Transcriptomic analysis of the mouse retina after acute and chronic normobaric and hypobaric hypoxia.

Oxygen delivery to the retinal pigment epithelium and the outer retina is essential for metabolism, function, and survival of photoreceptors. Chronically reduced oxygen supply leads to retinal pathologies in patients and causes age-dependent retinal degeneration in mice. Hypoxia can result from decreased levels of inspired oxygen (normobaric hypoxia) or reduced barometric pressure (hypobaric hypoxia). Since the response of retinal cells to chronic normobaric or hypobaric hypoxia is mostly unknown, we examined the effect of six hypoxic conditions on the retinal transcriptome and photoreceptor morphology. Mice were exposed to short- and long-term normobaric hypoxia at 400 m or hypobaric hypoxia at 3450 m above sea level. Longitudinal studies over 11 weeks in normobaric hypoxia revealed four classes of genes that adapted differentially to the hypoxic condition. Seventeen genes were specifically regulated in hypobaric hypoxia and may affect the structural integrity of the retina, resulting in the shortening of photoreceptor segment length detected in various hypoxic groups. This study shows that retinal cells have the capacity to adapt to long-term hypoxia and that consequences of hypobaric hypoxia differ from those of normobaric hypoxia. Our datasets can be used as references to validate and compare retinal disease models associated with hypoxia.

Reduced cancer mortality at high altitude: The role of glucose, lipids, iron and physical activity.

Residency at high altitude (HA) demands adaptation to challenging environmental conditions with hypobaric hypoxia being the most important one. Epidemiological and experimental data suggest that chronic exposure to HA reduces cancer mortality and lowers prevalence of metabolic disorders like diabetes and obesity implying that adaption to HA modifies a broad spectrum of physiological, metabolic and cellular programs with a generally beneficial outcome for humans. However, the complexity of multiple, potentially tumor-suppressive pathways at HA impedes the understanding of mechanisms leading to reduced cancer mortality. Many adaptive processes at HA are tightly interconnected and thus it cannot be ruled out that the entirety or at least some of the HA-related alterations act in concert to reduce cancer mortality. In this review we discuss tumor formation as a concept of competition between healthy and cancer cells with improved fitness - and therefore higher competitiveness - of healthy cells at high altitude. We discuss HA-related changes in glucose, lipid and iron metabolism that may have an impact on tumorigenesis. Additionally, we discuss two parameters with a strong impact on tumorigenesis, namely drug metabolism and physical activity, to underpin their potential contribution to HA-dependent reduced cancer mortality. Future studies are needed to unravel why cancer mortality is reduced at HA and how this knowledge might be used to prevent and to treat cancer patients.

The differential role of Jak/STAT signaling in retinal degeneration.

Retinal degenerative diseases are a major cause of severe visual impairment or blindness in humans. To develop therapeutic strategies it is of particular importance to understand the molecular mechanisms taking place during the progression of the disease. Genes and proteins of the Janus kinase/Signal Transducer and Activator of Transcription (Jak/STAT) signaling pathway have been shown to play an important role in models of retinal degeneration (RD). Here we investigated the expression of additional genes involved in the Jak/STAT pathway in an induced (light exposure) and an inherited (rd1 mouse) model of RD. We show that STAT mRNAs as well as the Jak2/shp-1 pathway are differentially regulated in the two models. In contrast, we show that Jak3 mRNA is upregulated in both, the light damaged and the degenerative retina of the rd1 mouse. This common answer to probably different apoptotic stimuli suggests a prominent role for Jak3 in the damaged retina and could therefore be interesting for further investigations.