TBK1 suppresses RIPK1-driven apoptosis and inflammation during development and in aging

Aging is a major risk factor for both genetic and sporadic neurodegenerative disorders. However, it is unclear how aging interacts with genetic predispositions to promote neurodegeneration. Here we investigate how partial loss-of-function of TBK1, a major genetic cause for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) comorbidity, leads to age-dependent neurodegeneration. We show that TBK1 is an endogenous inhibitor of RIPK1 and the embryonic lethality of Tbk1-/- mice is dependent on RIPK1 kinase activity. In aging human brains, another endogenous RIPK1 inhibitor, TAK1, exhibits a marked decrease in expression. We show that in Tbk1+/- mice, the reduced myeloid TAK1 expression promotes all the key hallmarks of ALS/FTD, including neuroinflammation, TDP-43 aggregation, axonal degeneration, neuronal loss and behavior deficits, which are blocked upon inhibition of RIPK1. Thus, aging facilitates RIPK1 activation by reducing TAK1 expression, which cooperates with genetic risk factors to promote the onset of ALS/FTD. mRNA profiles of primary microglia derived from 2-day old wild type (WT), Tbk1+/-, Tbk1+/-;Ripk1D138N/D138N, Tak1deltaM/+, Tbk1+/-;Tak1deltaM/+ and Tbk1+/-;Tak1deltaM/+;RIpk1D138N/+ mice were generated by bulk RNA sequencing, in triplicate.衰老是遗传性与散发性神经退行性疾病共同的主要风险因素。然而，目前尚不清楚衰老如何与遗传易感性相互作用，进而促进神经退行性变。在此，我们探究了TBK1——肌萎缩侧索硬化症 (amyotrophic lateral sclerosis, ALS) 与额颞叶痴呆 (frontotemporal dementia, FTD) 共病的主要遗传病因——的部分功能缺失如何导致年龄依赖性神经退行性变。我们证实，TBK1是受体相互作用蛋白激酶1 (RIPK1) 的内源性抑制剂，且Tbk1-/-小鼠的胚胎致死性依赖于RIPK1激酶活性。在衰老的人类大脑中，另一种内源性RIPK1抑制剂转化生长因子β激活激酶1 (TAK1) 的表达水平显著下降。我们发现，在Tbk1+/-小鼠中，髓系细胞内TAK1表达的降低会诱发ALS/FTD的所有关键病理特征，包括神经炎症、Tar DNA结合蛋白43 (TDP-43) 聚集、轴突退行性变、神经元丢失以及行为缺陷，上述表型均可通过抑制RIPK1得以阻断。综上，衰老通过降低TAK1的表达促进RIPK1激活，进而与遗传风险因子协同作用，推动ALS/FTD的发病。本研究通过批量RNA测序 (bulk RNA sequencing)，对2日龄野生型 (wild type, WT)、Tbk1+/-、Tbk1+/-;Ripk1D138N/D138N、Tak1deltaM/+、Tbk1+/-;Tak1deltaM/+及Tbk1+/-;Tak1deltaM/+;Ripk1D138N/+小鼠来源的原代小胶质细胞的mRNA表达谱进行了检测，所有样本均设置3次生物学重复。