Taylor, M. R. | Search bioRxiv

bioRxiv2019

Arl13b regulates Sonic Hedgehog signaling from outside primary cilia

ARL13B is a regulatory GTPase highly enriched in cilia. Complete loss of Arl13b disrupts cilia architecture, protein trafficking and Sonic hedgehog signaling. To determine whether ARL13B is required within cilia, we knocked in a cilia-excluded variant of ARL13B (V358A) and showed it retains all known biochemical function. We found that ARL13BV358A protein was expressed but could not be detected in cilia, even when retrograde ciliary transport was blocked. We showed Arl13bV358A/V358A mice are viable and fertile with normal Shh signal transduction. However, in contrast to wild type cilia, Arl13bV358A/V358A cells displayed short cilia and lacked ciliary ARL3 and INPP5E. These data indicate that ARL13Bs role within cilia can be uncoupled from its function outside of cilia. Furthermore, these data imply that the cilia defects upon complete absence of ARL13B do not underlie the alterations in Shh transduction, which is unexpected given the requirement of cilia for Shh transduction.

developmental biology↗

bioRxiv2019

Vancomycin Relieves Mycophenolate Mofetil-Induced Gastrointestinal Toxicity by Eliminating Gut Bacterial β-Glucuronidase Activity

Mycophenolate mofetil (MMF) is commonly prescribed after transplantation and has proven advantages over other immunosuppressive drugs but gastrointestinal (GI) side effects frequently limit its use. The pathways involved in the metabolism of the prodrug MMF and the bioactive derivative mycophenolic acid (MPA) are well characterized but the mechanism responsible for toxicity is unknown. Here we extend our previous observation that an intact gut microbiome is required for MMF-induced toxicity and demonstrate that gut bacterial metabolism is responsible for the GI inflammation and weight loss associated with MMF exposure. In mice consuming MMF, the introduction of vancomycin alone was sufficient to prevent or reverse MMF-induced weight loss and colonic inflammation. MMF induced the expansion of bacteria expressing {beta}-glucuronidase (GUS) in the cecum and proximal colon. GUS activity, which is responsible for the catabolism of glucuronidated MPA (MPAG) to free MPA, was increased in the presence of MMF and eliminated by vancomycin. Vancomycin eliminated multiple Bacteroides spp. that flourished in the presence of MMF and prevented the breakdown of MPAG without negatively affecting serum MPA levels. Human data suggests that increased stool GUS activity can be associated with MMF-related toxicity. Our work provides a mechanism for the GI toxicity associated with MMF and a future direction for the development of therapeutics.

microbiology↗