Abstract
Background and aims: Ask1 is a MAP3K known in certain cells to mediate
the activation of p38MAP kinase and JNK in response to oxidative stress,
inflammatory signals (TNF-R, Toll-like receptors) and endoplasmic reticulum stress. We previously reported that in human obesity omental fat exhibits
activation of JNK and p38MAP kinase in correlation with the degree of obesity-related cardio-metabolic risk. The aim of the present study was to assess
the possible role of Ask1 specifically in adipocytes in adipose tissue stress
response.
Materials and methods: We utilized two independent cohorts, in Leipzig,
Germany, and in Beer-Sheva, Israel, from whom paired omental (OM) and
subcutaneous abdominal (SC) fat samples were obtained. The protein expression and phosphorylation of Ask1 and its mRNA levels were assessed. To
investigate Ask1 activation specifically in adipocytes we separated adipocytes
from the stromal-vascular fraction (SVF) by collagenase digestion, and utilized 3T3-L1 adipocytes.
Results: Obesity was associated with elevated expression of Ask1 in OM at
both the mRNA (~1.5-fold, p<0.05) and protein levels (~2-fold, p<0.05),
as compared to the paired SC depot, and as compared to OM fat from lean
people. Ask1-mRNA levels correlated in OM more strongly than in SC with
fasting insulin levels and the glucose infusion rate during euglycemic-hyperinsulinic clamp (r=0.349 and r=-0.510, respectively, both p<0.001, n=196),
and with triglycerides and non-esterified fatty acid levels. Moreover, Ask1
phosphorylation on its auto-phosphorylation site, which confers activation, was elevated 2-2.5 fold in OM of obese women, and correlated with the
phosphorylation of the MAP2K MKK4 (r=0.474, p<0.01, n=19) and that of
p38MAP kinase (r=0.596, p<0.01, n=19). To verify the specific contribution
of adipocytes to the increased OM Ask1, collagenase digestion of fat biopsies
was performed, and Ask1-mRNA was assessed separately in OM adipocytes
versus OM SVF. Whereas in lean persons SVF had 6-fold higher expression of
Ask1, persons with predominantly subcutaneous obesity (determined by CT)
had ~2.5-fold higher expression in the adipocytes, with no change in the SVF.
In persons with predominantly intra-abdominal obesity Ask1 mRNA levels
increased 4.3-fold and 1.5-fold in adipocytes and SVF fraction, respectively
(both p<0.05) compared to the lean group. Furthermore, the Ask1-MKK4-
p38MAPkinase cascade could be activated in 3T3-L1 adipocytes by TNFα,
IL-1β and by exposure to H2O2
Conclusion: Ask1, specifically in adipocytes, is a MAP3K activated in intraabdominal fat in human obesity, being regulated at both the expression and
phosphorylation levels. In cultured adipocytes it can be activated by pro-inflammatory cytokines and by oxidants, potentially reflecting on the stresstype and stress response developing in intra-abdominal fat in obesity
the activation of p38MAP kinase and JNK in response to oxidative stress,
inflammatory signals (TNF-R, Toll-like receptors) and endoplasmic reticulum stress. We previously reported that in human obesity omental fat exhibits
activation of JNK and p38MAP kinase in correlation with the degree of obesity-related cardio-metabolic risk. The aim of the present study was to assess
the possible role of Ask1 specifically in adipocytes in adipose tissue stress
response.
Materials and methods: We utilized two independent cohorts, in Leipzig,
Germany, and in Beer-Sheva, Israel, from whom paired omental (OM) and
subcutaneous abdominal (SC) fat samples were obtained. The protein expression and phosphorylation of Ask1 and its mRNA levels were assessed. To
investigate Ask1 activation specifically in adipocytes we separated adipocytes
from the stromal-vascular fraction (SVF) by collagenase digestion, and utilized 3T3-L1 adipocytes.
Results: Obesity was associated with elevated expression of Ask1 in OM at
both the mRNA (~1.5-fold, p<0.05) and protein levels (~2-fold, p<0.05),
as compared to the paired SC depot, and as compared to OM fat from lean
people. Ask1-mRNA levels correlated in OM more strongly than in SC with
fasting insulin levels and the glucose infusion rate during euglycemic-hyperinsulinic clamp (r=0.349 and r=-0.510, respectively, both p<0.001, n=196),
and with triglycerides and non-esterified fatty acid levels. Moreover, Ask1
phosphorylation on its auto-phosphorylation site, which confers activation, was elevated 2-2.5 fold in OM of obese women, and correlated with the
phosphorylation of the MAP2K MKK4 (r=0.474, p<0.01, n=19) and that of
p38MAP kinase (r=0.596, p<0.01, n=19). To verify the specific contribution
of adipocytes to the increased OM Ask1, collagenase digestion of fat biopsies
was performed, and Ask1-mRNA was assessed separately in OM adipocytes
versus OM SVF. Whereas in lean persons SVF had 6-fold higher expression of
Ask1, persons with predominantly subcutaneous obesity (determined by CT)
had ~2.5-fold higher expression in the adipocytes, with no change in the SVF.
In persons with predominantly intra-abdominal obesity Ask1 mRNA levels
increased 4.3-fold and 1.5-fold in adipocytes and SVF fraction, respectively
(both p<0.05) compared to the lean group. Furthermore, the Ask1-MKK4-
p38MAPkinase cascade could be activated in 3T3-L1 adipocytes by TNFα,
IL-1β and by exposure to H2O2
Conclusion: Ask1, specifically in adipocytes, is a MAP3K activated in intraabdominal fat in human obesity, being regulated at both the expression and
phosphorylation levels. In cultured adipocytes it can be activated by pro-inflammatory cytokines and by oxidants, potentially reflecting on the stresstype and stress response developing in intra-abdominal fat in obesity
| Original language | English |
|---|---|
| Pages | S51-S52 |
| Number of pages | 2 |
| DOIs | |
| State | Published - 1 Sep 2009 |
