Transgenic NADH dehydrogenase restores oxygen regulation of breathing in mitochondrial complex I-deficient mice.

The hypoxic ventilatory response (HVR) is a life-saving reflex, triggered by the activation of chemoreceptor glomus cells in the carotid body (CB) connected with the brainstem respiratory center. The molecular mechanisms underlying glomus cell acute oxygen (O2) sensing are unclear. Genetic disruption of mitochondrial complex I (MCI) selectively abolishes the HVR and glomus cell responsiveness to hypoxia. However, it is unknown what functions of MCI (metabolic, proton transport, or signaling) are essential for O2 sensing. Here we show that transgenic mitochondrial expression of NDI1, a single-molecule yeast NADH/quinone oxidoreductase that does not directly contribute to proton pumping, fully recovers the HVR and glomus cell sensitivity to hypoxia in MCI-deficient mice. Therefore, maintenance of mitochondrial NADH dehydrogenase activity and the electron transport chain are absolutely necessary for O2-dependent regulation of breathing. NDI1 expression also rescues other systemic defects caused by MCI deficiency. These data explain the role of MCI in acute O2 sensing by arterial chemoreceptors and demonstrate the optimal recovery of complex organismal functions by gene therapy.

T2 Biomarkers as Predictors of Exacerbations of Chronic Obstructive Pulmonary Disease.

INTRODUCTION: Type 2 (T2) biomarkers such as blood eosinophil count (BEC) and FeNO have been related to a higher risk of exacerbations in COPD. It is unknown whether combining these biomarkers could be useful in forecasting COPD exacerbations. METHODS: COPD patients were enrolled in this prospective, multicenter, observational study and followed up for 1 year, during which BEC were analysed at baseline (V0) while FeNO analyses were performed at baseline (V0), 6 months (V1) and 12 months (V2). The risk of moderate or severe exacerbation during follow up was assessed by Cox regression analysis, and the predictive capacity of both measurements was assessed by ROC curves and the DeLong test. Statistical significance was assumed at P<.05. RESULTS: Of the 322 COPD patients initially recruited, 287 were followed up. At baseline, 28.0% were active smokers, and experienced moderate airflow limitation (mean FEV1 56.4%±17.0% predicted). Patients with at least one elevated T2 biomarker (n=125, 42.5%) were at increased risk of COPD exacerbation (HR 1.75, 95% CI 1.25-2.45, P=.001) and of shorter time to first COPD exacerbation. There was no difference between BEC and FeNO regarding the predictive capacity for moderate to severe exacerbation (AUC 0.584 vs 0.576, P=.183) but FeNO predicted severe episodes more accurately than BEC (AUC 0.607 vs 0.539, P<.05). Combining the two biomarkers enhanced the detection of moderate and severe COPD exacerbations. CONCLUSIONS: Both eosinophil count and FeNO have limited utility for predicting COPD exacerbations. Combining these T2 biomarkers could enhance the detection of future COPD exacerbations.

On the single and multiple associations of COVID-19 post-acute sequelae: 6-month prospective cohort study.

Medical research is progressing to clarify the full spectrum of sub-acute and long-term effects of the post-COVID-19 syndrome. However, most manuscripts published to date only analyze the effects of post-COVID-19 in patients discharged from hospital, which may induce significant bias. Here, we propose a pioneering study to analyze the single and multiple associations between post-COVID-19 characteristics with up to 6-months of follow-up in hospitalized and non-hospitalized COVID-19 patients. The cohort study was conducted from May to October 2020 at the University Hospital Virgen de la Nieves, the leading hospital assigned for patients with COVID-19 in Granada, Spain. A total of 372 and 217 patients-with 217 and 207 included in the first and second follow-up visits-were referred 2 and 6 months after diagnosing COVID-19, respectively. We find out that post-COVID-19 clinical and mental health impairment symptoms are correlated with patient gender. Logistic adjustments showed strong statistically robust single and multiple associations of demographic, clinical, mental health, X-ray, laboratory indices, and pulmonary function variables. The functional lung tests are good predictors of chest CT imaging abnormalities in elderly patients. Bilateral lung involvement, subpleural reticulum, ground-glass opacity, peripheral lung lesions, and bronchiectasis were the most common findings of the high-resolution computed tomography images. Non-hospitalized patients suffer more severe thromboembolic events and fatigue than those hospitalized.

Acute O2 sensing through HIF2α-dependent expression of atypical cytochrome oxidase subunits in arterial chemoreceptors.

