bims-proarb 2023-05-07 papers

bims-proarb

Biomed News

on Proteostasis in aging and regenerative biology

Issue of 2023–05–07
six papers selected by
Rich Giadone, Harvard University

Dynamics and composition of small heat shock protein condensates and aggregates.
Atransgenic mouse line for assaying tissue-specific changes in endoplasmic reticulum proteostasis.
The mitochondrial unfolded protein response regulates hippocampal neural stem cell aging.
The proteasome: A key modulator of nervous system function, brain aging, and neurodegenerative disease.
Pharmacological chaperones restore proteostasis of epilepsy-associated GABA A receptor variants.
Pharmacological regulation of endoplasmic reticulum structure and calcium dynamics: importance for neurodegenerative diseases.

J Mol Biol. 2023 May 03. pii: S0022-2836(23)00217-6. [Epub ahead of print] 168139

Dynamics and composition of small heat shock protein condensates and aggregates.

Joep Joosten, Bob van Sluijs, Wilma Vree Egberts, Martin Emmaneel, Pascal W T C Jansen, Michiel Vermeulen, Wilbert Boelens, Kimberly M Bonger, Evan Spruijt.

  Small heat shock proteins (sHSPs) are essential ATP-independent chaperones that protect the cellular proteome. These proteins assemble into polydisperse oligomeric structures, the composition of which dramatically affects their chaperone activity. The biomolecular consequences of variations in sHSP ratios, especially inside living cells, remain elusive. Here, we study the consequences of altering the relative expression levels of HspB2 and HspB3 in HEK293T cells. These chaperones are partners in a hetero-oligomeric complex, and genetic mutations that abolish their mutual interaction are associated with myopathic disorders. HspB2 displays three distinct phenotypes when co-expressed with HspB3 at varying ratios. Expression of HspB2 alone leads to formation of liquid nuclear condensates, while shifting the stoichiometry towards HspB3 resulted in the formation of large solid-like aggregates. Only cells co-expressing HspB2 with a limited amount of HspB3 formed fully soluble complexes that were distributed homogeneously throughout the nucleus. Strikingly, both condensates and aggregates were reversible, as shifting the HspB2:HspB3 balance in situ resulted in dissolution of these structures. To uncover the molecular composition of HspB2 condensates and aggregates, we used APEX-mediated proximity labelling. Most proteins interact transiently with the condensates and were neither enriched nor depleted in these cells. In contrast, we found that HspB2:HspB3 aggregates sequestered several disordered proteins and autophagy factors, suggesting that the cell is actively attempting to clear these aggregates. This study presents a striking example of how changes in the relative expression levels of interacting proteins affects their phase behavior. Our approach could be applied to study the role of protein stoichiometry and the influence of client binding on phase behavior in other biomolecular condensates and aggregates.

Keywords:  HspB2; HspB3; liquid-liquid phase separation; molecular chaperone; proximity labeling

DOI:  https://doi.org/10.1016/j.jmb.2023.168139
Transgenic Res. 2023 May 03.

Atransgenic mouse line for assaying tissue-specific changes in endoplasmic reticulum proteostasis.

Reinis Svarcbahs, Sarah M Blossom, Helena S Baffoe-Bonnie, Kathleen A Trychta, Lacey K Greer, James Pickel, Mark J Henderson, Brandon K Harvey.

  Maintenance of calcium homeostasis is important for proper endoplasmic reticulum (ER) function. When cellular stress conditions deplete the high concentration of calcium in the ER, ER-resident proteins are secreted into the extracellular space in a process called exodosis. Monitoring exodosis provides insight into changes in ER homeostasis and proteostasis resulting from cellular stress associated with ER calcium dysregulation. To monitor cell-type specific exodosis in the intact animal, we created a transgenic mouse line with a Gaussia luciferase (GLuc)-based, secreted ER calcium-modulated protein, SERCaMP, preceded by a LoxP-STOP-LoxP (LSL) sequence. The Cre-dependent LSL-SERCaMP mice were crossed with albumin (Alb)-Cre and dopamine transporter (DAT)-Cre mouse lines. GLuc-SERCaMP expression was characterized in mouse organs and extracellular fluids, and the secretion of GLuc-SERCaMP in response to cellular stress was monitored following pharmacological depletion of ER calcium. In LSL-SERCaMP × Alb-Cre mice, robust GLuc activity was observed only in the liver and blood, whereas in LSL-SERCaMP × DAT-Cre mice, GLuc activity was seen in midbrain dopaminergic neurons and tissue samples innervated by dopaminergic projections. After calcium depletion, we saw increased GLuc signal in the plasma and cerebrospinal fluid collected from the Alb-Cre and DAT-Cre crosses, respectively. This mouse model can be used to investigate the secretion of ER-resident proteins from specific cell and tissue types during disease pathogenesis and may aid in the identification of therapeutics and biomarkers of disease.

