Table_1_Effect of Caloric Restriction on the in vivo Functional Properties of Aging Microglia.pdf

Throughout the lifespan, microglia, the primary innate immune cells of the brain, fulfill a plethora of homeostatic as well as active immune defense functions, and their aging-induced dysfunctionality is now considered as a key trigger of aging-related brain disorders. Recent evidence suggests that both organism’s sex and age critically impact the functional state of microglia but in vivo determinants of such state(s) remain unclear. Therefore, we analyzed in vivo the sex-specific functional states of microglia in young adult, middle aged and old wild type mice by means of multicolor two-photon imaging, using the microglial Ca2 + signaling and directed process motility as main readouts. Our data revealed the sex-specific differences in microglial Ca2 + signaling at all ages tested, beginning with young adults. Furthermore, for both sexes it showed that during the lifespan the functional state of microglia changes at least twice. Already at middle age the cells are found in the reactive or immune alerted state, characterized by heightened Ca2 + signaling but normal process motility whereas old mice harbor senescent microglia with decreased Ca2 + signaling, and faster but disorganized directed movement of microglial processes. The 6–12 months long caloric restriction (70% of ad libitum food intake) counteracted these aging-induced changes shifting many but not all functional properties of microglia toward a younger phenotype. The improvement of Ca2 + signaling was more pronounced in males. Importantly, even short-term (6-week-long) caloric restriction beginning at old age strongly improved microglial process motility and induced a significant albeit weaker improvement of microglial Ca2 + signaling. Together, these data provide first sex-specific in vivo characterization of functional properties of microglia along the lifespan and identify caloric restriction as a potent, cost-effective, and clinically relevant tool for rejuvenation of microglia.

在整个生命周期中，小胶质细胞（microglia）作为大脑主要的先天免疫细胞，承担着大量稳态维持与主动免疫防御功能；如今其衰老诱导的功能异常被认为是衰老相关性脑部疾病的关键触发因素。现有研究表明，生物体的性别与年龄均会显著影响小胶质细胞的功能状态，但该状态的体内决定因素仍不明确。为此，本研究以野生型（wild type）小鼠为对象，选取小胶质细胞钙信号（Ca²+ signaling）与突起定向运动作为核心检测指标，通过多色双光子成像技术，在体内分析了青年、中年与老年小鼠中小胶质细胞的性别特异性功能状态。研究数据显示，在所有检测的年龄阶段（自青年小鼠起），小胶质细胞的钙信号均存在性别特异性差异。此外，研究还发现，无论雌雄，小胶质细胞的功能状态在生命周期中至少会发生两次转变。在中年阶段，小胶质细胞即已处于活化或免疫警觉状态，其特征为钙信号水平升高，但突起运动仍维持正常；而老年小鼠体内则存在衰老型小胶质细胞，其钙信号水平降低，且突起定向运动速度加快但呈现无序状态。为期6至12个月的热量限制（caloric restriction，摄入量为自由采食的70%）可抵消上述衰老诱导的变化，使小胶质细胞的多数（而非全部）功能特性向年轻表型逆转。雄性小鼠的钙信号改善更为显著。值得注意的是，即便在老年阶段开始实施短期（6周）热量限制，也可显著改善小胶质细胞的突起运动，并小幅但显著地提升其钙信号水平。综上，本研究首次在体内对生命周期中不同阶段的小胶质细胞功能特性进行了性别特异性表征，并证实热量限制是一种高效、经济且具有临床转化价值的小胶质细胞年轻化手段。