Cellular senescence is a biological process by which cells lose their capacity to proliferate yet remain metabolically active. Although originally considered a protective mechanism to limit the formation of cancer, it is now appreciated that cellular senescence also contributes to the development of disease, including common respiratory ailments such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. While many factors have been linked to the development of cellular senescence, mitochondrial dysfunction has emerged as an important causative factor. In this study, we uncovered that the mitochondrial biogenesis pathway driven by the mammalian target of rapamycin/peroxisome proliferator-activated receptor-γ complex 1α/β (mTOR/PGC-1α/β) axis is markedly upregulated in senescent lung epithelial cells. Using two different models, we show that activation of this pathway is associated with other features characteristic of enhanced mitochondrial biogenesis, including elevated number of mitochondrion per cell, increased oxidative phosphorylation, and augmented mitochondrial reactive oxygen species (ROS) production. Furthermore, we found that pharmacological inhibition of the mTORC1 complex with rapamycin not only restored mitochondrial homeostasis but also reduced cellular senescence to bleomycin in lung epithelial cells. Likewise, mitochondrial-specific antioxidant therapy also effectively inhibited mTORC1 activation in these cells while concomitantly reducing mitochondrial biogenesis and cellular senescence. In summary, this study provides a mechanistic link between mitochondrial biogenesis and cellular senescence in lung epithelium and suggests that strategies aimed at blocking the mTORC1/PGC-1α/β axis or reducing ROS-induced molecular damage could be effective in the treatment of senescence-associated lung diseases.

The mitogen-activated protein kinase (MAPK) pathway, consisting of the Ras-Raf-MEK-ERK signaling cascade, regulates genes that control cellular development, differentiation, proliferation, and apoptosis. Within the cascade, multiple isoforms of Ras and Raf each display differences in functionality, efficiency, and, critically, oncogenic potential. According to the NCI, over 30% of all human cancers are driven by Ras genes. This dysfunctional signaling is implicated in a wide variety of leukemias and solid tumors, both with and without viral etiology. Due to the strong evidence of Ras-Raf involvement in tumorigenesis, many have attempted to target the cascade to treat these malignancies. Decades of unsuccessful experimentation had deemed Ras undruggable, but recently, the approval of Sotorasib as the first ever KRas inhibitor represents a monumental breakthrough. This advancement is not without novel challenges. As a G12C mutant-specific drug, it also represents the issue of drug target specificity within Ras pathway; not only do many drugs only affect single mutational profiles, with few pan-inhibitor exceptions, tumor genetic heterogeneity may give rise to drug-resistant profiles. Furthermore, significant challenges in targeting downstream Raf, especially the BRaf isoform, lie in the paradoxical activation of wild-type BRaf by BRaf mutant inhibitors. This literature review will delineate the mechanisms of Ras signaling in the MAPK pathway and its possible oncogenic mutations, illustrate how specific mutations affect the pathogenesis of specific cancers, and compare available and in-development treatments targeting the Ras pathway.

Background Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder characterized by oculocutaneous albinism and platelet dysfunction and can sometimes lead to a highly aggressive form of pulmonary fibrosis that mimics the fatal lung condition called idiopathic pulmonary fibrosis (IPF). Although the activities of various matrix metalloproteinases (MMPs) are known to be dysregulated in IPF, it remains to be determined whether similar changes in these enzymes can be detected in HPS. Results Here, we show that transcript and protein levels as well as enzymatic activities of MMP-2 and -9 are markedly increased in the lungs of mice carrying the HPS Ap3b1 gene mutation. Moreover, immunohistochemical staining localized this increase in MMP expression to the distal pulmonary epithelium, and shRNA knockdown of the Ap3b1 gene in cultured lung epithelial cells resulted in a similar upregulation in MMP-2 and -9 expression. Mechanistically, we found that upregulation in MMP expression associated with increased activity of the serine/threonine kinase Akt, and pharmacological inhibition of this enzyme resulted in a dramatic suppression of MMP expression in Ap3b1 deficient lung epithelial cells. Similarly, levels and activity of different MMPs were also found to be increased in the lungs of mice carrying the Bloc3 HPS gene mutation and in the bronchoalveolar lavage fluid of subjects with HPS. However, an association between MMP activity and disease severity was not detected in these individuals. Conclusions In summary, our findings indicate that MMP activity is dysregulated in the HPS lung, suggesting a role for these proteases as biological markers or pathogenic players in HPS lung disease. Electronic supplementary material The online version of this article (10.1186/s13023-019-1143-0) contains supplementary material, which is available to authorized users.

