Role of compartmentalization on HiF-1α degradation dynamics during changing oxygen conditions: a computational approach

Modelling the Impact of HIF on Metabolism and the Extracellular Matrix: Consequences for Tumour Growth and Invasion

The extracellular matrix (ECM) is a complex structure involved in many biological processes with collagen being the most abundant protein. Density of collagen fibers in the matrix is a factor influencing cell motility and migration speed. In cancer, this affects the ability of cells to migrate and invade distant tissues which is relevant for designing new therapies. Furthermore, increased cancer cell migration and invasion have been observed in hypoxic conditions. Interestingly, it has been revealed that the Hypoxia Inducible Factor (HIF) can not only impact the levels of metabolic genes but several collagen remodeling genes as well. The goal of this paper is to explore the impact of the HIF protein on both the tumour metabolism and the cancer cell migration with a focus on the Warburg effect and collagen remodelling processes. Therefore, we present an agent-based model (ABM) of tumour growth combining genetic regulations with metabolic and collagen-related processes involved in HIF pathways. Cancer cell migration is influenced by the extra-cellular collagen through a biphasic response dependant on collagen density. Results of the model showed that extra-cellular collagen within the tumour was mainly influenced by the local cellular density while collagen also influenced the shape of the tumour. In our simulations, proliferation was reduced with higher extra-cellular collagen levels or with lower oxygen levels but reached a maximum in the absence of cell-cell adhesion. Interestingly, combining lower levels of oxygen with higher levels of collagen further reduced the proliferation of the tumour. Since HIF impacts the metabolism and may affect the appearance of the Warburg Effect, we investigated whether different collagen conditions could lead to the adoption of the Warburg phenotype. We found that this was not the case, results suggested that adoption of the Warburg phenotype seemed mainly controlled by inhibition of oxidative metabolism by HIF combined with oscillations of oxygen.

On the Importance of Acidity in Cancer Cells and Therapy

Cancer cells are associated with high glycolytic activity, which results in acidification of the tumor microenvironment. The occurrence of this stressful condition fosters tumor aggressiveness, with the outcome of invasiveness and metastasis that are linked to a poor clinical prognosis. Acidosis can be both the cause or consequence of alterations in the functions and expressions of transporters involved in intracellular acidity regulation. This review aims to explore the origin of acidity in cancer cells and the various mechanisms existing in tumors to resist, survive, or thrive in the acidic environment. It highlights the difficulties in measuring the intracellular pH evolution that impedes our understanding of the many regulatory and feedback mechanisms. It finally presents the consequences of acidity on tumor development as well as the friend or foe role of acidity in therapy.

UBXN7 cofactor of CRL3KEAP1 and CRL2VHL ubiquitin ligase complexes mediates reciprocal regulation of NRF2 and HIF-1α proteins

UBXN7 is a cofactor protein that provides a scaffold for both CRL3^KEAP1 and CRL2^VHL ubiquitin ligase complexes involved in the regulation of the NRF2 and HIF-1α protein levels respectively. NRF2 and HIF-1α are surveillance transcription factors that orchestrate the cellular response to oxidative stress (NRF2) or to hypoxia (HIF-1α). Since mitochondria are the main oxygen sensors as well as the principal producers of ROS, it can be presumed that they may be able to modulate the activity of CRL3^KEAP1 and CRL2^VHL complexes in response to stress. We have uncovered a new mechanism of such regulation that involves the UBXN7 cofactor protein and its regulation by mitochondrial MUL1 E3 ubiquitin ligase. High level of UBXN7 leads to HIF-1α accumulation, whereas low level of UBXN7 correlates with an increase in NRF2 protein. The reciprocal regulation of HIF-1α and NRF2 by UBXN7 is coordinated under conditions of oxidative stress or hypoxia. In addition, this molecular mechanism leads to different metabolic states; high level of UBXN7 and accumulation of HIF-1α support glycolysis, whereas inactivation of UBXN7 and activation of NRF2 confer increased OXPHOS. We describe a new mechanism by which MUL1 E3 ubiquitin ligase modulates the UBXN7 cofactor protein level and provides a reciprocal regulation of CRL3^KEAP1 and CRL2^VHL ubiquitin ligase complexes. Furthermore, we delineate how this regulation is reflected in NRF2 and HIF-1α accumulation and determines the metabolic state as well as the adaptive response to mitochondrial stress.

