Norepinephrine dependent inhibition of proteolysis in brown adipocytes
Date
2002
Authors
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Publisher
ORCID
Type
Degree Level
Masters
Abstract
Brown adipose tissue (BAT) is specialized for heat production. Brown
adipocytes contain an uncoupling protein (UCP-1) in the mitochondria, which
uncouples oxidative phosphorylation and produces heat. Thermogenesis in BAT is
under the control of sympathetic nervous system. In addition, BAT growth and
atrophy occurs in response to changes in the sympathetic activity. So, the focus of this
research was to evaluate the mechanism by which norepinephrine (NE) affects
proteolysis in brown fat cells differentiated in culture. An inhibitory effect of NE on
proteolysis and ATP level was observed in mature brown adipocytes but not in pre-adipocytes
and 3T3-L1 adipocytes. The inhibitory effect of NE was not affected by
the amount of UCP1 in mature brown adipocytes. To see if NE's action on
proteolysis in mature brown adipocytes was linked to the onset of thermogenesis via
activation of UCP-1 and decreasing energy level of the cell, the effect of NE on
proteolysis and ATP was compared with that of fatty acids known to activate UCP-1
directly. Unlike in pre-adipocytes and 3T3-L1 adipocytes, both proteolysis and cell
ATP level were decreased in mature brown adipocytes. Furthermore, bromopalmitate,
a non-metabolisable fatty acid, which is known to activate UCP-1, reduced
proteolysis and ATP by a greater extent than NE. There was a linear relationship
between reduction in cell ATP and protein degradation. So, NE may inhibit
proteolysis in mature brown adipocytes by decreasing the cell ATP level, and thus
may play a significant role in affecting the cell content of protein under certain
physiological and pathological conditions, known to activate thermogenesis and
stimulate BAT growth.
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Degree
Master of Science (M.Sc.)
Department
Physiology
Program
Physiology