Limits...
Identification of fat mass and obesity associated (FTO) protein expression in cardiomyocytes: regulation by leptin and its contribution to leptin-induced hypertrophy.

Gan XT, Zhao G, Huang CX, Rowe AC, Purdham DM, Karmazyn M - PLoS ONE (2013)

Bottom Line: The recently-identified fat mass and obesity-associated (FTO) protein is associated with various physiological functions including energy and body weight regulation.Responses in cardiomyocytes were accompanied by JAK2/STAT3 activation whereas JAK2/STAT3 inhibition abolished these effects.Two other pro-hypertrophic factors, endothelin-1 or angiotensin II had no effect on FTO expression and FTO knockdown did not alter the hypertrophic response to either agent.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada.

ABSTRACT
The recently-identified fat mass and obesity-associated (FTO) protein is associated with various physiological functions including energy and body weight regulation. Ubiquitously expressed, FTO was identified in heart homogenates although its function is unknown. We studied whether FTO is specifically expressed within the cardiac myocyte and its potential role pertaining to the hypertrophic effect of the adipokine leptin. Most experiments were performed using cultured neonatal rat cardiomyocytes which showed nuclei-specific FTO expression. Leptin significantly increased FTO expression which was associated with myocyte hypertrophy although both events were abrogated by FTO knockdown with siRNA. Administration of a leptin receptor antibody to either normal or obese rats significant reduced myocardial FTO protein expression. Responses in cardiomyocytes were accompanied by JAK2/STAT3 activation whereas JAK2/STAT3 inhibition abolished these effects. Expression of the cut-like homeobox 1(CUX1) transcriptional factor was significantly increased by leptin although this was restricted to the cathepsin L-dependent, proteolytically-derived shorter p110CUX1 isoform whereas the longer p200CUX1 protein was not significantly affected. Cathepsin L expression and activity were both significantly increased by leptin whereas a cathepsin L peptide inhibitor or siRNA specific for CUX1 completely prevented the leptin-induced increase in FTO expression. The cathepsin L peptide inhibitor or siRNA-induced knockdown of either CUX1 or FTO abrogated the hypertrophic response to leptin. Two other pro-hypertrophic factors, endothelin-1 or angiotensin II had no effect on FTO expression and FTO knockdown did not alter the hypertrophic response to either agent. This study demonstrates leptin-induced FTO upregulation in cardiomyocytes via JAK2/STAT3- dependent CUX1 upregulation and suggests an FTO regulatory function of leptin. It also demonstrates for the first time a functional role of FTO in the cardiomyocyte.

Show MeSH

Related in: MedlinePlus

Immunofluorescence identification of FTO in cardiomyocytes.Panel A demonstrates immunofluorescence images and their quantitative assessment demonstrating nuclear localization of FTO in cardiomyocytes and its upregulation by leptin whereas panel B shows identical data in myocytes transfected with siFTO illustrating suppression of FTO. Corresponding images of myocytes stained with the nuclear dye Hoechst 33342 as well as merged images are also presented. Quantitative data in panel C are presented as mean+SEM, N = 8. *P<0.05 from respective control (Ctl) group; +P<0.05 from respective group in the absence of siFTO (−siFTO). Lep, leptin; A, leptin receptor antagonist. Horizontal bar in bottom right images indicates 200 µm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3760875&req=5

pone-0074235-g002: Immunofluorescence identification of FTO in cardiomyocytes.Panel A demonstrates immunofluorescence images and their quantitative assessment demonstrating nuclear localization of FTO in cardiomyocytes and its upregulation by leptin whereas panel B shows identical data in myocytes transfected with siFTO illustrating suppression of FTO. Corresponding images of myocytes stained with the nuclear dye Hoechst 33342 as well as merged images are also presented. Quantitative data in panel C are presented as mean+SEM, N = 8. *P<0.05 from respective control (Ctl) group; +P<0.05 from respective group in the absence of siFTO (−siFTO). Lep, leptin; A, leptin receptor antagonist. Horizontal bar in bottom right images indicates 200 µm.

Mentions: As shown in the immunofluorescence images (Figure 2), FTO expression under control conditions as well as in myocytes treated with leptin was restricted to nuclei with FTO intensity increasing more than three-fold by leptin in those myocytes not treated with siFTO (Figure 2A and 2C)). However, myocytes treated with siFTO demonstrated significantly reduced FTO fluorescence intensity with no significant increase in response to leptin (Figure 2B and 2C). The ability of leptin to upregulate FTO expression within nuclei was abrogated by the leptin receptor antagonist (Figure 2A and 2C).


