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Classically considered a by-product of anaerobic metabolism, lactate is now viewed as a fundamental fuel for oxidative phosphorylation in mitochondria, and preferred over glucose by many tissues. Lactate is also a signaling molecule of increasing medical relevance. Lactate levels in the blood can increase in both normal and pathophysiological conditions (e.g., hypoxia, physical exercise, or sepsis), however the manner by which these changes are sensed and induce adaptive responses is unknown. Here we show that the carotid body (CB) is essential for lactate homeostasis and that CB glomus cells, the main oxygen sensing arterial chemoreceptors, are also lactate sensors. Lactate is transported into glomus cells, leading to a rapid increase in the cytosolic NADH/NAD + ratio. This in turn activates membrane cation channels, leading to cell depolarization, action potential firing, and Ca 2+ influx. Lactate also decreases intracellular pH and increases mitochondrial reactive oxygen species production, which further activates glomus cells. Lactate and hypoxia, although sensed by separate mechanisms, share the same final signaling pathway and jointly activate glomus cells to potentiate compensatory cardiorespiratory reflexes. Lactate levels in blood change during hypoxia or exercise, however whether this variable is sensed to evoke adaptive responses is unknown. Here the authors show that oxygen-sensing carotid body cells stimulated by hypoxia are also activated by lactate to potentiate a compensatory ventilatory response.

Loss of functional mitochondrial complex I (MCI) in the dopaminergic neurons of the substantia nigra is a hallmark of Parkinson’s disease 1 . Yet, whether this change contributes to Parkinson’s disease pathogenesis is unclear 2 . Here we used intersectional genetics to disrupt the function of MCI in mouse dopaminergic neurons. Disruption of MCI induced a Warburg-like shift in metabolism that enabled neuronal survival, but triggered a progressive loss of the dopaminergic phenotype that was first evident in nigrostriatal axons. This axonal deficit was accompanied by motor learning and fine motor deficits, but not by clear levodopa-responsive parkinsonism—which emerged only after the later loss of dopamine release in the substantia nigra. Thus, MCI dysfunction alone is sufficient to cause progressive, human-like parkinsonism in which the loss of nigral dopamine release makes a critical contribution to motor dysfunction, contrary to the current Parkinson’s disease paradigm 3 , 4 . Dysfunction of mitochondrial complex I in mice is sufficient to cause progressive parkinsonism in which the loss of nigral dopamine release critically contributes to motor dysfunction.

Understanding the cellular adaptation to oxygen deficiency -hypoxia- has a profound impact on our knowledge of the pathogenesis of several diseases. The elucidation of the molecular machinery that regulates response to hypoxia has been awarded the Nobel Prize in Physiology or Medicine.

Induced pluripotent stem cells (iPSC) offer an unprecedented opportunity to model human disease in relevant cell types, but it is unclear whether they could successfully model age‐related diseases such as Parkinson's disease (PD). Here, we generated iPSC lines from seven patients with idiopathic PD (ID‐PD), four patients with familial PD associated to the G2019S mutation in the Leucine‐Rich Repeat Kinase 2 ( LRRK2 ) gene (LRRK2‐PD) and four age‐ and sex‐matched healthy individuals (Ctrl). Over long‐time culture, dopaminergic neurons (DAn) differentiated from either ID‐PD‐ or LRRK2‐PD‐iPSC showed morphological alterations, including reduced numbers of neurites and neurite arborization, as well as accumulation of autophagic vacuoles, which were not evident in DAn differentiated from Ctrl‐iPSC. Further induction of autophagy and/or inhibition of lysosomal proteolysis greatly exacerbated the DAn morphological alterations, indicating autophagic compromise in DAn from ID‐PD‐ and LRRK2‐PD‐iPSC, which we demonstrate occurs at the level of autophagosome clearance. Our study provides an iPSC‐based in vitro model that captures the patients' genetic complexity and allows investigation of the pathogenesis of both sporadic and familial PD cases in a disease‐relevant cell type.

