Regulation of macrophage dynamics and adipose stromal cells by laminins during adipose tissue remodelling in obesity

肥胖可在脂肪组织、肝脏和骨骼肌中诱导胰岛素抵抗状态，并与2型糖尿病密切相关。在肥胖过程中，脂肪组织的扩张是一个持续的过程，其特征是脂肪细胞的增殖和肥大，巨噬细胞和其他免疫细胞的聚集，以及异常的细胞外基质沉积。这种炎症状态会破坏体内平衡，损害脂肪细胞的功能，并导致胰岛素抵抗。这位中国合作伙伴已经证明，血液单核细胞的渗透和不寻常的IL-4/STAT6驱动的组织驻留巨噬细胞的增殖导致肥胖脂肪组织中的巨噬细胞聚集。阻断单核细胞的渗透可以减少肥胖和对胰岛素的抵抗，这表明驻留在组织中的巨噬细胞和渗透中的巨噬细胞扮演着不同的角色。虽然其他人描述了与脂肪组织相关的不同的巨噬细胞群，但中国合作伙伴已经显示出脂肪组织巨噬细胞(ATM)和一种新的代表承诺的前脂肪细胞的CD45-CD31-NegICAM-1+脂肪基质细胞群之间的密切联系，并定位于血管周围。初步研究表明，在高脂饮食(HFD)的小鼠中，基质细胞ICAM-1+表达的消除促进了脂肪细胞的增殖，这表明对脂肪稳态至关重要的不仅仅是ATM本身，而是它们与ICAM+基质细胞的相互作用。每个脂肪细胞都被包裹在自己的基底膜(BM)中，德国合作伙伴已经证明，基底膜主要含有层粘连蛋白411，由脂肪原的基质细胞产生。层粘连蛋白411(lama4-/-)的基因消除减少了脂肪的发育，并使人对高脂饮食引起的肥胖和胰岛素抵抗产生抵抗。对野生型(WT)脂肪组织进行单细胞RNA分析，发现CD45-CD31-NegICAM-1+脂肪基质细胞中层粘连蛋白411高表达。与WT胎相比，Lama4-/-鼠出现的这些细胞的数量明显更多，ATM减少。这表明ICAM-1+基质细胞在肥胖中起中心作用，并暗示层粘连蛋白411直接和/或通过改变ATM数量或功能来调节这些细胞。然而，层粘连蛋白411、ICAM-1+脂肪基质细胞和ATM之间的关系尚不清楚。我们假设ICAM-1+脂肪基质细胞和巨噬细胞之间的相互作用是肥胖时脂肪组织重塑的关键，这些细胞群受层粘连蛋白411调控。我们将调查1.ICAM-1在定向前脂肪细胞谱系确定中的作用及其受层粘连蛋白411和巨噬细胞的影响；2.组织内滞留和浸润性巨噬细胞在肥胖中的作用，以及层粘连蛋白是否影响巨噬细胞的渗透或其极化/表型；3.ICAM-1+脂肪基质细胞和巨噬细胞群体相互作用的分子本质以及层粘连蛋白是否影响这一作用。

Obesity can induce an insulin resistant state in adipose tissue, liver and skeletal muscle and is strongly related to type 2 diabetes. During obesity, adipose tissue expansion is an ongoing process, characterized by hyperplasia and hypertrophy of adipocytes, accumulation of macrophages and other immune cells, and aberrant extracellular matrix deposition. Such an inflammatory state disrupts homeostasis, impairs adipocyte function and leads to insulin resistance. The Chinese partner has shown that both infiltration of blood monocytes and an unusual IL-4/STAT6 driven proliferation of tissue resident macrophages result in macrophage accumulation in obese adipose tissue. Blocking monocyte infiltration reduces obesity and resistance to insulin, suggesting different roles for tissue resident and infiltrating macrophages. While others have described distinct populations of macrophages associated with adipose tissue, the Chinese partner has shown a close association between adipose tissue macrophages (ATM) and a novel CD45negCD31negICAM-1+ population of adipose stromal cells, which represent committed preadipocytes, and localise peri-vascularly. Preliminary studies show that elimination of ICAM-1+ expression in stromal cells promotes adipocyte hyperplasia in mice on a high fat diet (HFD), suggesting that it is not ATMs alone but rather their cross-talk with ICAM+ stromal cells that is critical for fat homeostasis.Each adipocyte is encased in its own basement membrane (BM), which the German partner has shown contains mainly laminin 411, produced by stromal cells of the fat anlage. Genetic elimination of laminin 411 (Lama4-/-) reduces fat development and confers resistance to HFD induced obesity and insulin resistance. Single cell RNA analysis of wild type (WT) adipose tissue has revealed high expression of laminin 411 in the CD45negCD31negICAM-1+ adipose stromal cells. Significantly higher numbers of these cells occur Lama4-/- mice compared to WT littermates and ATMs are reduced. This suggests a central role for ICAM-1+ stromal cells in obesity and implicates laminin 411 in regulating these cells either directly and/or by altering ATM number or function. However, the relationship between laminin 411, the ICAM-1+ adipose stromal cells and ATMs remains unclear.We hypothesize that interactions between ICAM-1+ adipose stromal cells and macrophages are critical to remodelling of fat tissue during obesity and that these cell populations are regulated by laminin 411. We will investigate1. The role of ICAM-1 in lineage specification of committed preadipocytes and how this is affected by laminin 411 and macrophages;2. The contribution of tissue resident versus infiltrating macrophages to obesity and whether laminins affect macrophage infiltration or their polarization/phenotype;3. The molecular nature of interactions between ICAM-1+ adipose stromal cells and macrophage populations and whether this is affected by laminins.