Akshaya Chandrasekaran

Redox control of senescence and age-related disease

The signaling networks that drive the aging process, associated functional deterioration, and pathologies has captured the scientific communitys attention for decades. While many theories exist to explain the aging process, the production of reactive oxygen species (ROS) provides a signaling link between engagement of cellular senescence and several age-associated pathologies. Cellular senescence has evolved to restrict tumor progression but the accompanying senescence-associated secretory phenotype (SASP) promotes pathogenic pathways. Here, we review known biological theories of aging and how ROS mechanistically control senescence and the aging process. We also describe the redox-regulated signaling networks controlling the SASP and its important role in driving age-related diseases. Finally, we discuss progress in designing therapeutic strategies that manipulate the cellular redox environment to restrict age-associated pathology.

Francisella tularensis Catalase Restricts Immune Function by Impairing TRPM2 Channel Activity.

As an innate defense mechanism, macrophages produce reactive oxygen species that weaken pathogens and serve as secondary messengers involved in immune function. The Gram-negative bacterium Francisella tularensis utilizes its antioxidant armature to limit the host immune response, but the mechanism behind this suppression is not defined. Here we establish that F. tularensis limits Ca2+ entry in macrophages, thereby limiting actin reorganization and IL-6 production in a redox-dependent fashion. Wild type (live vaccine strain) or catalase-deficient F. tularensis (ΔkatG) show distinct profiles in their H2O2 scavenging rates, 1 and 0.015 pm/s, respectively. Murine alveolar macrophages infected with ΔkatG display abnormally high basal intracellular Ca2+ concentration that did not increase further in response to H2O2. Additionally, ΔkatG-infected macrophages displayed limited Ca2+ influx in response to ionomycin, as a result of ionophore H2O2 sensitivity. Exogenously added H2O2 or H2O2 generated by ΔkatG likely oxidizes ionomycin and alters its ability to transport Ca2+. Basal increases in cytosolic Ca2+ and insensitivity to H2O2-mediated Ca2+ entry in ΔkatG-infected cells are reversed by the Ca2+ channel inhibitors 2-aminoethyl diphenylborinate and SKF-96365. 2-Aminoethyl diphenylborinate but not SKF-96365 abrogated ΔkatG-dependent increases in macrophage actin remodeling and IL-6 secretion, suggesting a role for H2O2-mediated Ca2+ entry through the transient receptor potential melastatin 2 (TRPM2) channel in macrophages. Indeed, increases in basal Ca2+, actin polymerization, and IL-6 production are reversed in TRPM2-null macrophages infected with ΔkatG. Together, our findings provide compelling evidence that F. tularensis catalase restricts reactive oxygen species to temper macrophage TRPM2-mediated Ca2+ signaling and limit host immune function.

Redox-sensitive gene-regulatory events controlling aberrant matrix metalloproteinase-1 expression

Aberrant matrix metalloproteinase-1 (MMP-1) expression contributes to the pathogenesis of many degenerative disease processes that are associated with increased oxidative damage or stress. We and others have established that shifts in steady-state H2O2 production resulting from enforced antioxidant gene expression, senescence, or UV irradiation control MMP-1 expression. Here we establish that histone deacetylase-2 (HDAC2) protein levels and its occupancy of the MMP-1 promoter are decreased in response to enforced manganese superoxide dismutase (Sod2) expression. Inhibition of HDAC activity further accentuates the redox-dependent expression of MMP-1. Sod2-dependent decreases in HDAC2 are associated with increases in a proteasome-sensitive pool of ubiquitinylated HDAC2 and MMP-1-specific histone H3 acetylation. Sod2 overexpression also enhanced recruitment of Ets-1, c-Jun, c-Fos, and the histone acetyltransferase PCAF to the distal and proximal regions of the MMP-1 promoter. Furthermore, the Sod2-dependent expression of MMP-1 can be reversed by silencing the transcriptional activator c-Jun. All of the above Sod2-dependent alterations are largely reversed by catalase coexpression, indicating that the redox control of MMP-1 is H2O2-dependent. These findings identify a novel redox regulation of MMP-1 transcription that involves site-specific promoter recruitment of both activating factors and chromatin-modifying enzymes, which converge to maximally drive MMP-1 gene expression.