Acute cardiorespiratory responses to O2 deficiency are essential for physiological homeostasis. The prototypical acute O2-sensing organ is the carotid body, which contains glomus cells expressing K+ channels whose inhibition by hypoxia leads to transmitter release and activation of nerve fibers terminating in the brainstem respiratory center. The mechanism by which changes in O2 tension modulate ion channels has remained elusive. Glomus cells express genes encoding HIF2α (Epas1) and atypical mitochondrial subunits at high levels, and mitochondrial NADH and reactive oxygen species (ROS) accumulation during hypoxia provides the signal that regulates ion channels. We report that inactivation of Epas1 in adult mice resulted in selective abolition of glomus cell responsiveness to acute hypoxia and the hypoxic ventilatory response. Epas1 deficiency led to the decreased expression of atypical mitochondrial subunits in the carotid body, and genetic deletion of Cox4i2 mimicked the defective hypoxic responses of Epas1-null mice. These findings provide a mechanistic explanation for the acute O2 regulation of breathing, reveal an unanticipated role of HIF2α, and link acute and chronic adaptive responses to hypoxia.

Small cell lung cancer: Recent changes in clinical presentation and prognosis.

BACKGROUND: Small cell lung cancer (SCLC) is a leading cause of death all over the world. Diagnostic and therapeutic arsenals have improved in recent years, but we are unsure as to whether these advances have been transferred to clinical practice. The aim of this study was to evaluate differences in SCLC diagnostic processes and short-term survival rates between two recent cohorts. METHODS: A prospective, observational study was conducted with patients diagnosed with SCLC (either at extensive or limited stages) in the 2011-2016 period. Patients were divided into two cohorts (2011-2013 and 2014-2016) and followed up for 1 year after diagnosis. RESULTS: Around 713 patients with lung cancer were selected, 134 of whom had SCLC (74 patients in the 2011-2013 cohort and 60 in the 2014-2016 cohort). We observed a chronological increase in the use of endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) and positron emission tomography-computed tomography (PET-CT) between the cohorts. Overall, short-term survival was similar between the two groups and improved survival was associated with age and limited stage. CONCLUSIONS: Changes in diagnostic process in SCLC have been observed towards a more precise stadification. Although short-term survival has not changed for SCLC, it is unclear that the real benefit of PET-CT and EBUS-TBNA is far from correct disease staging.

Changes in non-small cell lung cancer diagnosis, molecular testing and prognosis 2011-2016.

BACKGROUND: Non-small cell lung cancer (NSCLC) is a leading cause of death all over the world. Diagnostic and therapeutic arsenals have improved in recent years, but we are unsure as to whether these advances have been transferred to clinical practice. The aim of this study was to evaluate differences in NSCLC diagnostic processes and short-term survival rates between two recent cohorts. METHODS: A prospective, observational study was conducted with patients diagnosed with NSCLC in the period of 2011-2016. Patients were divided into two cohorts (2011-2013 and 2014-2016), and monitored for up to 1 year after diagnosis. RESULTS: A total of 713 patients with lung cancer were selected, 500 of whom had NSCLC (222 patients in the 2011-2013 cohort, and 278 in the 2014-2016 cohort). We observed a chronological increase in the use of endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) and ultrasound-guided transthoracic puncture (US-TTP) between the cohorts. Overall short-term survival was similar between the two groups, both for locally and for advanced disease. Treatment with tyrosine kinase inhibitors (TKI) was the only therapeutic factor associated with an improved likelihood of survival. CONCLUSIONS: Changes in diagnostic process in NSCLC have been observed towards a more precise stratification. Although short-term survival has not changed for advanced NSCLC, some of the newer therapeutic options are associated with increased survival in real-world scenarios.

Gene expression analyses reveal metabolic specifications in acute O2 -sensing chemoreceptor cells.

