An Essential Role of NRF2 in Diabetic Wound Healing.

The high mortality and disability of diabetic nonhealing skin ulcers create an urgent need for the development of more efficacious strategies targeting diabetic wound healing. In the current study, using human clinical specimens, we show that perilesional skin tissues from patients with diabetes are under more severe oxidative stress and display higher activation of the nuclear factor-E2-related factor 2 (NRF2)-mediated antioxidant response than perilesional skin tissues from normoglycemic patients. In a streptozotocin-induced diabetes mouse model, Nrf2(-/-) mice have delayed wound closure rates compared with Nrf2(+/+) mice, which is, at least partially, due to greater oxidative DNA damage, low transforming growth factor-ß1 (TGF-ß1) and high matrix metalloproteinase 9 (MMP9) expression, and increased apoptosis. More importantly, pharmacological activation of the NRF2 pathway significantly improves diabetic wound healing. In vitro experiments in human immortalized keratinocyte cells confirm that NRF2 contributes to wound healing by alleviating oxidative stress, increasing proliferation and migration, decreasing apoptosis, and increasing the expression of TGF-ß1 and lowering MMP9 under high-glucose conditions. This study indicates an essential role for NRF2 in diabetic wound healing and the therapeutic benefits of activating NRF2 in this disease, laying the foundation for future clinical trials using NRF2 activators in treating diabetic skin ulcers.

Collective cell migration of smooth muscle and endothelial cells: impact of injury versus non-injury stimuli.

BACKGROUND: Cell migration is a vital process for growth and repair. In vitro migration assays, utilized to study cell migration, often rely on physical scraping of a cell monolayer to induce cell migration. The physical act of scrape injury results in numerous factors stimulating cell migration - some injury-related, some solely due to gap creation and loss of contact inhibition. Eliminating the effects of cell injury would be useful to examine the relative contribution of injury versus other mechanisms to cell migration. Cell exclusion assays can tease out the effects of injury and have become a new avenue for migration studies. Here, we developed two simple non-injury techniques for cell exclusion: 1) a Pyrex® cylinder - for outward migration of cells and 2) a polydimethylsiloxane (PDMS) insert - for inward migration of cells. Utilizing these assays smooth muscle cells (SMCs) and human umbilical vein endothelial cells (HUVECs) migratory behavior was studied on both polystyrene and gelatin-coated surfaces. RESULTS: Differences in migratory behavior could be detected for both smooth muscle cells (SMCs) and endothelial cells (ECs) when utilizing injury versus non-injury assays. SMCs migrated faster than HUVECs when stimulated by injury in the scrape wound assay, with rates of 1.26 % per hour and 1.59 % per hour on polystyrene and gelatin surfaces, respectively. The fastest overall migration took place with HUVECs on a gelatin-coated surface, with the in-growth assay, at a rate of 2.05 % per hour. The slowest migration occurred with the same conditions but on a polystyrene surface at a rate of 0.33 % per hour. CONCLUSION: For SMCs, injury is a dominating factor in migration when compared to the two cell exclusion assays, regardless of the surface tested: polystyrene or gelatin. In contrast, the migrating surface, namely gelatin, was a dominating factor for HUVEC migration, providing an increase in cell migration over the polystyrene surface. Overall, the cell exclusion assays - the in-growth and out-growth assays, provide a means to determine pure migratory behavior of cells in comparison to migration confounded by cell wounding and injury.

p62 links autophagy and Nrf2 signaling.

The Nrf2-Keap1-ARE pathway is a redox and xenobiotic sensitive signaling axis that functions to protect cells against oxidative stress, environmental toxicants, and harmful chemicals through the induction of cytoprotective genes. To enforce strict regulation, cells invest a great deal of energy into the maintenance of the Nrf2 pathway to ensure rapid induction upon cellular insult and rapid return to basal levels once the insult is mitigated. Because of the protective role of Nrf2 transcriptional programs, controlled activation of the pathway has been recognized as a means for chemoprevention. On the other hand, constitutive activation of Nrf2, due to somatic mutations of genes that control Nrf2 degradation, promotes carcinogenesis and imparts chemoresistance to cancer cells. Autophagy, a bulk protein degradation process, is another tightly regulated complex cellular process that functions as a cellular quality control system to remove damaged proteins or organelles. Low cellular nutrient levels can also activate autophagy, which acts to restore metabolic homeostasis through the degradation of macromolecules to provide nutrients. Recently, these two cellular pathways were shown to intersect through the direct interaction between p62 (an autophagy adaptor protein) and Keap1 (the Nrf2 substrate adaptor for the Cul3 E3 ubiquitin ligase). Dysregulation of autophagy was shown to result in prolonged Nrf2 activation in a p62-dependent manner. In this review, we will discuss the progress that has been made in dissecting the intersection of these two pathways and the potential tumor-promoting role of prolonged Nrf2 activation.