We performed liquid chromatography-tandem mass spectrometry (LC-MS/MS) on control and TGF-β1-exposed rat lung fibroblasts to identify proteins differentially expressed between cell populations. A total of 1648 proteins were found to be differentially expressed in response to TGF-β1 treatment and 196 proteins were expressed at ≥ 1.2 fold relative to control. Guided by these results, we next determined whether similar changes in protein expression were detectable in the rat lung after chronic exposure to silica dust. Of the five proteins selected for further analysis, we found that levels of all proteins were markedly increased in the silica-exposed rat lung, including the proteins for the very low density lipoprotein receptor (VLDLR) and the transmembrane (type I) heparin sulfate proteoglycan called syndecan 2 (SDC2). Because VLDLR and SDC2 have not, to our knowledge, been previously linked to the pathobiology of silicosis, we next examined whether knockdown of either gene altered responses to TGF-β1 in MRC-5 lung fibroblasts. Interestingly, we found knockdown of either VLDLR or SDC2 dramatically reduced collagen production to TGF-β1, suggesting that both proteins might play a novel role in myofibroblast biology and pathogenesis of silica-induced pulmonary fibrosis. In summary, our findings suggest that performing LC-MS/MS on TGF-β1 stimulated lung fibroblasts can uncover novel molecular targets of activated myofibroblasts in silica-exposed lung.

Adult T-cell leukemia and lymphoma (ATLL) is an intractable T-cell neoplasia caused by a retrovirus, namely Human T-cell leukemia virus type 1 (HTLV-1). Patients suffering from ATLL present a poor prognosis and have a dearth of treatment options. In contrast to the sporadic expression of viral transactivator protein Tax present at the 5’ promoter region Long terminal repeats (LTR), HTLV-1 bZIP gene (HBZ) is encoded by 3’LTR (the antisense promoter) and maintains its constant expression in ATLL cells and patients. The antisense promoter is associated with selective retroviral gene expression and has been an understudied phenomenon. Herein, we delineate the activity of transcription factor MEF (Myocyte enhancer factor)-2 family members, which were found to be enriched at the 3'LTR and play an important role in the pathogenesis of ATLL. Of the four MEF isoforms (A-D), MEF-2A and 2C were highly overexpressed in a wide array of ATLL cell lines and in acute ATLL patients. The activity of MEF-2 isoforms were determined by knock-down experiments that led to decreased cell proliferation and regulated cell cycle progression. High enrichment of MEF-2C was observed at the 3'LTR along with cofactors Menin and JunD resulting in binding of MEF-2C to HBZ at this region. Chemical inhibition of MEF-2 proteins resulted in the cytotoxicity of ATLL cells in vitro and reduction of proviral load in humanized mouse model. Taken together, this study provides a novel mechanism of 3’LTR regulation and establishes MEF-2 signaling a potential target for therapeutic intervention for ATLL.

