Human monocyte-derived macrophages are heterogenous: Proteomic profile of different phenotypes

Tissue macrophages play a key role in many aspects of human physiology and pathology. These cells are heterogeneous both in term of morphology and function. As an example, heterogeneity has been reported within the atherosclerotic lesions where distinct populations exert opposite functions driving plaque progression or stability. Tissue macrophages are not easily obtained and differentiated blood-derived monocytes are largely used as surrogate model. We previously reported that human macrophages spontaneously differentiated from adherent monocytes show two dominant subsets, distinct for morphology (spindle and round) and functions. The aim of this study was to evaluate the intracellular proteome of these two macrophage subsets by means of a microproteomic workflow properly set up to simultaneously identify and quantify proteins from a minimal number of morphotypically heterogeneous cells in culture. We report two distinct proteomic profiles that distinguish round from spindle macrophages. In particular, differential abundances were observed for proteins involved in membrane traffic regulation, lipid handling, efferocytosis, and protection against stress conditions. Results reinforce and extend previous data on the functional and antigenic profile of these macrophage phenotypes strengthening the suitability of our model to focus on macrophage heterogeneity.

Tissue macrophages patrol homeostatic functions, immune surveillance, and resolution of inflammation. The spectrum of macrophage activation states is, therefore, wide and gives ground for the heterogeneity of these cells, documented in health and disease. This study provides knowledge of the distinct proteome that characterises the two dominant morphotypes (round and spindle) of human macrophages that, in our culture condition, are generated by spontaneous differentiation from blood-derived monocytes. Results extend previous data about the different antigenic, transcriptional, and functional profiles of these morphotypes and further strengthen the suitability of this in vitro model to study macrophage heterogeneity and to address the effects of environmental challenges and drugs.