A Descriptive Study of Hot Aches: a Previously Unreported Winter Climbing Phenomenon.

BACKGROUND: Hot aches, also known as the screaming barfies in North America, are a recognised phenomenon amongst winter climbers, assumed to be triggered by the reperfusion of cold peripheries which then rapidly progresses to a systemic vasodilatory syndrome. Symptoms experienced in the hands include pain, numbness and throbbing followed by systemic symptoms such as nausea, irritability, dizziness and in extreme cases a transient loss of vision and hearing. Despite being well known amongst the winter climbing community, there are no publications in the scientific literature characterising the hot aches. METHODS: A survey was posted online at http://www.ukclimbing.com between the dates of 28th September 2014 to 1st December 2014. Data was collected and analysed offline using Microsoft excel. RESULTS: This is a descriptive epidemiological study of UK winter climbers and their experience of hot aches. We found that hot aches are experienced by 96 % of these climbers. They generally last 1-5 min, and 75 % rate them as being 3-4 (out of 5) on a pain scale. The most common local symptoms are pain (87 %), throbbing (70 %) and tingling (52 %). The most common systemic symptoms are nausea (44 %), irritability (32 %) and dizziness (20 %). Twenty percent of climbers experience hot aches in locations other than their hands. CONCLUSIONS: The hot aches are a highly predictable and consistent experience for almost all winter climbers. This study has characterised, for the first time, a recognised but previously unreported phenomenon that occurs in extreme winter climbers. The short- and long-term consequences are currently unknown and warrant further investigation.

Chromatin as an oxygen sensor and active player in the hypoxia response.

Changes in the availability or demand for oxygen induce dramatic changes at the cellular level. Primarily, activation of a family of oxygen labile transcription factors, Hypoxia Inducible Factor (HIF), initiates a variety of cellular processes required to re-instate oxygen homeostasis. Oxygen is sensed by molecular dioxygenases in cells, such as the prolyl-hydroxylases (PHDs), enzymes which are responsible for the oxygen-dependent regulation of HIF. As HIF is a transcription factor it must bind DNA sequences of its target genes possibly in the context of a complex chromatin structure. How chromatin structure changes in response to hypoxia is currently unknown. However, the identification of a novel class of histone demethylases as true dioxygenases suggests that chromatin can act as an oxygen sensor and plays an active role in the coordination of the cellular response to hypoxia. This review will discuss the current knowledge on how hypoxia engages with different proteins involved in chromatin organisation and dynamics.

The chromatin remodeler ISWI regulates the cellular response to hypoxia: role of FIH.

The hypoxia-inducible factor (HIF) is a master regulator of the cellular response to hypoxia. Its levels and activity are controlled by dioxygenases called prolyl-hydroxylases and factor inhibiting HIF (FIH). To activate genes, HIF has to access sequences in DNA that are integrated in chromatin. It is known that the chromatin-remodeling complex switch/sucrose nonfermentable (SWI/SNF) is essential for HIF activity. However, no additional information exists about the role of other chromatin-remodeling enzymes in hypoxia. Here we describe the role of imitation switch (ISWI) in the cellular response to hypoxia. We find that unlike SWI/SNF, ISWI depletion enhances HIF activity without altering its levels. Furthermore, ISWI knockdown only alters a subset of HIF target genes. Mechanistically, we find that ISWI is required for full expression of FIH mRNA and protein levels by changing RNA polymerase II loading to the FIH promoter. Of interest, exogenous FIH can rescue the ISWI-mediated upregulation of CA9 but not BNIP3, suggesting that FIH-independent mechanisms are also involved. Of importance, ISWI depletion alters the cellular response to hypoxia by reducing autophagy and increasing apoptosis. These results demonstrate a novel role for ISWI as a survival factor during the cellular response to hypoxia.

HIF-1α depletion results in SP1-mediated cell cycle disruption and alters the cellular response to chemotherapeutic drugs.

