Forkhead box O transcription factors (FoxOs) play an important role in maintaining normal cell physiology by regulating survival, apoptosis, autophagy, oxidative stress, the development and maturation of T and B lymphocytes, and the secretion of inflammatory cytokines. Cell types whose functions are regulated by FoxOs include keratinocytes, mucosal dermis, neutrophils, macrophages, dendritic cells, tumor-infiltrating activated regulatory T (Tregs) cells, B cells, and natural killer (NK) cells. FoxOs plays a crucial role in physiological and pathological immune responses. FoxOs control the development and function of Foxp3+ Tregs. Treg cells and Th17 cells are subsets of CD4+ T cells, which play an essential role in immune homeostasis and infection. Dysregulation of the Th17/Treg cell balance has been implicated in the development and progression of several disorders, such as autoimmune diseases, inflammatory diseases, and cancer. In addition, FoxOs are stimulated by the mitogen-activated protein (MAP) kinase pathway and inhibited by the PI3 kinase/AKT pathway. Downstream target genes of FoxOs include pro-inflammatory signaling molecules (toll-like receptor (TLR) 2, TLR4, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α), chemokine receptors (CCR7 and CXCR2), B-cell regulators (APRIL and BLYS), T-regulatory modulators (Foxp3 and CTLA-4), and DNA repair enzymes (GADD45α). Here, we review the recent progress in our understanding of FoxOs as the key molecules involved in immune cell differentiation and its role in the initiation of autoimmune diseases caused by dysregulation of immune cell balance. Additionally, in various diseases, FoxOs act as a cancer repressor, and reviving the activity of FoxOs forces Tregs to egress from various tissues. However, FoxOs regulate the cytotoxicity of both CD8+ T and NK cells against tumor cells, aiding in the restoration of redox and inflammatory homeostasis, repair of the damaged tissue, and activation of immune cells. A better understanding of FoxOs regulation may help develop novel potential therapeutics for treating immune/oxidative stress-related diseases.

The ocean is a rich resource of flora, fauna, food, and biological products. We found a wild-type bacterial strain, Pseudoalteromonas sp. M2, from marine water and isolated various secondary metabolites. Pseudane-VII is a compound isolated from the Pseudoalteromonas sp. M2 metabolite that possesses anti-melanogenic activity. Inflammation is a response of the innate immune system to microbial infections. Macrophages have a critical role in fighting microbial infections and inflammation. Recent studies reported that various compounds derived from natural products can regulate immune responses including inflammation. However, the anti-inflammatory effects and mechanism of pseudane-VII in macrophages are still unknown. In this study, we investigated the anti-inflammatory effects of pseudane-VII. In present study, lipopolysaccharide (LPS)-induced nitric oxide (NO) production was significantly decreased by pseudane-VII treatment at 6 μM. Moreover, pseudane-VII treatment dose-dependently reduced mRNA levels of pro-inflammatory cytokines including inos, cox-2, il-1β, tnf-α, and il-6 in LPS-stimulated macrophages. Pseudane-VII also diminished iNOS protein levels and IL-1β secretion. In addition, Pseudane-VII elicited anti-inflammatory effects by inhibiting ERK, JNK, p38, and nuclear factor (NF)-κB-p65 phosphorylation. Consistently, pseudane-VII was also shown to inhibit the LPS-stimulated release of IL-1β and expression of iNOS in mice. These results suggest that pseudane-VII exerted anti-inflammatory effects on LPS-stimulated macrophage activation via inhibition of ERK, JNK, p38 MAPK phosphorylation, and pro-inflammatory gene expression. These findings may provide new approaches in the effort to develop anti-inflammatory therapeutics.

We previously isolated pseudane-VII from the secondary metabolites of Pseudoalteromonas sp. M2 in marine water, and demonstrated its anti-inflammatory efficacy on macrophages. However, the molecular mechanism by which pseudane-VII suppresses neuroinflammation has not yet been elucidated in brain microglia. Microglia is activated by immunological stimulation or brain injury. Activated microglia secrete proinflammatory mediators which damage neurons. Neuroinflammation appears to be associated with certain neurological diseases, including Parkinson’s disease and Alzheimer’s disease. Natural compounds that suppress microglial inflammatory responses could potentially be used to prevent neurodegenerative diseases or slow their progression. In the present study, we found that pseudane-VII suppresses neuroinflammation in lipopolysaccaride (LPS)-stimulated BV-2 microglial cells and brain. Pseudane-VII was shown to inhibit the LPS-stimulated NO, ROS production and the expression of iNOS and COX-2. To identify the signaling pathway targeted by pseudane-VII, we used western blot analysis to assess the LPS-induced phosphorylation state of p38, ERK1/2, JNK1/2, and nuclear factor-kappaB (NF-κB). We found that pseudane-VII attenuated LPS-induced phosphorylation of MAPK and NF-κB. Moreover, administration of pseudane-VII in mice significantly reduced LPS-induced iNOS expression and microglia activation in brain. Taken together, our findings suggest that pseudane-VII may represent a potential novel target for treatment for neurodegenerative diseases.

Inflammation exacerbates systemic pathophysiological conditions and chronic inflammation is a sustained and systemic phenomenon that aggravates aging that can lead to chronic age-related diseases. These inflammatory phenomena have recently been redefined and delineated at the molecular, cellular, and systemic levels. Many transcription factors that are activated in response to tumor metabolic state have been reported to be regulated by a class of histone deacetylase called sirtuins (SIRTs). Sirtuins play a pivotal role in the regulation of tumor cell metabolism, proliferation, and angiogenesis, including oxidative stress and inflammation. The SIRT1-mediated signaling pathway in diabetes and cancer is the SIRT1/forkhead-box class O (FoxO)/nuclear factor-kappa B (NF-κB) pathway. In this review, we describe the accumulation of SIRT1-, NF-κB-, and FoxO-mediated inflammatory processes and cellular proinflammatory signaling pathways. We also describe the proinflammatory mechanisms underlying metabolic molecular pathways in various diseases such as liver cancer and diabetes. Finally, the regulation of cancer and diabetes through the anti-inflammatory effects of natural compounds is highlighted. Evidence from inflammation studies strongly suggests that cells may be a major source of cytokines secreted during various diseases. A better understanding of the mechanisms that underpin the inflammatory response and palliative role of natural compounds will provide insights into the molecular mechanisms of inflammation and various diseases for potential intervention.