Characterization of TREM2-related pathogenic macrophages in aging and diseased peripheral nerves

衰老是神经系统功能和结构衰退的主要危险因素。我们之前已经证明，周围神经在结构和功能上也会受到衰老的影响。在横切面上，衰老神经的髓鞘轴突显示其最初圆形的变化以及脱髓鞘的迹象。虽然轴突形状的变化与炎症无关，但我们发现神经巨噬细胞是衰老相关脱髓鞘的强大驱动因素。后一个过程让人想起脱髓鞘的特点，以前描述了我们的小组在遗传病变的神经。有趣的是，TREM2，一个通常的调节分子，是脱髓鞘过程所必需的。在本项目中，我们旨在表征衰老和病变神经中致病性巨噬细胞的分子特征。为此，我们将通过单细胞RNA测序比较分离和预分化的神经巨噬细胞的转录组。我们将比较来自衰老和遗传病变神经的巨噬细胞与正常成年小鼠的神经巨噬细胞。将正常和衰老的trem2缺陷神经与trem2缺陷、遗传病变神经的非致病性神经巨噬细胞进行比较，可能有助于鉴定致病性巨噬细胞的核心特征基因。将进行验证实验，以研究鉴定的致病性巨噬细胞是否确实定位于与发病相关的室室，如脱髓鞘纤维基底层和外雪旺细胞膜之间的界面。最后，我们将测试病原巨噬细胞是单核细胞起源的假设，使用适当的突变体来绘制命运图。我们的研究旨在对衰老和周围神经病变的细胞和分子发病机制有新的认识。

Aging is a major risk factor for the functional and structural decline of the nervous system. We have previously shown that also peripheral nerves are structurally and functionally affected by aging. In cross sections, myelinated axons of aging nerves show both changes in their initially rounded shape as well as signs of demyelination. While changes in axonal shape occur independently of inflammation, we identified nerve macrophages as robust drivers for aging-related demyelination. The latter process is reminiscent of demyelinating features previously described by our group in genetically diseased nerves. Interestingly, TREM2, a usually modulating molecule, is necessary for the demyelinating processes. In the present project we aim to characterize the molecular features of pathogenic macrophages in aging and diseased nerves. For this purpose, we will compare the transcriptome of isolated and presorted nerve macrophages by single-cell RNA sequencing. We will compare macrophages from aging and genetically diseased nerves with nerve macrophages of normal adult mice. The comparison with non-pathogenic nerve macrophages of normal and aging TREM2-deficient nerves and TREM2-deficient, genetically diseased nerves will likely be instrumental for identifying core signature genes of pathogenic macrophages. Validation experiments will be performed to investigate whether the identified pathogenic macrophages are indeed localized at pathogenetically-relevant compartments, like the interface between basal laminae and outer Schwann cell membranes of demyelinating fibers. Finally, we will test the hypothesis that pathogenic macrophages are of monocytic origin, using appropriate mutants for fate mapping. Our studies aim to gain novel insights into the cellular and molecular pathogenesis of aging and diseased peripheral nerves.