Single-cell transcriptomics-based MacSpectrum reveals macrophage activation signatures in diseases

Abstract

Adipose tissue macrophages (ATMs) are crucial for maintaining adipose tissue homeostasis and mediating obesity-induced metabolic abnormalities, including prediabetic conditions and type 2 diabetes mellitus. Despite their key functions in regulating adipose tissue metabolic and immunologic homeostasis under normal and obese conditions, a high-resolution transcriptome annotation system that can capture ATM multifaceted activation profles has not yet been developed. This is primarily attributed to the complexity of their di?erentiation/activation process in adipose tissue and their diverse activation profles in response to microenvironmental cues. Although the concept of multifaceted macrophage action is well accepted, no current model precisely depicts their dynamically regulated in vivo features. To address this knowledge gap, we generated single-cell transcriptome data from primary bone marrow-derived macrophages under polarizing and nonpolarizing conditions to develop new high-resolution algorithms. The outcome was the creation of a 2-index platform, MacSpectrum (https://macspectrum.uconn.edu), that enables comprehensive high-resolution mapping of macrophage activation states from diverse mixed cell populations. MacSpectrum captured dynamic transitions of macrophage subpopulations under both in vitro and in vivo conditions. Importantly, MacSpectrum revealed unique signature gene sets in ATMs and circulating monocytes that displayed signifcant correlation with BMI and homeostasis model assessment of insulin resistance (HOMA-IR) in obese human patients. Thus, MacSpectrum provides unprecedented resolution to decode macrophage heterogeneity and will open new areas of clinical translation.