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

肥胖可诱发脂肪组织、肝脏和骨骼肌的胰岛素抵抗状态，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生和肥大，巨噬细胞和其他免疫细胞的积累，以及细胞外基质的异常沉积。这种炎症状态会破坏体内平衡，损害脂肪细胞功能，导致胰岛素抵抗。中国合作伙伴已经证明，血液单核细胞的浸润和异常的IL-4/STAT6驱动的组织巨噬细胞增殖导致巨噬细胞在肥胖脂肪组织中积聚。阻断单核细胞浸润可减少肥胖和胰岛素抵抗，提示组织常驻和浸润性巨噬细胞的作用不同。虽然其他人已经描述了与脂肪组织相关的不同巨噬细胞群，但中国合作伙伴已经表明脂肪组织巨噬细胞（ATM）与一种新的CD45negCD31negICAM-1+脂肪基质细胞群之间存在密切联系，这些细胞代表了固定的前脂肪细胞，并定位于血管周围。初步研究表明，在高脂饮食（HFD）小鼠中，消除基质细胞中ICAM-1+的表达促进了脂肪细胞的增生，这表明不是atm单独，而是它们与ICAM+基质细胞的相互作用对脂肪稳态至关重要。每个脂肪细胞都包裹在自己的基底膜（BM）中，德国合作伙伴已经证明，基底膜主要包含由脂肪基质细胞产生的层粘连蛋白411。遗传消除层粘连蛋白411 （Lama4-/-）可减少脂肪的形成，并对HFD引起的肥胖和胰岛素抵抗产生抵抗。野生型（WT）脂肪组织的单细胞RNA分析显示，层粘连蛋白411在CD45negCD31negICAM-1+脂肪基质细胞中高表达。Lama4-/-小鼠与WT幼崽相比，这些细胞的数量明显增加，atm减少。这表明ICAM-1+基质细胞在肥胖中起核心作用，并暗示层粘连蛋白411直接或通过改变ATM数量或功能调节这些细胞。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对肥胖期间脂肪组织的重塑至关重要，并且这些细胞群受层粘连蛋白411的调节。我们会调查的。1 . ICAM-1在固定前脂肪细胞谱系特异性中的作用，以及它如何受到层粘连蛋白411和巨噬细胞的影响；2 .巨噬细胞驻留与浸润对肥胖的贡献，层粘连蛋白是否影响巨噬细胞浸润或其极化/表型；ICAM-1+脂肪基质细胞与巨噬细胞之间相互作用的分子性质，以及这种相互作用是否受到层粘连蛋白的影响。

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.