Aberrant Autolysosomal Regulation Is Linked to The Induction of Embryonic Senescence: Differential Roles of Beclin 1 and p53 in Vertebrate Spns1 Deficiency

Spinster (Spin) in Drosophila or Spinster homolog 1 (Spns1) in vertebrates is a putative lysosomal H+-carbohydrate transporter, which functions at a late stage of autophagy. The Spin/Spns1 defect induces aberrant autolysosome formation that leads to embryonic senescence and accelerated aging symptoms, but little is known about the mechanisms leading to the pathogenesis in vivo. Beclin 1 and p53 are two pivotal tumor suppressors that are critically involved in the autophagic process and its regulation. Using zebrafish as a genetic model, we show that Beclin 1 suppression ameliorates Spns1 loss-mediated senescence as well as autophagic impairment, whereas unexpectedly p53 deficit exacerbates both of these characteristics. We demonstrate that ‘basal p53’ activity plays a certain protective role(s) against the Spns1 defect-induced senescence via suppressing autophagy, lysosomal biogenesis, and subsequent autolysosomal formation and maturation, and that p53 loss can counteract the effect of Beclin 1 suppression to rescue the Spns1 defect. By contrast, in response to DNA damage, ‘activated p53’ showed an apparent enhancement of the Spns1-deficient phenotype, by inducing both autophagy and apoptosis. Moreover, we found that a chemical and genetic blockage of lysosomal acidification and biogenesis mediated by the vacuolar-type H+-ATPase, as well as of subsequent autophagosome-lysosome fusion, prevents the appearance of the hallmarks caused by the Spns1 deficiency, irrespective of the basal p53 state. Thus, these results provide evidence that Spns1 operates during autophagy and senescence differentially with Beclin 1 and p53.

果蝇中的Spinster（Spin）以及脊椎动物中的Spinster同源物1（Spns1）是一种假定的溶酶体H+-碳水化合物转运蛋白，可在自噬（autophagy）的晚期阶段发挥功能。Spin/Spns1缺陷会诱导异常的自噬溶酶体（autolysosome）形成，进而引发胚胎衰老与加速衰老表型，但目前对于其体内致病的具体分子机制仍知之甚少。Beclin 1与p53是两种关键的肿瘤抑制因子，二者均深度参与自噬过程及其调控。本研究以斑马鱼作为遗传模型，实验结果显示，抑制Beclin 1可改善Spns1缺失介导的衰老及自噬功能损伤；但令人意外的是，p53缺失反而会加剧这两种表型。本研究证实，‘基础水平p53’活性可通过抑制自噬、溶酶体生物发生以及后续的自噬溶酶体形成与成熟，对Spns1缺陷诱导的衰老发挥一定的保护作用；而p53缺失可抵消Beclin 1抑制的效果，从而挽救Spns1缺陷表型。与之相反，在应对DNA损伤时，‘活化型p53’可通过诱导自噬与细胞凋亡（apoptosis），显著加重Spns1缺陷型表型。此外，本研究还发现，无论是通过化学手段还是遗传手段阻断空泡型H+-ATP酶（vacuolar-type H+-ATPase）介导的溶酶体酸化与生物发生，以及后续的自噬体（autophagosome）-溶酶体融合过程，均可阻止Spns1缺陷引发的特征性表型出现，且这一效果不受基础p53状态的影响。综上，本研究结果证实，Spns1在自噬与衰老过程中，与Beclin 1和p53存在差异化的调控关系。