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Research Article: Metabolic reprogramming of NK cells in chronic brucellar arthritis: role of the HIF-1?/mTOR axis

Date Published: 2026-10-06

Abstract:
Brucellar arthritis is the most common complication of brucellosis, and its chronic progression is closely associated with immune cell dysfunction. Natural killer (NK) cells play a central role in anti-infective immunity; however, their functional status and regulatory mechanisms in brucellar arthritis remain poorly understood. Peripheral blood and synovial tissue samples were collected from healthy controls, as well as from patients with acute-phase and chronic-phase brucellar arthritis. Single-cell RNA sequencing (scRNA-seq), flow cytometry, quantitative real-time PCR (qPCR), JC-1 mitochondrial membrane potential assay, Seahorse metabolic analysis, and Western blotting were employed to systematically evaluate NK cell phenotypes, functions, metabolic profiles, and HIF-1?/mTOR pathway activity. In vitro , heat-killed Brucella melitensis 16M (HKBA) was used to stimulate NK-92 cells and HIF-1?-knockout (KO) cell lines, with mTOR inhibitor intervention, to dissect the regulatory mechanism of the HIF-1?/mTOR axis in NK cell metabolic reprogramming. scRNA-seq revealed enrichment of NK cells in the synovium of brucellar arthritis patients, with aberrant expression of oxidative phosphorylation (OXPHOS)-related genes. Clinical sample analyses showed that, compared with healthy controls, the proportion of peripheral blood NK cells increased in both acute- and chronic-phase patients; however, NK cells from chronic-phase patients exhibited significantly reduced IFN-?, Granzyme B, and CD107a degranulation levels. HIF-1? protein was consistently overexpressed in patient NK cells, whereas phosphorylated mTOR-pathway proteins (p-PI3K, p-AKT, p-mTOR) were markedly suppressed. In vitro , HKBA treatment inhibited mTOR pathway activity in NK-92 cells in a dose- and time-dependent manner and reduced mitochondrial membrane potential as shown by JC-1 staining. HIF-1? knockout significantly restored NK cell cytotoxic function, upregulated OXPHOS- and glycolysis-related gene expression, and improved mitochondrial membrane potential. Transcriptomic sequencing confirmed enrichment of mTOR signaling and energy metabolism gene sets after knockout. Importantly, mTOR pathway inhibition completely blocked the HIF-1?-knockout-mediated restoration of NK cell function and mitochondrial fitness, indicating that HIF-1? primarily drives NK cell metabolic and functional abnormalities through mTOR suppression. Brucella infection induces HIF-1? overexpression, which suppresses mTOR signaling and drives metabolic reprogramming of NK cells characterized by impaired OXPHOS and functional exhaustion, thereby promoting chronicity of brucellar arthritis. Targeting the HIF-1?/mTOR axis may offer a novel therapeutic strategy for brucellar arthritis.

Introduction:
Brucellar arthritis is the most common complication of brucellosis, and its chronic progression is closely associated with immune cell dysfunction. Natural killer (NK) cells play a central role in anti-infective immunity; however, their functional status and regulatory mechanisms in brucellar arthritis remain poorly understood.

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