Nkx2–5 as well as the phosphorylation state of GATA4 (Ser 261) in the heart of I. tridecemlineatus over the torpor-arousal cycle.Representative Western blots are shown for selected pairs of sampling points that are labeled to the left (lanes 1–4) and right (lanes 5–8) of the gel. Histograms show mean standardized band densities (± S.E.M., n = 4 independent protein isolations from different animals). Other information as in Fig. 1.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4334527&req=5

pone.0117747.g002: Relative changes in the protein levels of the transcription factors GATA4 and Nkx2–5 as well as the phosphorylation state of GATA4 (Ser 261) in the heart of I. tridecemlineatus over the torpor-arousal cycle.Representative Western blots are shown for selected pairs of sampling points that are labeled to the left (lanes 1–4) and right (lanes 5–8) of the gel. Histograms show mean standardized band densities (± S.E.M., n = 4 independent protein isolations from different animals). Other information as in Fig. 1.
Mentions: Immunoblotting was use to assess changes in the relative protein levels of GATA4 and Nkx2–5 in ground squirrel heart over the torpor-arousal cycle as well as the phosphorylation state of GATA4 at Ser 261 (Fig. 2). Phosphorylation of GATA4 at Ser 261 has been previously established as a marker of transcription factor activity [30–31]. As compared to EC, total protein levels of GATA4 increased significantly by 1.7-fold in EN (P = 0.005), before returning to EC levels during ET, LT, and EA. During interbout arousal, however, total GATA4 protein levels decreased significantly to just 40% of EC values (P = 0.012). Similar to the GATA4 protein expression pattern, phosphorylation of GATA4 at Ser 261 also increased significantly in EN, rising strongly to levels that were 5.7-fold higher than EC (P<0.001). Phosphorylation state was reduced during torpor but peaked again during EA to 2.4-fold higher than EC (P = 0.023). Total protein levels of Nkx2–5 did not change significantly over the torpor-arousal cycle.

Bottom Line: Unlike its binding partner, the relative mRNA/protein expression and DNA binding of Nkx2-5 did not change during hibernation.This suggests that either Nkx2-5 does not play a substantial role or other regulatory mechanisms not presently studied (e.g. posttranslational modifications) are important during hibernation.The data suggest a significant role for GATA4-mediated gene transcription in the differential regulation of genes which aid cardiac-specific challenges associated with torpor-arousal.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada.

ABSTRACT
Hibernation is an adaptive strategy used by various mammals to survive the winter under situations of low ambient temperatures and limited or no food availability. The heart of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) has the remarkable ability to descend to low, near 0°C temperatures without falling into cardiac arrest. We hypothesized that the transcription factors GATA4 and Nkx2-5 may play a role in cardioprotection by facilitating the expression of key downstream targets such as troponin I, troponin C, and ANP (atrial natriuretic peptide). This study measured relative changes in transcript levels, protein levels, protein post-translational modifications, and transcription factor binding over six stages: euthermic control (EC), entrance into torpor (EN), early torpor (ET), late torpor (LT), early arousal (EA), and interbout arousal (IA). We found differential regulation of GATA4 whereby transcript/protein expression, post-translational modification (phosphorylation of serine 261), and DNA binding were enhanced during the transitory phases (entrance and arousal) of hibernation. Activation of GATA4 was paired with increases in cardiac troponin I, troponin C and ANP protein levels during entrance, while increases in p-GATA4 DNA binding during early arousal was paired with decreases in troponin I and no changes in troponin C and ANP protein levels. Unlike its binding partner, the relative mRNA/protein expression and DNA binding of Nkx2-5 did not change during hibernation. This suggests that either Nkx2-5 does not play a substantial role or other regulatory mechanisms not presently studied (e.g. posttranslational modifications) are important during hibernation. The data suggest a significant role for GATA4-mediated gene transcription in the differential regulation of genes which aid cardiac-specific challenges associated with torpor-arousal.

Show MeSH
Related in: MedlinePlus