Anna V. Golubeva

Prenatal stress-induced alterations in major physiological systems correlate with gut microbiota composition in adulthood

Early-life adverse experiences, including prenatal stress (PNS), are associated with a higher prevalence of neurodevelopmental, cardiovascular and metabolic disorders in affected offspring. Here, in a rat model of chronic PNS, we investigate the impact of late gestational stress on physiological outcomes in adulthood. Sprague-Dawley pregnant dams were subjected to repeated restraint stress from embryonic day 14 to day 20, and their male offspring were assessed at 4 months of age. PNS induced an exaggeration of the hypothalamic-pituitary-adrenal (HPA) axis response to stress, as well as an elevation of blood pressure and impairment of cognitive function. Altered respiratory control was also observed, as demonstrated by increased variability in basal respiratory frequency and abnormal frequency responses to both hypoxic and hypercapnic challenges. PNS also affected gastrointestinal neurodevelopment and function, as measured by a decrease in the innervation density of distal colon and an increase in the colonic secretory response to catecholaminergic stimulation. Finally, PNS induced long lasting alterations in the intestinal microbiota composition. 16S rRNA gene 454 pyrosequencing revealed a strong trend towards decreased numbers of bacteria in the Lactobacillus genus, accompanied by elevated abundance of the Oscillibacter, Anaerotruncus and Peptococcus genera in PNS animals. Strikingly, relative abundance of distinct bacteria genera significantly correlated with certain respiratory parameters and the responsiveness of the HPA axis to stress. Together, these findings provide novel evidence that PNS induces long-term maladaptive alterations in the gastrointestinal and respiratory systems, accompanied by hyper-responsiveness to stress and alterations in the gut microbiota.

Toll-Like Receptor 4 Regulates Chronic Stress-Induced Visceral Pain in Mice

BACKGROUND Functional gastrointestinal disorders, which have visceral hypersensitivity as a core symptom, are frequently comorbid with stress-related psychiatric disorders. Increasing evidence points to a key role for toll-like receptor 4 (TLR4) in chronic pain states of somatic origin. However, the central contribution of TLR4 in visceral pain sensation remains elusive. METHODS With pharmacological and genetic approaches, we investigated the involvement of TLR4 in the modulation of visceral pain. The TLR4-deficient and wild-type mice were exposed to chronic stress. Visceral pain was evaluated with colorectal distension. Protein expression levels for TLR4, Cd11b, and glial fibrillary acidic protein (glial cells markers) were quantified in the lumbar region of the spinal cord, prefrontal cortex (PFC), and hippocampus. To evaluate the effect of blocking TLR4 on visceral nociception, TAK-242, a selective TLR4 antagonist, was administered peripherally (intravenous) and centrally (intracerebroventricular and intra-PFC) (n = 10-12/experimental group). RESULTS The TLR4 deficiency reduced visceral pain and prevented the development of chronic psychosocial stress-induced visceral hypersensitivity. Increased expression of TLR4 coupled with enhanced glia activation in the PFC and increased levels of proinflammatory cytokines were observed after chronic stress in wild-type mice. Administration of a TLR4 specific antagonist, TAK-242, attenuated visceral pain sensation in animals with functional TLR4 when administrated centrally and peripherally. Moreover, intra-PFC TAK-242 administration also counteracted chronic stress-induced visceral hypersensitivity. CONCLUSIONS Our results reveal a novel role for TLR4 within the PFC in the modulation of visceral nociception and point to TLR4 as a potential therapeutic target for the development of drugs to treat visceral hypersensitivity.

Behavioural and neurochemical consequences of chronic gut microbiota depletion during adulthood in the rat

Gut microbiota colonization is a key event for host physiology that occurs early in life. Disruption of this process leads to altered brain development which ultimately manifests as changes in brain function and behaviour in adulthood. Studies using germ-free (GF) mice highlight the extreme impact on brain health that results from life without commensal microbes. However, the impact of microbiota disturbances occurring in adulthood is less studied. To this end, we depleted the gut microbiota of 10-week-old male SpragueDawley rats via chronic antibiotic treatment. Following this marked, sustained depletion of the gut bacteria, we investigated behavioural and molecular hallmarks of gut-brain communication. Our results reveal that depletion of the gut microbiota during adulthood results in deficits in spatial memory as tested by Morris water maze, decreased visceral sensitivity and a greater display of depressive-like behaviours in the forced swim test. In tandem with these clear behavioural alterations we found changes in altered CNS serotonin concentration along with changes in the mRNA levels of corticotrophin releasing hormone receptor 1 and glucocorticoid receptor. Additionally, we found changes in the expression of brain derived neurotrophic factor (BDNF), a hallmark of altered microbiota-gut-brain axis signalling. In summary, this model of antibiotic-induced depletion of the gut microbiota can be used for future studies interested in the impact of the gut microbiota on host health without the confounding developmental influence of early-life microbial alterations.

