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1 Section of Nephrology, Department of Medicine, Departments of 3 Pharmacology and 4 Physiology and Biophysics, University of Illinois at Chicago College of Medicine, and 2 Veterans Affairs Chicago Health Care System, West Side Division, Chicago, Illinois 60612-7315
The
prototypical extracellular phospholipid mediator, lysophosphatidic acid
(LPA), exhibits growth factor-like properties and represents an
important survival factor in serum. This potent mesangial cell mitogen
is increased in conditions associated with glomerular injury. It is
also a known activator of the classic mitogen-activated protein kinase
(MAPK) pathway, which plays an important role in the regulation of
mesangial cell hexokinase (HK) activity. To better understand the
mechanisms coupling metabolism to injury, we examined the ability of
LPA to regulate HK activity and expression in cultured murine mesangial
cells. LPA increased total HK activity in a concentration- and
time-dependent manner, with maximal increases of >50% observed within
12 h of exposure to LPA concentrations
25 µM (apparent
ED50 2 µM). These effects were associated with
increased extracellular signal-regulated kinase (ERK) activity and were
prevented by the pharmacological inhibition of either MAPK/ERK kinase
or protein kinase C (PKC). Increased HK activity was also associated
with increased glucose (Glc) utilization and lactate accumulation, as
well as selectively increased HKII isoform abundance. The ability of
exogenous LPA to increase HK activity was both Ca2+
independent and pertussis toxin insensitive and was mimicked by
LPA-generating phospholipase A2. We conclude that LPA
constitutes a novel lipid regulator of mesangial cell HK activity and
Glc metabolism. This regulation requires sequential activation of both
Ca2+-independent PKC and the classic MAPK pathway and
culminates in increased HKII abundance. These previously unrecognized
metabolic consequences of LPA stimulation have both physiological and
pathophysiological implications. They also suggest a novel mechanism
whereby metabolism may be coupled to cellular injury via extracellular
lipid mediators.
lysophosphatidic acid; mitogen-activated protein kinase; glucose; phospholipase A2; renal injury
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