Tat-Beclin 1

Autophagy maintains cartilage homeostasis and is compromised during osteoarthritis (OA), contributing to cartilage degeneration. We sought to determine if D-isomer TAT-Beclin-1, a potent inducer of autophagy, could attenuate post-traumatic OA in mice.

10-week-old mice underwent destabilization of the medial meniscus (DMM) surgery to induce post-traumatic OA, or sham surgery (control), and injected intra-articularly with D-isomer TAT-Beclin-1 (0.5-2 mg/kg) or PBS 1 week post-surgery for up to 9 weeks. Mice were sacrificed at 2 or 10 weeks post-surgery. Knee joint sections were evaluated by histopathology for cartilage degeneration and synovitis, and immunostaining for key markers of autophagy (LC3B), cell proliferation (nuclear Ki67), activated fibroblasts (αSMA), and cells of hematopoietic origin (CD45).

All D-isomer TAT-Beclin-1-treated DMM mice had no difference in the degree of cartilage degeneration compared to PBS-injected DMM mice. Surprisingly, all D-isomer TAT-Beclin-1-treated mice exhibited substantial synovial hyperplasia, with increased cellularity and ECM deposition (fibrosis-like phenotype), as compared to PBS-injected mice. Synovial effects of D-isomer TAT-Beclin-1 were dose- and injection frequency-dependent. An increased percentage of cells positive for LC3B and nuclear Ki67 were found in the synovial intima early after injection, which persisted after frequent injections.

D-isomer TAT-Beclin-1 did not attenuate cartilage degeneration, but rather induced synovial hyperplasia associated with increased expression of key markers of autophagy and cell proliferation and a fibrosis-like phenotype, independent of markers of fibroblast activation or persistent hematopoietic-origin cell infiltration. These data suggest that, if not tissue-targeted, caution should be taken using autophagy activators due to diverse cellular responses in the joint.

A review.The term autophagy, which means 'self-eating' in Greek, was coined at a conference in 1963 by Christian de Duve, one of the scientists who first studied how lysosomes degrade cell debris.In the subsequent years, most researchers viewed autophagy as a basic metabolic process.The first autophagy-related genes were discovered in experiments with starved yeast in the 1990s.Autophagy is an old, well-conserved cellular pathway, which means that it has had many years for its underlying genes to develop into multi-taskers that do not just handle processes of cell metabolism, such as recycling cell bits during times of starvation, but also serve a role in cellular defense mechanisms.Autophagy is a "primordial defense mechanism," says Washington University School of Medicine immunologist Herbert Virgin."There's an evolutionary battle of wills where the pathogen is blocking the pathway, and the pathway is blocking the pathogen.".When a cell needs fuel, it activates a process that brings cell material such as old mitochondria or ribosomes to a lysosome, which then degrades these parts into needed nutrients, such as amino acids and essential proteins.But as it turns out, this is not an all-or-nothing process.The autophagy machinery can be selective in what bits of debris get designated for this fate.One of the main goals of the CETR's work is to identify the pathways of autophagy that selectively target intracellular pathogens.When seeking out ways to increase autophagy to fight pathogens, scientists' biggest focus is to refine the Tat-beclin 1 peptide into a "drug-like mol. that can advance through preclin. development," Levine says.But, she adds, they are also on the lookout for the 'next' Tat-beclin 1, by doing several genome-wide RNA-interference screens to identify autophagy proteins that respond to different viral infections.Tat-beclin 1 is a good general-autophagy enhancer, but these screens could lead researchers to a peptide that selectively targets specific types of pathogens even more effectively."In the past decade or so, there's been an explosion of work on selective autophagy," says Levine.Such research has drawn in scientists from a variety of backgrounds.Virgin, for instance, was chasing after the proteins that controlled interferon-γ, an immune signaler, when he found that some of the same genes also controlled autophagy.He then developed mice with a depleted version of a core mammalian autophagy-related gene called Apg16l1 (later changed to Atg16l1).This gene was first discovered in 2003, as the mammalian version of the yeast autophagy-related gene Atg16.The mutated gene expressed lower than normal levels of its autophagy protein.At a conference a decade ago, Virgin met Ramnik Xavier, a gastroenterologist at Massachusetts General Hospital, who was studying the same autophagy gene and its role in Crohn's disease.The two started to collaborate.They found that mice with a mutated Atg16l1 gene produce malfunctioning Paneth cells, which normally secrete a lysozyme to help limit and control the types of bacterial growth in the lining of the gut.The same mutation and abnormal Paneth cells can be found Crohn's disease patients."The study of autophagy is this amazing thing, where you start studying one thing and if you keep an open mind, you discover that there's relationships between autophagy and a lot of different kinds of biol.," Virgin says.Xavier now heads one branch of the CETR project, focusing on the genetic mechanisms behind selective bacterial autophagy.In unpublished work, he says, his team has been able to take advantage of the link between Crohn's disease and autophagy by using the disorder as way to screen for even more autophagy-related genes.