Abstract
Protein-tyrosine phosphatase 1B (PTP1B) is a major negative regulator of insulin and leptin sensitivity. PTP1B overexpression in adipose tissue and skeletal muscle of humans and rodents may contribute to insulin resistance and obesity. The mechanisms mediating PTP1B overexpression in obese and diabetic states have been unclear. We find that adipose tissue inflammation and the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) regulate PTP1B expression in vivo. High fat feeding of mice increased PTP1B expression 1.5- to 7-fold in adipose tissue, liver, skeletal muscle, and arcuate nucleus of hypothalamus. PTP1B overexpression in high fat-fed mice coincided with increased adipose tissue expression of the macrophage marker CD68 and TNFalpha, which is implicated in causing obesity-induced insulin resistance. TNFalpha increased PTP1B mRNA and protein levels by 2- to 5-fold in a dose- and time-dependent manner in adipocyte and hepatocyte cell lines. TNFalpha administration in mice increased PTP1B mRNA 1.4- to 4-fold in adipose tissue, liver, skeletal muscle, and hypothalamic arcuate nucleus and PTP1B protein 2-fold in liver. Actinomycin D treatment blocked, and high dose salicylate treatment inhibited by 80%, TNFalpha-induced PTP1B expression in adipocyte cell lines, suggesting TNFalpha may induce PTP1B transcription via nuclear factor kappaB (NFkappaB) activation. Chromatin immunoprecipitation from adipocyte cell lines and liver of mice demonstrated TNFalpha-induced recruitment of NFkappaB subunit p65 to the PTP1B promoter in vitro and in vivo. In mice with diet-induced obesity, TNFalpha deficiency also partly blocked PTP1B overexpression in adipose tissue. Our data suggest that PTP1B overexpression in multiple tissues in obesity is regulated by inflammation and that PTP1B may be a target of anti-inflammatory therapies.
Highlights
According to current World Health Organization estimates, twice as many people worldwide suffer ill health effects from the accumulation of excess adipose mass (1.6 billion) than from
TNF␣ mRNA levels were increased in Coincides with the Development of Inflammation—To deter- adipose tissue of mice with DIO compared with chow-fed mice at mine whether Protein-tyrosine phosphatase 1B (PTP1B) is overexpressed in insulin- and leptin- both 15 and 20 weeks, but the magnitude of increase was substantarget tissues of mice with high fat diet-induced obesity (DIO) tially higher in mice at 20 weeks (Fig. 3, a versus b)
Together with previous studies [3], indicate that PTP1B expression is dynamically regulated by different metabolic states and that this regulation is an important mechanism by which PTP1B negatively regulates signaling pathways involved in growth and metabolism. chow-fed tumor necrosis factor ␣ (TNF␣)ϩ/ϩ and TNF␣Ϫ/Ϫ mice (Fig. 9d)
Summary
Animals—Mice and rats were housed at 22 °C with a 12-h/ 12-h or 14-h/10-h light/dark cycle and fed ad libitum. To detect CD68 protein in adipose tissue lysates, 400 g of protein was incubated with wheat germ agarose overnight and washed three times with lysis buffer, and bound proteins were separated by SDS-PAGE on 7.5% gels and subjected to immunoblotting with polyclonal anti-mouse CD68 antibodies (Serotec, Raleigh, NC). ChIP assays were performed on frozen livers of randomly fed 8 –9-week-old female FVB mice harvested 4 h after intravenous injection of mice with saline or 3.3 g of murine TNF␣, as described above. PTP1B was overexpressed 1.3-fold in liver and 3-fold in adipose tissue of obese, insulin-resistant ob/ob mice serum insulin (ng/ml) d. PTP1B protein was not overexpressed in liver, skeletal muscle, or adipose tissue of obese, insulin-resistant, type 2 diabetic db/db mice compared with lean controls (Fig. 1b) By ϳ35% in liver (Fig. 1d) compared with untreated mice
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