Team:BGU Israel/Project/Aspiration Shift

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         Abnormal aggregation of fatty acid in non-adipose tissues, particularly skeletal muscles and liver.
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         <b>The problem: </b>Abnormal accumulation of fatty acids in non-adipose tissues, particularly skeletal muscles and liver
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         <b>Goal: </b>Increase fatty acid oxidation, lipid transport and mitochondrial biogenesis processes
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         <b>Goal: </b>Increase fatty acid oxidation, lipid transport and mitochondrial biogenesis processes, while limiting the state of insulin resistance
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         <h3 style="border-bottom:dashed;border-color:#000000">Modeling </h3>
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         We designed a mathematical model of our ‘Aspiration Shift’ mechanism, and analyzed the treatment effects on the dynamic system of the genetic circuit.
    
    
        
        
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One of the most serious effects of unbalanced fat metabolism, is an abnormal aggregation of fatty acid in non-adipose tissues, particularly skeletal muscles and liver. This effect is strongly associated with insulin resistance and obesity. One of the key members which can reduce abnormal fat accumulation is peroxisome proliferator-activated receptor γ (PPARγ), a member of the nuclear hormone receptor family of ligand-activated transcription factors. This receptor increases the expression of genes important to fatty acid oxidation, lipid transport<div id="test"></div> and mitochondrial biogenesis processes (Aharoni-simon, Hann-obercyger, Pen, Madar, & Tirosh, 2011).
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One of the most serious effects of unbalanced fat metabolism is an abnormal accumulation of fatty acids in non-adipose tissues, particularly skeletal muscles and liver. This effect is strongly associated with insulin resistance and obesity. One of the key members, which can reduce abnormal fat accumulation, is peroxisome proliferator-activated receptor γ (PPARγ), a member of the nuclear hormone receptor family of ligand-activated transcription factors.  
          
