Biology subjects

Mitchell, G. S.

Publications and source records attributed to Mitchell, G. S..

7 recordsLinked to original sources

bioRxiv2026

Systemic hypoxia drives glycogen-fueled progression of lung adenocarcinoma

In advanced stages, lung adenocarcinoma obstructs airways and disrupts ventilation-perfusion relationships in the lung, causing systemic hypoxemia and enabling a feed-forward loop that accelerates malignancy. Systemic hypoxemia is also experienced due to common respiratory comorbidities such as chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA), potentially accelerating malignancy. In a statewide electronic health record network, pre-existing COPD (598 matched pairs) or sleep apnea (235 matched pairs) independently predicted worse survival following incident lung cancer diagnosis. Since the mechanistic basis of the link between malignancy and hypoxia is not well understood, we created systemic hypoxia in KrasLSL-G12D/+;Trp53fl/fl (KP) mice by delivering low inspired oxygen concentrations (8% inspired oxygen; 8 h daily). Hypoxia nearly doubled tumor multiplicity and selectively remodeled cancer central carbon metabolism. Spatially resolved metabolomics revealed marked tumor-compartment glycogen accumulation, elevated tricarboxylic-acid cycle intermediates, and depleted glycolytic pools. Quantitative proteomics across cellular models and autochthonous tumors demonstrated that systemic hypoxia drives glycogen mobilization selectively through the lysosomal enzyme acid -glucosidase (GAA). Tumor-cell-autonomous deletion of GAA eliminated the hypoxia-driven growth advantage and disrupted downstream anabolic biosynthetic pathways. Thus, systemic hypoxia drives lung adenocarcinoma expansion by mobilizing lysosomal glycogen reserves through GAA to sustain proliferative growth.

cancer biology↗

bioRxiv2026

A multi-organ spatial metabolomic atlas of exercising mice reveals neuronal Complex I as a convergent and sufficient axis for tau pathology reduction in PS19

We constructed a spatially resolved metabolomic atlas of long-term exercise across six major organs in wild-type mice: brain, heart, lung, liver, kidney, and skeletal muscle, cataloguing 224 metabolic features and revealing coordinated inter-organ remodeling. Surprisingly, the brain showed particularly pronounced region-specific adaptation. Because pathological tau associates with synaptic mitochondria from early stages of tauopathy, we extended this multi-organ spatial metabolomic approach to PS19 mice and found that exercise reduced over 70% of observable tau pathology in PS19 hippocampus and restored the mitochondrial-related metabolome. Integrated proteomic and spatial metabolomic analyses identified NADH dehydrogenase Complex I as the convergent node. To test this finding biologically, we expressed the yeast NADH dehydrogenase, Ndi1, in PS19 neurons in the absence of exercise. This increased cerebral antioxidants, restored shuttle-linked metabolites, and reduced tau pathology. Increasing NADH dehydrogenase activity through NDI1 reproduces the core anti-tau and metabolic effects of exercise. These findings provide a molecular mechanism for how exercise may prevent or slow tau pathology accumulation, complementing the human-cohort literature linking exercise to delayed cognitive decline.

neuroscience↗

bioRxiv2024

Microglia regulate motor neuron plasticity via reciprocal fractalkine/adenosine signaling

Microglia are innate CNS immune cells that play key roles in supporting key CNS functions including brain plasticity. We now report a previously unknown role for microglia in regulating neuroplasticity within spinal phrenic motor neurons, the neurons driving diaphragm contractions and breathing. We demonstrate that microglia regulate phrenic long-term facilitation (pLTF), a form of respiratory memory lasting hours after repetitive exposures to brief periods of low oxygen (acute intermittent hypoxia; AIH) via neuronal/microglial fractalkine signaling. AIH-induced pLTF is regulated by the balance between competing intracellular signaling cascades initiated by serotonin vs adenosine, respectively. Although brainstem raphe neurons release the relevant serotonin, the cellular source of adenosine is unknown. We tested a model in which hypoxia initiates fractalkine signaling between phrenic motor neurons and nearby microglia that triggers extracellular adenosine accumulation. With moderate AIH, phrenic motor neuron adenosine 2A receptor activation undermines serotonin-dominant pLTF; in contrast, severe AIH drives pLTF by a unique, adenosine-dominant mechanism. Phrenic motor neuron fractalkine knockdown, cervical spinal fractalkine receptor inhibition on nearby microglia, and microglial depletion enhance serotonin-dominant pLTF with moderate AIH but suppress adenosine-dominant pLTF with severe AIH. Thus, microglia play novel functions in the healthy spinal cord, regulating hypoxia-induced neuroplasticity within the motor neurons responsible for breathing.

