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ER AS A

metabolic guardian

 

 

 

 

 

 

 

 

 

 

The ER is a central organelle for protein synthesis and protein folding in the cell, and as such, is key to maintenance of cellular homeostasis. ER proteins including chaperones, oxidoreductases, and glycosylating enzymes direct proper folding, modification and assembly of newly synthesized polypeptides before they are directed to secretory pathways. Despite this active machinery, the error-prone nature of the folding process results in misfolding of up to one third of nascent polypeptides. These improper forms of proteins are recognized and disposed of by robust quality-control systems such as ER-associated degradation, removing misfolded peptides to the cytosol for ubiquitylation and degradation by the proteasome.

Our lab is interested in the metabolic biology of the ER and how this organelle adapts, or fails to do so, under specialized and extreme challenges, particularly in key metabolic organs. This interest has recently led us to the discovery of the role of Nrf1 (also known as Nfe2L1) in two circumstances where the canonical Unfolded Protein Response (UPR) is insufficient or even dispensable to account for the adaptation to metabolic stresses, specifically in the liver upon cholesterol overload and in brown adipose tissue upon cold exposure. Nrf1 belongs to a family of four related transcription factors and is a ubiquitously expressed ER-membrane spanning protein, belonging to the Cap’N’Collar (CNC) family of transcription factors involved in stress adaptation and detoxification.

So far, our studies have shown that Nrf1 has a role in guarding homeostasis through various mechanisms in the liver and brown adipose tissue, and thus could be utilized under pathological conditions to restore health of organs. We are incredibly excited for the potential of this protein to create novel therapeutic avenues to treat liver diseases and other disorders with underlying ER maladaptation.  

 

Suggested Readings:

Widenmaier SB, Snyder N, Nguyen T, Arduini A, Lee GY, Arruda AP, Saksi J, Bartelt A, Hotamışlıgil GS. NRF1 Is an ER Membrane Sensor that Is Central to Cholesterol Homeostasis. Cell. 2017 Nov; DOI:10.1016/j.cell.2017.10.003. Abstract

 

Garfinkel BP, Hotamışlıgil GS. ER Stress Promotes Inflammation through Re-wIREd Macrophages in Obesity. Molecular Cell. 2017 Jun; DOI:10.1016/j.molcel.2017.05.037. Abstract

 

Bartelt A, Widenmeier SB, Schlein C, Johann K, Goncalves RLS, Eguchi K, Fischer AW, Parlakgul G, Snyder NA, Nguyen TB, Bruns OT, Franke D, Bawendi MG, Lynes MD, Leiria LO, Tseng YH, Inouye KE, Arruda AP, Hotamışlıgil GS. Brown adipose tissue thermogenic adaptation requires Nrf1-mediated proteasome activity. Nature Medicine. 2018 Mar; DOI: 10.1038/nm.4481. Abstract

Widenmaier et al, Cell 2017