          
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         In vivo induction of the PPARγ coactivator 1α (PGC-1α) shows increased insulin-sensitizing effects and a high level of oxidative capacity. However, overexpression of PGC-1α induced insulin resistance (Benton, Holloway, Han, & Yoshida, 2010).
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         Activation of this receptor increases the expression of genes important to fatty acid oxidation, lipid transport and mitochondrial biogenesis processes(Aharoni-simon, Hann-obercyger, Pen, Madar, & Tirosh, 2011). In vivo induction of the PPARγ co-activator 1α (PGC-1α) showed a high level of fatty acid oxidation capacity. However, overexpression of PGC-1α also induced insulin resistance(Benton, Holloway, Han, & Yoshida, 2010).  
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          In order to prevent this phenomenon, we designed a self-regulating mechanism, which leads to modest overexpression of PGC-1α, shown in figure 1. We chose sterol regulatory elements (SRE) to promote the  expression of PGC-1α. When the cell is in an anabolic state, i.e. accumulating fatty acids, a transcription factor called SREBP (Sterol Regulatory Element-Binding, Proteins) is expressed (Shimomura, Bashmakov, &amp; Horton, 1999). As its name  suggests, the SREBP binds the sterol regulatory elements and induce the expression of PGC-1α.  <br>
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        In order to prevent the state of insulin resistance, we designed a self-regulating mechanism, to limit overexpression of PGC-1α, as shown in figure 1. The mechanism is based on the sterol regulatory elements (SRE) to control PGC-1α expression. When cell is found in an anabolic state, i.e., accumulating fatty acids, a transcription factor called SREBP (Sterol Regulatory Element-Binding Proteins) is expressed(Shimomura, Bashmakov, & Horton, 1999). The SREBP binds the sterol regulatory elements and induces the expression of PGC-1α. Thus, to control PGC-1α overexpression, a PPARγ sensitive promoter controlling the expression of a repressor, which binds to an operator downstream the sterol regulatory elements, was added to the system. This way, PGC-1α inhibits its own overexpression and remains in a modest physiological level; a level which does not lead to insulin resistance.  
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          In order to limit  the expression of PGC-1α and  prevent supra-physiological overexpression, we add a PPARγ sensitive promoter which controls the expression of a repressor which binds to an operator downstream the sterol regulatory elements. This way, PGC-1α inhibits its own expression and stays in a modest physiological concentration.
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         <p align="center" style="border: thin solid; border-radius: 8px; background: #5FA6B8; font-style: normal; font-weight: 700; font-size: 24px; font-family: Allan, 'Hoefler Text', 'Liberation Serif', Times, 'Times New Roman', serif;"> Click on the picture to check out the machanism <img src="https://static.igem.org/mediawiki/2014/d/dd/BGU14finger-point.gif" width="26px"/></p>
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          <p align="center" style="font-size:14px; font-weight:bold; line-height:normal">A construct with PGC1-α under the regulation of sterol regulatory element (SRE), is introduced into the liver cell. </p>
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        <p align="center" style="font-size:14px; font-weight:bold; line-height:normal">SREBP expression in the cell induces PGC1-α expression by binding to the sterol regulatory element.</p>
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         <p align="center" style="font-size:14px; font-weight:bold; line-height:normal">Figure 1 –  SREBP serves as a molecular indicator for fat accumulation in the cell and  induces the expression of PGC1-α by binding to the sterol regulatory elements in our construct (SRE). PGC1-α then activates a negative feedback loop,  inhibiting its own expression. The result is a modest expression of PGC1-α in  the cell.</p>
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         <p align="center" style="font-size:14px; font-weight:bold; line-height:normal">PGC1-α activates PPAR-γ transcription factor. </p>
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        <p align="center" style="font-size:14px; font-weight:bold; line-height:normal">PPAR-γ induces the expression of an orthogonal repressor. </p>
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        <img  src="https://static.igem.org/mediawiki/2014/b/b8/BGU14PGC-1-6a.png" onclick="change_pic()" width="400" style="border: thin solid; cursor: pointer;" />
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        <p align="center" style="font-size:14px; font-weight:bold; line-height:normal">The repressor binds to an operator downstream the SRE and inhibits PGC1-α synthesis. </p>
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       <h3 style="border-bottom:dashed;border-color:#000000">References </h3>
       <h3 style="border-bottom:dashed;border-color:#000000">References </h3>
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       <p>Aharoni-simon, M.,  Hann-obercyger, M., Pen, S., Madar, Z., &amp; Tirosh, O. (2011). Fatty liver is  associated with impaired activity of PPAR g -coactivator 1 a ( PGC1 a ) and  mitochondrial biogenesis in mice, <em>91</em>(July),1018–1028.   </p>
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       <p>Aharoni-simon, M.,  Hann-obercyger, M., Pen, S., Madar, Z., &amp; Tirosh, O. (2011). Fatty liver is  associated with impaired activity of PPAR g -coactivator 1 a ( PGC1 a ) and  mitochondrial biogenesis in mice, <em>91</em>(July), 1018–1028. doi:10.1038/labinvest.2011.55</p>
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      <p>doi:10.1038/labinvest.2011.55</p>
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       <p><br>
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       <p>Benton, C. R., Holloway, G. P., Han,  X., &amp; Yoshida, Y. (2010). Increased levels of peroxisome  proliferator-activated receptor gamma , coactivator 1 alpha ( PGC-1 α ) improve  lipid utilisation , insulin signalling and glucose transport in skeletal muscle  of lean and insulin-resistant obese Zucker rats, 2008–2019.</p>
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        Benton, C. R., Holloway, G. P., Han,  X., &amp; Yoshida, Y. (2010). Increased levels of peroxisome  proliferator-activated receptor gamma , coactivator 1 alpha ( PGC-1 α ) improve  lipid utilisation , insulin signalling and glucose transport in skeletal muscle  of lean and insulin-resistant obese Zucker rats, 2008–2019. doi:10.1007/s00125-010-1773-1</p>
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      <p> doi:10.1007/s00125-010-1773-1<br><br>
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      <p><br>
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         Shimomura, I., Bashmakov, Y., &amp;  Horton, J. D. (1999). Increased Levels of Nuclear SREBP-1c Associated with  Fatty Livers in Two Mouse Models of Diabetes Mellitus. <em>Journal of Biological  Chemistry</em>, <em>274</em>(42), 30028–30032. </p>
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         Shimomura, I., Bashmakov, Y., &amp;  Horton, J. D. (1999). Increased Levels of Nuclear SREBP-1c Associated with  Fatty Livers in Two Mouse Models of Diabetes Mellitus. <em>Journal of Biological  Chemistry</em>, <em>274</em>(42), 30028–30032. doi:10.1074/jbc.274.42.30028</p>
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      <p>doi:10.1074/jbc.274.42.30028</p>
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Latest revision as of 23:54, 17 October 2014