Comparative analysis of redox and inflammatory properties of pristine nanomaterials and commonly used semiconductor manufacturing nano-abrasives

Continued expansion of the nanotechnology industry has necessitated the self-assessment of manufacturing processes, specifically in regards to understanding the health related aspects following exposure to nanomaterials. There exists a growing concern over potential occupational exposure in the semiconductor industry where Al2O3, CeO2 and SiO2 nanoparticles are commonly featured as part of the chemical mechanical planarization (CMP) process. Chronic exposure to toxicants can result not only in acute cytotoxicity but also initiation of a chronic inflammatory state associated with diverse pathologies. In the current investigation, pristine nanoparticles and CMP slurry formulations of Al2O3, SiO2 and CeO2 were employed to assess their ability to induce cytotoxicity, inflammatory responses and reactive oxygen species in a mouse alveolar macrophage cell model. The pristine nanoparticles and slurries were not intrinsically cytotoxic and did not generate free radicals but were found to act as scavengers in the presence of an oxidant stimulant. Al2O3 and SiO2 nanoparticles increased levels of pro-inflammatory cytokines while pristine SiO2 nanoparticles induced generation of F2-Isoprostanes. In co-treatment studies, the pristine nanomaterials modulated the response to the inflammatory stimulant lipopolysaccharide. The studies have established that pristine nanoparticles and slurries do not impact the cells in a similar way indicating that they should not be used as slurry substitutes in toxicity evaluations. Further, we have defined how an alveolar cell line, which would likely be the first challenged upon nanomaterial aerosolization, responds to diverse mixtures of nanomaterials. Moreover, our findings reinforce the importance of using multiple analytic methods to define the redox state of the cell following exposure to commonly used industrial nanomaterials and toxicants.

Regulation of the Cellular Redox Environment by Superoxide Dismutases, Catalase, and Glutathione Peroxidases During Tumor Metastasis

The lethality of most cancers can be attributed to metastatic progression. Metastatic tumor cells adapt and cope with various stressful environments to enable survival during their metastatic journey which starts with the escape from the primary tumor and ends in colonization of secondary sites. Stressors of metastatic tumor microenvironments include deprivation of oxygen (hypoxia), inflammation, and chemo- and radiotherapeutic exposure, which have the propensity to expose cells to reactive oxygen species (ROS). Further, many tumor-associated cells, including cancer-associated fibroblasts, macrophages, and senescent cells within the tumor microenvironment, contribute to this ROS production. In addition to these exogenous sources, tumor cells themselves produce and are able to cope with elevated intracellular ROS. Increased ROS production outside and within metastatic tumor cells has been associated with a number of pro-metastatic events including angiogenesis, invasion, migration, survival, and anchorage-independent cell survival (anoikis resistance). Large surges of ROS can lead to oxidation of macromolecules and largely irreversible damage that may cause mitochondrial damage, leading to alterations in cancer metabolism, and genomic instability and carcinogenesis. More subtle changes in ROS lead to redox-signaling, primarily by reversible oxidation of thiols, which has been shown to contribute to pro-metastatic behavior. To cope with these changes in both intracellular and extracellular redox environments, tumor cells have uniquely evolved to alter their antioxidant enzyme expression. The present review focuses on antioxidant enzymes important in the regulation of H2O2 balance within metastatic tumor cells. It aims to highlight some of the dichotomous roles demonstrated for these enzymes in cancer etiology, and how their enzymatic activity may further influence the tumor redox environment and consequently regulate carcinogenesis and metastasis. We focus on the role of superoxide dismutases, catalase, and glutathione peroxidases and give examples on their demonstrated roles as both tumor suppressors and promoters. Specifically, we discuss how metastatic cancer cells uniquely adapt to alter expression of these enzymes and how this may contribute to changes in the intracellular redox environment to drive certain metastatic phenotypes. To therapeutically target these ROS-mediated pathways in metastatic disease will require further insights into the specificity of the ROS involved and their spatiotemporal regulation in the context of the antioxidant enzymes present.