Dr. Joseph Chambers

Background:

Newly synthesised secretory proteins fold inside the endoplasmic reticulum (ER) via a complex process that can fail when client proteins are mutated, giving rise to a toxic state termed ER stress. In contrast, specific mutants of α₁-antitrypsin adopt a well folded conformation yet accumulate as polymers in the ER leading to hypersensitivity to physiological ER stress. However, the mechanism linking polymer accumulation to liver pathology remains unclear.

Protein folding is a major function of the ER and is governed by molecular motion. To address how α₁-antitrypsin polymers affect protein diffusion in the ER, we developed novel methods to measure biophysical properties of the ER lumen in live cells expressing mutant α₁-antitrypsin. Our preliminary data suggests that α₁-antitrypsin polymers reduce mobility of a number of ER proteins vital to organelle function.

AIM:

Using a human induced pluripotent stem cell (hiPSC) model of α₁-antitrypsin deficiency, I will investigate how polymer-induced changes to ER shape and biophysical properties, such as macromolecular crowding and microviscosity, impact on protein mobility in the hepatocyte ER. Using genetic and small molecule induced challenges to ER-protein folding homeostasis, I will assess how polymer-induced changes to ER properties influence the cellular consequences of ER stress. These questions will be addressed through the following specific aims.

1. Establish hiPSC lines gene edited by CRISPR to encode fluorescently tagged endogenous α₁-antitrypsin to enable quantitative imaging of protein mobility in hepatocyte ER-inclusions.
2. Determine how α₁-antitrypsin polymers affect protein mobility within intact reticular ER, which is present in a large proportion of hepatocytes in patients carrying polymerogenic α₁-antitrypsin mutations.
3. Investigate mechanisms underlying polymer accumulation and the impact on cell fitness during ER stress.

This work will be hosted by the lab of Stefan Marciniak (CIMR, University of Cambridge, UK) and performed in collaboration with the lab of Ludovic Vallier (Cambridge Stem Cell Institute, UK).
 

Curriculum vitae Dr. Joseph Chambers

After completing his BSc in biochemistry at the University of Bristol, Joe obtained a PhD at the University of Manchester, studying oxidative protein folding in the lab of Neil Bulleid. He undertook his first post-doc with David Ron at the Institute of Metabolic Science (University of Cambridge), where he characterised post-translational mechanisms by which cells adapt to ER stress. He then Joined Stefan Marciniak's lab at the Cambridge Institute of Medical Research (Cambridge, UK) where he continued to study mechanisms that control ER protein folding homeostasis. Recently, he has developed fluorescence imaging tools used to interrogate the biophysical properties within organelles of live cells. Utilising this research background, he now investigates ER biology in the context of α₁-antitrypsin deficiency.