Chronic hypoxia leads to a glycolytic phenotype and suppressed HIF-2 signaling in PC12 cells.

BACKGROUND Along with other regulators of cell metabolism, hypoxia-inducible factors HIF-1 and HIF-2 differentially regulate cell adaptation to hypoxia. Switches in HIF-1/HIF-2 signaling in chronic hypoxia have not been fully investigated. METHODS Proliferation, viability, apoptosis, neuronal and bioenergetic markers, mitochondrial function, respiration, glycolysis, HIF signalling, responses to O2 and glucose deprivation (OGD) were examined using tumor PC12 and SH-SY5Y cells continuously grown at 3% O2. RESULTS Hypoxic PC12 cells (H-cells) exhibit reduced proliferation and histone H4 acetylation, NGF-independent differentiation, activation of AMPK, inhibition of Akt, altered mitochondria and response to NGF. Cellular cytochrome c is increased with no effect on apoptosis. Reduction in respiration has minor effect on cellular ATP which is maintained through activated uptake (GLUT1) and utilization (HK2, PFK2) of glucose. H-cells exhibit resistance to OGD linked to increased glycogen stores. HIF-2alpha protein is decreased without changes in mRNA. Unlike HIF-1alpha, HIF-2alpha is not stabilized pharmacologically or by O2 deprivation. Capacity for HIF-2alpha stabilization is partly restored when H-cells are cultured at normoxia. In low-respiring SH-SY5Y cells cultured under the same conditions HIF-2alpha stabilization and energy budget are not affected. CONCLUSIONS In chronically hypoxic PC12 cells glycolytic energy budget, increased energy preservation and low susceptibility to OGD are observed. HIF-2alpha no longer orchestrates adaptive responses to anoxia. GENERAL SIGNIFICANCE Demonstrated switch in HIF-1/HIF-2 signaling upon chronic hypoxia can facilitate cell survival in energy crisis, by regulating balance between energy saving and decrease in proliferation, on one hand and active cell growth and tumor expansion, on the other.

Availability of the key metabolic substrates dictates the respiratory response of cancer cells to the mitochondrial uncoupling.

Active glycolysis and glutaminolysis provide bioenergetic stability of cancer cells in physiological conditions. Under hypoxia, metabolic and mitochondrial disorders, or pharmacological treatment, a deficit of key metabolic substrates may become life-threatening to cancer cells. We analysed the effects of mitochondrial uncoupling by FCCP on the respiration of cells fed by different combinations of Glc, Gal, Gln and Pyr. In cancer PC12 and HCT116 cells, a large increase in O2 consumption rate (OCR) upon uncoupling was only seen when Gln was combined with either Glc or Pyr. Inhibition of glutaminolysis with BPTES abolished this effect. Despite the key role of Gln, addition of FCCP inhibited respiration and induced apoptosis in cells supplied with Gln alone or Gal/Gln. For all substrate combinations, amplitude of respiratory responses to FCCP did not correlate with Akt, Erk and AMPK phosphorylation, cellular ATP, and resting OCR, mitochondrial Ca(2+) or membrane potential. However, we propose that proton motive force could modulate respiratory response to FCCP by regulating mitochondrial transport of Gln and Pyr, which decreases upon mitochondrial depolarisation. As a result, an increase in respiration upon uncoupling is abolished in cells, deprived of Gln or Pyr (Glc). Unlike PC12 or HCT116 cells, mouse embryonic fibroblasts were capable of generating pronounced response to FCCP when deprived of Gln, thus exhibiting lower dependence on glutaminolysis. Overall, the differential regulation of the respiratory response to FCCP by metabolic environment suggests that mitochondrial uncoupling has a potential for substrate-specific inhibition of cell function, and can be explored for selective cancer treatment.

Microbiota-related Changes in Bile Acid & Tryptophan Metabolism are Associated With Gastrointestinal Dysfunction in a Mouse Model of Autism

Autism spectrum disorder (ASD) is one of the most prevalent neurodevelopmental conditions worldwide. There is growing awareness that ASD is highly comorbid with gastrointestinal distress and altered intestinal microbiome, and that host-microbiome interactions may contribute to the disease symptoms. However, the paucity of knowledge on gut-brain axis signaling in autism constitutes an obstacle to the development of precision microbiota-based therapeutics in ASD. To this end, we explored the interactions between intestinal microbiota, gut physiology and social behavior in a BTBR T+Itpr3tf/J mouse model of ASD. Here we show that a reduction in the relative abundance of very particular bacterial taxa in the BTBR gut – namely, bile-metabolizing Bifidobacterium and Blautia species, - is associated with deficient bile acid and tryptophan metabolism in the intestine, marked gastrointestinal dysfunction, as well as impaired social interactions in BTBR mice. Together these data support the concept of targeted manipulation of the gut microbiota for reversing gastrointestinal and behavioral symptomatology in ASD, and offer specific plausible targets in this endeavor.

