Hemoglobin Expression Increases as the Diameter of Human Arterial Branches Narrows, A Role in Vascular Resistance?

Recent studies have identified the expression and function of hemoglobin-α subunit in mouse resistance arteries. Our latest research extends these findings by demonstrating the presence of tetrameric hemoglobin (comprising both α and β subunits) in human resistance arteries, where it regulates nitric oxide (NO) mediated endothelial feedback. However, the size range of human blood vessels expressing hemoglobin remains unclear. To elucidate the distribution of hemoglobin within the human vascular network, we hypothesized that hemoglobin is preferentially expressed in smaller resistance arteries (<200 µm) compared to medium-sized (200–600 µm) and larger (600–1000 µm) arteries. To test this hypothesis, we micro-dissected arteries of varying diameters from human omental tissues, collecting approximately 10–15 segments for each size group, and processed them for analysis. We employed multi-photon imaging to detect autofluorescence signals representing hemoglobin protein, and digital droplet PCR to quantify endothelial expression of target hemoglobin genes, such as HBA1 (hemoglobin-α1), HBA2 (hemoglobin-α2), HBB (hemoglobin-β), along with NOS3 (eNOS), MYLK (myosin light-chain kinase) and CYGB (cytoglobin). One-way ANOVA with trend test was performed in statistical analysis of gene expression data. Imaging findings suggest a differential expression pattern of hemoglobin, with higher expression observed in smaller segments. Supporting this, gene expression analysis demonstrates that the expression of hemoglobin genes is elevated in smaller arteries. Specifically, the expression levels (normalized to GAPDH, mean ±SEM, p represents value for linear trend, with n=3 individuals except for HBA1 in large with n=2) are as follows: HBA1 in large (1.3±0.2), medium (4.8±1.7), and small (7.7±1.3), p=0.003; HBA2 in large (10.6±5.9), medium (15.3±4.7), and small (23.2±3.1), p=0.010; HBB in large (7.5±4.0), medium (11.9±4.6), and small (15.3±3.2), p=0.002; NOS3 in large (26.8±10.7), medium (39.3±15.1), and small (43.0±7.0), p=0.076; MYLK in large (958.7±63.1), medium (797.8±61.7, 797.8±61.7) and small (836.0±154.6), p=0.382; CYGB in large (18.43±4.1), medium (22.7±1.7) and small (21.3±0.8), p=0.353. These data indicate a significant trend in the expression of HBA1, HBA2, and HBB, but not in NOS3, MYLK, or CYGB genes, suggesting higher hemoglobin expression in small resistance arteries, while providing new insights into its distribution along the vascular network. This raises the possibility that increased hemoglobin expression may contribute to the resistance exerted by these arteries. NIH Intramural Research Program This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.