Lung squamous cell carcinoma downregulates haptoglobin expression to inhibit M2 macrophage ferroptosis via the hemoglobin-dependent CD163/HO-1 pathway.

Lung squamous cell carcinoma (LUSC) is a highly malignant tumor that poses significant challenges for targeted therapy. Thus, there is a need to identify novel treatment targets. Acute-phase proteins (APPs) have been implicated in various physiological and pathophysiological processes, including cancer progression and ferroptosis. However, it remains unclear whether APPs serve a role in the progression and ferroptosis of LUSC. In the present study, bioinformatics analysis identified a haptoglobin (HP) gene as a hub gene in LUSC, and its expression levels were negatively associated with patient prognosis. HP was notably downregulated in LUSC and significantly enriched in the ferroptosis pathway. In vitro experiments demonstrated that overexpression of HP in LUSC cells did not induce ferroptosis, as there were no significant differences in lactate dehydrogenase (LDH) release, the frequency of 7-aminoactinomycin D (7-AAD)-positive cells, Fe(2+) levels and lipid peroxidation among the cells in the LV-Ctrl, LV-HP, LV-Ctrl/Hb and LV-HP/Hb groups. However, when M2 macrophages were cultured with conditioned medium from LUSC cells overexpressing HP in the presence of hemoglobin (LV-HP/Hb group), there was a significant induction of ferroptosis in the M2 macrophages compared with those in the LV-Ctrl, LV-HP and LV-Ctrl/Hb and groups. This was evidenced by the increase in LDH release, the frequency of 7-AAD-positive cells, Fe(2+) levels, lipid peroxidation and typical ultrastructural changes observed under transmission electron microscopy. Further mechanistic investigations revealed that the anti-CD163 antibody, the HO-1 inhibitor Tin protoporphyrin IX dichloride and the Fe(2+) chelator deferoxamine effectively alleviated M2 macrophage ferroptosis in the LV-HP/Hb group. These results indicated that HP could promote M2 macrophage ferroptosis by promoting intracellular Fe(2+) accumulation via a hemoglobin-dependent CD163/heme oxygenase 1 pathway, indicating a potential avenue for future investigations in LUSC research.