KEY POINTS: Glomus cells in the carotid body (CB) and chromaffin cells in the adrenal medulla (AM) are essential for reflex cardiorespiratory adaptation to hypoxia. However, the mechanisms whereby these cells detect changes in O2 tension are poorly understood. The metabolic properties of acute O2 -sensing cells have been investigated by comparing the transcriptomes of CB and AM cells, which are O2 -sensitive, with superior cervical ganglion neurons, which are practically O2 -insensitive. In O2 -sensitive cells, we found a characteristic prolyl hydroxylase 3 down-regulation and hypoxia inducible factor 2α up-regulation, as well as overexpression of genes coding for three atypical mitochondrial electron transport subunits and pyruvate carboxylase, an enzyme that replenishes tricarboxylic acid cycle intermediates. In agreement with this observation, the inhibition of succinate dehydrogenase impairs CB acute O2 sensing. The responsiveness of peripheral chemoreceptor cells to acute hypoxia depends on a 'signature metabolic profile'. ABSTRACT: Acute O2 sensing is a fundamental property of cells in the peripheral chemoreceptors, e.g. glomus cells in the carotid body (CB) and chromaffin cells in the adrenal medulla (AM), and is necessary for adaptation to hypoxia. These cells contain O2 -sensitive ion channels, which mediate membrane depolarization and transmitter release upon exposure to hypoxia. However, the mechanisms underlying the detection of changes in O2 tension by cells are still poorly understood. Recently, we suggested that CB glomus cells have specific metabolic features that favour the accumulation of reduced quinone and the production of mitochondrial NADH and reactive oxygen species during hypoxia. These signals alter membrane ion channel activity. To investigate the metabolic profile characteristic of acute O2 -sensing cells, we used adult mice to compare the transcriptomes of three cell types derived from common sympathoadrenal progenitors, but exhibiting variable responsiveness to acute hypoxia: CB and AM cells, which are O2 -sensitive (glomus cells > chromaffin cells), and superior cervical ganglion neurons, which are practically O2 -insensitive. In the O2 -sensitive cells, we found a characteristic mRNA expression pattern of prolyl hydroxylase 3/hypoxia inducible factor 2α and up-regulation of several genes, in particular three atypical mitochondrial electron transport subunits and some ion channels. In addition, we found that pyruvate carboxylase, an enzyme fundamental to tricarboxylic acid cycle anaplerosis, is overexpressed in CB glomus cells. We also observed that the inhibition of succinate dehydrogenase impairs CB acute O2 sensing. Our data suggest that responsiveness to acute hypoxia depends on a 'signature metabolic profile' in chemoreceptor cells.

Oxygen Sensing by Arterial Chemoreceptors Depends on Mitochondrial Complex I Signaling.

O2 sensing is essential for mammalian homeostasis. Peripheral chemoreceptors such as the carotid body (CB) contain cells with O2-sensitive K(+) channels, which are inhibited by hypoxia to trigger fast adaptive cardiorespiratory reflexes. How variations of O2 tension (PO2) are detected and the mechanisms whereby these changes are conveyed to membrane ion channels have remained elusive. We have studied acute O2 sensing in conditional knockout mice lacking mitochondrial complex I (MCI) genes. We inactivated Ndufs2, which encodes a protein that participates in ubiquinone binding. Ndufs2-null mice lose the hyperventilatory response to hypoxia, although they respond to hypercapnia. Ndufs2-deficient CB cells have normal functions and ATP content but are insensitive to changes in PO2. Our data suggest that chemoreceptor cells have a specialized succinate-dependent metabolism that induces an MCI state during hypoxia, characterized by the production of reactive oxygen species and accumulation of reduced pyridine nucleotides, which signal neighboring K(+) channels.

Resistance of glia-like central and peripheral neural stem cells to genetically induced mitochondrial dysfunction--differential effects on neurogenesis.

Mitochondria play a central role in stem cell homeostasis. Reversible switching between aerobic and anaerobic metabolism is critical for stem cell quiescence, multipotency, and differentiation, as well as for cell reprogramming. However, the effect of mitochondrial dysfunction on neural stem cell (NSC) function is unstudied. We have generated an animal model with homozygous deletion of the succinate dehydrogenase subunit D gene restricted to cells of glial fibrillary acidic protein lineage (hGFAP-SDHD mouse). Genetic mitochondrial damage did not alter the generation, maintenance, or multipotency of glia-like central NSCs. However, differentiation to neurons and oligodendrocytes (but not to astrocytes) was impaired and, hence, hGFAP-SDHD mice showed extensive brain atrophy. Peripheral neuronal populations were normal in hGFAP-SDHD mice, thus highlighting their non-glial (non hGFAP(+)) lineage. An exception to this was the carotid body, an arterial chemoreceptor organ atrophied in hGFAP-SDHD mice. The carotid body contains glia-like adult stem cells, which, as for brain NSCs, are resistant to genetic mitochondrial damage.

A conditional mouse mutant in the tumor suppressor SdhD gene unveils a link between p21(WAF1/Cip1) induction and mitochondrial dysfunction.

