Function and mutual interaction of BiP-, PERK-, and IRE1α-dependent signalling pathways in vascular tumours

IRE1α regulates the PTHrP-IHH feedback loop to orchestrate chondrocyte hypertrophy and cartilage mineralization

Cartilage development is controlled by the highly synergistic proliferation and differentiation of growth plate chondrocytes, in which the Indian hedgehog (IHH) and parathyroid hormone-related protein-parathyroid hormone-1 receptor (PTHrP-PTH1R) feedback loop is crucial. The inositol-requiring enzyme 1α/X-box-binding protein-1 spliced (IRE1α/XBP1s) branch of the unfolded protein response (UPR) is essential for normal cartilage development. However, the precise role of ER stress effector IRE1α, encoded by endoplasmic reticulum to nucleus signaling 1 (ERN1), in skeletal development remains unknown. Herein, we reported that loss of IRE1α accelerates chondrocyte hypertrophy and promotes endochondral bone growth. ERN1 acts as a negative regulator of chondrocyte proliferation and differentiation in postnatal growth plates. Its deficiency interrupted PTHrP/PTH1R and IHH homeostasis leading to impaired chondrocyte hypertrophy and differentiation. XBP1s, produced by p-IRE1α-mediated splicing, binds and up-regulates PTH1R and IHH, which coordinate cartilage development. Meanwhile, ER stress cannot be activated normally in ERN1-deficient chondrocytes. In conclusion, ERN1 deficiency accelerates chondrocyte hypertrophy and cartilage mineralization by impairing the homeostasis of the IHH and PTHrP/PTH1R feedback loop and ER stress. ERN1 may have a potential role as a new target for cartilage growth and maturation.

Unfolded protein response and angiogenesis in malignancies

Cellular stress, arising from accumulation of unfolded proteins, occurs frequently in rapidly proliferating cancer cells. This cellular stress, in turn, activates the unfolded protein response (UPR), an interconnected set of signal transduction pathways that alleviate the proteostatic stress. The UPR is implicated in cancer cell survival and proliferation through upregulation of pro-tumorigenic pathways that ultimately promote malignant metabolism and neoangiogenesis. Here, we reviewed mechanisms of signaling crosstalk between the UPR and angiogenesis pathways, as well as transmissible ER stress and the role in tumor growth and development. To characterize differences in UPR and UPR-mediated angiogenesis in malignancy, we employed a data mining approach using patient tumor data from The Cancer Genome Atlas (TCGA). The analysis of TCGA revealed differences in UPR between malignant samples versus their non-malignant counterparts.

X-box binding protein 1 as a key modulator in “healing endothelial cells”, a novel EC phenotype promoting angiogenesis after MCAO

Background

Endothelial cells (ECs) play an important role in angiogenesis and vascular reconstruction in the pathophysiology of ischemic stroke. Previous investigations have provided a profound cerebral vascular atlas under physiological conditions, but have failed to identify new disease-related cell subtypes. We aimed to identify new EC subtypes and determine the key modulator genes.

Methods

Two datasets GSE174574 and GSE137482 were included in the study. Seurat was utilized as the standard quality-control pipeline. UCell was used to calculate single-cell scores to validate cellular identity. Monocle3 and CytoTRACE were utilized in aid of pseudo-time differentiation analysis. CellChat was utilized to infer the intercellular communication pathways. The angiogenesis ability of ECs was validated by MTS, Transwell, tube formation, flow cytometry, and immunofluorescence assays in vitro and in vivo. A synchrotron radiation-based propagation contrast imaging was introduced to comprehensively portray cerebral vasculature.

Results

We successfully identified a novel subtype of EC named “healing EC” that highly expressed pan-EC marker and pro-angiogenic genes but lowly expressed all the arteriovenous markers identified in the vascular single-cell atlas. Further analyses showed its high stemness to differentiate into other EC subtypes and potential to modulate inflammation and angiogenesis via excretion of signal molecules. We therefore identified X-box binding protein 1 (Xbp1) as a key modulator in the healing EC phenotype. In vitro and in vivo experiments confirmed its pro-angiogenic roles under both physiological and pathological conditions. Synchrotron radiation-based propagation contrast imaging further proved that Xbp1 could promote angiogenesis and recover normal vasculature conformation, especially in the corpus striatum and prefrontal cortex under middle cerebral artery occlusion (MCAO) condition.

Conclusions

Our study identified a novel disease-related EC subtype that showed high stemness to differentiate into other EC subtypes. The predicted molecule Xbp1 was thus confirmed as a key modulator that can promote angiogenesis and recover normal vasculature conformation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00399-5.

An Overview on Immunogenic Cell Death in Cancer Biology and Therapy

Immunogenic cell death (ICD) is a modality of regulated cell death that is sufficient to promote an adaptive immune response against antigens of the dying cell in an immunocompetent host. An important characteristic of ICD is the release and exposure of damage-associated molecular patterns, which are potent endogenous immune adjuvants. As the induction of ICD can be achieved with conventional cytotoxic agents, it represents a potential approach for the immunotherapy of cancer. Here, different aspects of ICD in cancer biology and treatment are reviewed.

Dual topology of co-chaperones at the membrane of the endoplasmic reticulum

Dual topologies of proteins at the ER membrane are known for a variety of proteins allowing the same protein to exert different functions according to the topology adopted. A dual topology of the co-chaperone ERdj4, which resides in the endoplasmic reticulum (ER), was proposed recently, a thesis that we found to align all published data and existing controversies into one whole picture. The aim of this review is to reassess all primary data available in the literature on ER-resident Hsp40 co-chaperones with respect to their topology. After careful and critical analyses of all experimental data published so far, we identified, next to ERdj4, two other co-chaperones, ERdj3 and ERdj6, that also display features of a dual topology at the ER membrane. We assume that during cellular stress subpools of some ER-resident J protein can alter their topology so that these proteins can exert different functions in order to adapt to cellular stress.