Oxidative stress, mammospheres and Nrf2-new implication for breast cancer therapy?

Mammosphere culture of breast cancer cell lines is an important approach used for enrichment of cancer stem cells (CSCs), which exhibit high tumorigenicity and chemoresistance features. Evidence shows that CSCs maintain lower ROS levels due to elevated expression of ROS-scavenging molecules and antioxidative enzymes, which favors the survival of the CSCs and their chemoresistance. The transcription factor NF-E2-related factor 2 (Nrf2) has emerged as the master regulator of cellular redox homeostasis, by up-regulating antioxidant response element (ARE)-bearing genes products. Although Nrf2 has long-term been regarded as a beneficial defense mechanism, accumulating studies have revealed the "dark side" of Nrf2. High constitutive levels of Nrf2 was observed in many types of tumors and cancer cell lines promoting their resistance to chemotherapeutics. In this study, we report a high expression of Nrf2 and its target genes in mammospheres compared to corresponding adherent cells. In MCF-7 and MDA-MB-231 mammmosphere cells, the Nrf2-mediated cellular protective response is significantly elevated which is associated with increased resistance to taxol and anchorage-independent growth. Brusatol, an inhibitor of the Nrf2 pathway, suppressed the protein level of Nrf2 and its target genes, enhanced intracellular ROS and sensitized mammospheres to taxol, and reduced the anchorage-independent growth. These results suggest that mammospheres rely on abnormal up-regulation of Nrf2 to maintain low intracellular ROS levels. Nrf2 inhibitors, such as brusatol, have the potential to be developed into novel adjuvant chemotherapeutic drug combinations in order to combat refractory tumor initiating CSCs.

Oncogenic KRAS confers chemoresistance by upregulating NRF2.

Oncogenic KRAS mutations found in 20% to 30% of all non-small cell lung cancers (NSCLC) are associated with chemoresistance and poor prognosis. Here we demonstrate that activation of the cell protective stress response gene NRF2 by KRAS is responsible for its ability to promote drug resistance. RNAi-mediated silencing of NRF2 was sufficient to reverse resistance to cisplatin elicited by ectopic expression of oncogenic KRAS in NSCLC cells. Mechanistically, KRAS increased NRF2 gene transcription through a TPA response element (TRE) located in a regulatory region in exon 1 of NRF2. In a mouse model of mutant KrasG12D-induced lung cancer, we found that suppressing the NRF2 pathway with the chemical inhibitor brusatol enhanced the antitumor efficacy of cisplatin. Cotreatment reduced tumor burden and improved survival. Our findings illuminate the mechanistic details of KRAS-mediated drug resistance and provide a preclinical rationale to improve the management of lung tumors harboring KRAS mutations with NRF2 pathway inhibitors.

Hrd1 suppresses Nrf2-mediated cellular protection during liver cirrhosis.

Increased endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) are the salient features of end-stage liver diseases. Using liver tissues from liver cirrhosis patients, we observed up-regulation of the XBP1-Hrd1 arm of the ER stress response pathway and down-regulation of the Nrf2-mediated antioxidant response pathway. We further confirmed this negative regulation of Nrf2 by Hrd1 using Hrd1 conditional knockout mice. Down-regulation of Nrf2 was a surprising result, since the high levels of ROS should have inactivated Keap1, the primary ubiquitin ligase regulating Nrf2 levels. Here, we identified Hrd1 as a novel E3 ubiquitin ligase responsible for compromised Nrf2 response during liver cirrhosis. In cirrhotic livers, activation of the XBP1-Hrd1 arm of ER stress transcriptionally up-regulated Hrd1, resulting in enhanced Nrf2 ubiquitylation and degradation and attenuation of the Nrf2 signaling pathway. Our study reveals not only the convergence of ER and oxidative stress response pathways but also the pathological importance of this cross-talk in liver cirrhosis. Finally, we showed the therapeutic importance of targeting Hrd1, rather than Keap1, to prevent Nrf2 loss and suppress liver cirrhosis.

Tanshinone I activates the Nrf2-dependent antioxidant response and protects against As(III)-induced lung inflammation in vitro and in vivo.