Keywords:  ER calcium sensor; ER stress; Exodosis; Gaussia luciferase; SERCaMP; Secreted ER-resident proteins

DOI:  https://doi.org/10.1007/s11248-023-00349-7
Cell Metab. 2023 Apr 28. pii: S1550-4131(23)00139-0. [Epub ahead of print]

The mitochondrial unfolded protein response regulates hippocampal neural stem cell aging.

Chih-Ling Wang, Rika Ohkubo, Wei-Chieh Mu, Wei Chen, Jiang Lan Fan, Zehan Song, Ayane Maruichi, Peter H Sudmant, Angela O Pisco, Dena B Dubal, Na Ji, Danica Chen.

  Aging results in a decline in neural stem cells (NSCs), neurogenesis, and cognitive function, and evidence is emerging to demonstrate disrupted adult neurogenesis in the hippocampus of patients with several neurodegenerative disorders. Here, single-cell RNA sequencing of the dentate gyrus of young and old mice shows that the mitochondrial protein folding stress is prominent in activated NSCs/neural progenitors (NPCs) among the neurogenic niche, and it increases with aging accompanying dysregulated cell cycle and mitochondrial activity in activated NSCs/NPCs in the dentate gyrus. Increasing mitochondrial protein folding stress results in compromised NSC maintenance and reduced neurogenesis in the dentate gyrus, neural hyperactivity, and impaired cognitive function. Reducing mitochondrial protein folding stress in the dentate gyrus of old mice improves neurogenesis and cognitive function. These results establish the mitochondrial protein folding stress as a driver of NSC aging and suggest approaches to improve aging-associated cognitive decline.

Keywords:  SIRT1; SIRT2; SIRT3; SIRT6; SIRT7; cognitive aging; mitochondrial unfolded protein response; neural stem cell aging; sirtuin; stem cell aging

DOI:  https://doi.org/10.1016/j.cmet.2023.04.012
Front Cell Dev Biol. 2023 ;11 1124907

The proteasome: A key modulator of nervous system function, brain aging, and neurodegenerative disease.

Kanisa Davidson, Andrew M Pickering.

  The proteasome is a large multi-subunit protease responsible for the degradation and removal of oxidized, misfolded, and polyubiquitinated proteins. The proteasome plays critical roles in nervous system processes. This includes maintenance of cellular homeostasis in neurons. It also includes roles in long-term potentiation via modulation of CREB signaling. The proteasome also possesses roles in promoting dendritic spine growth driven by proteasome localization to the dendritic spines in an NMDA/CaMKIIα dependent manner. Proteasome inhibition experiments in varied organisms has been shown to impact memory, consolidation, recollection and extinction. The proteasome has been further shown to impact circadian rhythm through modulation of a range of 'clock' genes, and glial function. Proteasome function is impaired as a consequence both of aging and neurodegenerative diseases. Many studies have demonstrated an impairment in 26S proteasome function in the brain and other tissues as a consequence of age, driven by a disassembly of 26S proteasome in favor of 20S proteasome. Some studies also show proteasome augmentation to correct age-related deficits. In amyotrophic lateral sclerosis Alzheimer's, Parkinson's and Huntington's disease proteasome function is impaired through distinct mechanisms with impacts on disease susceptibility and progression. Age and neurodegenerative-related deficits in the function of the constitutive proteasome are often also accompanied by an increase in an alternative form of proteasome called the immunoproteasome. This article discusses the critical role of the proteasome in the nervous system. We then describe how proteasome dysfunction contributes to brain aging and neurodegenerative disease.

