Autolysosome biogenesis and developmental senescence are regulated by both Spns1 and v-ATPase

Spns1 (Spinster homolog 1 [<i>Drosophila</i>]) in vertebrates, as well as Spin (Spinster) in <i>Drosophila</i>, is a hypothetical lysosomal H⁺-carbohydrate transporter, which functions at a late stage of macroautophagy (hereafter autophagy). The Spin/Spns1 defect induces aberrant autolysosome formation that leads to developmental senescence in the embryonic stage and premature aging symptoms in adulthood. However, the molecular mechanism by which loss of Spin/Spns1 leads to the specific pathogenesis remains to be elucidated. Using chemical, genetic and CRISPR/Cas9-mediated genome-editing approaches in zebrafish, we investigated and determined a mechanism that suppresses embryonic senescence as well as autolysosomal impairment mediated by Spns1 deficiency. Unexpectedly, we found that a concurrent disruption of the vacuolar-type H⁺-ATPase (v-ATPase) subunit gene, <i>atp6v0ca</i> (ATPase, H⁺ transporting, lysosomal, V0 subunit ca) led to suppression of the senescence induced by the Spns1 defect, whereas the sole loss of Atp6v0ca led to senescent embryos similar to the single <i>spns1</i> mutation. Moreover, we discovered that the combined stable defect seen in the presence of both the <i>spns1</i> and <i>atp6v0ca</i> mutant genes still subsequently induced premature autophagosome-lysosome fusion marked by insufficient acidity, while extending developmental life span, compared with the solely mutated <i>spns1</i> defect. Our data suggest that Spns1 and the v-ATPase orchestrate proper autolysosomal biogenesis with optimal acidification that is critically linked to developmental senescence and survival.