Single-cell profiling reveals a critical role for hypoxia-inducible factor-1a signaling in leukocytes during human craniotomy infection

Neurosurgeries complicated by bacterial infection are often associated with poor clinical prognosis and prolonged treatment strategies involving multiple surgeries, placing additional morbidity on an already fragile patient population. Craniotomy is one of the most common neurosurgical procedures with an infection rate of 1-7%; however, the cellular and molecular signatures associated with craniotomy infection in human subjects have not yet been investigated. We performed a retrospective study of over 2,500 craniotomies, which revealed diversity in patient demographics, pathogen identity, and surgical landscapes associated with infection. Leukocyte profiling in tissues procured from craniotomy infection patients revealed a predominance of granulocytic myeloid-derived suppressor cells (G-MDSCs), which were absent from the blood. Single-cell transcriptomics identified immunometabolic shifts in leukocytes invading infected tissues, including a prominent hypoxia-inducible factor-1 (HIF-1) signature, whereas peripheral blood cells from the same patient were largely quiescent. The importance of HIF-1 signaling was validated using a mouse model of Staphylococcus aureus craniotomy infection, where the local delivery of HIF-1 inhibitor microparticles attenuated proinflammatory cytokine production concomitant with a significant increase in leukocyte infiltrates into the infected brain and galea. These findings establish G-MDSCs as a major infiltrate during human craniotomy infection and identify conserved transcriptional signatures across several leukocyte populations that may represent promising therapeutic targets for craniotomy infection in the face of increasing antimicrobial resistance. To better understand the human immune response to craniotomy infection, we collected residual surgical tissue from patients with craniotomy infection. These specimens included blood, subgaleal, epidural, bone flap, and intracranial tissue samples. Samples were collected from 4 patients, designated patient 7, 11, 14, or 15. We processed each sample into a single-cell solution and enriched each sample for CD45+ immune cells via fluorescence-activated cell sorting, before analysis via scRNA-seq.