Keywords:  Alzheimer’s disease; Parkinson's disease; brain aging; huntington’s disease; immunoproteasome; proteasome; synaptic plasticity; ubiquitin proteasomal system

DOI:  https://doi.org/10.3389/fcell.2023.1124907
bioRxiv. 2023 Apr 19. pii: 2023.04.18.537383. [Epub ahead of print]

Pharmacological chaperones restore proteostasis of epilepsy-associated GABA A receptor variants.

Ya-Juan Wang, Hailey Seibert, Lucie Y Ahn, Ashleigh E Schaffer, Ting-Wei Mu.

Recent advances in genetic diagnosis identified variants in genes encoding GABA A receptors as causative for genetic epilepsy. Here, we selected eight disease-associated variants in the α1 subunit of GABA A receptors causing mild to severe clinical phenotypes and showed that they are loss of function, mainly by reducing the folding and surface trafficking of the α1 protein. Furthermore, we sought client protein-specific pharmacological chaperones to restore the function of pathogenic receptors. Applications of positive allosteric modulators, including Hispidulin and TP003, increase the functional surface expression of the α1 variants. Mechanism of action study demonstrated that they enhance the folding and assembly and reduce the degradation of GABA A variants without activating the unfolded protein response in HEK293T cells and human iPSC-derived neurons. Since these compounds cross the blood-brain barrier, such a pharmacological chaperoning strategy holds great promise to treat genetic epilepsy in a GABA A receptor-specific manner.

DOI: https://doi.org/10.1101/2023.04.18.537383
Pharmacol Rev. 2023 May 01. pii: PHARMREV-AR-2022-000701. [Epub ahead of print]

Pharmacological regulation of endoplasmic reticulum structure and calcium dynamics: importance for neurodegenerative diseases.

Ilmari Parkkinen, Anna Their, Muhammad Yasir Asghar, Sreesha Sree, Eija Jokitalo, Mikko Airavaara.

  The endoplasmic reticulum (ER) is the largest organelle of the cell, composed of a continuous network of sheets and tubules, and is involved in protein, calcium (Ca2+) and lipid homeostasis. In neurons, the ER extends throughout the cell, both somal and axodendritic compartments, and is highly important for neuronal functions. A third of the proteome of a cell, secreted and membrane-bound proteins, are processed within the ER lumen and most of these proteins are vital for neuronal activity. The brain itself is high in lipid content and many structural lipids are produced, in part, by the ER. Cholesterol and steroid synthesis are strictly regulated in the ER of the blood-brain barrier protected brain cells. The high Ca2+ level in the ER lumen and low cytosolic concentration is needed for Ca2+-based intracellular signaling, also for synaptic signaling and Ca2+ waves, as well as preparing proteins for correct folding in the presence of high Ca2+ concentrations to cope with the high concentrations of extracellular milieu. Particularly, ER Ca2+ is controlled in axodendritic areas for proper neurito- and synaptogenesis and synaptic plasticity and remodeling. In this review, we cover the physiological functions of the neuronal ER and discuss it in context of common neurodegenerative diseases focusing on pharmacological regulation of ER Ca2+ Furthermore, we postulate that heterogeneity of the ER, its protein folding capacity and ensuring Ca2+ regulation is a crucial factor for the aging and selective vulnerability of neurons in various neurodegenerative diseases. Significance Statement ER Ca2+ regulators are promising therapeutic targets for degenerative diseases for which efficacious drug therapies do not exist. The use of pharmacological probes targeting maintenance and restoration of ER Ca2+ can provide restoration of protein homeostasis, e.g. folding of complex plasma membrane signalling receptors and slow down the degeneration process of neurons.

Keywords:  Alzheimer's Disease; Endoplasmic reticulum stress; Parkinson's Disease; calcium; endoplasmic reticulum; endorphin; neurodegeneration

DOI:  https://doi.org/10.1124/pharmrev.122.000701