Siglec-7 orchestrates mitochondrial dynamics and metabolic reprogramming to restrain human NK cell cytotoxic function

Natural killer (NK) cells are innate lymphocytes that directly eliminate tumor and virus-infected cells by integrating signals from activating and inhibitory receptors, and their effector functions are tightly coupled to cellular metabolism. Given that the inhibitory receptor PD-1 reprograms T cell metabolism to shape functional fate, the bioenergetic consequences of inhibitory receptor engagement on human NK cells remain largely unexplored, particularly for sialic acid-binding immunoglobulin-like lectin (Siglec-7), a glyco-immune checkpoint receptor. Here, we investigated metabolic programs and effector functions associated with Siglec-7 expression and antibody-mediated Siglec-7 ligation in primary NK cells and NK-92MI cells. Siglec-7^POS NK cells exhibited selectively impaired CD107a degranulation under glycolytic and oxidative phosphorylation inhibition, whereas Siglec-7^NEG cells remained relatively resistant, indicating distinct energetic wiring between these subsets. Engagement of Siglec-7 by an agonistic antibody induced mitochondrial fission with altered Drp1 phosphorylation, transient mitochondrial depolarization, and broadly suppressed mitochondrial respiration, while concurrently enhancing glycolytic capacity, consistent with a dual metabolic shift upon Siglec-7 ligation. In contrast, sustained Siglec-7 expression in NK-92MI-S cells was associated with globally enhanced mitochondrial respiratory capacity, indicating that sustained Siglec-7 expression and short-term treatment with an agonistic anti-Siglec-7 antibody were associated with distinct metabolic profiles in NK cells. Furthermore, Siglec-7^POS NK cells showed increased accumulation of autophagic vacuole, reduced proliferation, and heightened apoptotic susceptibility compared with Siglec-7^NEG counterparts. Collectively, these findings support an association between Siglec-7 status, mitochondrial homeostasis, and metabolic fitness in NK cells, with Siglec-7^NEG cells retaining a metabolically robust, cytotoxic phenotype.