Distinct anti-inflammatory macrophage (M2) subtypes, namely M2a and M2c, are reported to modulate the tissue repair process tightly and chronologically by modulating fibroblast differentiation state and functions. To establish a well-defined three-dimensional (3D) cell culture model to mimic the tissue repair process, we utilized THP-1 human monocytic cells and a 3D collagen matrix as a biomimetic tissue model. THP-1 cells were differentiated into macrophages, and activated using IL-4/IL-13 (MIL-4/IL-13) and IL-10 (MIL-10). Both activated macrophages were characterized by both their cell surface marker expression and cytokine secretion profile. Our cell characterization suggested that MIL-4/IL-13 and MIL-10 demonstrate M2a- and M2c-like subtypes, respectively. To mimic the initial and resolution phases during the tissue repair, both activated macrophages were co-cultured with fibroblasts and myofibroblasts. We showed that MIL-4/IL-13 were able to promote matrix synthesis and remodeling by induction of myofibroblast differentiation via transforming growth factor beta-1 (TGF-β1). On the contrary, MIL-10 demonstrated the ability to resolve the tissue repair process by dedifferentiation of myofibroblast via IL-10 secretion. Overall, our study demonstrated the importance and the exact roles of M2a and M2c-like macrophage subtypes in coordinating tissue repair in a biomimetic model. The established model can be applied for high-throughput platforms for improving tissue healing and anti-fibrotic drugs testing, as well as other biomedical studies.

Microgravity accelerates the aging of various physiological systems, and it is well acknowledged that aged individuals and astronauts both have increased susceptibility to infections and poor response to vaccination. Immunologically, dendritic cells (DCs) are the key players in linking innate and adaptive immune responses. Their distinct and optimized differentiation and maturation phases play a critical role in presenting antigens and mounting effective lymphocyte responses for long-term immunity. Despite their importance, no studies to date have effectively investigated the effects of microgravity on DCs in their native microenvironment, which is primarily located within tissues. Here, we address a significantly outstanding research gap by examining the effects of simulated microgravity via a random positioning machine on both immature and mature DCs cultured in biomimetic collagen hydrogels, a surrogate for tissue matrices. Furthermore, we explored the effects of loose and dense tissues via differences in collagen concentration. Under these various environmental conditions, the DC phenotype was characterized using surface markers, cytokines, function, and transcriptomic profiles. Our data indicate that aged or loose tissue and exposure to RPM-induced simulated microgravity both independently alter the immunogenicity of immature and mature DCs. Interestingly, cells cultured in denser matrices experience fewer effects of simulated microgravity at the transcriptome level. Our findings are a step forward to better facilitate healthier future space travel and enhance our understanding of the aging immune system on Earth.

The processes of aging and space travel both have significant adverse effects on the immune system, resulting in increased susceptibility to infections. Using simulated microgravity platforms, such as the random positioning machine (RPM), on Earth allows us to investigate these effects to better facilitate future space travel and our understanding of the aging immune system. Dendritic cells (DCs) are key players in linking the innate and adaptive immune responses. Their distinct differentiation and maturation phases play vital roles in presenting antigens and mounting effective T-cell responses. However, DCs primarily reside in tissues such as the skin and lymph nodes. To date, no studies have effectively investigated the effects of aging via RPM on DCs in their native microenvironment. With 3D biomimetic collagen hydrogels, we can study the effects on DCs in more physiologically relevant microenvironments. In this study, we investigated the effects of loose and dense culture matrices on the phenotype, function, and transcriptome profile of immature and mature DCs utilizing an RPM to simulate an accelerated aging model. Our data indicate that an aged, or loose tissue microenvironment, and exposure to RPM conditions decrease the immunogenicity of iDCs and mDCs. Interestingly, cells cultured in dense matrices experienced fewer effects by the RPM at the transcriptome level.

Hyaluronic acid (HA) is a major glycosaminoglycan found in the extracellular matrix (ECM) and exhibits immunoregulatory properties depending on its molecular weight (MW). However, the impact of tissue bound HA on dendritic cell (DC) functions is not well understood due to the varying distribution of HA MW under different physiological and pathological conditions. To investigate DCs in defined biosystems, we used three-dimensional (3D) collagen matrices modified with HA of specific MW, while maintaining similar microstructure and HA levels. Using these matrices, we examined the influence of HA on cytokine binding and observed distinct properties depending on the presence and MW of HA, suggesting modulation of cytokine availability by the different MW of HA. Our studies on DC immune potency revealed that low molecular weight HA (LMW-HA; 8-15 kDa) enhances immature DC (iDC) differentiation and antigen uptake, while medium (MMW-HA; 500-750 kDa) and high molecular weight HA (HMW-HA; 1250-1500 kDa) increase cytokine secretion in matured DCs (mDCs). Interestingly, the modulation of DCs surface marker expression and cytokine secretion by different MW of HA appeared to be independent of CD44. However, we found that cytokine secretion of DCs was dependent on the CD44 receptor regardless of the presence or absence of HA in the matrix. Additionally, we observed reduced migratory capacity of iDCs and mDCs when cultured on MMW- and HMW-HA matrices, and this effect was dependent on CD44. In summary, our findings provide new insights into the MW-dependent effects of tissue-bound HA on DCs, opening avenues for the design of DC-modulating materials to enhance DC-based therapy.