Interleukin-15 Signaling in HIF-1α Regulation in Natural Killer Cells, Insights Through Mathematical Models

Natural killer (NK) cells belong to the first line of host defense against infection and cancer. Cytokines, including interleukin-15 (IL-15), critically regulate NK cell activity, resulting in recognition and direct killing of transformed and infected target cells. NK cells have to adapt and respond in inflamed and often hypoxic areas. Cellular stabilization and accumulation of the transcription factor hypoxia-inducible factor-1α (HIF-1α) is a key mechanism of the cellular hypoxia response. At the same time, HIF-1α plays a critical role in both innate and adaptive immunity. While the HIF-1α hydroxylation and degradation pathway has been recently described with the help of mathematical methods, less is known concerning the mechanistic mathematical description of processes regulating the levels of HIF-1α mRNA and protein. In this work we combine mathematical modeling with experimental laboratory analysis and examine the dynamic relationship between HIF-1α mRNA, HIF-1α protein, and IL-15-mediated upstream signaling events in NK cells from human blood. We propose a system of non-linear ordinary differential equations with positive and negative feedback loops for describing the complex interplay of HIF-1α regulators. The experimental design is optimized with the help of mathematical methods, and numerical optimization techniques yield reliable parameter estimates. The mathematical model allows for the investigation and prediction of HIF-1α stabilization under different inflammatory conditions and provides a better understanding of mechanisms mediating cellular enrichment of HIF-1α. Thanks to the combination of in vitro experimental data and in silico predictions we identified the mammalian target of rapamycin (mTOR), the nuclear factor-κB (NF-κB), and the signal transducer and activator of transcription 3 (STAT3) as central regulators of HIF-1α accumulation. We hypothesize that the regulatory pathway proposed here for NK cells can be extended to other types of immune cells. Understanding the molecular mechanisms involved in the dynamic regulation of the HIF-1α pathway in immune cells is of central importance to the immune cell function and could be a promising strategy in the design of treatments for human inflammatory diseases and cancer.

Retracted Article: Exosomal miR-25-3p derived from hypoxia tumor mediates IL-6 secretion and stimulates cell viability and migration in breast cancer

Hypoxia is a major hallmark of solid tumors and is associated with malignant phenotypes. Exosomal miRNAs derived from hypoxia tumor cells are implicated in the modulation of cancer progression, whereas, the mechanisms underlying the association between hypoxia and exosomal miR-25-3p during breast cancer progression remain to be further clarified. The present study aimed to investigate the role of exosomal miR-25-3p in regulating breast cancer progression. Herein, we found that miR-25-3p expression was increased in hypoxia tumor-derived exosomes a HIF-1α-dependent manner. Hypoxia exosomes markedly stimulated the viability and migration of normoxia breast cancer cells, which was reversed by miR-25-3p depletion. Inhibition of exosomes miR-25-3p lowered hypoxic-induced the expression of IL-6 and NF-κB from THP-1 and RAW264.7 cells in a TLR7/8-dependent way. Treatment of macrophage supernatant (MS) initially incubated with hypoxic-responsed exosomes accelerated the viability and migration of breast cancer cells, and miR-25-3p depletion relieved the stimulatory effects of hypoxic on cell viability and migration. Moreover, miR-25-3p knockdown dramatically suppressed HIF-1α-induced tumor growth in vivo via inactivation of IL-6/STAT3 signaling pathway, reflected by the abated abundances of IL-6 and p-STAT3. These data suggested that absence of exosomal miR-25-3p rescued breast cancer aggressiveness through inhibiting cell viability and migration by regulation of IL-6 secretion from macrophages, providing a potential biomarker for breast cancer treatment.

Hypoxia is a major hallmark of solid tumors and is associated with malignant phenotypes.

Mathematical modelling of interacting mechanisms for hypoxia mediated cell cycle commitment for mesenchymal stromal cells

Background

Existing experimental data have shown hypoxia to be an important factor affecting the proliferation of mesenchymal stromal cells (MSCs), but the contrasting observations made at various hypoxic levels raise the questions of whether hypoxia accelerates proliferation, and how. On the other hand, in order to meet the increasing demand of MSCs, an optimised bioreactor control strategy is needed to enhance in vitro production.