Identification of fat mass and obesity associated (FTO) protein expression in cardiomyocytes: regulation by leptin and its contribution to leptin-induced hypertrophy.

Gan XT, Zhao G, Huang CX, Rowe AC, Purdham DM, Karmazyn M - PLoS ONE (2013)

Immunofluorescence identification of FTO in cardiomyocytes.Panel A demonstrates immunofluorescence images and their quantitative assessment demonstrating nuclear localization of FTO in cardiomyocytes and its upregulation by leptin whereas panel B shows identical data in myocytes transfected with siFTO illustrating suppression of FTO. Corresponding images of myocytes stained with the nuclear dye Hoechst 33342 as well as merged images are also presented. Quantitative data in panel C are presented as mean+SEM, N = 8. *P<0.05 from respective control (Ctl) group; +P<0.05 from respective group in the absence of siFTO (−siFTO). Lep, leptin; A, leptin receptor antagonist. Horizontal bar in bottom right images indicates 200 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3760875&req=5

pone-0074235-g002: Immunofluorescence identification of FTO in cardiomyocytes.Panel A demonstrates immunofluorescence images and their quantitative assessment demonstrating nuclear localization of FTO in cardiomyocytes and its upregulation by leptin whereas panel B shows identical data in myocytes transfected with siFTO illustrating suppression of FTO. Corresponding images of myocytes stained with the nuclear dye Hoechst 33342 as well as merged images are also presented. Quantitative data in panel C are presented as mean+SEM, N = 8. *P<0.05 from respective control (Ctl) group; +P<0.05 from respective group in the absence of siFTO (−siFTO). Lep, leptin; A, leptin receptor antagonist. Horizontal bar in bottom right images indicates 200 µm.
Mentions: As shown in the immunofluorescence images (Figure 2), FTO expression under control conditions as well as in myocytes treated with leptin was restricted to nuclei with FTO intensity increasing more than three-fold by leptin in those myocytes not treated with siFTO (Figure 2A and 2C)). However, myocytes treated with siFTO demonstrated significantly reduced FTO fluorescence intensity with no significant increase in response to leptin (Figure 2B and 2C). The ability of leptin to upregulate FTO expression within nuclei was abrogated by the leptin receptor antagonist (Figure 2A and 2C).

Bottom Line: The recently-identified fat mass and obesity-associated (FTO) protein is associated with various physiological functions including energy and body weight regulation.Responses in cardiomyocytes were accompanied by JAK2/STAT3 activation whereas JAK2/STAT3 inhibition abolished these effects.Two other pro-hypertrophic factors, endothelin-1 or angiotensin II had no effect on FTO expression and FTO knockdown did not alter the hypertrophic response to either agent.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada.

ABSTRACT
The recently-identified fat mass and obesity-associated (FTO) protein is associated with various physiological functions including energy and body weight regulation. Ubiquitously expressed, FTO was identified in heart homogenates although its function is unknown. We studied whether FTO is specifically expressed within the cardiac myocyte and its potential role pertaining to the hypertrophic effect of the adipokine leptin. Most experiments were performed using cultured neonatal rat cardiomyocytes which showed nuclei-specific FTO expression. Leptin significantly increased FTO expression which was associated with myocyte hypertrophy although both events were abrogated by FTO knockdown with siRNA. Administration of a leptin receptor antibody to either normal or obese rats significant reduced myocardial FTO protein expression. Responses in cardiomyocytes were accompanied by JAK2/STAT3 activation whereas JAK2/STAT3 inhibition abolished these effects. Expression of the cut-like homeobox 1(CUX1) transcriptional factor was significantly increased by leptin although this was restricted to the cathepsin L-dependent, proteolytically-derived shorter p110CUX1 isoform whereas the longer p200CUX1 protein was not significantly affected. Cathepsin L expression and activity were both significantly increased by leptin whereas a cathepsin L peptide inhibitor or siRNA specific for CUX1 completely prevented the leptin-induced increase in FTO expression. The cathepsin L peptide inhibitor or siRNA-induced knockdown of either CUX1 or FTO abrogated the hypertrophic response to leptin. Two other pro-hypertrophic factors, endothelin-1 or angiotensin II had no effect on FTO expression and FTO knockdown did not alter the hypertrophic response to either agent. This study demonstrates leptin-induced FTO upregulation in cardiomyocytes via JAK2/STAT3- dependent CUX1 upregulation and suggests an FTO regulatory function of leptin. It also demonstrates for the first time a functional role of FTO in the cardiomyocyte.

Show MeSH
Related in: MedlinePlus