AIMS: The NF-E2 p45-related factor 2 (Nrf2) signaling pathway regulates the cellular antioxidant response and activation of Nrf2 has recently been shown to limit tissue damage from exposure to environmental toxicants, including As(III). In an attempt to identify improved molecular agents for systemic protection against environmental insults, we have focused on the identification of novel medicinal plant-derived Nrf2 activators. RESULTS: Tanshinones [tanshinone I (T-I), tanshinone IIA, dihydrotanshinone, cryptotanshinone], phenanthrenequinone-based redox therapeutics derived from the medicinal herb Salvia miltiorrhiza, have been tested as experimental therapeutics for Nrf2-dependent cytoprotection. Using a dual luciferase reporter assay overexpressing wild-type or mutant Kelch-like ECH-associated protein-1 (Keap1), we demonstrate that T-I is a potent Keap1-C151-dependent Nrf2 activator that stabilizes Nrf2 by hindering its ubiquitination. In human bronchial epithelial cells exposed to As(III), T-I displays pronounced cytoprotective activity with upregulation of Nrf2-orchestrated gene expression. In Nrf2 wild-type mice, systemic administration of T-I attenuates As(III) induced inflammatory lung damage, a protective effect not observed in Nrf2 knockout mice. INNOVATION: Tanshinones have been identified as a novel class of Nrf2-inducers for antioxidant tissue protection in an in vivo As(III) inhalation model, that is relevant to low doses of environmental exposure. CONCLUSION: T-I represents a prototype Nrf2-activator that displays cytoprotective activity upon systemic administration targeting lung damage originating from environmental insults. T-I based Nrf2-directed systemic intervention may provide therapeutic benefit in protecting other organs against environmental insults.

Therapeutic potential of Nrf2 activators in streptozotocin-induced diabetic nephropathy.

OBJECTIVE: To determine whether dietary compounds targeting NFE2-related factor 2 (Nrf2) activation can be used to attenuate renal damage and preserve renal function during the course of streptozotocin (STZ)-induced diabetic nephropathy. RESEARCH DESIGN AND METHODS: Diabetes was induced in Nrf2(+/+) and Nrf2(-/-) mice by STZ injection. Sulforaphane (SF) or cinnamic aldehyde (CA) was administered 2 weeks after STZ injection and metabolic indices and renal structure and function were assessed (18 weeks). Markers of diabetes including blood glucose, insulin, polydipsia, polyuria, and weight loss were measured. Pathological alterations and oxidative damage in glomeruli were also determined. Changes in protein expression of the Nrf2 pathway, as well as transforming growth factor-ß1 (TGF-ß1), fibronectin (FN), collagen IV, and p21/WAF1Cip1 (p21) were analyzed. The molecular mechanisms of Nrf2-mediated protection were investigated in an in vitro model using human renal mesangial cells (HRMCs). RESULTS: SF or CA significantly attenuated common metabolic disorder symptoms associated with diabetes in Nrf2(+/+) but not in Nrf2(-/-) mice, indicating SF and CA function through specific activation of the Nrf2 pathway. Furthermore, SF or CA improved renal performance and minimized pathological alterations in the glomerulus of STZ-Nrf2(+/+) mice. Nrf2 activation reduced oxidative damage and suppressed the expression of TGF-ß1, extracellular matrix proteins and p21 both in vivo and in HRMCs. In addition, Nrf2 activation reverted p21-mediated growth inhibition and hypertrophy of HRMCs under hyperglycemic conditions. CONCLUSIONS: We provide experimental evidence indicating that dietary compounds targeting Nrf2 activation can be used therapeutically to improve metabolic disorder and relieve renal damage induced by diabetes.

Micro sensors: linking real-time oscillatory shear stress with vascular inflammatory responses.

The important interplay between blood circulation and vascular cell behavior warrants the development of highly sensitive but small sensing systems. The emerging micro electro mechanical systems (MEMS) technology, thus, provides the high spatiotemporal resolution to link biomechanical forces on the microscale with large-scale physiology. We fabricated MEMS sensors, comparable to the endothelial cells (ECs) in size, to link real-time shear stress with monocyte/EC interactions in an oscillatory flow environment, simulating the moving and unsteady separation point at arterial bifurcations. In response to oscillatory shear stress (tau) at +/- 2.6 dyn/cm2, time-averaged shear stress (tauave) = 0 at 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories, undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Incorporating with cell-tracking velocimetry, we visualized that these real-time events occurred over a dynamic range of oscillating shear stress between +/- 2.6 dyn/cm2 and Reynolds number between 0 and 22.2 in the presence of activated adhesion molecule and chemokine mRNA expression.

Monocyte recruitment to endothelial cells in response to oscillatory shear stress.

Leukocyte recruitment to endothelial cells is a critical event in inflammatory responses. The spatial, temporal gradients of shear stress, topology, and outcome of cellular interactions that underlie these responses have so far been inferred from static imaging of tissue sections or studies of statically cultured cells. In this report, we developed micro-electromechanical systems (MEMS) sensors, comparable to a single endothelial cell (EC) in size, to link real-time shear stress with monocyte/EC binding kinetics in a complex flow environment, simulating the moving and unsteady separation point at the arterial bifurcation with high spatial and temporal resolution. In response to oscillatory shear stress (tau) at +/- 2.6 dyn/cm2 at a time-averaged shear stress (tau(ave))=0 and 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Our study quantified individual monocyte/EC binding kinetics in terms of displacement and velocity profiles. Oscillatory flow induces up-regulation of adhesion molecules and cytokines to mediate monocyte/EC interactions over a dynamic range of shear stress +/- 2.6 dyn/cm2 (P=0.50, n=10).