physiology↗

bioRxiv2024

Daily Acute Intermittent Hypoxia Elicits Age & Sex-Dependent Changes in Molecules Regulating Phrenic Motor Plasticity

Acute intermittent hypoxia (AIH) elicits a form of respiratory motor plasticity known as phrenic long-term facilitation (LTF). Repetitive daily AIH (dAIH) exposure enhances phrenic LTF, demonstrating a form of metaplasticity. Two additional factors impacting phrenic LTF are age and sex. For example, moderate AIH-induced phrenic LTF decreases with age in males, but increases in middle-aged females. However, little is known concerning cellular mechanisms of dAIH effects or age-dependent sexual dimorphism in phrenic LTF. Moderate AIH elicits distinct signaling cascades within phrenic motor neurons initiated by 5HT2 receptors (Q pathway) versus adenosine 2A or 5HT7 receptors (S pathway), respectively. The Q and S pathways interact via mutual crosstalk inhibition, a powerful regulator of phrenic LTF. To test the hypothesis that dAIH, age and sex effects on phrenic LTF are associated with differential expression of molecules known to regulate the Q and S pathways, we assessed mRNA of key regulatory molecules in ventral cervical homogenates from spinal segments containing the phrenic motor nucleus from young (3 month) and middle-aged (12 month) male and female Sprague-Dawley rats. Since CNS estrogen levels impact molecules regulating the Q and/or S pathways, mRNA was correlated with serum estradiol. Rats (n=8/group) were exposed to sham (21% O2) or dAIH (15, 1 min episodes of 10.5% inspired O2 per day) for 14 days, and sacrificed 24 hours post-dAIH. mRNA for molecules known to regulate phrenic LTF were assessed via RT PCR, including: brain derived neurotrophic factor (Bdnf); serotonin 2A (Htr2a); 2B (Htr2b); and (Htr7) receptors; adenosine 2a (Adora2a) receptors; exchange protein activated by cAMP (Epac1); p38 MAP kinase [Mapk14 () & Mapk11 ({beta})]; PKA catalytic subunit (Prkaa1); PKA regulatory subunit (Prkar1a); fractalkine (Cx3cl1); phosphodiesterase type 4 (Pde4b); NAPDH-gp91 (Cybb) and p47 (ncf1); and the PKC{delta} isoform (Prkcd). Significantly higher Pde4b, Adora2a, and Prkcd mRNA were found in young and middle-aged females versus age-matched males; Epac1 was elevated, but only in young females (p<0.001). Ncf1 was increased in middle-aged versus young adult rats of both sexes (p<0.01). Ncf1, Cx3cl1, Adora2a and Prkcd mRNA were reduced by dAIH in middle-aged females (p<0.01), but not other groups. Serum estradiol levels positively correlated with Epac1 (r2=0.29, p=0.002), Mapk14 (r2=0.31, p=0.001), Mapk11 (r2=0.20, p=0.014), and Prkar1a (r2=0.20 p=0.013) mRNA. With higher serum estradiol levels, dAIH decreased Mapk14 mRNA (slope difference p=0.001). Thus, age, sex and dAIH preconditioning influence molecules known to regulate the Q and S pathways to phrenic motor facilitation. These novel findings advance our understanding of phrenic LTF, and inform translational research concerning the therapeutic potential of dAIH to treat breathing deficits in individuals of different ages or sex.

neuroscience↗

bioRxiv2023

APOE4, Age & Sex Regulate Respiratory Plasticity Elicited By Acute Intermittent Hypercapnic-Hypoxia