Mammalian adaptation to oxygen flux occurs at many levels, from shifts in cellular metabolism to physiological adaptations facilitated by the sympathetic nervous system and carotid body (CB). Interactions between differing forms of adaptive response to hypoxia, including transcriptional responses orchestrated by the Hypoxia Inducible transcription Factors (HIFs), are complex and clearly synergistic. We show here that there is an absolute developmental requirement for HIF-2α, one of the HIF isoforms, for growth and survival of oxygen sensitive glomus cells of the carotid body. The loss of these cells renders mice incapable of ventilatory responses to hypoxia, and this has striking effects on processes as diverse as arterial pressure regulation, exercise performance, and glucose homeostasis. We show that the expansion of the glomus cells is correlated with mTORC1 activation, and is functionally inhibited by rapamycin treatment. These findings demonstrate the central role played by HIF-2α in carotid body development, growth and function.

The epigenomic landscape of Parkinson's disease (PD) remains unknown. We performed a genomewide DNA methylation and a transcriptome studies in induced pluripotent stem cell (iPSC)‐derived dopaminergic neurons (DAn) generated by cell reprogramming of somatic skin cells from patients with monogenic LRRK2‐associated PD (L2PD) or sporadic PD (sPD), and healthy subjects. We observed extensive DNA methylation changes in PD DAn, and of RNA expression, which were common in L2PD and sPD. No significant methylation differences were present in parental skin cells, undifferentiated iPSCs nor iPSC‐derived neural cultures not‐enriched‐in‐DAn. These findings suggest the presence of molecular defects in PD somatic cells which manifest only upon differentiation into the DAn cells targeted in PD. The methylation profile from PD DAn, but not from controls, resembled that of neural cultures not‐enriched‐in‐DAn indicating a failure to fully acquire the epigenetic identity own to healthy DAn in PD. The PD‐associated hypermethylation was prominent in gene regulatory regions such as enhancers and was related to the RNA and/or protein downregulation of a network of transcription factors relevant to PD (FOXA1, NR3C1, HNF4A, and FOSL2). Using a patient‐specific iPSC‐based DAn model, our study provides the first evidence that epigenetic deregulation is associated with monogenic and sporadic PD. Synopsis This is the first proof‐of‐principle that induced pluripotent stem cell (iPSC)‐derived dopaminergic neurons (DAn) from sporadic and monogenetic Parkinson's disease (PD) patients show the same epigenomic changes as compared to healthy controls. For a video version of this synopsis, see: http://embopress.org/video_EMM-2015-05439 . Epigenomic changes are common in patients with sporadic PD and patients with a monogenic form of PD associated with mutations in the gene LRRK2. PD‐associated methylation changes are latent in parental somatic cells or undifferentiated iPSCs and become uncovered upon differentiation into DAn (cells targeted in PD) but not into other neural types. PD‐associated methylation changes correlate with gene expression, target functionally‐ active sequences (enhancers), and are related to the aberrant down‐regulation of a network of transcription factors relevant to PD. Graphical Abstract This is the first proof‐of‐principle that induced pluripotent stem cell (iPSC)‐derived dopaminergic neurons (DAn) from sporadic and monogenetic Parkinson's disease (PD) patients show the same epigenomic changes as compared to healthy controls.

Vasodilation in response to low oxygen (O 2 ) tension (hypoxic vasodilation) is an essential homeostatic response of systemic arteries that facilitates O 2 supply to tissues according to demand. However, how blood vessels react to O 2 deficiency is not well understood. A common belief is that arterial myocytes are O 2 -sensitive. Supporting this concept, it has been shown that the activity of myocyte L-type Ca 2+ channels, the main ion channels responsible for vascular contractility, is reversibly inhibited by hypoxia, although the underlying molecular mechanisms have remained elusive. Here, we show that genetic or pharmacological disruption of mitochondrial electron transport selectively abolishes O 2 modulation of Ca 2+ channels and hypoxic vasodilation. Mitochondria function as O 2 sensors and effectors that signal myocyte Ca 2+ channels due to constitutive Hif1α-mediated expression of specific electron transport subunit isoforms. These findings reveal the acute O 2 -sensing mechanisms of vascular cells and may guide new developments in vascular pharmacology. Hypoxia inhibits the activity of calcium channels in arterial myocytes by unknown mechanisms and contributes to arterial vasodilation. Here, the authors show that myocyte mitochondria are essential for sensing acute hypoxia and generate signals (NADH and H 2 O 2 ) that modulate membrane calcium channels.

