Dr. Richard Steet

Active Research Projects

Defining the metabolic and phenotypic consequences of CDG. A major area of emphasis in Dr. Steet’s lab is the study of CDGs (congenital disorders of glycosylation). His primary focus in this area is two-fold: 1) to elucidate the mechanisms that govern cell type specific changes in glycosylation and 2) to identify the glycoproteins most sensitive to abnormal glycosylation as a means of defining organ pathophysiology. This work is carried out using both zebrafish and cell-based models, and is currently focused on PMM2-CDG, STT3A/B-CDG and glycolipid biosynthesis defects such as GM3 synthase deficiency. Dr. Steet’s group is using chemical glycobiology methods to profile how loss of specific glycogenes causes underglycosylation of specific glycoproteins and how altered glycosylation on some of these proteins alters their cell surface residence. An exciting new avenue in Dr. Steet’s CDG work comes from the development and characterization of iPSC and iPSC-derived cell lines from CDG patients. This work is done in collaboration with Steve Dalton and Mike Tiemeyer at UGA and is beginning to uncover insights into the molecular pathogenesis of these diseases by defining the cell type specific consequences of abnormal glycosylation. 

Expanding the chemical biology toolbox for the study of genetic disorders.This area of research has undergone a major expansion in Dr. Steet’s laboratory over the last four years and will remain a significant focus in the future. His lab’s efforts in chemical glycobiology are primarily driven by Dr. Seok-Ho Yu, a talented research scientist in his group, and done in close collaboration with former CCRC colleagues Geert-Jan Boons, Lance Wells and Kelley Moremen. The early collaborative studies with the Boons group were aimed at optimizing new reagents and resulted in a number of publications. The current projects in the Steet laboratory focus on applications for this emerging technology. They are employing both metabolic labeling with azide-modified sugar precursors as well as enzymatic labeling approach termed SEEL (selective exo-enzymatic labeling) in a host of ongoing projects. The latter methodology takes advantage of recombinant glycosyltransferases and modified nucleotide-sugars to selectively label glycoproteins at the cell surface. The collaborative team recently demonstrated that SEEL can be performed in a single step to greatly increase the efficiency of labeling. Once labeled, these glycoproteins can be directly visualized by Western blot or immunofluorescence or enriched and identified using proteomics. Both methods provide a powerful platform to explore how the cell surface abundance and trafficking of glycoproteins in the context of human genetic diseases.

There are numerous ongoing projects in his lab aimed at using SEEL to profile cell surface glycoproteins in different disease cell models. These projects highlight the breadth of collaborators who are interested in working with his group to investigate disease pathogenesis: 1) Using SEEL to define the molecular basis for the cardiomyocyte-specific glycosylation defects in Pompe (external collaborator: Tim Kamp, University of Wisconsin Medical School); 2) SEEL as a diagnostic tool for GNE myopathy (external collaborator: Marjan Huizing, NIH); 3) Using SEEL to identify sensitive glycoproteins in the context of CDG and glycogene-deficient cells (external collaborators: Hudson Freeze, Steve Dalton and Joe Contessa).

Understanding the pathogenesis of lysosomal storage disorders. The Steet laboratory continues to focus on the pathogenesis of the lysosomal disease, mucolipidosis II or I-cell disease, in an effort to unravel how loss of carbohydrate-dependent lysosomal targeting causes the life-threatening symptoms of this disease. Supported by both public and private grants, his lab’s current focus (done in collaboration with Dr. Heather Flanagan-Steet) is to understand how glycosaminoglycans modulate extracellular cathepsin K activity to drive pathogenesis in cartilage. His group is also developing new cell culture models of lung epithelial cells to ask whether extracellular cathepsins are capable of remodeling the surface of these cells in a similar manner to what is seen in patients with cystic fibrosis. Dr. Steet’s team is broadly interested in defining the pathogenic mechanisms that underlie a variety of lysosomal storage disorders and is also working to improve existing therapies.

Select Publications:

  • Cline A, Gao N, Flanagan-Steet H, Sharma V, Rosa S, Sonon R, Azadi P, Sadler KC, Freeze HH, Lehrman MA, Steet R. (2012). A zebrafish model of PMM2-CDG reveals altered neurogenesis and a substrate-accumulation mechanism for N-linked glycosylation deficiency. Mol Biol Cell. 23(21): 4175-4187. [PMC3484097] 
  • Mbua NE, Flanagan-Steet H, Johnson S, Wolfert MA, Boons GJ, Steet R. (2013). Abnormal accumulation and recycling of glycoproteins visualized in Niemann-Pick type C cells using the chemical reporter strategy. Proc Natl Acad Sci USA 110(25): 10207-10212. [PMC3690855] 
  • Flanagan-Steet H, Aarnio M, Kwan B, Guihard P, Petrey A, Haskins M, Blanchard F, Steet R. (2016). Cathepsin-mediated alterations in TGFß-related signaling underlie disrupted cartilage and bone maturation associated with impaired lysosomal targeting. J Bone Miner Res. 31(3): 535-548. [PMC4808492] 
  • Flanagan-Steet H, Christian C, Lu PN, Aarnio-Peterson M, Sanman L, Archer-Hartmann S, Azadi P, Bogyo M, Steet RA. (2018) TGF-ß Regulates Cathepsin Activation during Normal and Pathogenic Development. Cell Reports Mar 13;22(11):2964-2977. [PMID28724630]. 


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