Myeloid-specific deficiency of ribosomal protein L13a alters macrophage polarity and diversity during differentiation from bone marrow.

Macrophages show substantial plasticity, leading to a diverse population of these cells with different states of polarization during differentiation from bone marrow. However, the mechanisms underlying this process are not well understood. Here, we identified a novel role of ribosomal protein L13a previously shown to be engaged in the physiological control of inflammation regulating macrophage diversity and polarity. Using an ex-vivo differentiation model of bone marrow-derived macrophages (BMDM) from the control (L13aflox/flox) and myeloid-specific L13a KO (L13aflox/flox LysMCre+) mice (L13a-KO), we present compelling evidence of the role of L13a in regulating macrophage polarization that goes beyond the M1-M2-based binary concept. We show that macrophages from L13a-KO mice lead to enhanced expression of classical markers of both M1 and M2 and surprising deviation from the expected response under known inducers of polarity. The phosphorylation-dependent activation of a number of signaling molecules played a role in this process. Bulk RNA and single-cell RNA sequencing of the BMDM from the L13a-KO mice show widespread change in overall gene expression and robust differences in the diverse populations of the bone marrow-derived cells from the control and KO mice. In addition, this study also shows a substantial increase of Th1 and Th2 signature genes in CD4+ T cells isolated from the L13a-KO animals. Together, our studies provide new insights into the regulations of macrophage polarization by L13a-driven novel intermediate effectors or mediators.