Identification of a chemorepellent
Although a relatively large amount is known about eukaryotic chemoattractants (signals that attract cells), very little is known about eukaryotic chemorepellents. We noticed that at the edges of wild-type Dictyostelium colonies, cells move away from the colony and explore the environment beyond the colony. At the edges of colonies of mutant Dictyostelium cells that lack the secreted protein AprA, there are very few cells that move away from the colony. The aprA¯ mutant cells however show normal motility, and thus would be capable of moving away from the colony. Videomicroscopy indicated that wild-type cells move in a deliberate fashion away from the colony, whereas aprA¯ cells at the edge of a colony just move in a random walk pattern. We then found that in an artificial gradient of AprA, Dictyostelium cells move away from the source of the AprA. This indicated that AprA is a chemorepellent. We found that the AprA receptor is the G protein-coupled receptor GrlH, and we are currently working to elucidate the AprA signal transduction pathway.
Identification of a potential therapeutic for ARDS, rheumatoid arthritis, and pressure and venous ulcers
In acute respiratory distress syndrome (ARDS), damage to the lungs from acute smoke inhalation, infection, or aspirated vomitus causes a massive influx of neutrophils, which can exacerbate the damage, leading to more neutrophil influx and lung failure in a destructive positive feedback loop. In the US, there are ~200,000 cases of ARDS per year. Due to the lack of effective treatments, the mortality rate is ~40%. Being able to repel neutrophils from the lungs could help reduce the damage. Other diseases where there are too many neutrophils in a specific area, and the neutrophils seem to be causing damage, include rheumatoid arthritis and pressure, venous, and diabetic ulcers. Although AprA has little sequence similarity to mammalian proteins, we used structure prediction programs to obtain a predicted 3-dimensional structure of AprA, and then found that this predicted structure has similarity to the known structure of a human secreted protein called dipeptidyl peptidase IV (DPPIV). We then tested the hypothesis that DPPIV might act as a chemorepellent, and after testing DPPIV on several cell types, found that human DPPIV is a chemorepellent for human and mouse neutrophils. To our surprise and delight, we then found that in a mouse model of ARDS, inhalation of DPPIV prevents the accumulation of neutrophils in the lungs. A single injection of DPPIV into the joint in a mouse model of rheumatoid arthritis also seems to drive neutrophils out of the joint, resulting in a reduced arthritis score. We then found that the DPPIV receptor is the protease-activated receptor PAR 2, that PAR 2 agonists induce human neutrophil chemorepulsion, and when administered by aspiration into the airways, PAR 2 agonists show good efficacy at reducing the inappropriate influx of neutrophils into the lungs in a mouse model of ARDS. We are currently working to elucidate how DPPIV functions as a chemorepellent, and do further tests of DPPIV and PAR2 ligands to see these could be used as therapeutics for neutrophil-driven diseases such as ARDS.
Sex differences in chemorepulsion
We tend to think of neutrophils as a very fundamental part of the innate immune system, and that this should be the same in men and women. We unexpectedly observed that there are several differences in the neutrophil chemorepulsion mechanisms of healthy young men and healthy young women, including differences in the amounts and localization of key proteins in neutrophils. This may well impact how we would administer neutrophil repellent therapeutics to male and female ARDS patients, and we are pursuing these studies to understand this intriguing sex difference in a basic aspect of the innate immune system.
Key papers
Phillips, J. E. and Gomer, R. H. A secreted protein is an endogenous chemorepellant in Dictyostelium discoideum. Proc. Natl. Acad. Sci. USA, 109, 10990-10995 (2012).
Herlihy, S. E., Pilling, D., Maharjan, A. S., and Gomer, R. H. Dipeptidyl-peptidase IV is a neutrophil chemorepellent. Journal of Immunology, 190, 6468-6477 (2013).
Herlihy, S.E., Tang, Y., and Gomer, R.H. A Dictyostelium secreted factor requires a PTEN-like phosphatase to slow proliferation and induce chemorepulsion. PLoS ONE, 8, e59365 (2013).
Phillips, J.E. and Gomer, R.H. The p21-activated kinase (PAK) family member PakD is required for chemorepulsion and proliferation inhibition by autocrine signals in Dictyostelium discoideum. PLoS ONE, 9, e96633 (2014).
Herlihy, S.E., Brown, M.L., Pilling, D., Weeks, B.R., Myers, L.K., and Gomer, R.H. Role of the Neutrophil Chemorepellent Soluble Dipeptidyl Peptidase IV in Decreasing Inflammation in a Murine Model of Arthritis. Arthritis & Rheumatology, 67, 2634-2638 (2015).
Herlihy, S.E., Tang, Y., Phillips, J.E., and Gomer, R.H. Functional similarities between the Dictyostelium protein AprA and the human protein Dipeptidyl-Peptidase IV. Protein Science, 26, 578-585 (2017).
White, M.J.V., Chinea, L.E., Pilling, D., and Gomer, R.H. Protease activated-receptor 2 is necessary for neutrophil chemorepulsion induced by trypsin, tryptase, or dipeptidyl peptidase IV. Journal of Leukocyte Biology, 103, 119-128 (2018).
Tang, Y., Wu, Y., Herlihy, S.E., Brito-Aleman, F.J., Ting, J.H., Janetopoulos, C., and Gomer, R.H. An autocrine proliferation repressor regulates Dictyostelium discoideum proliferation and chemorepulsion using the G protein-coupled receptor GrlH. mBio, 9, e02443-17 (2018).
Pilling, D., Chinea, L.E., Consalvo, K.M., and Gomer, R.H. Different isoforms of the neuronal guidance molecule Slit2 directly cause chemoattraction or chemorepulsion of human neutrophils. Journal of Immunology, 202, 239-248 (2019).
Rijal, R., Consalvo, K.M., Lindsey, C.K., and Gomer, R.H. An endogenous chemorepellent directs cell movement by inhibiting pseudopods at one side of cells. Molecular Biology of the Cell, 30, 242-255 (2019).
Karmakar, R., Tyree, T., Gomer, R.H., and Rappel, W-J. Cell dispersal by localized degradation of a chemoattractant. Proc. Natl. Acad. Sci. USA, 118, e2008126118 (2021).
Kirolos, S.A., Rijal, R., Consalvo, K.M., and Gomer, R.H. Using Dictyostelium to Develop Therapeutics for Acute Respiratory Distress Syndrome. Frontiers Cell and Developmental Biology, 9, 710005 (2021).
Kirolos, S.A. and Gomer, R.H. A chemorepellent inhibits local Ras activation to inhibit pseudopod formation to bias cell movement away from the chemorepellent. Molecular Biology of the Cell, 33, ar9 (2022).
Consalvo, K.M., Kirolos, S.A., Sestak, C.E., and Gomer, R.H. Sex-based differences in human neutrophil chemorepulsion. Journal of Immunology, in press.