153
especially in mitochondria where spin-off of
superoxides during mitochondria transfer of electrons to oxygen occurs, was increased in exercised mammalian muscle, heat-stressed bivalve
gills, heat-shocked chicken muscles, and cultured
cells as compared with non-stressed control (Ji
1995 ; Pörtner 2002 ; Heise et al. 2003 ; MartínezÁlvarez et al. 2005 ; Mujahid et al. 2005 ; Lesser
2006 ; Valavanidis et al. 2006 ; Shin et al. 2008 ).
Inductions of hepatic HSP and GSH in stressed
coho salmon have been observed in this study
(Nakano et al. 2014 ). Thus, the present results
regarding the plasma levels of cortisol and glucose and the expression patterns of redox staterelated biomarkers, such as LPO, GSH, SOD,
and HSP, in response to heat shock suggest that
heat shock induces oxidative stress in fi sh. The
resulting oxidative stress may enhance oxidation
in the body and result in damage to tissues
(Nakano and Takeuchi 1997 ; Nakano et al.
1999a ; Martínez-Álvarez et al. 2005 ; Lesser
2006 ; Valavanidis et al. 2006 ; Nakano 2007 ,
2011 ; Lushchak 2011 ). Under oxidative stress
conditions, the levels of antioxidative agents,
such as GSH, SOD, and HSP, may increase due
to their de novo synthesis.
The pituitary is the major organ of the
GH-IGF-1 axis in fi sh (Kobayashi et al. 2002 ;
Takei and Loretz 2006 ). In the present study, ghr
gene expression in the pituitary increased in
response to heat stress. In contrast, pituitary ghr
gene expression signifi cantly decreased in
response to moderate acute physiological stress
induced by handling (Nakano et al. 2013 ). This
may involve interactions between glucocorticoids, such as cortisol and factors of the
GH-IGF-1 axis, and be related to the differences
observed between heat shock-induced oxidative
stress and mild physiological stress derived from
handling. The effects of stress on growth-related
gene expression in fi sh may be affected differently by the strength of stress.
Hepatic igf1 expression gradually decreased
after heat shock treatment, whereas ghr expression levels increased after heat shock in this
study. Thus, ghr and igf1 genes responded differently to heat stress. Furthermore, pituitary gh
mRNA expression did not change in response to
oxidative stress. These observations suggest that
igf1 gene expression may not be directly regulated by circulating GH levels alone.
A decrease in plasma IGF-1 level at 2–24 h
post-stress has often been observed in many fi sh
species (Beckman 2011 ). Our results for the
changes in hepatic igf1 gene expression levels in
stressed fi sh are in agreement with those
reported for fi sh that were administered exogenous cortisol and under confi nement stress
(Kajimura et al. 2003 ; Dyer et al. 2004 ; SaeraVila et al. 2009 ). However, our results for
hepatic ghr and igf1 gene expression patterns in
fi sh under oxidative stress appear to be different
from those in coho salmon under mild physiological stress caused by handling (Nakano et al.
2013 ). These observations suggest that the hormonal regulation of hepatic both ghr and igf1
gene expression can vary depending on the
types of hormones and stress.
5
Conclusions
and Perspectives
Oxidative stress could affect the expression of
growth-related genes accompanying the changing in circulating glucocorticoids, such as cortisol, and alterations in signal transduction.
Intercellular signaling is known to be affected by
ROS (Schoeniger et al. 1994 ; Ji 1995 ; Franco
et al. 1999 ; Arrigo 1999 ; Allen and Tresini 2000 ;
Droge 2002 ; Lesser 2006 ; Valavanidis et al.
2006 ; Shin et al. 2008 ; Nakano 2011 ; Lushchak
2011 ). An antioxidative supplement that could
dramatically reduce oxidative stress-induced
damage in fi sh has been observed (Nakano et al.
1999a , b , 2004 ; Bell et al. 2000 ; MartínezÁlvarez et al. 2005 ; Nakano 2007 , 2011 ).
Accordingly, further studies are required on the
possible benefi cial effects of antioxidative
nutraceutical supplements on growth-related
factors in oxidative stressed fi sh.