RationaleAcute intermittent hypoxia (AIH) is a promising strategy to induce functional motor recovery following chronic spinal cord injuries and neurodegenerative diseases. Although significant results are obtained, human AIH trials report considerable inter-individual response variability. ObjectivesIdentify individual factors (e.g., genetics, age, and sex) that determine response magnitude of healthy adults to an optimized AIH protocol, acute intermittent hypercapnic-hypoxia (AIHH). MethodsAssociations of individual factors with the magnitude of AIHH (15, 1-min O2=9.5%, CO2=5% episodes) induced changes in diaphragm motor-evoked potential amplitude (MEP) and inspiratory mouth occlusion pressures (P0.1) were evaluated in 17 healthy individuals (age=27{+/-}5 years) compared to Sham. Single nucleotide polymorphisms (SNPs) in genes linked with mechanisms of AIH induced phrenic motor plasticity (BDNF, HTR2A, TPH2, MAOA, NTRK2) and neuronal plasticity (apolipoprotein E, APOE) were tested. Variations in AIHH induced plasticity with age and sex were also analyzed. Additional experiments in humanized (h)ApoE knock-in rats were performed to test causality. ResultsAIHH-induced changes in diaphragm MEP amplitudes were lower in individuals heterozygous for APOE4 (i.e., APOE3/4) allele versus other APOE genotypes (p=0.048). No significant differences were observed between any other SNPs investigated, notably BDNFval/met (all p>0.05). Males exhibited a greater diaphragm MEP enhancement versus females, regardless of age (p=0.004). Age was inversely related with change in P0.1 within the limited age range studied (p=0.007). In hApoE4 knock-in rats, AIHH-induced phrenic motor plasticity was significantly lower than hApoE3 controls (p<0.05). ConclusionsAPOE4 genotype, sex and age are important biological determinants of AIHH-induced respiratory motor plasticity in healthy adults. ADDITION TO KNOWLEDGE BASEAcute intermittent hypoxia (AIH) is a novel rehabilitation strategy to induce functional recovery of respiratory and non-respiratory motor systems in people with chronic spinal cord injury and/or neurodegenerative diseases. Since most AIH trials report considerable inter-individual variability in AIH outcomes, we investigated factors that potentially undermine the response to an optimized AIH protocol, acute intermittent hypercapnic-hypoxia (AIHH), in healthy humans. We demonstrate that genetics (particularly the lipid transporter, APOE), age and sex are important biological determinants of AIHH-induced respiratory motor plasticity.

neuroscience↗

bioRxiv2022

Daily fluctuations in spinal adenosine determine mechanisms of respiratory motor plasticity

Plasticity is a fundamental property of the neuromotor system controlling breathing. One key example of respiratory motor plasticity is phrenic long-term facilitation (pLTF), a persistent increase in phrenic nerve activity after exposure to intermittent low oxygen or acute intermittent hypoxia (AIH). pLTF can arise from distinct intracellular signaling cascades initiated by serotonin and adenosine; these cascades interact via powerful crosstalk inhibition. We demonstrate the serotonin/adenosine balance varies dramatically with time-of-day and details of the AIH protocol. Using a "standard" AIH protocol, the mechanism driving pLTF shifts from serotonin-dominant, adenosine-constrained during rest, to adenosine-dominant, serotonin-constrained in the active phase. This mechanistic flip results from daily changes in basal spinal adenosine levels across time-of-day combined with hypoxia-evoked spinal adenosine release. Since AIH is emerging as a promising therapeutic modality to restore respiratory (and non-respiratory) movements in people with spinal injury or ALS, new knowledge that time-of-day and protocol details impact mechanisms driving pLTF has experimental, biological and translational implications.

physiology↗

bioRxiv2018

Real-time whole-plant dynamics of heavy metal transport in Arabidopsis halleri and Arabidopsis thaliana by gamma-ray imaging

Heavy metals such as zinc are essential for plant growth, but toxic at high concentrations. Despite our knowledge of the molecular mechanisms of heavy metal uptake by plants, experimentally addressing the real-time whole-plant dynamics of heavy metal uptake and partitioning has remained a challenge. To overcome this, we applied a high sensitivity gamma-ray imaging system to image uptake and transport of radioactive 65Zn in whole-plant assays of Arabidopsis thaliana and the Zn hyperaccumulator A. halleri. We show that our system can be used to quantitatively image and measure uptake and root-to-shoot translocation dynamics of zinc in real time. In the metal hyperaccumulator Arabidopsis halleri, 65Zn uptake and transport from its growth media to the shoot occurs rapidly and on time scales similar to those reported in rice. In transgenic A. halleri plants in which expression of the zinc transporter gene HMA4 is suppressed by RNAi, 65Zn uptake is completely abolished.\n\nHIGHLIGHTWe have used gamma-ray imaging to visualize the stark differences of real-time whole-plant dynamics of zinc root-to-shoot transport in heavy metal hyperaccumulating and non-accumulating Arabidopsis.

plant biology↗