Accumulation of F-actin drives brain aging and limits healthspan in Drosophila.

The actin cytoskeleton is a key determinant of cell and tissue homeostasis. However, tissue-specific roles for actin dynamics in aging, notably brain aging, are not understood. Here, we show that there is an age-related increase in filamentous actin (F-actin) in Drosophila brains, which is counteracted by prolongevity interventions. Critically, modulating F-actin levels in aging neurons prevents age-onset cognitive decline and extends organismal healthspan. Mechanistically, we show that autophagy, a recycling process required for neuronal homeostasis, is disabled upon actin dysregulation in the aged brain. Remarkably, disrupting actin polymerization in aged animals with cytoskeletal drugs restores brain autophagy to youthful levels and reverses cellular hallmarks of brain aging. Finally, reducing F-actin levels in aging neurons slows brain aging and promotes healthspan in an autophagy-dependent manner. Our data identify excess actin polymerization as a hallmark of brain aging, which can be targeted to reverse brain aging phenotypes and prolong healthspan.

Rapamycin modulates tissue aging and lifespan independently of the gut microbiota in Drosophila.

The FDA approved drug rapamycin can prolong lifespan in diverse species and delay the onset of age-related disease in mammals. However, a number of fundamental questions remain unanswered regarding the mechanisms by which rapamycin modulates age-related pathophysiology and lifespan. Alterations in the gut microbiota can impact host physiology, metabolism and lifespan. While recent studies have shown that rapamycin treatment alters the gut microbiota in aged animals, the causal relationships between rapamycin treatment, microbiota dynamics and aging are not known. Here, using Drosophila as a model organism, we show that rapamycin-mediated alterations in microbiota dynamics in aged flies are associated with improved markers of intestinal and muscle aging. Critically, however, we show that the beneficial effects of rapamycin treatment on tissue aging and lifespan are not dependent upon the microbiota. Indeed, germ-free flies show delayed onset of intestinal barrier dysfunction, improved proteostasis in aged muscles and a significant lifespan extension upon rapamycin treatment. In contrast, genetic inhibition of autophagy impairs the ability of rapamycin to mediate improved gut health and proteostasis during aging. Our results indicate that rapamycin-mediated modulation of the microbiota in aged animals is not causally required to slow tissue and organismal aging.

Keeping it tight: The relationship between bacterial dysbiosis, septate junctions, and the intestinal barrier in Drosophila.

Maladaptive changes in the intestinal flora, typically referred to as bacterial dysbiosis, have been linked to intestinal aging phenotypes, including an increase in intestinal stem cell (ISC) proliferation, activation of inflammatory pathways, and increased intestinal permeability1,2. However, the causal relationships between these phenotypes are only beginning to be unravelled. We recently characterized the age-related changes that occur to septate junctions (SJ) between adjacent, absorptive enterocytes (EC) in the fly intestine. Changes could be observed in the overall level of SJ proteins, as well as the localization of a subset of SJ proteins. Such age-related changes were particularly noticeable at tricellular junctions (TCJ)3. Acute loss of the Drosophila TCJ protein Gliotactin (Gli) in ECs led to rapid activation of stress signalling in stem cells and an increase in ISC proliferation, even under axenic conditions; a gradual disruption of the intestinal barrier was also observed. The uncoupling of changes in bacteria from alterations in ISC behaviour and loss of barrier integrity has allowed us to begin to explore the interrelationship of these intestinal aging phenotypes in more detail and has shed light on the importance of the proteins that contribute to maintenance of the intestinal barrier.

Tricellular junctions regulate intestinal stem cell behaviour to maintain homeostasis.

Ageing results in loss of tissue homeostasis across taxa. In the intestine of Drosophila melanogaster, ageing is correlated with an increase in intestinal stem cell (ISC) proliferation, a block in terminal differentiation of progenitor cells, activation of inflammatory pathways, and increased intestinal permeability. However, causal relationships between these phenotypes remain unclear. Here, we demonstrate that ageing results in altered localization and expression of septate junction proteins in the posterior midgut, which is quite pronounced in differentiated enterocytes (ECs) at tricellular junctions (TCJs). Acute loss of the TCJ protein Gliotactin (Gli) in ECs results in increased ISC proliferation and a block in differentiation in intestines from young flies, demonstrating that compromised TCJ function is sufficient to alter ISC behaviour in a non-autonomous manner. Blocking the Jun N-terminal kinase signalling pathway is sufficient to suppress changes in ISC behaviour, but has no effect on loss of intestinal barrier function, as a consequence of Gli depletion. Our work demonstrates a pivotal link between TCJs, stem cell behaviour, and intestinal homeostasis and provides insights into causes of age-onset and gastrointestinal diseases.

A novel genetic tool for clonal analysis of fourth chromosome mutations.

The fourth chromosome of Drosophila remains one of the most intractable regions of the fly genome to genetic analysis. The main difficulty posed to the genetic analyses of mutations on this chromosome arises from the fact that it does not undergo meiotic recombination, which makes recombination mapping impossible, and also prevents clonal analysis of mutations, a technique which relies on recombination to introduce the prerequisite recessive markers and FLP-recombinase recognition targets (FRT). Here we introduce a method that overcomes these limitations and allows for the generation of single Minute haplo-4 clones of any fourth chromosome mutant gene in tissues of developing and adult flies.