Endogenous glucocorticoids (GCs) are steroid hormones that signal in virtually all cell types to modulate tissue homeostasis throughout life. Also, synthetic GC derivatives (pharmacological GCs) constitute the first-line treatment in many chronic inflammatory conditions with unquestionable therapeutic benefits despite the associated adverse effects. GC actions are principally mediated through the GC receptor (GR), a ligand-dependent transcription factor. Despite the ubiquitous expression of GR, imbalances in GC signalling affect tissues differently, and with variable degrees of severity through mechanisms that are not completely deciphered. Congenital or acquired GC hypersensitivity or resistance syndromes can impact responsiveness to endogenous or pharmacological GCs, causing disease or inadequate therapeutic outcomes, respectively. Acquired GC resistance is defined as loss of efficacy or desensitization over time, and arises as a consequence of chronic inflammation, affecting around 30% of GC-treated patients. It represents an important limitation in the management of chronic inflammatory diseases and cancer, and can be due to impairment of multiple mechanisms along the GC signalling pathway. Among them, activation of the mitogen-activated protein kinases (MAPKs) and/or alterations in expression of their regulators, the dual-specific phosphatases (DUSPs), have been identified as common mechanisms of GC resistance. While many of the anti-inflammatory actions of GCs rely on GR-mediated inhibition of MAPKs and/or induction of DUSPs, the GC anti-inflammatory capacity is decreased or lost in conditions of excessive MAPK activation, contributing to disease susceptibility in tissue- and disease- specific manners. Here, we discuss potential strategies to modulate GC responsiveness, with the dual goal of overcoming GC resistance and minimizing the onset and severity of unwanted adverse effects while maintaining therapeutic potential.

Insulin resistance is a key condition in the development of type 2 diabetes. It is well established that exacerbated Jun NH2-terminal kinase (JNK) activity is involved in promoting insulin resistance in peripheral insulin-target tissues; however, this involvement is less documented in pancreatic β-cells. Using a transgenic mouse model, here we show that JNK activation in β-cells led to glucose intolerance as a result of impaired capacity to increase insulinemia in response to hyperglycemia. Pancreatic islets from these mice showed no obvious morphostructural abnormalities or decreased insulin content. In contrast, these islets failed to secrete insulin in response to glucose or insulin but were competent in succinate-, ketoisocaproate-, 3-isobutyl-1-methylxanthine (IBMX-), KCl-, and tolbutamide-induced insulin secretion. At the molecular level, JNK activation in β-cells inhibited insulin-induced Akt phosphorylation, pancreatic and duodenal homeobox 1 nucleocytoplasmic shuttling, and transcription of insulin-target genes. Remarkably, rosiglitazone restored insulin secretion in response to hyperglycemia in mice and insulin-induced insulin secretion and signaling in isolated islets. In conclusion, the mere activation of JNK suffices to induce insulin resistance in pancreatic β-cells by inhibition of insulin signaling in these cells, but it is not sufficient to elicit β-cell death. In addition, we provide the first evidence that thiazolidinediones exert insulin-sensitizing action directly on pancreatic β-cells.

IL(Interleukin)-4 is the main macrophage M2-type activator and induces an anti-inflammatory phenotype called alternative activation. The IL-4 signaling pathway involves the activation of STAT (Signal Transducer and Activator of Transcription)-6 and members of the MAPK (Mitogen-activated protein kinase) family. In primary-bone-marrow-derived macrophages, we observed a strong activation of JNK (Jun N-terminal kinase)-1 at early time points of IL-4 stimulation. Using selective inhibitors and a knockout model, we explored the contribution of JNK-1 activation to macrophages’ response to IL-4. Our findings indicate that JNK-1 regulates the IL-4-mediated expression of genes typically involved in alternative activation, such as Arginase 1 or Mannose receptor, but not others, such as SOCS (suppressor of cytokine signaling) 1 or p21^Waf−1 (cyclin dependent kinase inhibitor 1A). Interestingly, we have observed that after macrophages are stimulated with IL-4, JNK-1 has the capacity to phosphorylate STAT-6 on serine but not on tyrosine. Chromatin immunoprecipitation assays revealed that functional JNK-1 is required for the recruitment of co-activators such as CBP (CREB-binding protein)/p300 on the promoter of Arginase 1 but not on p21^Waf−1. Taken together, these data demonstrate the critical role of STAT-6 serine phosphorylation by JNK-1 in distinct macrophage responses to IL-4.

Plant polysaccharides can exert immunomodulatory activities. In this study we provided chemical characterization of wheat cell culture-derived polysaccharides (WCCPS) and assessed their capacity to modulate inflammatory responses in mouse macrophages. The total sample (T-010) contained arabinogalactans, arabinans, glucans and xyloglucans. Fractionation by anion-exchange chromatography rendered a bound acidic fraction (B-010) and an unbound neutral fraction (UB-010). The B-010 fraction was enriched in arabinogalactans and arabinans, with some galactans, homogalacturonans, and arabinoxylans. The neutral UB-010 fraction was composed of glucans and xyloglucans. None of the WCCPS preparations triggered cytokine production on their own, but each potentiated different macrophage responses to bacterial lipopolysaccharide (LPS). The total WCCPS in T-010 increased LPS-induced tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6 secretion, whereas the acidic arabinogalactan-rich fraction B-010 boosted IL-6 release and selectively upregulated nitric oxide synthase 2 (Nos2) and cholesterol 25-hydroxylase (Ch25h) expression in response to LPS. In contrast, the neutral UB-010 fraction enhanced IL-6 levels and induced Nos2 expression without altering Ch25h expression. These results suggest that WCCPS can modulate distinct aspects of the inflammatory response, with their effects shaped by their composition and structural features. Future research will focus on elucidating the molecular mechanisms underlying the immunomodulatory activity of WCCPS.