Proteostasis refers to the ability of cells to maintain protein homeostasis. Approaches to the contribution of proteostasis to disease have mostly assumed that regulation of proteostasis networks is a cell autonomous process. However, it is becoming apparent that organisms have evolved transcellular means of protection against proteotoxicity.
In our lab we are interested in exploring this new concept whereby tissues and organs cooperate to maintain proteostasis, using the retina as our privileged model. We are particularly interested in exosomes, in how these extracellular vesicles are critical vehicles in transferring proteotoxic material and/or machinery that supports proteostasis across cells and how, upon ageing, the ability to sustain a robust proteostasis network is lost.
To understand the compositions of exosomes and their function also means that we need to know the molecular mechanisms that regulate exosomes biogenesis. In our lab we are particularly interested in the mechanisms that mediated the triage of cytosolic proteins into nascent exosomes and how these mechanisms affect exosome-mediated intercellular communication.

During ageing and disease cells are exposed to increased levels of stress that damages various biomolecules, including cellular proteins. Dysregulation of proteostasis, including protein damage, often leads to the accumulation of toxic oligomers and insoluble protein aggregates intracellularly and/or in the extracellular space, frequently leading to disease.
In our lab we are interested in exploring a new concept whereby tissues and organs cooperate to maintain proteostasis, particularly in how cells can:
1) transfer proteostasis machinery, such as molecular chaperones and proteasome subunits, between them to help more vulnerable cells, thus improving tissue and organ fitness;
2) secrete proteotoxic material that can be uptaken and subsequently eliminated by neighboring cells. We are particularly interested in exosomes, in how these extracellular vesicles are critical vehicles in transferring proteotoxic material and/or machinery that supports proteostasis across cells and how, upon ageing, the ability to sustain a robust proteostasis networks is lost.

In our lab we use the retina as a privileged model to study transcellular proteostasis. The retina is a highly specialized tissue with a wide variety of postmitotic cells, including the Retina Pigmented Epithelium (RPE). RPE cells provide trophic support to photoreceptors, while ensuring phagocytosis of the shedding photoreceptor outer segments. We believe that loss of proteostasis by ageing RPE cells plays a critical role in degeneration of the photoreceptors, leading to loss of vision in ageing individuals such as in Age-related Macular Degeneration (AMD), which is still the leading cause of vision loss in the elderly in developed countries. In this context we are investigating how transcellular proteostasis contributes to RPE and overall retinal fitness, while trying to understand how we might improve proteostasis during ageing to prevent retinal degeneration and AMD.

Figure 1

Legend
The RPE cells in the retina are subject to an increased burden in the macula (as the concentration of photoreceptors is higher). We propose that RPE cells use exosomes to share and redistribute both proteotoxic material and chaperone machinery across the RPE monolayer so that cells with intact proteostasis networks assist overburden RPE in the macula to cope with proteotoxic material, either by incorporating exosomes containing proteotoxic material (red arrows) or by releasing exosomes containing machinery that supports proteostasis (green arrows)

Recently we have also been interested in the molecular mechanisms whereby cells load specific proteins into exosomes. There is ample evidence suggesting that the cargo repertoire of exosomes does not necessarily reflect the cytosolic contents of the originating cell, indicating the existence of some type of active sol

LAMP2A regulates the loading of proteins into exosomes. Ferreira JV, da Rosa Soares A, Ramalho JS, Carvalho CM, Cardoso MH, Pintado P, Carvalho AS, Beck HC, Matthiesen R, Zuzarte M, Girão H, van Niel G, Pereira P. bioRxiv Preprint (2021), https://doi.org/10.1101/2021.07.26.453637

Exosomes and STUB1/CHIP cooperate to maintain intracellular proteostasis. Ferreira JV, Soares AR, Ramalho JS, Ribeiro-Rodrigues T, Carvalho CM, Zuzarte M, Girão H, Pereira P. PLoS One, 2019 Oct 15;14(10).

Ferreira JV (2017) Diabetes, hypoxia and cardiovascular disease: From molecular mechanism to treatment. Rev Port Cardiol. 2017 May;36(5):375-376. doi: 10.1016/j.repc.2017.03.003. Epub 2017 May 10.

Anjo SI, Martins-Marques T, Pereira P, Girão H, Manadas B. (2017) Elucidation of the dynamic nature of interactome networks: A practical tutorial. J Proteomics. 2017 Apr 19. pii: S1874-3919(17)30131-8. doi: 10.1016/j.jprot.2017.04.011. [Epub ahead of print]

Klionsky DJ, et al. (2016) Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition). Autophagy. 2016 Jan 2;12(1):1-222.