Results

A comprehensive, single-cell mathematical model has been constructed in this work, which combines cellular oxygen sensing with hypoxia-mediated cell cycle progression to predict cell cycle commitment as a proxy to proliferation rate. With oxygen levels defined for in vitro cell culture, the model predicts enhanced proliferation under intermediate (2–8%) and mild (8–15%) hypoxia and cell quiescence under severe (< 2%) hypoxia. Global sensitivity analysis and quasi-Monte Carlo simulation revealed that within a certain range (+/− 100%), model parameters affect (with varying significance) the minimum commitment time, but the existence of a range of optimal oxygen tension could be preserved with the hypothesized effects of Hif2α and reactive oxygen species (ROS). It appears that Hif2α counteracts Hif1α and ROS-mediated protein deactivation under intermediate hypoxia and normoxia (20%), respectively, to regulate the response of cell cycle commitment to oxygen tension.

Conclusion

Overall, this modelling study offered an integrative framework to capture several interacting mechanisms and allowed in silico analysis of their individual and collective roles in shaping the hypoxia-mediated commitment to cell cycle. The model offers a starting point to the establishment of a suitable mechanism that can satisfactorily explain the different existing experimental observations from different studies, and warrants future extension and dedicated experimental validation to eventually support bioreactor optimisation.

Electronic supplementary material

The online version of this article (10.1186/s12918-018-0560-3) contains supplementary material, which is available to authorized users.

How tumour-induced vascular changes alter angiogenesis: Insights from a computational model

A computational model was developed to describe experimentally observed vascular changes induced by the introduction of a tumour on a mouse equipped with a dorsal skinfold chamber. The vascular structure of the host tissue was segmented from in vivo images and transposed into the computational framework. Simulations of tumour-induced vascular changes were performed and include the destabilizing effects of the growth factor VEGF on the integrity of the vessels walls. The integration of those effects, that include alteration of the vessel wall elasticity and wall breaching, were required to realistically reproduce the experimental observations. The model was then used to investigate the importance of the vascular changes for oxygen delivery and tumour development. To that end, we compared simulations obtained with a dynamic vasculature with those obtained with a static one. The results showed that the tumour growth was strongly impeded by the constant vascular changes. More precisely, it is the angiogenic process itself that was affected by vascular changes occurring in bigger upstream vessels and resulting in a less efficient angiogenic network for oxygen delivery. As a consequence, tumour cells are mostly kept in a non-proliferative hypoxic state. Tumour dormancy thus appears as one potential consequence of the intense vascular changes in the host tissue.

Chronic intermittent hypoxia leads to insulin resistance and impaired glucose tolerance through dysregulation of adipokines in non-obese rats

BACKGROUND AND OBJECTIVES

The aim of this study was to determine whether chronic intermittent hypoxia (CIH) could affect the secretion of adipokines, such as resistin, leptin, and adiponectin, in non-obese rats and to investigate the potential mechanisms.

METHODS

An established rodent model of CIH was utilized, in which rats were exposed to varying oxygen levels (7-21 %) respectively over a period of 5 weeks. The area under the curve (AUCG) and the insulin resistance index (homeostasis model of assessment for insulin resistance index, HOMA-IR) were calculated. The levels of several secretory factors in the blood were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA levels and protein expression in adipose tissues was measured by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Glucose tolerance and the levels of adiponectin in non-obese rats were decreased in the CIH group both in the serum and adipose tissue compared with the controls, while the insulin resistance index and the levels of resistin and leptin were increased. Moreover, the expressions of hypoxia inducible factor-1α and lactate dehydrogenase A were significantly higher in chronic intermittent hypoxia rats than in control rats, suggesting the presence of adipose tissue hypoxia.

CONCLUSIONS

These results show that CIH leads to insulin resistance (IR) and impaired glucose tolerance (IGT) in a non-obese rodent model of obstructive sleep apnea-hypopnea syndrome, and these effects may be due to the dysregulation of adiponectin, resistin, and leptin.