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Chronic alcohol consumption renders the lung more susceptible to infections, in large part, by disrupting essential alveolar macrophage functions. Emerging evidence suggests that these functional deficits could be due to a suppression of GM-CSF signaling, which is believed to compromise monocyte growth and maturation in the lung. However, in addition to controlling monocyte behaviors, GM-CSF is also important for regulating surfactant homeostasis in the lung. For example, mice with targeted deletion of the gene for GM-CSF accumulate large amounts of phospholipids in their lung. Moreover, decreased GM-CSF signaling in humans has been mechanistically linked to the development of pulmonary alveolar proteinosis (PAP), a rare disorder in which surfactant lipids and proteins accumulate in alveolar macrophages and the lung exhibits enhanced susceptibility to respiratory infections. Consistent with parallel mechanisms in the PAP and alcoholic lung, we recently reported that levels of intrapulmonary lipids, albeit triglycerides and free fatty acids, were markedly increased in BAL fluid, whole lung digests and alveolar macrophages of chronically alcohol exposed rats. Additionally, we showed that uptake of saturated fatty acids alone was capable of inducing phenotypic and functional changes in alveolar macrophages that mimicked those in the alcohol-exposed rat and human lung. Herein, we discuss the role of GM-CSF in surfactant homeostasis and highlight the evidence that links decreased GM-CSF signaling to alveolar macrophage dysfunction in both the PAP and alcohol-exposed lung. Moreover, we propose a mechanism by which lipid accumulation itself can contribute to altering alveolar macrophage behaviors and propose how targeting this mechanism could potentially reduce the susceptibility to pulmonary infections in alcoholics.

Loss of proteostasis and cellular senescence are key hallmarks of aging. Recent studies suggest that lung fibroblasts from idiopathic pulmonary fibrosis (IPF) show features of cellular senescence, decline in heat shock proteins (HSPs) expression and impaired protein homeostasis (proteostasis). However, direct cause-effect relationships are still mostly unknown. In this study, we sought to investigate whether the heat shock factor 1 (HSF1), a major transcription factor that regulates the cellular HSPs network and cytoplasmic proteostasis, contributes to cellular senescence in lung fibroblasts. We found that IPF lung fibroblasts showed an upregulation in the expression of various cellular senescence markers, including β -galactosidase activity (SA-β-gal) staining, the DNA damage marker γ H2Ax, the cell cycle inhibitor protein p21, and multiple senescence-associated secretory proteins (SASP), as well as upregulation of collagen 1a1, fibronectin and alpha-smooth muscle actin (α-SMA) gene expression compared with age-matched controls. These changes were associated with impaired proteostasis, as judged by an increase in levels of p-HSF1 ser307 and HSF1 K298 sumo , downregulation of HSPs expression, and increased cellular protein aggregation. Similarly, lung fibroblasts isolated from a mouse model of bleomycin-induced lung fibrosis and mouse lung fibroblast chronically treated with H 2 O 2 showed downregulation in HSPs and increased in cellular senescence and SASP markers. Moreover, sustained pharmacologic activation of HSF1 increased the expression of HSPs, reduced cellular senescence markers and effectively reduced the expression of pro-fibrotic genes in IPF fibroblast. Our data provide evidence that the HSF1-mediated proteostasis is important for driving lung fibroblasts toward cellular senescence and a myofibroblast phenotype. We postulate that enhancing HSF1 activity could be effective in the treatment of lung fibrosis. METHODSAnimals. C57B/6J mice (8-10 weeks old) were purchased from the Jackson Laboratory (Bar Harbor, ME) and housed in a pathogen-free animal facility at Thomas Jefferson University. Throughout the study period, mice were maintained on a standard chow diet (13.5% calories from fat, 58% from carbohydrates, and 28.5% from protein) and permitted to feed ad libitum. ). They were isolated from the uninvolved periphery of the organ of six lung cancer patients. Fresh tissues were transported immediately to the laboratory for isolating fibroblasts according to procedures described before [35].Bleomycin-induced lung injury: Bleomycin sulphate (Enzo life science, BML-AP302-0050) was dissolved in phosphate buffered saline. Lung injury was induced by instilling 0.04U of bleomycin into the posterior oropharynx of anesthetized mice every other week for five doses [36]. The mice were observed following intubation to ensure complete recovery from anesthesia. Mice were euthanized 2 weeks after the last dose by exposure to carbon dioxide, and lungs were harvested for fibroblast isolation and histological preparation...