Targeting Chitinase 1 and Chitinase 3-Like 1 as Novel Therapeutic Strategy of Pulmonary Fibrosis

Chitinase 1 (CHIT1) and chitinase 3-like-1 (CHI3L1), two representative members of 18-Glycosyl hydrolases family, are significantly implicated in the pathogenesis of various human diseases characterized by inflammation and remodeling. Notably, dysregulated expression of CHIT1 and CHI3L1 was noted in the patients with pulmonary fibrosis and their levels were inversely correlated with clinical outcome of the patients. CHIT1 and CHI3L1, mainly expressed in alveolar macrophages, regulate profibrotic macrophage activation, fibroblast proliferation and myofibroblast transformation, and TGF-β signaling and effector function. Although the mechanism or the pathways that CHIT1 and CHI3L1 use to regulate pulmonary fibrosis have not been fully understood yet, these studies identify CHIT1 and CHI3L1 as significant modulators of fibroproliferative responses leading to persistent and progressive pulmonary fibrosis. These studies suggest a possibility that CHIT1 and CHI3L1 could be reasonable therapeutic targets to intervene or reverse established pulmonary fibrosis. In this review, we will discuss specific roles and regulatory mechanisms of CHIT1 and CHI3L1 in profibrotic cell and tissue responses as novel therapeutic targets of pulmonary fibrosis.

Quercetin prevents isoprenaline-induced myocardial fibrosis by promoting autophagy via regulating miR-223-3p/FOXO3

Atrial fibrillation (AF) is the common arrhythmias. Myocardial fibrosis (MF) is closely related to atrial remodeling and leads to AF. MF is the main cause of cardiovascular diseases and a pathological basis of AF. Thus, the underlying mechanism in MF and AF development should be fully elucidated for AF therapeutic innovation. Autophagy is a highly conserved lysosomal degradation pathway, and the relationship between autophagy and MF has been previously shown. Moreover, research reported that quercetin (Que) could ameliorate MF. The current study aimed to explore the mechanism of Que in MF. The results in this study showed that in clinical AF patients and in aged rats, miR-223-3p was high-expressed, while FOXO3 and autophagy pathway related proteins, such as ATG7, p62/SQSTM1 and the ratio of LC3B-II/LC3B-I were significantly inhibited. In vivo and in vitro studies, we found that Que can effectively inhibit the expression of miR-223-3p in AF model cells and rats myocardial tissues, and meanwhile enhance the expression of FOXO3 and activate the autophagy pathway, and significantly inhibit myocardial fibrosis, and improve myocardial remodeling in atrial fibrillation. All in all, in this study, we found that Que prevents isoprenaline-induced MF by increasing autophagy via regulating miR-223-3p/FOXO3.

SIRT5 prevents cigarette smoke extract-induced apoptosis in lung epithelial cells via deacetylation of FOXO3

Cigarette smoking plays an important role in increased incidence of chronic obstructive pulmonary disease (COPD). The underlying mechanism in which cigarette smoking induced impairment of lung epithelial cells is still unknown. SIRT5 is a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase, which has been implicated in the regulation of metabolism, stress responses, and aging. Forkhead box O3 (FOXO3) belongs to the O subclass of the forkhead family of transcription factors. It is also involved in protection from oxidative stress by upregulating antioxidants in epithelial cells. Here, we show that cigarette smoke extract (CSE) induces SIRT5 to deacetylate FOXO3 at K271 and K290. Deacetylation of FOXO3 promotes its nuclear localization. Notably, transfection with FOXO3 K271R- or K290R-attenuated CSE-induced apoptosis in SIRT5 knocked down cells, suggesting the protective effects of SIRT5, is mediated by FOXO3. In contrast, CSE stress upregulates SIRT5, which activates FOXO3α leading to rescuing apoptosis. Thus, SIRT5 constitutes a determinant of apoptosis by CSE in lung epithelial cells.

Sp1-mediated microRNA-182 expression regulates lung cancer progression

Our recent study indicated that overexpression of Sp1 enhances the proliferation of lung cancer cells, while represses metastasis. In this study, we found that the transcriptional activity of FOXO3 was increased, but its protein levels decreased following Sp1 expression. Sp1 increased expression of miR-182, which was then recruited to the 3'-untranslated region of FOXO3 mRNA to silence its translational activity. Knockdown of miR-182 inhibited lung cancer cells growth, but enhanced the invasive and migratory abilities of these cells through increased N-cadherin expression. Repression of FOXO3 expression in the miR-182 knockdown cells partially reversed this effect, suggesting that miR-182 promotes cancer cell growth and inhibits cancer metastatic activity by regulating the expression of FOXO3. The expression of several cancer metastasis-related genes such as ADAM9, CDH9 and CD44 was increased following miR-182 knockdown. In conclusion, in the early stages of lung cancer progression, Sp1 stimulates miR-182 expression, which in turn decreases FOXO3 expression. This stimulates proliferation and tumor growth. In the late stages, Sp1 and miR-182 decline, thus increasing FOXO3 expression, which leads to lung metastasis.

