bims-unfpre 2025-08-24 papers

Issue of 2025–08–24
three papers selected by
Susan Logue, University of Manitoba

FASEB J. 2025 Aug 31. 39(16): e70940

Transcriptomic Profiling of Small Molecule Atf6 Modulators in the Retina.

Monica Sophia Diaz-Aguilar, Angela Galdamez, Leon Chea, Masako Le, Soyoung Park, Hyejung Min, Eun-Jin Lee, Jonathan H Lin.

The Unfolded Protein Response (UPR) maintains endoplasmic reticulum (ER) homeostasis and is essential for retinal health. Activating Transcription Factor 6 (ATF6) controls a key UPR branch and upregulates genes that mitigate ER stress. Small molecule modulators of ATF6 have been characterized in cell culture models that increase or decrease the amount of the cleaved, transcriptional activator domain of ATF6 generated from the full-length precursor. However, the effects of these small molecule ATF6 modulators remain unclear in vivo, in part because of the lack of antibodies that robustly detect the cleaved, activated form of ATF6 in model organisms like mice. Here, we used targeted RNA sequencing (RNA-seq) to assess the transcriptional response to intraocular delivery of Ceapin-A7 (an ATF6 inhibitor) and AA147 (an ATF6 activator) in the mouse retina. Using this strategy, we demonstrate that Ceapin-A7 significantly suppressed ATF6 transcriptional targets, whereas AA147 induced ATF6-regulated genes in retinal tissue of the eye. We also show that neither small molecule ATF6 modulator caused retinal cell death, compromised vision, or triggered ER stress by histology, functional testing, and transcriptional analysis. These results identify a transcriptional strategy to sensitively detect and quantify Ceapin-A7 and AA147 modulation of ATF6 in vivo. These findings also identify nontoxic conditions for further in vivo evaluation of small molecule ATF6 modulators in mouse vision loss disease models linked to ER stress.

Keywords: RNA‐seq; activating transcription factor 6; endoplasmic reticulum; retina; transcriptome; unfolded protein response

DOI: https://doi.org/10.1096/fj.202501459R

bioRxiv. 2025 Aug 13. pii: 2025.08.11.669714. [Epub ahead of print]

Proteostasis and Unfolded Protein Response Dynamics in Human Neuron and Mouse Glia Co-culture Reveal Cell-Specific Aging Responses.

Lea A Barny, Sarah K Garcia, Aiden J Houcek, Burak Uzay, Minsoo Kim, Ege T Kavalali, Lars Plate.

Proteostasis, or protein homeostasis, is a tightly regulated network of cellular pathways essential for maintaining proper protein folding, trafficking, and degradation. Neurons are particularly vulnerable to proteostasis collapse due to their post-mitotic and long-lived nature and thus represent a unique cell type to understand the dynamics of proteostasis throughout development, maturation, and aging. Here, we utilized a dual-species co-culture model of human excitatory neurons and mouse glia to investigate cell type- specific, age-related changes in the proteostasis network using data-independent acquisition (DIA) LC-MS/MS proteomics. We quantified branch-specific unfolded protein response (UPR) activation by monitoring curated effector proteins downstream of the ATF6, IRE1/XBP1s, and PERK pathways, enabling a comprehensive, unbiased evaluation of UPR dynamics during neuronal aging. Species-specific analysis revealed that aging neurons largely preserved proteostasis, although they showed some signs of collapse, primarily in ER-to-Golgi transport mechanisms. However, these changes were accompanied by upregulation of proteostasis-related machinery and activation of the ATF6 branch, as well as maintenance of the XBP1s and PERK branches of the UPR with age. In contrast, glia exhibited broad downregulation of proteostasis factors and UPR components, independent of neuronal presence. Furthermore, we quantified stimulus-specific modulation of select UPR branches in aged neurons exposed to pharmacologic ER stressors. These findings highlight distinct, cell-type-specific stress adaptations during aging and provide a valuable proteomic resource for dissecting proteostasis and UPR regulation in the aging brain.
Significance: Understanding how the unfolded protein response (UPR) and proteostasis network change with age is often studied in model organisms, where pathways are assessed across mixed cell types. Such systems can obscure cell-type-specific regulation. Here, we evaluate age-associated remodeling of the UPR and proteostasis network in a dual-species co-culture of human neurons and mouse glia using DIA proteomics. This approach enables species-specific proteomic profiling without physical separation, supported by a customizable data analysis pipeline. We show that neurons and glia exhibit divergent age-related responses, with neurons maintaining adaptive proteostasis and glia showing broader declines. The analytical framework presented here supports future studies to uncover additional cell-type-specific aging phenotypes or to probe the effects of pharmacologic or physical manipulation of biological systems.

DOI: https://doi.org/10.1101/2025.08.11.669714

Sci Rep. 2025 Aug 16. 15(1): 30028

A spectrum of cysteine mutations in fibulin-3 highlight its disulfide bonding complexity and potential to induce ER stress.

Gracen E Collier, Anna L Roovers, John D Hulleman.

Fibulin-3 (FBLN3), also known as EFEMP1, is a secreted extracellular matrix (ECM) glycoprotein that contains forty cysteine residues. These cysteines, which are distributed across one atypical and five canonical calcium-binding epidermal growth factor (EGF) domains, are important for regulating FBLN3 structure, secretion, and presumably function. As evidence of this importance, a rare homozygous p.C55R mutation in FBLN3 negates its function, alters disulfide bonding, and causes marfanoid syndrome. Additional studies suggest that heterozygous premature stop codon mutations in FBLN3 may also cause similar, albeit less severe, connective tissue disorders. Interestingly, a series of twenty-four cysteine mutations in FBLN3 have been identified in the human population and published in the Clinical Variation (ClinVar) and gnomAD databases. We tested how seven of these cysteine mutants (five loss-of-cysteine variants: C42Y, C190R, C218R, C252F, and C365S, two gain-of-cysteine variants: R358C, Y369C) and two newly-developed mutations (G57C and Y397C) altered FBLN3 secretion and disulfide bonding. We selected three variants to test alterations in MMP2 zymography and stress response activation. Surprisingly, we found a wide variety of biochemical behaviors: i) loss-of-cysteine variants correlated with an increased likelihood of disulfide dimer formation, ii) N-terminal mutations were less likely to disrupt secretion, and were less prone to aggregation, iii) in contrast to wild-type FBLN3, multiple, but not all variants failed to induce MMP2 levels in cell culture, and iv) C-terminal mutations (either loss or gain of cysteines) were more prone to significant secretion defects, intracellular accumulation/misfolding, and stress response activation. These results provide molecular and biochemical insight into FBLN3 folding, secretion, and function for many cysteine mutations found in the human population, some of which may increase the likelihood of subclinical connective tissue or other FBLN3-associated haploinsufficiency diseases.

Keywords: Disulfide bonds; EFEMP1; FBLN3; Fibulin-3; Protein folding

DOI: https://doi.org/10.1038/s41598-025-14561-4