Xiao Lab

Xiao Lab

Tsan Sam Xiao, PhD

Associate Professor, Department of Pathology, School of Medicine
Member, Developmental Therapeutics Program, Case Comprehensive Cancer Center
Member, Center for AIDS Research, School of Medicine
Member, Cleveland Center for Membrane and Structural Biology


The Xiao lab uses structural and chemical biology approaches to study the inflammasome signaling pathways, with the goal of targeting diverse diseases such as sepsis, multiple sclerosis, and AIDS using small molecule compounds. Two areas of active research are as follows:

Research Projects


‌Molecular mechanism of pyroptosis mediated by the gasdermin family of pore-forming proteins
DNA5

Pyroptosis is an inflammatory form of programmed cell death that plays important roles in immune protection against infections and in inflammatory disorders. Gasdermin D (GSDMD) is an executor of pyroptosis upon cleavage by inflammatory caspases-1/4/5/11 following canonical and noncanonical inflammasome activation. GSDMD N-terminal domain assembles membrane pores to induce cytolysis, whereas its C-terminal domain inhibits cell death through intramolecular association with the N domain. The GSDMD pores also contribute to the release of mature cytokines such as IL-1β and IL-18, which in turn recruit more immune cells implicated in inflammation. Our ongoing study of GSDMD revealed its distinct mode of intramolecular domain interaction and autoinhibition, which may be relevant to its unique role in pyroptosis downstream of inflammasome activation. It remains to be determined how most of the gasdermin family members are maintained in their autoinhibited states and how they are activated through protease cleavage or other post-translational modifications, and ultimately how they function under physiological and pathological conditions. Understanding the molecular mechanisms of gasdermin transformation from soluble proteins to transmembrane pores will provide valuable insights into the roles of pyroptosis in immune protection against infections and in inflammatory disorders. These will pave the way for therapeutic targeting of various inflammatory disorders such as sepsis, multiple sclerosis and inflammatory bowel disease.

Regulation of inflammatory caspases using chemical biology approaches for drug development

Caspase is a family of cysteine proteases that are expressed as zymogens activated through autocleavage. Mature caspases predominantly cleave at P1-site aspartate residues within their substrates and play crucial roles in cell death, tissue remodeling, and differentiation. Caspases can be divided into inflammatory caspases (such as caspases-1, -4, -5, and -12 in humans and caspases-1, -11, and -12 in mice) and apoptotic caspases (such as caspases-2, -3, -6, -7, -8, -9, and -10). Even though inflammatory caspases-1, -4, -5, and -11 all cleave GSDMD, only caspase-1 cleaves pro-IL-1β and a number of other substrates. The molecular mechanisms of such substrate specificity are poorly understood, but may implicate regions outside the cleavage site (the “exosites”) that contribute to specific enzyme-substrate recognition. Our recent study demonstrated that a GSDMD-derived inhibitor, N-acetyl-Phe-Leu-Thr-Asp-chloromethylketone (Ac-FLTD-CMK), inhibits GSDMD cleavage by caspases-1, -4, -5, and -11 in vitro, suppresses pyroptosis downstream of both canonical and noncanonical inflammasomes, as well as reduces IL-1β release following inflammasome activation. By contrast, the inhibitor does not target caspase-3 or apoptotic cell death, suggesting that Ac-FLTD- CMK is a specific inhibitor for inflammatory caspases. This is significant because few inhibitor specific for all inflammatory caspases has been reported. Crystal structure of caspase-1 in complex with Ac-FLTD-CMK reveals extensive enzyme- inhibitor interactions involving both hydrogen bonds and hydrophobic contacts. Our ongoing studies of inflammatory caspases and inhibitors have elucidated the mechanisms for several lead compounds currently in clinical trials for liver diseases and epilepsy, and may have therapeutic potential for sepsis, multiple sclerosis, Alzheimer's disease, myocardial infarction, and AIDS.

 

Overall, progress made in the Xiao lab may reveal fundamental molecular mechanisms of innate immunity, and pave the way for targeting of inflammatory signaling pathways using small molecule compounds for diagnostic and therapeutic applications. As we embark on this exciting journey, we welcome applications from qualified and motivated individuals to join our team.

Lab Members:

Syrena Bracey
MSTP Student

Syrena obtained her B.S. in Biochemistry and Molecular Biology from the University of Maryland, Baltimore County in 2017 before matriculating into the Case Western Reserve University School of Medicine’s Medical Scientist Training Program. She joined the Xiao lab in December 2020 and is studying the molecular interactions involved in the processing and secretion of proinflammatory cytokines.

Publications 


Brianna Busscher
BSTP Student


Email: bmb118@case.edu
ORCiD: 0000-0002-3030-211X

Brianna graduated from Calvin University (formerly known as Calvin College) in 2018 with a B.S. in Biochemistry, a B.A. in Writing, and a minor in French. During her undergraduate years, she participated in summer research in the fields of biochemistry, immunology, microbiology, and epigenetics. In 2019 she entered the Biomedical Sciences Training Program (BSTP) at Case Western Reserve University as a PhD student and is investigating the virus-host interactions of SARS-CoV-2, focusing specifically on accessory protein Open Reading Frame 3a (ORF3a). 

Publications


Sai Li, PhD
Postdoc

Email: sxl1959@case.edu
Lab phone: 216-368-5106

Sai received her PhD in structural biology at University of Science and Technology of China in 2015. She joined Xiao lab in the Department of Pathology at Case Western Reserve University in 2022. Her research focuses on the roles of gasdemins in facilitating non-lytic release of inflammatory cytokines.

Publications