Physiological skin oxygen levels: An important criterion for skin cell functionality and therapeutic approaches

The skin is made up of different layers with various gradients, which maintain a complex microenvironment, particularly in terms of oxygen levels. However, all types of skin cells are cultured in conventional incubators that do not reproduce physiological oxygen levels. Instead, they are cultured at atmospheric oxygen levels, a condition that is far removed from physiology and may lead to the generation of free radicals known to induce skin ageing. This review aims to summarize the current literature on the effect of physiological oxygen levels on skin cells, highlight the shortcomings of current in vitro models, and demonstrate the importance of respecting skin oxygen levels. We begin by clarifying the terminology used about oxygen levels and describe the specific distribution of oxygen in the skin. We review and discuss how skin cells adapt their oxygen consumption and metabolism to oxygen levels environment, as well as the changes that are induced, particularly, their redox state, life cycle and functions. We examine the effects of oxygen on both simple culture models and more complex reconstructed skin models. Finally, we present the implications of oxygen modulation for a more therapeutic approach.

[Iron and age-related macular degeneration: a new track]

Iron has a fundamental role for cell physiology and especially in retina as a cofactor of many pathways of the visual transduction. A tightly regulated homeostasis avoids the accumulation of prooxidant and proinflammatory free iron. A dysfunction of iron retinal homeostasis is associated with many genetic or age-related degenerative diseases such as age-related macular degeneration (AMD). Here, we describe various mechanisms reported during AMD, enhanced by iron accumulation and its homeostasis dysregulation. We have investigated a local treatment with transferrin, the natural iron carrier, to control these pathological pathways and iron dysfunction, without side effects. Iron has a central role in pathogenesis of AMD and is a target for futures therapies.

[A new paradigm in the treatment of ischemia. Learning from drosophila]

Ischemia is one of the major concerns of clinicians who are constantly confronted with it, both in surgical and pathological aspects. The consequences of ischemic stress are dramatic and can lead to organic, motor or cognitive disabilities. Currently, there is no identified specific molecular target whose targeting could be beneficial in this area. The drosophila melanogaster fly, used as a model animal, has made it possible to highlight a major advance by allowing the identification of a completely new pharmacological target whose inhibition significantly increases tolerance to hypoxia. Applied to a preclinical model of renal transplantation, this new approach significantly improves the functional recovery of the graft in the long term. This mini-synthesis retraces the steps that made it possible to transfer to higher mammals a concept highlighted in Drosophila that clearly shows, beyond basic research, the contribution that a model organism can make to the clinic.

[Genetics of paragangliomas and pheochromocytomas]

Pheochromocytomas and paragangliomas are rare tumors that arise from chromaffin tissues of the adrenal medulla and from sympathetic and parasympathetic ganglia. Ten susceptibility genes (VHL, RET, NF1, SDHA, B, C and D, SDHAF2, TMEM127 and finally MAX) are responsible for at least 30% of the cases. These patients can either have a familial history of the disease, a syndromic presentation, but can also emerge as apparently sporadic forms. Moreover, recent transcriptomic studies have led to the identification of somatic mutations in VHL and RET genes in 15% of sporadic cases, thus bringing a molecular explanation for nearly half of all cases. These findings have had a major impact on the understanding of the molecular mechanisms of tumorigenesis in pheochromocytomas and paragangliomas. It was shown that the genetic status of tumors is associated with particular transcription signatures, such as the activation of the pseudohypoxic response or the activation of MAPK or mTOR signalling. From nowadays to a close future, these advances will have important consequences on the monitoring of patients, from genetic counseling to a personalized clinical management.

Hypoxia: the tumor's gateway to progression along the angiogenic pathway

Decreased aerobic (hypoxic) conditions in tumors induce the release of cytokines that promote vascularization and thereby enhance tumor growth and metastasis. Recent major advances have provided insight into the role hypoxia plays in cancer biology. The domain structure of the hypoxia-inducible factor 1alpha (HIF-1alpha) has been elucidated, as has the mechanism by which stabilization of HIF-1alpha leads to initiation of the transcription of target genes involved in growth of blood vessels.