Hypoxia inducible factor (HIF) is the major transcription factor involved in the regulation of the cellular response to hypoxia, or low oxygen tensions. Even though HIF-1 function is mostly studied following hypoxic stress, well oxygenated areas of several diseased tissues have detectable levels of this transcription factor. Therefore, it is surprising how little is known about the function of HIF in normoxia. This study seeks to fill this gap. Using transient HIF-1α knockdown, as well as, stable cell lines generated using short hairpin RNAs (shRNA), we have further characterized the role of HIF-1α in normoxia. Our data reveals that knockdown of HIF-1α results in a significant increase in cells in the G1 phase of the cell cycle. We find that HIF-1α depletion increases the protein and mRNA of both p21 and p27. p21 is induced via, at least in part, p53-independent but SP1-dependent mechanisms. Interestingly, HIF-1α knockdown also alters the cellular response to chemotherapeutic agents. These data have important implications in not only for the further understanding of HIF-1α, a major transcription factor, but also for the use of HIF-targeted and combination therapies in cancer treatment.

Further insights into the mechanism of hypoxia-induced NFκB. [corrected].

The cellular response to hypoxia relies on the activation of a specific transcriptional program. Although, most of the attention is focused on the transcription factor HIF, other transcription factors are also activated in hypoxia. We have recently described the mechanism for hypoxia induced NFκB. We have demonstrated the crucial dependency on the IKK complex as well as in the upstream IKK kinase TAK1. TAK1 and IKK activation is dependent upon the calcium calmodulin kinase, CaMK2 and requires Ubc13 as the E2 ubiquitin conjugation enzyme. We report a role for XIAP as the possible E3-ubiquitin ligase for this system. Interestingly, hypoxia induced IKK mediated phosphorylation of IκBα, does not lead to degradation. Hypoxia prevents IκBα de-sumoylation of Sumo-2/3 chains on critical lysine residues, normally required for K-48 linked polyubiquitination. Our results define a novel pathway regulating NFκB activation.

Mechanism of hypoxia-induced NF-kappaB.

NF-κB activation is a critical component in the transcriptional response to hypoxia. However, the underlying mechanisms that control its activity under these conditions are unknown. Here we report that under hypoxic conditions, IκB kinase (IKK) activity is induced through a calcium/calmodulin-dependent kinase 2 (CaMK2)-dependent pathway distinct from that for other common inducers of NF-κB. This process still requires IKK and the IKK kinase TAK1, like that for inflammatory inducers of NF-κB, but the TAK1-associated proteins TAB1 and TAB2 are not essential. IKK complex activation following hypoxia requires Ubc13 but not the recently identified LUBAC (linear ubiquitin chain assembly complex) ubiquitin conjugation system. In contrast to the action of other NF-κB inducers, IKK-mediated phosphorylation of IκBα does not result in its degradation. We show that this results from IκBα sumoylation by Sumo-2/3 on critical lysine residues, normally required for K-48-linked polyubiquitination. Furthermore, inhibition of specific Sumo proteases is sufficient to release RelA from IκBα and activate NF-κB target genes. These results define a novel pathway regulating NF-κB activation, important to its physiological role in human health and disease.

Methylation of H3K4 Is required for inheritance of active transcriptional states.

BACKGROUND: Maintenance of differentiation programs requires stability, when appropriate, of transcriptional states. However, the extent to which inheritance of active transcriptional states occurs from mother to daughter cells has not been directly addressed in unperturbed cell populations. RESULTS: By live imaging of single-gene transcriptional events in individual cells, we have directly recorded the potential for mitotic inheritance of transcriptional states down cell lineages. Our data showed strong similarity in frequency of transcriptional firing between mother and daughter cells. This memory persisted for complete cell cycles. Both transcriptional pulse length and pulsing rate contributed to overall inheritance, and memory was determined by lineage, not cell environment. Analysis of transcription in chromatin mutants demonstrated that the histone H3K4 methylase Set1 and Ash2, a component of the methylase complex, are required for memory. The effects of Set1 methylation may be mediated directly by chromatin, because loss of memory also occurred when endogenous H3K4 was replaced by alanine. Although methylated H3K4 is usually associated with active transcriptional units, the modification was not required for gene activity but stabilized transcriptional frequency between generations. CONCLUSIONS: Our data indicate that methylated H3K4 can act as a chromatin mark reflecting the original meaning of "epigenetic."