Professor of the Graduate School Division of Cell and Developmental BiologyLab Homepage: http://mcb.berkeley.edu/labs/machen/
The general goal is to determine how lung airway epithelial cells respond to and prevent bacterial infections, particularly in the genetic disease cystic fibrosis.
The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is an anion channel that conducts Cl, HCO3 and other anions. This channel is located in the apical membrane of trachea and other secretory and absorptive epithelial cells. The genetic disease cystic fibrosis (CF) is caused by mutations in CFTR that lead to reduced function, resulting in altered luminal ionic milieu, accumulation of viscous mucus with altered biochemical properties, reduced activities of anti-bacterial products secreted by epithelial cells and accumulation of bacteria (most prominently Pseudomonas aeruginosa) and neutrophils. Disease symptoms result from the damaging effects of the bacteria and the neutrophils.
In the past we used patch clamp and transepithelial electrophysiology to investigate the Cl and HCO3 permeability properties of the CFTR channel, which is key to determining the secretory and absorptive properties of epithelial cells in the lung airways. To test the hypothesis that CFTR controls or modulates pH and redox of the airway surface liquid and organelles (ER, Golgi, and mucus secretory granules), we used digital imaging microscopy and genetic targeting of green fluorescent protein (GFP) and organic fluorescent dyes to determine how the channel affects the pH properties of organelles in living cells. Widefield and confocal microscopy coupled with electrophysiology were used to characterize the interactions between epithelial cells and bacteria to determine how epithelial cells prevent infection and identify early events that precede invasion by neutrophils. We found that flagellin (released from bacteria) triggers toll-like receptors that signal cells to open CFTR, leading to secretion of anions and osmotically obliged fluid (facilitates bacterial flushing) and also production of proinflammatory cytokines (recruit neutrophils to the infection).
Since retiring, my lab has collaborated with groups at other institutions in three major efforts: (i) In collaboration with Chi Li (U. Louisville) we are determining how the quorum sensing molecule N-(3-oxo-acyl)-homoserine lactone (C12) secreted by Pseudomonas aeruginosa triggers apoptosis (cell suicide) in airway epithelial cells. These studies showed that Paraoxonase 2 (a lactonase in airway epithelial cells) cleaves C12 to smaller molecules that activate a novel form of apoptosis that involves mitochondria but not the pro-apoptotic molecules Bax and Bak. Li is attempting to use this information to identify other small molecules that can be used to treat cancers that are resistant to chemical treatments that activate Bax and Bak. (ii) In collaboration with Christian Schwarzer (UCB) and Horst Fischer (Children's Hospital Oakland Research Institute) we showed that amino acids released from airway epithelial cells are strong chemoattractants for Pseudomonas aeruginosa to locate and bind to wounded cells. (iii) With Juan Ianowski (U. Saskatchewan) we helped show that Pseudomonas aeruginosa trigger ion and fluid secretion from the glands of tracheas in living pigs, similar to what we found in human cells grown in culture. Their novel synchrotron-based method has also been used to show that nerves in the airways may provide a stimulatory pathway for secretion in CF airways. Experiments in progress are attempting to discover whether this neural pathway might be used in conjunction with recently discovered chemical stimulants of mutant CFTR to improve CF treatments.
Pseudomonas aeruginosa triggers CFTR-mediated airway surface liquid secretion in swine trachea. [Luan X, Campanucci VA, Nair M, Yilmaz O, Belev G, Machen TE, Chapman LD, Ianowski JP. Proc. Nat. Acad. Sci., 111:12930-5, 2014] Noted in Nature as a “Research Highlight”: http://www.nature.com/nature/journal/v512/n7515/full/512350d.html
Paraoxonase 2 serves a proapopotic function in mouse and human cells in response to the Pseudomonas aeruginosa quorum-sensing molecule N-(3-Oxododecanoyl)-homoserine lactone. [Schwarzer C, Fu Z, Morita T, Whitt AG, Neely AM, Li C, Machen TE. J Biol Chem. 290(11):7247-5, 2015]
N-(3-oxo-acyl) homoserine lactone inhibits tumor growth independent of Bcl-2 proteins. [Zhao G, Neely AM, Schwarzer C, Lu H, Whitt AG, Stivers NS, Burlison JA, White C, Machen TE, Li C. Oncotarget. 7(5):5924-42, 2016]
Chemotaxis and binding of Pseudomonas aeruginosa to scratch-wounded human cystic fibrosis airway epithelial cells. [Schwarzer C, Fischer H, Machen TE. 2016. PLoS One. 11(3):e0150109, 2016]
Cystic fibrosis swine fail to secrete airway surface liquid in response to inhalation of pathogens [Luan X, Campanucci VA, Nair M, Yilmaz O, Belev G, Machen TE, Chapman D, Ianowski JP. Nat Commun. 8:786, 2017]
N-(3-oxo-acyl)-homoserine lactone induces apoptosis primarily through a mitochondrial pathway in fibroblasts [Neely AM, Zhao G, Schwarzer C, Stivers NS, Whitt AG, Meng S, Burlison JA, Machen TE, Li C. Cellular Microbiology, 20. doi: 10.1111/cmi, 2018.
Nebulized hypertonic saline triggers nervous system-mediated active liquid secretion in cystic fibrosis swine trachea. [Luan X, Tam JS, Belev G, Jagadeeshan S, Murray B, Hassan N, Machen TE, Chapman DE, Ianowski JP. Nature Sci. Rep. in press, 2019]
Photo credit: Mark Joseph Hanson of Mark Joseph Studio.
Last Updated 2019-01-24