| Topic | Key claim | Evidence type/model | Quantitative/statistical detail | Primary source (authors, journal, year) | URL/DOI | PaperQA citation id |
|---|---|---|---|---|---|---|
| Function | COX4I2 is the alternative nuclear-encoded COX4 subunit of cytochrome c oxidase (complex IV), localized in the inner mitochondrial membrane; its matrix-facing domain is regulatory and its C-terminal region contributes to cytochrome c docking architecture. | Human cell/biochemical literature synthesis; structural-functional interpretation | No single pooled statistic; review-level synthesis of domain orientation and regulatory role | Reguera et al., *Cells*, 2020 | https://doi.org/10.3390/cells9020443 | (pqac-00000003) |
| Localization | COX4I2 is a mitochondrial precursor protein incorporated into complex IV in the inner mitochondrial membrane; expression is enriched in lung, heart, and brain, with especially high expression in pulmonary artery smooth muscle cells. | Human HEK293 knock-in work and review synthesis | Tissue enrichment described qualitatively; no unified fold-change reported in retrieved excerpts | Reguera et al., *Cells*, 2020; Čunátová et al., *Physiological Research*, 2020 | https://doi.org/10.3390/cells9020443; https://doi.org/10.33549/physiolres.934446 | (pqac-00000003, pqac-00000004, pqac-00000005) |
| Function | Replacing COX4I1 with COX4I2 lowers complex IV oxygen affinity while leaving overall COX activity, cytochrome c affinity, and maximal respiration broadly similar. | HEK293 COX4i1/2 double-KO followed by single-isoform knock-in | p50 increased about 2-fold in COX4I2 versus COX4I1 cells, indicating decreased O2 affinity | Reguera et al., *Cells*, 2020 | https://doi.org/10.3390/cells9020443 | (pqac-00000002, pqac-00000003, pqac-00000006, pqac-00000016) |
| Function/Metabolism | COX4I2-containing cells are biased toward oxidative metabolism and a more oxidized redox state under normoxia. | HEK293 isoform-specific knock-in lines | OCR/ECAR ratio 1.4-fold higher; NAD+/NADH ratio ~20% higher in COX4I2 cells | Reguera et al., *Cells*, 2020 | https://doi.org/10.3390/cells9020443 | (pqac-00000005, pqac-00000016) |
| Function/ROS | COX4I2 expression is associated with lower mitochondrial ROS in normoxia, but is also linked in specialized oxygen-sensing tissues to hypoxia-evoked ROS signaling. | HEK293 knock-in metabolic phenotyping; physiology literature synthesis | Basal ROS production ~1.5-fold decreased in COX4I2 knock-in cells under normoxia | Reguera et al., *Cells*, 2020 | https://doi.org/10.3390/cells9020443 | (pqac-00000005, pqac-00000016) |
| Regulation | COX4I2 is oxygen-regulated and induced by hypoxia through HIF pathways; HIF-1α acts on promoter hypoxia-response elements/ORE, while RBPJ, CHCHD2 (MNRR1), and CXXC5 also regulate promoter activity. | Review of human/mammalian mechanistic studies | Regulatory elements described qualitatively; no single summary effect size | Čunátová et al., *Physiological Research*, 2020 | https://doi.org/10.33549/physiolres.934446 | (pqac-00000004, pqac-00000006) |
| Regulation | In COX4I1 deficiency, COX4I2 can be upregulated as a compensatory hypoxia-like response mediated by HIF-1α. | Human fibroblast/patient-cell study summary | Retrieved excerpt gives no specific fold-change in COX4I2, but reports HIF-1α stabilization and nuclear localization with COX4I2 upregulation | Douiev et al., *Cells*, 2021 | https://doi.org/10.3390/cells10020452 | (pqac-00000007) |
| Physiology | COX4I2 is required for acute arterial O2 sensing that modulates L-type Ca2+ channels and contributes to hypoxic vasodilation. | Conditional mouse genetics (COX4I2-SM, COX4I2-UBC), acutely dispersed femoral artery myocytes, arterial ring assays | Hypoxic modulation of Ca2+ currents was strongly inhibited in COX4I2-deficient myocytes; reported sample sizes include WT n=11/4 cells/mice vs COX4I2-UBC n=10/4 for electrophysiology, and n=12/4 rings/mice for vascular force assays | Moreno-Domínguez et al., *Nature Communications*, 2024 | https://doi.org/10.1038/s41467-024-51023-3 | (pqac-00000010, pqac-00000011) |