Measles virus nucleocapsid protein, a key contributor to Paget's disease, increases IL-6 expression via down-regulation of FoxO3/Sirt1 signaling

Measles virus plays an important role as an environmental factor in the pathogenesis of Paget's disease (PD). Previous studies have shown that IL-6 is increased in the bone marrow of Paget's patients and that measles virus nucleocapsid protein (MVNP) induces IL-6 secretion by pagetic osteoclasts. Further, IL-6 plays a critical role in the development of pagetic osteoclasts and bone lesions induced by PD, but the mechanisms regulating IL-6 production by MVNP remain unclear. Our current studies revealed that MVNP expression in osteoclast precursors down-regulated Sirt1 mRNA and protein, a negative regulator of NF-κB activity, which is a key factor for IL-6 expression. MVNP expression in NIH3T3 cells also elevated Il-6 transcription and impaired the expression of Sirt1 mRNA both under basal conditions and upon activation of the Sirt1 upstream regulator FoxO3 by LY294002 (a PI3K/AKT inhibitor). Luciferase activity assays showed that constitutively active FoxO3 abolished the repressive effect of MVNP on reporters driven by either FoxO3 response elements or the Sirt1 promoter. Further, protein stability assays revealed that FoxO3 was degraded more rapidly in MVNP-expressing cells than in control cells following the addition of cycloheximide. Similarly, co-transfection of MVNP and FoxO3 into HEK293 cells demonstrated that MVNP decreased the protein levels of over-expressed FoxO3 in a dose-dependent manner. Treatment with the proteasome inhibitor, MG132, blocked the MVNP-triggered decrease of FoxO3, and the treatment with the serine/threonine phosphatase inhibitor, calyculin A, revealed that MVNP increased phosphorylation of FoxO3. Further, over-expression of Sirt1 or treatment with the Sirt1 activator resveratrol blocked the increase in Il-6 transcription by MVNP. Finally, resveratrol reduced the numbers of TRAP positive multi-nuclear cells in bone marrow cultures from TRAP-MVNP transgenic mice to wild type levels. These results indicate that MVNP decreases FoxO3/Sirt1 signaling to enhance the levels of IL-6, which in part mediate MVNP's contribution to the development of Paget's disease.

Tumor suppressor FOXO3 mediates signals from the EGF receptor to regulate proliferation of colonic cells

Epithelial proliferation, critical for homeostasis, healing, and colon cancer progression, is in part controlled by epidermal growth factor receptor (EGFR). Proliferation of colonic epithelia can be induced by Citrobacter rodentium infection, and we have demonstrated that activity of tumor suppressor FOXO3 was attenuated after this infection. Thus the aim of this study was to determine the contribution of FOXO3 in EGFR-dependent proliferation of intestinal epithelia and colon cancer cell lines. In this study we show that, during infection with C. rodentium, EGFR was significantly phosphorylated in colonic mucosa and Foxo3 deficiency in this model lead to an increased number of bromodeoxyuridine-positive cells. In vitro, in human colon cancer cells, increased expression and activation of EGFR was associated with proliferation that leads to FOXO3 phosphorylation (inactivation). Following EGFR activation, FOXO3 was phosphorylated (via phosphatidylinositol 3-kinase/Akt) and translocated to the cytosol where it was degraded. Moreover, inhibition of proliferation by overexpressing FOXO3 was not reversed by the EGFR signaling, implicating FOXO3 as one of the regulators downstream of EGFR. FOXO3 binding to the promoter of the cell cycle inhibitor p27kip1 was decreased by EGFR signaling, suggesting its role in EGFR-dependent proliferation. In conclusion, we show that proliferation in colonic epithelia and colon cancer cells, stimulated by EGFR, is mediated via loss of FOXO3 activity and speculate that FOXO3 may serve as a target in the development of new pharmacological treatments of proliferative diseases.

Tumor suppressor FOXO3 participates in the regulation of intestinal inflammation

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is characterized by chronic mucosal injury and the infiltration of inflammatory cells. Tumor suppressor FOXO3 regulates gene expression and its translocation to the cytosol leads to the abrogation of its transcriptional function. We have previously shown that bacterial infection regulates FOXO3 in intestinal epithelial cells and increases cytokine levels. As TNFalpha is a major contributor in intestinal inflammation, the aim of this study was to assess its effect on FOXO3 and FOXO3's contribution to intestinal inflammation in vitro and in vivo. TNFalpha induces the translocation of nuclear FOXO3 into the cytosol where it undergoes proteasomal degradation in human intestinal HT-29 cells. Proximally, the PI3K and IKK pathways mediate TNFalpha-induced FOXO3 phosphorylation. In FOXO3-silenced HT-29 cells, TNFalpha-induced IL-8 expression is increased approximately 83%. In vivo, Foxo3 is present in the nuclei and cytosol of colonic crypt epithelia. In DSS-induced colonic inflammation, Foxo3's nuclear localization is lost and it is only found in the cytosol. Consistent with a role for Foxo3 in colitis, Foxo3-deficient mice treated with DSS developed more severe colonic inflammation with an increased number of intraepithelial lymphocytes and PMNs infiltrated in the epithelia, than wild-type mice. In summary, TNFalpha inactivates FOXO3 in intestinal epithelia through the PI3K and IKK pathways and FOXO3 inactivation leads to the upregulation of IL-8 in vitro; in vivo Foxo3 is in the cytosol of inflamed colonic epithelia and Foxo3 deficiency leads to severe intestinal inflammation.