Transcriptomic Analysis of Human Astrocytes In Vitro Reveals Hypoxia-Induced Mitochondrial Dysfunction, Modulation of Metabolism, and Dysregulation of the Immune Response

Abstract

Hypoxia is a feature of neurodegenerative diseases, and can both directly and indirectly impact on neuronal function through modulation of glial function. Astrocytes play a key role in regulating homeostasis within the central nervous system, and mediate hypoxia-induced changes in response to reduced oxygen availability. The current study performed a detailed characterization of hypoxia-induced changes in the transcriptomic profile of astrocytes in vitro. Human astrocytes were cultured under normoxic (5% CO2, 95% air) or hypoxic conditions (1% O2, 5% CO2, 94% N2) for 24 h, and the gene expression profile assessed by microarray analysis. In response to hypoxia 4904 genes were significantly differentially expressed (1306 upregulated and 3598 downregulated, FC ≥ 2 and p ≤ 0.05). Analysis of the significant differentially expressed transcripts identified an increase in immune response pathways, and dysregulation of signalling pathways, including HIF-1 (p = 0.002), and metabolism, including glycolysis (p = 0.006). To assess whether the hypoxia-induced metabolic gene changes observed affected metabolism at a functional level, both the glycolytic and mitochondrial flux were measured using an XF bioanalyser. In support of the transcriptomic data, under physiological conditions hypoxia significantly reduced mitochondrial respiratory flux (p = 0.0001) but increased basal glycolytic flux (p = 0.0313). However, when metabolically stressed, hypoxia reduced mitochondrial spare respiratory capacity (p = 0.0485) and both glycolytic capacity (p = 0.0001) and glycolytic reserve (p < 0.0001). In summary, the current findings detail hypoxia-induced changes in the astrocyte transcriptome in vitro, identifying potential targets for modifying the astrocyte response to reduced oxygen availability in pathological conditions associated with ischaemia/hypoxia, including manipulation of mitochondrial function, metabolism, and the immune response.

Transcriptome and Metabolome Integration Provides New Insights Into the Regulatory Networks of Tibetan Pig Alveolar Type II Epithelial Cells in Response to Hypoxia

“…The gene expression levels of HK1 and HK2 were significantly higher in the hypoxia groups (2% O 2 ) than in the normoxia groups (21% O 2 ) in our study, and the same pattern has been observed in pulmonary artery smooth muscle cells (PASMCs) (Chen et al, 2018a). The increase in glycolytic metabolism under hypoxia (TL and LL) may require the O 2 -independent glycolytic pathway to preferentially produce sufficient ATP to satisfy bioenergetic requirements, which profound effects on cellular physiology and hypoxic immunity in ATII cells under hypoxia (Semenza, 2017;Allen et al, 2020). Similarly, our results indicated that the expression of ENO2, the target gene of HIF, was significantly higher in the hypoxia (TL and LL) groups and promoted glycolysis, glucocorticoid resistance, and cell growth (Figure 7) (Liu et al, 2018).…”

Meta-analysis of human and mouse ALS astrocytes reveals multi-omic signatures of inflammatory reactive states

“…Hypoxia has previously been implicated in neurodegenerative diseases, including in ALS, where it has been suggested to aggravate motor neuron degeneration (Oosthuyse et al 2001;Sato et al 2012;Kim et al 2013;Nagara et al 2013). Although the hypoxic response is initially neuroprotective, prolonged hypoxia signaling can trigger neuroinflammation and oxidative stress, leading to neuronal dysfunction (Allen et al 2020). Astrocytes respond to hypoxia by increasing bloodbrain barrier permeability, neuroinflammation, and cytokine secretion (Marina et al 2016;Samy et al 2018).…”

HIF-1α promotes SARS-CoV-2 infection and aggravates inflammatory responses to COVID-19

“… 3 , 4 The hypoxia-inducible factor 1α (HIF-1α) acts as a key regulator in physiological functions including metabolism, cell proliferation, and angiogenesis. 11 – 13 HIF-1α is also an important activator in glycolysis and inflammatory response, which implies the effects of HIF-1α on the pathogenesis of COVID-19. 14 , 15 Therefore, it is of high concern to understand SARS-CoV-2 pathogenesis and to seek potential antiviral drugs.…”