Differential contribution of key metabolic substrates and cellular oxygen in HIF signalling

Changes in availability and utilisation of O2 and metabolic substrates are common in ischemia and cancer. We examined effects of substrate deprivation on HIF signalling in PC12 cells exposed to different atmospheric O2. Upon 2-4h moderate hypoxia, HIF-α protein levels were dictated by the availability of glutamine and glucose, essential for deep cell deoxygenation and glycolytic ATP flux. Nuclear accumulation of HIF-1α dramatically decreased upon inhibition of glutaminolysis or glutamine deprivation. Elevation of HIF-2α levels was transcription-independent and associated with the activation of Akt and Erk1/2. Upon 2h anoxia, HIF-2α levels strongly correlated with cellular ATP, produced exclusively via glycolysis. Without glucose, HIF signalling was suppressed, giving way to other regulators of cell adaptation to energy crisis, e.g. AMPK. Consequently, viability of cells deprived of O2 and glucose decreased upon inhibition of AMPK with dorsomorphin. The capacity of cells to accumulate HIF-2α decreased after 24h glucose deprivation. This effect, associated with increased AMPKα phosphorylation, was sensitive to dorsomorphin. In chronically hypoxic cells, glutamine played no major role in HIF-2α accumulation, which became mainly glucose-dependent. Overall, the availability of O2 and metabolic substrates intricately regulates HIF signalling by affecting cell oxygenation, ATP levels and pathways involved in production of HIF-α.

The orthosteric GABAA receptor ligand Thio-4-PIOL displays distinctly different functional properties at synaptic and extrasynaptic receptors

Explorations into the heterogeneous population of native GABA type A receptors (GABAARs) and the physiological functions governed by the multiple GABAAR subtypes have for decades been hampered by the lack of subtype‐selective ligands.

Imaging of oxygen gradients in giant umbrella cells: an ex vivo PLIM study

O2 plays a pivotal role in aerobic metabolism and regulation of cell and tissue function. Local differences and fluctuations in tissue O2 levels are well documented; however, the physiological significance of O2 microgradients, particularly at the subcellular level, remains poorly understood. Using the cell-penetrating phosphorescent O2 probe Pt-Glc and confocal fluorescence microscopy, we visualized O2 distribution in individual giant (>100-μm) umbrella cells located superficially in the urinary bladder epithelium. We optimized conditions for in vivo phosphorescent staining of the inner surface of the mouse bladder and subsequent ex vivo analysis of excised live tissue. Imaging experiments revealed significant (≤85 μM) and heterogeneous deoxygenation within respiring umbrella cells, with radial O2 gradients of up to 40 μM across the cell, or ∼0.6 μM/μm. Deeply deoxygenated (5-15 μM O2) regions were seen to correspond to the areas enriched with polarized mitochondria. Pharmacological activation of mitochondrial respiration decreased oxygenation and O2 gradients in umbrella cells, while inhibition with antimycin A dissipated the gradients and caused gradual reoxygenation of the tissue to ambient levels. Detailed three-dimensional maps of O2 distribution potentially can be used for the modeling of intracellular O2-dependent enzymatic reactions and downstream processes, such as hypoxia-inducible factor signaling. Further ex vivo and in vivo studies on intracellular and tissue O2 gradients using confocal imaging can shed light on the molecular mechanisms regulating O2-dependent (patho)physiological processes in the bladder and other tissues.

Negative allosteric modulation of the mGlu7 receptor reduces visceral hypersensitivity in a stress-sensitive rat strain

Glutamate, the main excitatory neurotransmitter in the central nervous system, exerts its effect through ionotropic and metabotropic receptors. Of these, group III mGlu receptors (mGlu 4, 6, 7, 8) are among the least studied due to a lack of pharmacological tools. mGlu7 receptors, the most highly conserved isoform, are abundantly distributed in the brain, especially in regions, such as the amygdala, known to be crucial for the emotional processing of painful stimuli. Visceral hypersensitivity is a poorly understood phenomenon manifesting as an increased sensitivity to visceral stimuli. Glutamate has long been associated with somatic pain processing leading us to postulate that crossover may exist between these two modalities. Moreover, stress has been shown to exacerbate visceral pain. ADX71743 is a novel, centrally penetrant, negative allosteric modulator of mGlu7 receptors. Thus, we used this tool to explore the possible involvement of this receptor in the mediation of visceral pain in a stress-sensitive model of visceral hypersensitivity, namely the Wistar Kyoto (WKY) rat. ADX71743 reduced visceral hypersensitivity in the WKY rat as exhibited by increased visceral sensitivity threshold with concomitant reductions in total number of pain behaviours. Moreover, AD71743 increased total distance and distance travelled in the inner zone of the open field. These findings show, for what is to our knowledge, the first time, that mGlu7 receptor signalling plays a role in visceral pain processing. Thus, negative modulation of the mGlu7 receptor may be a plausible target for the amelioration of stress-induced visceral pain where there is a large unmet medical need.