Pivotal role of protein tyrosine phosphatase 1B (PTP1B) in the macrophage response to pro-inflammatory and anti-inflammatory challenge.

Inhibition of protein tyrosine phosphatase 1B (PTP1B) has been suggested as an attractive target to improve insulin sensitivity in different cell types. In the present work, we have investigated the effect of PTP1B deficiency on the response of human and murine macrophages. Using in vitro and in vivo approaches in mice and silencing PTP1B in human macrophages with specific siRNAs, we have demonstrated that PTP1B deficiency increases the effects of pro-inflammatory stimuli in both human and rodent macrophages at the time that decreases the response to alternative stimulation. Moreover, the absence of PTP1B induces a loss of viability in resting macrophages and mainly after activation through the classic pathway. Analysis of early gene expression in macrophages treated with pro-inflammatory stimuli confirmed this exacerbated inflammatory response in PTP1B-deficient macrophages. Microarray analysis in samples from wild-type and PTP1B-deficient macrophages obtained after 24 h of pro-inflammatory stimulation showed an activation of the p53 pathway, including the excision base repair pathway and the insulin signaling pathway in the absence of PTP1B. In animal models of lipopolysaccharide (LPS) and D-galactosamine challenge as a way to reveal in vivo inflammatory responses, animals lacking PTP1B exhibited a higher rate of death. Moreover, these animals showed an enhanced response to irradiation, in agreement with the data obtained in the microarray analysis. In summary, these results indicate that, although inhibition of PTP1B has potential benefits for the treatment of diabetes, it accentuates pro-inflammatory responses compromising at least macrophage viability.

Critical role of the death receptor pathway in the antitumoral effects induced by hispanolone derivatives.

Labdane diterpenoids have a broad spectrum of biological activities including antibacterial, antiviral and anti-inflammatory properties. However, little is known about their possible role in the apoptotic cell death machinery. Here, we report that hispanolone derivatives, a group of labdane diterpenoids, induce apoptosis in different tumor cell lines by activating caspase-8 with subsequent participation of mitochondrial signaling. Activation of caspase-8 by hispanolone derivatives was followed by a decrease in mitochondrial membrane potential, the release of apoptotic factors from mitochondria to the cytosol, and activation of caspases-9 and 3. Hispanolone derivatives also led to a time-dependent cleavage of Bid. Inhibition of caspase-8 abrogated these processes, suggesting that the death receptor pathway has a critical role in the apoptotic events induced by hispanolone derivatives. In addition, silencing death receptors with small interfering RNA s or pretreating cells with neutralizing antibodies to Fas ligand, tumor necrosis factor receptor 1 (TNF-R1), and TNF-α receptor 2 (TRAIL) inhibited diterpenoid-induced apoptosis, revealing it to be dependent on these death receptors. Interestingly, hispanolone derivatives had no effect on non-tumor cells. Consistently, in vivo bioluminescence imaging corroborates this antineoplasic effect, as hispanolone derivatives significantly decrease cancer growth in tumor xenograft assays. These data demostrate the antitumoral effects of hispanolone derivatives and provide relevant preclinical validation for the use of these compounds as potent therapeutic agents in cancer treatment.

Lipoxin A4 impairment of apoptotic signaling in macrophages: implication of the PI3K/Akt and the ERK/Nrf-2 defense pathways.

Lipoxin A(4) (LXA(4)) is an endogenous lipid mediator that requires transcellular metabolic traffic for its synthesis. The targets of LXA(4) on neutrophils are well described, contributing to attenuation of inflammation. However, effects of lipoxins on macrophage are less known, particularly the action of LXA(4) on the regulation of apoptosis of these cells. Our data show that pretreatment of human or murine macrophages with LXA(4) at the concentrations prevailing in the course of resolution of inflammation (nanomolar range) significantly inhibits the apoptosis induced by staurosporine, etoposide and S-nitrosoglutathione or by more pathophysiological stimuli, such as LPS/IFNgamma challenge. The release of mitochondrial mediators of apoptosis and the activation of caspases was abrogated in the presence of LXA(4). In addition to this, the synthesis of reactive oxygen species induced by staurosporine was attenuated and antiapoptotic proteins of the Bcl-2 family accumulated in the presence of lipoxin. Analysis of the targets of LXA(4) identified an early activation of the PI3K/Akt and ERK/Nrf-2 pathways, which was required for the observation of the antiapoptotic effects of LXA(4). These data suggest that the LXA(4), released after the recruitment of neutrophils to sites of inflammation, exerts a protective effect on macrophage viability that might contribute to a better resolution of inflammation.