Cardio-respiratory failure is the major cause of death in patients of Duchenne Muscular Dystrophy (DMD), mainly due to diaphragm and heart fibrosis. It is well recognized that immune cells play a crucial role in regulating cardiac function, as well as fibrotic deposition, and there is growing appreciation of immune system involvement in ischaemic heart disease, as well as in non- ischaemic myocarditis. However, very little is known about the involvement of immune system in the cardiac functional defects observed in DMD. We recently found a previously undescribed macrophage subpopulation present in the heart and diaphragm from both WT and mdx (the mouse model of DMD) mice, based on a very high level of expression of F4/80 (F4/80hi) , which is not present in the limb muscle, and distinct from the classical F4/80 expressing population. In this context, it has been clearly demonstrated that cardiac macrophages are numerous, heterogenous and ontogenically diverse, and that different subpopulations might be involved in different cardiac functions. We aim to analyse in detail the relative abundance and kinetics of this population during the progression of the disease in mdx, compared to WT, by cytofluorimetric analysis. We will then analyse the trascriptome of this population FACS-sorted from the heart and diaphragm of both WT and mdx mice at different ages, and compare with that obtained from the classical F4/80 expressing population FACS-sorted from the same organs. The accomplishment of this study might add new insight on the role of different immune cell populations in the pathophysiological events regulating the cardio-respiratory defects observed in DMD patients.
The novelty of our proposal stands on the novelty of the macrophage cell population we aim to characterize. Indeed, this population was not described before, or was not considered worthy to further investigation.
Deciphering the complexity of the immune cell populations acting in cardiac and diaphragm function is a paramount to understand eventual alterations in cardio-respiratory defects during diseases, such as in DMD. The fact that this hitherto undescribed macrophage population was found specifically in the heart and diaphragm, suggest that they may play a peculiar function in theses organs, which requires further characterization. The transcriptome analysis we propose, should easily allow us to understand their activity in both physiological and pathological condition, and investigate whether they are involved in the maintenance of the organ function. Any hypothesis is, at this stage, a matter of speculation. However, if they represent, as we suggest, a specific ¿resident¿ population, they might be responsible of ¿sensing¿ the injuries, modify their transcriptome and release the appropriate cytokines and or signals to orchestrate the immune response. Cardio-immunology is, indeed, a recently highly expanding field of research, and the possibility to influence the activity of immune cells, through biologics, nanoparticle delivery of therapeutic cargo to macrophages and gene editing, is rapidly expanding, becoming ever more specific and efficient. In this context, understanding the function of each immune cell population, and in this case, of this newly described macrophage population, might add new insight in the physio-pathological events regulating DIA and heart maintenance and open the potential of novel therapeutic targets for cthe cardio-respiratory defects obseved in DMD..