Dr. Heather Flanagan-Steet

Active Research Projects

Dr. Flanagan-Steet’s research has largely focused on defining the mechanisms governing early tissue development. This has ranged from investigating how neuromuscular synapses form to development of the embryonic heart and craniofacial skeleton. Over the last thirteen years Dr. Flanagan-Steet’s efforts have centered on defining the molecular and cellular mechanisms underlying pathogenesis of rare genetic diseases. This has included several lysosomal storage disorders (LSDs) as well as the congenital disorders of glycosylation (CDGs). Her work on genetic diseases has largely involved generating zebrafish models to investigate gene function and disease pathogenesis. This work pioneered the use of zebrafish to model rare inherited diseases, bringing new insight into the molecular initiators and mechanisms underlying pathogenesis of mucolipidosis II and PMM2-CDG.

In her role as Director of Functional Studies, she works closely with the Divisions across the Center to advance our understanding of rare diseases. Our team uses a combination of genetic, molecular, biochemical and microscopic approaches to answer questions of disease pathogenesis. We have adapted both traditional and modern biochemical procedures to extend the utility of our zebrafish models to functionally understand the proteins and genes we are studying. We are keenly interested in elucidated the full pathogenic cascade so that we may identify biochemical pathways downstream of the causative genetic mutation that may be modulated for disease therapy. A summary of the current projects in her lab are shown below:

Disease models for the Congenital Disorders of Glycosylation (CDGs). 
We are using zebrafish models of PMM2-CDG to identify pathogenic cascades driving cartilage and bone malformations, as well as neuromuscular issues. We are currently addressing whether altered processing of specific proteins may initiate disease pathogenesis in these tissues. Our group is also interested in defining how loss of subunits of the OST complex impact development. We are using TALENS and CRISPR-Cas9 tools to generate zebrafish models of newly identified CDGs. Novel CDG models were initiated using patient-derived insight regarding CDG-associated genes.

Defining the pathogenesis of lysosomal storage disorders.
Our group has been interested in understanding the pathogenic mechanisms associated with loss of carbohydrate-dependent lysosomal sorting for many years. Using several zebrafish models of mucolipidosis II (MLII, I-cell), we have identified cathepsin proteases as key pathogenic initiators. When mislocalized outside the cell these proteases can inappropriately act on numerous substrates, including growth factors such as TGFß, causing abnormal chondrogenesis (see Figure 1). We continue to explore how extracellular cathepsin proteases influence normal and disease tissue development. Our work has largely focused on abnormal cartilage development, but recent efforts include the congenital heart defects associated with MLII. Within this work we are assessing novel nano-based therapies as a potential means to ameliorate disease pathology. 

Figure 1: Mistargeted Cathepsins Sustain TGFß Signaling and Drive Abnormal Chondrogenesis

Disease Associated Malformations of Interest 

Select Publications

  • Flanagan-Steet H, Sias C, Steet R. (2009). Altered chondrocyte differentiation and extracellular matrix homeostasis in a zebrafish model for mucolipidosis II. Am J Pathol. 175(5): 2063-2075. [PMC2774070] 
  • Petrey AC, Flanagan-Steet H, Johnson S, Fan X, De la Rosa M, Haskins ME, Nairn AV, Moremen KW, Steet R. (2012). Excessive activity of cathepsin K is associated with cartilage defects in a zebrafish model of mucolipidosis II. Dis Model Mech. 5(2): 177-190. [PMC3291639]   
  • 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]. 


Meet Ella

We will remember February 26th for the rest of our lives. On that day, we received the call from the Greenwood Genetic Center that they had discovered our daughter, Ella Marie, has Kleefstra syndrome. Very early on, my wife, Kelly, observed Ella being delayed in some of her milestones. Kelly monitored Ella’s progression and sought out testing in an effort to get Ella some assistance. Along the way, we were sent to GGC and met with LEARN MORE

In The News