Leptin‐like immunoreactivity in the muscle of juvenile sea bass (Dicentrarchus labrax)

Abstract

The mammalian hormone, leptin, is mainly synthesized in adipose tissue along with other tissues. Leptin plays a role in numerous processes such as in the control of food intake, homeostasis, immune function and reproduction. In this study, we detected and localized leptin immunoreactivity to the muscle of early juvenile sea bass (Dicentrarchus labrax) by Western blot analysis and immunohistochemistry. A leptin immunopositive band with a molecular weight of approximately 16 kDa, corresponding to mammalian leptin, was identified in trunk skeletal muscle homogenate. Furthermore, leptin immunopositive cells were detected in the endomysium of skeletal muscular fibers. These cells showed immunostained cytoplasmic granules and roundish and oval nuclei. The most intense immunostaining was observed in the endomysial space among the superficial red muscular fibers of the trunk. These findings suggest that in early juvenile sea bass, leptin is mostly produced by skeletal muscles. Therefore, during the developmental stage lacking adipose tissue, skeletal muscles can be considered an important source of leptin. As already suggested in mammals, we can hypothesize the potential roles of leptin not only in energy expenditure for muscle contraction but also during muscle differentiation and growth.

First Evidence of a Leptin‐Like Peptide in a Cartilaginous Fish

“…Western blot analysis showed IR with a ∼16 kDa band in the small‐spotted catshark stomach. This molecular weight is comparable to that previously obtained for leptin in other vertebrates (Cinti et al, 2000; Johnson et al, 2000; Yaghoubian et al, 2001; Vegusdal et al, 2003; Neglia et al, 2007; Gambardella et al, 2010).…”

Fasting and re-feeding impact on leptin and aquaglyceroporin 9 in the liver of European sea bass (Dicentrarchus labrax)

“…About 4 μm thick serial sections were cut, rehydrated and incubated overnight in a moist chamber at 4 °C with the following polyclonal antisera from Santa Cruz Biotechnology Inc. (CA, USA): rabbit antileptin (Cat. Sc-842, already used in sea bass muscle, see Gambardella et al, 2010) and mouse anti-AQP-9 (Cat. Sc-74409).…”

“…Liver of CTR fish was alternatively frozen at −80 °C and used for Western Blot analysis. Denaturing electrophoresis was performed using Laemmli protocol (Laemmli, 1970) with minor modifications, as already described in Gambardella et al (2010). The antibodies against LEP and AQP-9 were diluted 1:500 in PBS plus 3% BSA, for 1 h at 20 °C revealed using an alkaline phosphatase conjugated secondary antibody anti-rabbit for LEP and anti-mouse for AQP-9 (1:1000, Santa Cruz Biotechnology Inc. CA, USA) and BCIP/NBT alkaline phosphatase substrate.…”