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Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden
Address all correspondence and requests for reprints to: Björn Meister (Assoc. Prof.; M.D., Ph.D.), Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden. E-mail: bjorn.meister{at}neuro.ki.se
Leptin is a weight-reducing hormone produced by adipose tissue, which
reduces food intake via hypothalamic leptin receptors and the JAK-STAT
signaling pathway. In vivo studies have shown that
leptin activates specifically STAT3 in the hypothalamus. We have
studied the cellular localization of STAT3 messenger RNA (mRNA) and
STAT3 protein in the mouse mediobasal hypothalamus using, respectively,
in situ hybridization and immunohistochemistry. Strong
STAT3 mRNA and STAT3 immunoreactivity was demonstrated in neurons
located in the ventral part of the mouse arcuate nucleus. Comparison of
STAT3 mRNA levels in the arcuate nucleus of lean control mice and obese
leptin-deficient ob/ob mice showed that the levels of
STAT3 mRNA in the arcuate nucleus were significantly lower (31% less
in ob/ob mice), compared with control mice.
Hybridization with a probe specific for STAT3
mRNA showed that the
down-regulated STAT3 expression in the arcuate nucleus of
ob/ob mice is represented by STAT3
. There was a
marked difference in numbers and intensity of STAT3-immunoreactive cell
bodies, with virtually no STAT3-immunoreactive cell bodies in the
mediobasal hypothalamus of ob/ob mice, compared with
control mice. Direct double-labeling immunofluorescence histochemistry
of sections from control mice, combining a goat antiserum raised
against a peptide sequence present in all leptin receptor isoforms
(Ob-R) or a guinea pig antiserum generated to a peptide sequence
specific for Ob-Rb with rabbit STAT3 antiserum, demonstrated
colocalization of STAT3 and Ob-R as well as colocalization of STAT3 and
Ob-Rb, in many cell bodies of the arcuate nucleus. The results suggest
that circulating leptin acts via leptin receptor-/STAT3-containing
neurons in the ventral arcuate nucleus and that congenital leptin
deficiency, as seen in obese ob/ob mice, results in a
down-regulation of STAT3 mRNA and protein levels.
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