Introduction

High-altitude (HA) regions are increasingly visited by diverse populations for various purposes, including recreation and pilgrimage (Han et al., 2024). Successful acclimatization requires coordinated physiological regulation at the cellular, tissue, and organismal levels (Ortiz et al., 2021; Xu et al., 2022; Guo et al., 2026). Since population background, geographic origin, and evolutionary history significantly dictate HA-related responses (Ferraretti et al., 2025; Seifu et al., 2024; Getu et al., 2025), understanding the population-specific nuances of these adaptations is critical (Quan et al., 2021; Lin et al., 2023; Ferraretti et al., 2024; Li et al., 2024a). However, evidence regarding the variability of circRNA expression profiles among different populations in HA environments remains limited (Ge et al., 2021; Li et al., 2024b).

Circular RNAs (circRNAs) are a class of covalently closed-loop non-coding RNAs characterized by the absence of 5′caps and 3′poly(A) tails (Hansen et al., 2013; Kos et al., 1986; Wang et al., 2014). While primarily derived from exons, circRNAs can also originate from intronic sequences (Wang et al., 2014). Functionally, many circRNAs act as competitive endogenous RNAs (ceRNAs) or miRNA sponges; by sequestering specific microRNAs (miRNAs), they alleviate the post-transcriptional repression of target genes, thereby promoting their expression (Hansen et al., 2013). Recently, circRNAs have emerged as essential mediators of metabolic regulation and promising biomarkers for diverse pathologies, including cancer (Chen et al., 2023; Yu et al., 2022; Zhu et al., 2023). Notably, circRNAs are also critical to hypoxic adaptation. For instance, research on Tibetan chickens identified 93 differentially expressed circRNAs under hypoxic conditions, with the circBRD1/novel_miR-589/APOA1 axis specifically modulating angiogenesis and embryonic hypoxic tolerance (Chen et al., 2023). Similarly, in patients with high-altitude pulmonary edema (HAPE), 200 differentially expressed circRNAs were identified, among which hsa_circ_0058497, hsa_circ_0081006, and hsa_circ_0083220 showed significant correlations with clinical indices, highlighting their potential as diagnostic biomarkers (Li et al., 2024b).

In recent years, circRNAs have been considered key biomarkers for many human diseases, including cancer, due to their important roles in metabolism. However, whether circRNAs participate in human HA adaptation and regulation remains unclear. Advanced microarray technologies have facilitated experimental approaches, enabling detection of the expression of thousands of genes (Yu et al., 2022; Zhu et al., 2023). Microarray studies using genes from HAPC patients showed that LRRC18 and HCAR3 exhibit significant expression changes following early exposure to the Qinghai–Tibet Plateau, and these two genes may serve as hub genes in the occurrence and development of high-altitude-associated polycythemia (HAPC) (Wang et al., 2022). Genomic sequencing results from Tibetan patients with HAPC indicate that EGLN3/PHD3 and PPP1R2P1 may be associated with HAPC susceptibility (Gesang et al., 2019). Thus, microarray-based genome-wide expression profiling provides an ideal method for investigating HA adaptation.

To explore population-specific transcriptomic variability, we conducted a comprehensive gene expression profiling analysis using RNA samples from male participants across three cohorts: Tianjin (0 m), Ningxia Yinchuan (1,000 m), and Xizang Linzhi (3,000 m). Differential expression analysis identified numerous circRNAs in pairwise comparisons between these populations. Gene Ontology (GO) enrichment analysis revealed that the parent genes of these differentially expressed circRNAs were primarily involved in biological regulatory processes. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that these parent genes were significantly enriched in the hypoxia-inducible factor-1 (HIF-1) signaling pathway, among others. Notably, five circRNAs were consistently identified as differentially expressed across all three groups. Subsequent analysis of the predicted RNA-binding proteins for these candidates highlighted key interactions with proteins such as AGO2 and EIF4A3.

To validate the differential expression of the five identified candidate circRNAs, quantitative real-time PCR (qRT-PCR) was performed. The results revealed a progressive increase in the relative expression of these circRNAs across altitudes, with the highest levels observed in the 3,000 m group. Furthermore, overexpression of HIF-1 in human endothelial cells significantly upregulated the expression of these circRNAs compared to the control group. In conclusion, we identified five consistently differentially expressed circRNAs (hsa_circ_0044526, hsa_circ_0022498, hsa_circ_0044534, hsa_circ_0044520, and hsa_circ_0026102) across populations at varying altitudes, demonstrating their potential role in HIF-1-mediated high-altitude adaptation.