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New therapeutic targets for the treatment of insulin resistance…
our laboratory (57). As depicted in Figure 7, PTP1B CM-O.
protein content was decreased in hepatocytes treated with
Figure 7. Lower levels of PTP1B contribute to the insulin sensitization induced by CM-O in hepatocytes. Conditioned medium from
RAW 264.7 macrophages treated with BSA (CM-B) or oleate (CM-O) was added to immortalized mouse hepatocytes for 24 h. Total
protein was analyzed by Western blot using the indicated antibodies. Representative blots are shown. After quantification of all blots,
results are expressed as percentage of protein expression relative to CM-B condition (100%) and are mean ± SEM (n=3 independent
experiments performed in duplicate), ***p<0.001 CM-O vs CM-B.
As expected, insulin signaling was enhanced in DISCUSSION
immortalized neonatal hepatocytes preincubated with CM-
O whereas impaired insuling signaling was detected in In obesity-associated insulin resistance, M1-like
cells pretreated with CM-P (Figure 8). macrophages polarization state has been associated with
the enhancement of the proinflammatory milieu by the
Figure 8. Insulin signaling is differentially modulated in ability to secrete proinflammatory cytokines. This
hepatocytes pretreated with conditioned medium from RAW surrounding insulin resistant adipocytes that trigger
264.7 macrophages stimulated with oleate or palmitate. proinflammatory signaling pathways in macrophages
Conditioned medium from RAW 264.7 macrophages treated with trough their binding to Toll-like receptors (TLRs) (32-34).
BSA (CM-B), oleate (CM-O) or palmitate (CM-P) was added to However, we know now that beyond the interplay between
immortalized mouse hepatocytes for 24 h. Then, cells were adipocytes and adipose tissue resident macrophages, these
stimulated with 10 nM insulin for 10 min. Total protein was inflammatory signals also dysregulate key metabolic
analyzed by Western blot using the indicated antibodies. responses in other peripheral tissues, thereby exacerbating
Representative blots are shown (n=4 experiments performed in insulin resistance (3).
duplicate).
The liver is a target organ of the inflammatory
mediators. In obesity, the hepatic lipid accumulation (first
hit) together with the proinflammatory input (second hit)
trigger the necroinflammatory changes that are recognized
histopahologically as steatohepatitis (NASH) (35). Of
relevance, adipose tissue inflammation has been correlated
with hepatic steatosis in humans (36). Furthermore,
activation of Kupffer cells, the hepatic resident
macrophages, to secrete proinflammatory mediators is a
key event in the initiation of NAFLD, and limiting their
polarization into an M1 phenotype is considered an
attractive strategy against chronic liver inflammation (37-
40).
In this study, we have dissected for the first time the
molecular cross-talk between signals emerging from
macrophage-derived products in response to fatty acid
overload and insulin signaling in hepatocytes. A step
further, we attempted to compare the responses of
hepatocytes to macrophage-secreted cytokines derived
from oleate or palmitate together with FFAs mimicking the
circulating proinflammatory milieu. Interestingly, an
opposite response in insulin-mediated IR tyrosine
phosphorylation, the earliest event in the insulin signaling
cascade, was found in both mouse and human hepatocytes
@Real Academia Nacional de Farmacia. Spain 205