Marine ecosystems could provide various
products and services, including vital food
resources for us (Holmlund and Hammer 1999 ;
Worm et al. 2006 ). The ability of the ocean is
thought to maintain water quality and regulate
Effects of Thermal Stressors on Growth-Related Gene Expressions in Cultured Fish
especially in mitochondria where spin-off of
superoxides during mitochondria transfer of electrons to oxygen occurs, was increased in exercised mammalian muscle, heat-stressed bivalve
gills, heat-shocked chicken muscles, and cultured
cells as compared with non-stressed control (Ji
1995 ; Pörtner 2002 ; Heise et al. 2003 ; MartínezÁlvarez et al. 2005 ; Mujahid et al. 2005 ; Lesser
2006 ; Valavanidis et al. 2006 ; Shin et al. 2008 ).
Inductions of hepatic HSP and GSH in stressed
coho salmon have been observed in this study
(Nakano et al. 2014 ). Thus, the present results
regarding the plasma levels of cortisol and glucose and the expression patterns of redox staterelated biomarkers, such as LPO, GSH, SOD,
and HSP, in response to heat shock suggest that
heat shock induces oxidative stress in fi sh. The
resulting oxidative stress may enhance oxidation
in the body and result in damage to tissues
(Nakano and Takeuchi 1997 ; Nakano et al.
1999a ; Martínez-Álvarez et al. 2005 ; Lesser
2006 ; Valavanidis et al. 2006 ; Nakano 2007 ,
2011 ; Lushchak 2011 ). Under oxidative stress
conditions, the levels of antioxidative agents,
such as GSH, SOD, and HSP, may increase due
to their de novo synthesis.
The pituitary is the major organ of the
GH-IGF-1 axis in fi sh (Kobayashi et al. 2002 ;
Takei and Loretz 2006 ). In the present study, ghr
gene expression in the pituitary increased in
response to heat stress. In contrast, pituitary ghr
gene expression signifi cantly decreased in
response to moderate acute physiological stress
induced by handling (Nakano et al. 2013 ). This
may involve interactions between glucocorticoids, such as cortisol and factors of the
GH-IGF-1 axis, and be related to the differences
observed between heat shock-induced oxidative
stress and mild physiological stress derived from
handling. The effects of stress on growth-related
gene expression in fi sh may be affected differently by the strength of stress.
Hepatic igf1 expression gradually decreased
after heat shock treatment, whereas ghr expression levels increased after heat shock in this
study. Thus, ghr and igf1 genes responded differently to heat stress. Furthermore, pituitary gh
mRNA expression did not change in response to
oxidative stress. These observations suggest that
igf1 gene expression may not be directly regulated by circulating GH levels alone.
A decrease in plasma IGF-1 level at 2–24 h
post-stress has often been observed in many fi sh
species (Beckman 2011 ). Our results for the
changes in hepatic igf1 gene expression levels in
stressed fi sh are in agreement with those
reported for fi sh that were administered exogenous cortisol and under confi nement stress
(Kajimura et al. 2003 ; Dyer et al. 2004 ; SaeraVila et al. 2009 ). However, our results for
hepatic ghr and igf1 gene expression patterns in
fi sh under oxidative stress appear to be different
from those in coho salmon under mild physiological stress caused by handling (Nakano et al.
2013 ). These observations suggest that the hormonal regulation of hepatic both ghr and igf1
gene expression can vary depending on the
types of hormones and stress.
5
Conclusions
and Perspectives
Oxidative stress could affect the expression of
growth-related genes accompanying the changing in circulating glucocorticoids, such as cortisol, and alterations in signal transduction.
Intercellular signaling is known to be affected by
ROS (Schoeniger et al. 1994 ; Ji 1995 ; Franco
et al. 1999 ; Arrigo 1999 ; Allen and Tresini 2000 ;
Droge 2002 ; Lesser 2006 ; Valavanidis et al.
2006 ; Shin et al. 2008 ; Nakano 2011 ; Lushchak
2011 ). An antioxidative supplement that could
dramatically reduce oxidative stress-induced
damage in fi sh has been observed (Nakano et al.
1999a , b , 2004 ; Bell et al. 2000 ; MartínezÁlvarez et al. 2005 ; Nakano 2007 , 2011 ).
Accordingly, further studies are required on the
possible benefi cial effects of antioxidative
nutraceutical supplements on growth-related
factors in oxidative stressed fi sh.
Marine ecosystems could provide various
products and services, including vital food
resources for us (Holmlund and Hammer 1999 ;
Worm et al. 2006 ). The ability of the ocean is
thought to maintain water quality and regulate
Effects of Thermal Stressors on Growth-Related Gene Expressions in Cultured Fish