Effect of low and high stiffness on resting and zymosan stimulated bone marrow derived dendritic cells

Mechanical properties of tissues such as stiffness change throughout our lives during healthy development but also during chronic diseases like cancer. How stiffness changes during cancer progression affect leukocytes is not known. To address this, myeloid phenotypes resulting from mono- and cancer co-cultures of primary murine and human myeloid cells on 2D and 3D hydrogels with varying stiffnesses were analyzed. On soft hydrogels conventional DCs (cDCs) arose, whereas on stiff hydrogels plasmacytoid DCs (pDCs) developed. Cell populations expressing macrophage marker CD14, Ly6C, CD16 also increased on stiff hydrogels. In cancer co-cultures CD86+ populations decreased on higher stiffnesses across four different cancer model. High stiffness also led to increased VEGFA, MMP and CD206 expression; M2 markers expressed by tumour-associated macrophages (TAMs). Indeed, the majority of CD11c+ cells expressed CD206 across human cancer models. Targeting the PI3K-Akt pathway led to a decrease of CD206+ cells in murine cultures only, while human CD86+ cells increased. Increased stiffness in cancer could thus lead to the dysregulation of infiltrating myeloid cells and shift their phenotypes towards a M2-like TAM phenotype actively enabling tumour progression. Additionally, stiffness dependent signaling seems species dependent, which might contribute to the high failure rate of clinical trials.