Background


The problem: Abnormal accumulation of fatty acids in non-adipose tissues, particularly skeletal muscles and liver
Goal: Increase fatty acid oxidation, lipid transport and mitochondrial biogenesis processes, while limiting the state of insulin resistance

Mechanism


Activation of PPARγ by modest overexpression of PGC-1α

Modeling


We designed a mathematical model of our ‘Aspiration Shift’ mechanism, and analyzed the treatment effects on the dynamic system of the genetic circuit.

Background

One of the most serious effects of unbalanced fat metabolism is an abnormal accumulation of fatty acids in non-adipose tissues, particularly skeletal muscles and liver. This effect is strongly associated with insulin resistance and obesity. One of the key members, which can reduce abnormal fat accumulation, is peroxisome proliferator-activated receptor γ (PPARγ), a member of the nuclear hormone receptor family of ligand-activated transcription factors.

Activation of this receptor increases the expression of genes important to fatty acid oxidation, lipid transport and mitochondrial biogenesis processes(Aharoni-simon, Hann-obercyger, Pen, Madar, & Tirosh, 2011). In vivo induction of the PPARγ co-activator 1α (PGC-1α) showed a high level of fatty acid oxidation capacity. However, overexpression of PGC-1α also induced insulin resistance(Benton, Holloway, Han, & Yoshida, 2010).

Mechanism


In order to prevent the state of insulin resistance, we designed a self-regulating mechanism, to limit overexpression of PGC-1α, as shown in figure 1. The mechanism is based on the sterol regulatory elements (SRE) to control PGC-1α expression. When cell is found in an anabolic state, i.e., accumulating fatty acids, a transcription factor called SREBP (Sterol Regulatory Element-Binding Proteins) is expressed(Shimomura, Bashmakov, & Horton, 1999). The SREBP binds the sterol regulatory elements and induces the expression of PGC-1α. Thus, to control PGC-1α overexpression, a PPARγ sensitive promoter controlling the expression of a repressor, which binds to an operator downstream the sterol regulatory elements, was added to the system. This way, PGC-1α inhibits its own overexpression and remains in a modest physiological level; a level which does not lead to insulin resistance.



Click on the picture to check out the machanism

A construct with PGC1-α under the regulation of sterol regulatory element (SRE), is introduced into the liver cell.

References

Aharoni-simon, M., Hann-obercyger, M., Pen, S., Madar, Z., & Tirosh, O. (2011). Fatty liver is associated with impaired activity of PPAR g -coactivator 1 a ( PGC1 a ) and mitochondrial biogenesis in mice, 91(July), 1018–1028. doi:10.1038/labinvest.2011.55


Benton, C. R., Holloway, G. P., Han, X., & Yoshida, Y. (2010). Increased levels of peroxisome proliferator-activated receptor gamma , coactivator 1 alpha ( PGC-1 α ) improve lipid utilisation , insulin signalling and glucose transport in skeletal muscle of lean and insulin-resistant obese Zucker rats, 2008–2019. doi:10.1007/s00125-010-1773-1


Shimomura, I., Bashmakov, Y., & Horton, J. D. (1999). Increased Levels of Nuclear SREBP-1c Associated with Fatty Livers in Two Mouse Models of Diabetes Mellitus. Journal of Biological Chemistry, 274(42), 30028–30032. doi:10.1074/jbc.274.42.30028