Mutations in mitochondrial complex II (MCII; succinate dehydrogenase, Sdh) genes cause familiar pheochromocytoma/paraganglioma tumors. Several mechanisms have been proposed to account for Sdh-mutation-induced tumorigenesis, the most accepted of which is based on the constitutive expression of the hypoxia-inducible factor 1α (Hif1α) at normal oxygen tension, a theory referred to as "pseudo-hypoxic drive". Other molecular processes, such as oxidative stress, apoptosis, or chromatin remodeling have been also proposed to play a causative role. Nevertheless, the actual contribution of each of these mechanisms has not been definitively established. Moreover, the biological factors that determine the tissue-specificity of these tumors have not been identified. In this work, we made use of the inducible SDHD-ESR mouse, a conditional mutant in the SdhD gene, which encodes the small subunit of MCII, and that acts as a tumor suppressor gene in humans. The analysis of the Hif1α pathway in SDHD-ESR tissues and in two newly derived cell lines after complete SdhD loss -a requirement for hereditary paraganglioma type-1 tumor formation in humans- partially recapitulated the "pseudo-hypoxic" response and rendered inconsistent results. Therefore, we performed microarray analysis of adrenal medulla and kidney in order to identify other early gene expression changes elicited by SdhD deletion. Our results revealed that each mutant tissue displayed different variations in their gene expression profiles affecting to different biological processes. However, we found that the Cdkn1a gene was up-regulated in both tissues. This gene encodes the cyclin-dependent kinase inhibitor p21(WAF1/Cip1), a factor implicated in cell cycle, senescence, and cancer. The two SDHD-ESR cell lines also showed accumulation of this protein. This new and unprecedented evidence for a link between SdhD dysfunction and p21(WAF1/Cip1) will open new avenues for the study of the mechanisms that cause tumors in Sdh mutants. Finally, we discuss the actual role of Hif1α in tumorigenesis.

Differential impairment of catecholaminergic cell maturation and survival by genetic mitochondrial complex II dysfunction.

The SDHD gene (subunit D of succinate dehydrogenase) has been shown to be involved in the generation of paragangliomas and pheochromocytomas. Loss of heterozygosity of the normal allele is necessary for tumor transformation of the affected cells. As complete SdhD deletion is lethal, we have generated mouse models carrying a "floxed" SdhD allele and either an inducible (SDHD-ESR strain) or a catecholaminergic tissue-specific (TH-SDHD strain) CRE recombinase. Ablation of both SdhD alleles in adult SDHD-ESR mice did not result in generation of paragangliomas or pheochromocytomas. In contrast, carotid bodies from these animals showed smaller volume than controls. In accord with these observations, the TH-SDHD mice had decreased cell numbers in the adrenal medulla, carotid body, and superior cervical ganglion. They also manifested inhibited postnatal maturation of mesencephalic dopaminergic neurons and progressive cell loss during the first year of life. These alterations were particularly intense in the substantia nigra, the most affected neuronal population in Parkinson's disease. Unexpectedly, TH(+) neurons in the locus coeruleus and group A13, also lacking the SdhD gene, were unaltered. These data indicate that complete loss of SdhD is not sufficient to induce tumorigenesis in mice. They suggest that substantia nigra neurons are more susceptible to mitochondrial damage than other catecholaminergic cells, particularly during a critical postnatal maturation period.

Mitochondrial complex II participates in normoxic and hypoxic regulation of α-keto acids in the murine heart.

α-Keto acids (α-KAs) are not just metabolic intermediates but are also powerful modulators of different cellular pathways. Here, we tested the hypothesis that α-KA concentrations are regulated by complex II (succinate dehydrogenase=SDH), which represents an intersection between the mitochondrial respiratory chain for which an important function in cardiopulmonary oxygen sensing has been demonstrated, and the Krebs cycle, a central element of α-KA metabolism. SDH subunit D heterozygous (SDHD(+/-)) and wild-type (WT) mice were housed at normoxia or hypoxia (10% O(2)) for 4 days or 3 weeks, and right ventricular pressure, right ventricle/(left ventricle+septum) ratio, cardiomyocyte ultrastructure, pulmonary vascular remodelling, ventricular complex II subunit expression, SDH activity and α-KA concentrations were analysed. In both strains, hypoxia induced increases in right ventricular pressure and enhanced muscularization of distal pulmonary arteries. Right ventricular hypertrophy was less severe in SDHD(+/-) mice although the cardiomyocyte ultrastructure and mitochondrial morphometric parameters were unchanged. Protein amounts of SDHA, SDHB and SDHC, and SDH activity were distinctly reduced in SDHD(+/-) mice. In normoxic SDHD(+/-) mice, α-ketoisocaproate concentration was lowered to 50% as compared to WT animals. Right/left ventricular concentration differences and the hypoxia-induced decline in individual α-KAs were less pronounced in SDHD(+/-) animals indicating that mitochondrial complex II participates in the adjustment of cardiac α-KA concentrations both under normoxic and hypoxic conditions. These characteristics are not related to the hemodynamic consequences of hypoxia-induced pulmonary vascular remodelling, since its extent and right ventricular pressure were not affected in SDHD(+/-) mice albeit right ventricular hypertrophy was attenuated.