Martins-Marques T, Isabel Anjo S, Pereira P, Manadas B, Girao H. Interacting network of the gap junction protein connexin43 is modulated by ischemia and reperfusion in the heart. Mol Cell Proteomics, August 27, 2015, doi:10.1074/mcp.M115.052894.

Soares AR, Martins-Marques T, Ribeiro-Rodrigues T, Ferreira JV Catarino S, Pinho MJ, Zuzarte M, Anjo SI, Manadas B, Sluijter JPG, Pereira P, Girao H. Gap junctional protein Cx43 is involved in the communication between extracellular vesicles and mammalian cells. Sci Reports 2015, 5:13243.

Ferreira JV, Soares A, Ramalho JS, Pereira P, Girao H. K63 linked ubiquitin chain formation is a signal for HIF1A degradation by Chaperone-Mediated Autophagy. Sci Reports 2015, 5:10210

Martins-Marques T, Catarino S, Marques C, Matafome P, Ribeiro-Rodrigues T, Pereira P, Girão H. Heart ischemia results in Connexin43 ubiquitination localized at the intercalated discs. Biochimie 2015, 112:196-201

Ribeiro-Rodrigues T, Catarino S, Pinho MJ, Pereira P and Girao H. Connexin 43 ubiquitination determines the fate of gap junctions: restrict to survive. Biochem Soc Trans 2015, 3:471-5
Martins-Marques T, Catarino S, Marques C, Pereira P, Girão H. To beat or not to beat: degradation of Cx43 imposes the heart rhythm. Biochem Soc Trans 2015, 43:476-81
Martins-Marques T, Catarino S, Zuzarte M, Marques C, Matafome P, Pereira P, Girão H. Ischemia-induced autophagy leads to degradation of gap junction protein Connexin43 in cardiomyocytes. Biochem J. 2015, 467(2):231-45

Martins-Marques T, Ribeiro-Rodrigues T, Pereira P, Codogno P, Girao H. Autophagy and Ubiquitination in Cardiovascular Diseases. DNA Cell Biol. 2015, 34(4):243-51

Ribeiro-Rodrigues T, Catarino S, Marques C, Ferreira J, Marques T, Pereira P, Girao H. AMSH-mediated deubiquitination of Cx43 regulates internalization and degradation of gap junctions, FASEB J 2014, 28:4629-41

Simões-Correia J, Silva DI, Melo S, Figueiredo J, Caldeira J, Pinto MT, Girão H, Pereira P, Seruca R. DNAJB4 molecular chaperone distinguishes WT from mutant E-cadherin, determining their fate in vitro and in vivo. Hum Mol Genet 2014, 23:2094-2105

Ferreira JV, Fofo H, Bejarano E, Figueira Bento C, Ramalho JS, Girao H, Pereira P. CHIP/STUB1 is required for HIF-1A degradation by Chaperone-Mediated Autophagy. Autophagy 2013,9:1349-1366.

Bejarano E*, Girao H*, Yuste A, Patel B, Marques C, Spray D, Cuervo AM, Pereira P. Autophagy modulates dynamics of connexins at the plasma membrane in an ubiquitin-dependent manner. Mol Biol Cell 2012, 23:2156-69

Catarino SM, Ramalho JS, Marques C, Pereira PC, Girao H. Ubiquitin-mediated internalization of Connexin43 is independent on the canonical endocytic tyrosine-sorting signal. Biochem J. 2011, 437:255-67.

• Henrique Girão; CNC.IBILI, University of Coimbra, Portugal
• Claudia Pereira, CNC.IBILI, University of Coimbra, Portugal
• Paula Moreira, CNC.IBILI, University of Coimbra, Portugal
• Teresa Cruz, CNC.IBILI, University of Coimbra, Portugal
• Ana Maria Cuervo, Albert Einstein College of Medicine, NY, USA
• Alan Prescott, University of Dundee, UK
• Alan Tayllor, USDA – Tufts University, Boston, USA
• Fu Shang, Tufts University, Boston, USA
• Michael Clague, ITM, University of Liverpool, Liverpool, UK
• Ehud Cohen, Hebrew University, Faculty of Medicine, Jerusalem, Israel
• Guillaume van Niel, Université de Paris, Institute of Psychiatry and Neuroscience of Paris, France