| Regulation/Physiology | HIF1α maintains expression of atypical complex IV subunits including COX4I2 in vascular smooth muscle, linking constitutive transcriptional programming to acute O2 responsiveness. | Conditional Hif1α smooth-muscle knockout mouse study | HIF1α-SM deletion selectively decreased Hif1α mRNA and downregulated Cox4i2/Cox8b; representative Ca2+ current experiments report sample sizes such as n=14/4 cells/mice in some measures | Moreno-Domínguez et al., *Nature Communications*, 2024 | https://doi.org/10.1038/s41467-024-51023-3 | (pqac-00000009) |
| Physiology | In carotid body glomus cells, COX4I2 is part of the HIF2α-dependent atypical ETC program required for acute hypoxia signaling and the hypoxic ventilatory response (HVR). | Conditional knockout and whole-animal plethysmography; glomus-cell autofluorescence/ROS assays | Respiratory frequency quantified in WT vs COX4I2-null mice during normoxia/hypoxia/hypercapnia with Nx n=12, Hx n=12, CO2 n=8; glomus-cell NADPH autofluorescence WT n=16/4 vs KO n=15/5 cells/mice | Moreno-Domínguez et al., *Science Signaling*, 2020 | https://doi.org/10.1126/scisignal.aay9452 | (pqac-00000017, pqac-00000019) |
| Physiology | Genetic deletion of Cox4i2 phenocopies key defective hypoxic responses seen after Epas1/HIF2α loss in glomus cells, supporting a causal role in acute O2 sensing rather than a generic mitochondrial defect. | Conditional catecholaminergic-tissue knockout framework | Qualitative phenocopy claim; no additional pooled numeric effect size in retrieved excerpt | Moreno-Domínguez et al., *Science Signaling*, 2020; Colinas et al., *Advances in Experimental Medicine and Biology*, 2023 | https://doi.org/10.1126/scisignal.aay9452; https://doi.org/10.1007/978-3-031-32371-3_17 | (pqac-00000019, pqac-00000020) |
| Physiology | In pulmonary vasculature models, Cox4i2 deficiency abolishes hypoxic pulmonary vasoconstriction and prevents hypoxia-induced mitochondrial hyperpolarization, ROS increase, and membrane depolarization in PASMCs. | Mouse knockout/PASMC physiology summary | Qualitative effect in retrieved excerpt; one mechanistic threshold noted for mouse PASMC L-type Ca2+ channel activation at about −30 to −20 mV | Alebrahimdehkordi, dissertation/review synthesis, 2021 | https://doi.org/10.22029/jlupub-29 | (pqac-00000013) |
| Expert analysis | Reviews argue COX4I2 fine-tunes complex IV for low-O2 environments and specialized oxygen-sensing cells by altering ATP regulation, redox signaling, and O2 affinity rather than catalytic identity. | Authoritative review/expert synthesis | Review cites two-fold reduction in O2 affinity upon COX4I1→COX4I2 exchange and links this to oxygen sensing | Čunátová et al., *Physiological Research*, 2020; López-Barneo & Ortega-Sáenz, *Crit Rev Biochem Mol Biol*, 2022 | https://doi.org/10.33549/physiolres.934446; https://doi.org/10.1080/10409238.2021.2004575 | (pqac-00000004, pqac-00000006) |
| Disease | Current disease-link databases show limited but nonzero associations for COX4I2, including hypertension and rare phenotype terms, but evidence is sparse and based partly on older literature/variant assertions rather than strong target-validation datasets. | Open Targets knowledgebase aggregation | Open Targets reported evidence_size=5 for hypertension and for several phenotype/rare-disease terms; hypertension association score ~0.109 | Open Targets Platform query for COX4I2 | https://platform.opentargets.org/target/ENSG00000131055 | (pqac-00000000) |


*Table: This table summarizes key functional-annotation facts for human COX4I2, emphasizing experimentally supported roles in complex IV oxygen handling, hypoxia regulation, vascular and carotid-body physiology, and current disease-association evidence. It is useful as a compact evidence map linking specific claims to primary studies and citation IDs.*