Adapted Smart-seq3xpress Facilitates Selective Microglial Transcriptomic Profiling From Frozen Brain Tissue

Single-cell transcriptomics has revealed the central role of microglia in brain development, homeostasis, and disease, particularly in the context of neuroinflammation. While single-cell RNA-sequencing enables targeted microglial analysis from fresh tissue, studying these cells in cryopreserved or archival samples remains challenging due to the lack of a protocol for their specific enrichment and RNA-sequencing. In this study, we developed a method for profiling microglial nuclei from fresh-frozen tissue using Smart-seq3xpress. This approach relies on PU.1-based enrichment, made possible by a brief formaldehyde fixation step to preserve the antigen. To ensure compatibility with Smart-seq3xpress, we utilized a Thermolabile Proteinase K treatment to reverse cross-links, thereby maintaining high transcriptomic sensitivity. We benchmarked the method in a mouse model of ischemic stroke, evaluating both technical performance and its ability to capture biologically meaningful microglial states. Compared to standard single-nucleus protocols, our approach yielded higher gene and UMI counts and a greater proportion of coding reads. Transcriptomic profiles closely matched those from whole-cell RNA-sequencing, including the detection of activation markers and diverse microglial subpopulations. This approach enables high-resolution transcriptomic analysis of microglia from fresh-frozen or archival brain samples, overcoming major limitations of single-nucleus RNA sequencing. It broadens access to cellular insights from biobanked material, supporting both basic research and translational studies of neuroinflammatory disease.