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Joshua Broussard, PhD

Joshua Broussard, PhDDr. Joshua Broussard joined the lab of Dr. Kathleen Green on January 1st, 2013. The ability to translate mechanical forces into biochemical responses, a process called mechanotransduction, is fundamental to many biological and pathological processes such as proliferation, differentiation, cancer and fibrosis. Adhesive plaques are often the mechanosensitive organelles that execute the translation from force into biochemical signals. Desmosomes (DSMs) are cell-cell adhesion organelles that are most prominent in tissues that undergo high amounts of mechanical stress (such as the skin), and are thus ideal candidates to act as mechanosensors and mechanotransducers. However, unlike the roles of the adherens junction and associated actin cytoskeleton, the function of DSMs in these processes is understudied. Dr. Broussard has been studying this function of DSMs in mechanotransduction. He utilized a well-characterized mutant desmoplakin (DPNTP) that lacks the IF binding domain to uncouple IF from the DSM. In small colonies of normal human epidermal keratinocytes (NHEKs), this uncoupling led to distributional changes in the actin cytoskeleton and cell-substrate adhesions, suggesting alterations in tensional distribution. He established a system in the Green lab that allows for the direct mechanical manipulation of cells using a Flexcell Tension apparatus. While NHEKs subjected to cyclical stretch using this system responded by elongating and reorienting their main axis, expression of DPNTP inhibited these processes. Moreover, uncoupling the DSM/IF unit in NHEKs also led to changes in the other mechanically sensitive processes. These included a decrease in cell growth rate and an acceleration of calcium-induced differentiation, as determined by an increase in the protein expression of loricrin and differentiation specific desmosomal cadherins and keratins. Finally, uncoupling the DSM/IF unit led to an increase in active (phosphorylated) ErbB2. Using a pharmacological approach, he showed that active ErbB2 is required for NHEK differentiation and inhibiting ErbB2 abolishes the DPNTP-mediated effects on differentiation. ErbB2 has been shown to regulate the actin cytoskeleton; therefore, these data suggest a model in which DSMs regulate mechanically sensitive cellular behaviors potentially through modulation of ErbB2-mediated regulation of the contractile actin network. These studies will lead to a novel role for the desmosome as a mechanotransducer, and increase our understanding of how physical forces can be biochemically transformed into the form and function of essential tissues, such as the epidermis.

He took the formal course ‘Taking Responsibility for Responsible Conduct of Research’ and attended numerous seminars and workshops. His Mentoring Team consisted of Drs. Green, Lavker, Espinosa, and Ridge.

The data accumulated during the training period was used in the submission of an abstract to the 2015 Society for Investigative Dermatology annual meeting where Dr. Broussard was selected for an oral presentation in the Growth Factors, Cell Adhesion, & Matrix Biology minisymposium. Dr. Broussard was a Discussion Leader at the 2015 Gordon Research Seminar on Cell Contact and Adhesion and presented his work at the 2015 Gordon Research Conference on Cell Contact and Adhesion. He also presented his work at the 2016 Gordon Research Conference on Intermediate Filaments and will be attending the upcoming 2017 Epidermal Differentiation and Keratinization in May 2017 to present his work. In December of 2016, Dr. Broussard was selected to present his work at the annual American Society for Cell Biology (ASCB) meeting in the Intermediate Filaments from Cytoplasm to Nucleus minisymposium. Finally, the data accumulated during the training period was used in a successful application for a Chicago Biomedical Consortium Postdoctoral Research Award entitled “Adhesion-based regulation of intercellular forces in live-cell organotypic cultures”.

The Journal of Investigative Dermatology has invited Dr. Broussard to write a paper on FRET microscopy for their Research Techniques made Simple section. In addition, the Journal of Cell Science has invited Dr. Broussard to submit a review on intermediate filaments, desmosomes, and cell mechanics as a direct result of the reviews editor attending Dr. Broussard’s presentation at the ASCB meeting.

Publications

Broussard JA, Getsios S, Green KJ. Desmosome regulation and signaling in disease. Cell Tissue Res. 2015, 360: 501-512 PMID:25693896.

Broussard JA, Yang R, Huang C, Nathamgari SP, Beese AM, Godsel LM, Lee S, Zhou F, Sniadecki NJ, Green KJ, Espinosa HD. The desmoplakin/intermediate filament linkage regulates cell mechanics. Molecular Biology of the Cell, 2017. In press.

Nekrasova O, Harmon RM, Broussard JA, Koetsier JL, Godsel LM, Fitz GN, Green KJ.  Desmosomal cadherin association with Tctex-1 and cortactin-Arp2/3 drives perijunctional actin polymerization to promote epidermal stratification. Nat. Comm., 2017. In revision. 

Quinlan RA, Schwarz N, Windoffer R, Richardson C, Hawkins T, Broussard JA, Green KJ, Leube R. A New biomechanical role for intermediate filaments in the cortical cytoskeleton, hypothesis, Journal of Cell Science. In revision.

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