In response to hypoxia, neuron-like oxygen-sensitive glomus cells in the carotid body release neurotransmitters that rapidly activate afferent sensory fibres that stimulate the respiratory centre and induce hyperventilation1, although the mechanisms by which glomus cells detect changes in blood oxygen tension remain unclear2,3. [...]in 2017 a new cryorecovery was ordered and the resulting heterozygous mice were shipped directly to Seville and Duke Universities, without passing through the Frankfurt animal facility. [...]single dissociated glomus cells of wild-type and Olfr78-/- FRA mice, loaded with Fura-23,14, showed no difference in their increases of cytosolic Ca2+ levels to hypoxia (Fig. 2e-g). [...]our results at the cellular level are consistent with our results at the whole-animal level. Hortensia Torres-Torrelo1,2, Patricia Ortega-Sáenz1,2, David Macias3, Masayo Omura4, Ting Zhou5, Hiroaki Matsunami5,6, Randall S. Johnson3,7, Peter Mombaerts4 & José López-Barneo1,2· Instituto de Biomedicina de Sevilla (IBiS), Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain. 2Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Seville, Spain. 3Department of Physiology, Development & Neuroscience, University of Cambridge, Physiological Laboratory, Cambridge, UK. 4Max Planck Research Unit for Neurogenetics, Frankfurt, Germany. department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC, USA. department of Neurobiology and Duke Institute for Brain Sciences, Duke University Medical Center, Durham, NC, USA. department of Cell and Molecular Biology, Karolínska Institute, Stockholm, Sweden. ·e-mail: lbarneo@us.es Received: 13 February 2017; Accepted: 7 June 2018; Published online: 26 September 2018 Author contributions All authors participated in the design of the experiments.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Mutations of the von Hippel–Lindau ( VHL) gene are associated with pheochromocytomas and paragangliomas, but the role of VHL in sympathoadrenal homeostasis is unknown. We generated mice lacking Vhl in catecholaminergic cells. They exhibited atrophy of the carotid body (CB), adrenal medulla, and sympathetic ganglia. Vhl ‐null animals had an increased number of adult CB stem cells, although the survival of newly generated neuron‐like glomus cells was severely compromised. The effects of Vhl deficiency were neither prevented by pharmacological inhibition of prolyl hydroxylases or selective genetic down‐regulation of prolyl hydroxylase‐3, nor phenocopied by hypoxia inducible factor overexpression. Vhl‐deficient animals appeared normal in normoxia but survived for only a few days in hypoxia, presenting with pronounced erythrocytosis, pulmonary edema, and right cardiac hypertrophy. Therefore, in the normal sympathoadrenal setting, Vhl deletion does not give rise to tumors but impairs development and plasticity of the peripheral O 2 ‐sensing system required for survival in hypoxic conditions. Synopsis Instead of tumorigenesis, Vhl inactivation in rodent catecholaminergic cells in vivo causes atrophy of the adrenal medulla, carotid body (CB) and sympathetic ganglia. Hypoxia‐induced adult CB neurogenesis is inhibited and Vhl‐KO mice cannot acclimatize to hypoxia. Contrary to generally held beliefs Vhl is not a tumor suppressor gene in all cells. Vhl‐deficiency in mouse sympathoadrenal cells does not result in the appearance of tumors. Pheochromocytomas in man could be associated with gain‐of‐function mutations in VHL. Animals lacking Vhl exhibit atrophy of the CB and adrenal medulla and present a striking intolerance to systemic hypoxia that could give rise to death. Graphical Abstract Instead of tumorigenesis, Vhl inactivation in rodent catecholaminergic cells in vivo causes atrophy of the adrenal medulla, carotid body (CB) and sympathetic ganglia. Hypoxia‐induced adult CB neurogenesis is inhibited and Vhl‐KO mice cannot acclimatize to hypoxia.