Institute of Molecular Biology and Pathology, National Research Council (CNR), Rome, Italy.
Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy.
Cell Biochem Funct. 2022 Oct;40(7):718-728. doi: 10.1002/cbf.3737. Epub 2022 Sep 7.
Dendritic cells (DCs) are innate immune cells with a central role in immunity and tolerance. Under steady-state, DCs are scattered in tissues as resting cells. Upon infection or injury, DCs get activated and acquire the full capacity to prime antigen-specific CD4 and CD8 T cells, thus bridging innate and adaptive immunity. By secreting different sets of cytokines and chemokines, DCs orchestrate diverse types of immune responses, from a classical proinflammatory to an alternative pro-repair one. DCs are highly heterogeneous, and physiological differences in tissue microenvironments greatly contribute to variations in DC phenotype. Oxygen tension is normally low in some lymphoid areas, including bone marrow (BM) hematopoietic niches; nevertheless, the possible impact of tissue hypoxia on DC physiology has been poorly investigated. We assessed whether DCs are hypoxic in BM and spleen, by staining for hypoxia-inducible-factor-1α subunit (HIF-1α), the master regulator of hypoxia-induced response, and pimonidazole (PIM), a hypoxic marker, and by flow cytometric analysis. Indeed, we observed that mouse DCs have a hypoxic phenotype in spleen and BM, and showed some remarkable differences between DC subsets. Notably, DCs expressing membrane c-kit, the receptor for stem cell factor (SCF), had a higher PIM median fluorescence intensity (MFI) than c-kit DCs, both in the spleen and in the BM. To determine whether SCF (a.k.a. kit ligand) has a role in DC hypoxia, we evaluated molecular pathways activated by SCF in c-kit BM-derived DCs cultured in hypoxic conditions. Gene expression microarrays and gene set enrichment analysis supported the hypothesis that SCF had an impact on hypoxia response and inhibited autophagy-related gene sets. Our results suggest that hypoxic response and autophagy, and their modulation by SCF, can play a role in DC homeostasis at the steady state, in agreement with our previous findings on SCF's role in DC survival.
树突状细胞（DCs）是先天免疫细胞，在免疫和耐受中发挥核心作用。在稳态下，DC 作为静息细胞分散在组织中。在感染或损伤时，DC 被激活并获得完全的能力来启动抗原特异性 CD4 和 CD8 T 细胞，从而连接先天免疫和适应性免疫。通过分泌不同的细胞因子和趋化因子，DC 协调多种类型的免疫反应，从经典的促炎反应到替代性的促修复反应。DC 高度异质性，组织微环境中的生理差异极大地影响 DC 表型的变化。一些淋巴区域的氧张力通常较低，包括骨髓（BM）造血龛；然而，组织缺氧对 DC 生理学的可能影响尚未得到充分研究。我们通过染色缺氧诱导因子-1α亚基（HIF-1α），即缺氧诱导反应的主调控因子，以及缺氧标志物 pimonidazole（PIM），通过流式细胞术分析来评估 DC 在 BM 和脾脏中是否缺氧。实际上，我们观察到小鼠 DC 在脾脏和 BM 中具有缺氧表型，并且在 DC 亚群之间表现出一些显著差异。值得注意的是，表达膜 c-kit 的 DC（c-kit DC），即干细胞因子（SCF）的受体，其 PIM 中荧光强度（MFI）高于 c-kit DC，无论是在脾脏还是 BM 中。为了确定 SCF（也称为 kit 配体）在 DC 缺氧中的作用，我们评估了在缺氧条件下培养的 c-kit BM 来源的 DC 中激活的分子途径。基因表达微阵列和基因集富集分析支持了 SCF 对缺氧反应有影响并抑制自噬相关基因集的假说。我们的结果表明，缺氧反应和自噬，以及 SCF 的调节，可能在 DC 稳态中发挥作用，这与我们之前关于 SCF 在 DC 存活中的作用的发现一致。
