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.

Autophagy genes protect against Salmonella typhimurium infection and mediate insulin signaling-regulated pathogen resistance.

A conserved insulin-like pathway modulates both aging and pathogen resistance in Caenorhabditis elegans. However, the specific innate effector functions that mediate this pathogen resistance are largely unknown. Autophagy, a lysosomal degradation pathway, plays a role in controlling intracellular bacterial pathogen infections in cultured cells, but less is known about its role at the organismal level. We examined the effects of autophagy gene inactivation on Salmonella enterica Serovar Typhimurium (Salmonella typhimurium) infection in 2 model organisms, Caenorhabditis elegans and Dictyostelium discoideum. In both organisms, genetic inactivation of the autophagy pathway increases bacterial intracellular replication, decreases animal lifespan, and results in apoptotic-independent death. In C. elegans, genetic knockdown of autophagy genes abrogates pathogen resistance conferred by a loss-of-function mutation, daf-2(e1370), in the insulin-like tyrosine kinase receptor or by over-expression of the DAF-16 FOXO transcription factor. Thus, autophagy genes play an essential role in host defense in vivo against an intracellular bacterial pathogen and mediate pathogen resistance in long-lived mutant nematodes.

Autophagy genes protect against disease caused by polyglutamine expansion proteins in Caenorhabditis elegans.

Expanded polyglutamine (polyQ) proteins aggregate intracellularly in Huntington's disease and other neurodegenerative disorders. The lysosomal degradation pathway, autophagy, is known to promote clearance of polyQ protein aggregates in cultured cells. Moreover, basal autophagy in neuronal cells in mice prevents neurodegeneration by suppressing the accumulation of abnormal intracellular proteins. However, it is not yet known whether autophagy genes play a role in vivo in protecting against disease caused by mutant aggregate-prone, expanded polyQ proteins. To examine this question, we used two models of polyQ-induced toxicity in C. elegans, including the expression of polyQ40 aggregates in muscle and the expression of a human huntingtin disease fragment containing a polyQ tract of 150 residues (Htn-Q150) in ASH sensory neurons. Here, we show that genetic inactivation of autophagy genes accelerates the accumulation of polyQ40 aggregates in C. elegans muscle cells and exacerbates polyQ40-induced muscle dysfunction. Autophagy gene inactivation also increases the accumulation of Htn-Q150 aggregates in C. elegans ASH sensory neurons and results in enhanced neurodegeneration. These data provide in vivo genetic evidence that autophagy genes suppress the accumulation of polyQ aggregates and protect cells from disease caused by polyQ toxicity.