Deursen, Jan M. van

ABSTRACT Aging is a prominent risk factor for heart disease, driving pathological cardiac changes such as hypertrophy, fibrosis, and cellular senescence. While BubR1 has been linked to systemic aging in mammalian models, its specific role in regulating cardiac aging remains unclear. Here, we investigated how BubR1 regulates heart aging and its potential contribution to the pathogenesis of cardiac disease, including heart failure. BubR1 insufficiency in mice resulted in marked cardiac hypertrophy, increased fibrosis, and elevated markers of cellular senescence. Transcriptomic profiling revealed widespread disruption in key pathways involved in cardiac function, including ion channel regulation, cytoskeletal organization, and contractile fiber dynamics. Comparative analysis with aged hearts demonstrated shared dysregulated gene networks, linking BubR1 deficiency to age‐related cardiac dysfunction. Additionally, BubR1 hypomorphic hearts mirrored transcriptomic changes observed in end‐stage heart failure patients, and BubR1 protein levels were found to decline with age in the heart and were also significantly reduced in rodent models of heart failure and in heart failure patients. BubR1 reduction in cardiomyocytes in vitro led to an increased expression of markers of heart failure, hypertrophy, and cytoskeletal remodeling, underscoring an essential and direct role of BubR1 in maintaining cardiomyocyte health. Overall, our data suggest that BubR1 deficiency is a feature of cardiac aging and disease in humans, and that sustaining BubR1 expression may offer a potential therapeutic strategy to mitigate age‐associated cardiac decline and improve heart health in the elderly.

ABSTRACT His domain protein tyrosine phosphatase (HD-PTP; also known as PTPN23) facilitates function of the endosomal sorting complexes required for transport (ESCRTs) during multivesicular body (MVB) formation. To uncover its role in physiological homeostasis, embryonic lethality caused by a complete lack of HD-PTP was bypassed through generation of hypomorphic mice expressing reduced protein, resulting in animals that are viable into adulthood. These mice exhibited marked lipodystrophy and decreased receptor-mediated signaling within white adipose tissue (WAT), involving multiple prominent pathways including RAS/MAPK, phosphoinositide 3-kinase (PI3K)/AKT and receptor tyrosine kinases (RTKs), such as EGFR. EGFR signaling was dissected in vitro to assess the nature of defective signaling, revealing decreased trans-autophosphorylation and downstream effector activation, despite normal EGF binding. This corresponds to decreased plasma membrane cholesterol and increased lysosomal cholesterol, likely resulting from defective endosomal maturation necessary for cholesterol trafficking and homeostasis. The ESCRT components Vps4 and Hrs have previously been implicated in cholesterol homeostasis; thus, these findings expand knowledge on which ESCRT subunits are involved in cholesterol homeostasis and highlight a non-canonical role for HD-PTP in signal regulation and adipose tissue homeostasis.

Abstract Cellular senescence is a state of permanent growth arrest that plays an important role in wound healing, tissue fibrosis, and tumor suppression. Despite senescent cells’ (SnC) pathological role and therapeutic interest, their phenotype in vivo remains poorly defined. Here, we developed an in vivoderived senescence signature using a foreign body response (FBR) fibrosis model in a SnC reporter mouse. We identified pericytes and “cartilage-like” fibroblasts as senescent and defined cell typespecific senescence associated secretory phenotypes (SASP). Transfer learning and senescence scoring identified these two SnC populations along with endothelial and epithelial SnCs in new and publicly available murine and human data single cell RNAseq (scRNAseq) datasets from diverse pathologies. Signaling analysis uncovered crosstalk between SnCs and myeloid cells via an IL34- CSF1R-TGFßR signaling axis, contributing to tissue balance of vascularization and matrix production. Overall, our study provides a senescence signature and a computational approach that may be broadly applied to identify transcriptional profiles and SASP factors produced by SnCs that regulate tissue structure and pathology.

The clock is ticking for senescent cells Senescent cells promote their own recognition and removal through the immune system by generating a bioactive secretome called the senescence-associated secretory phenotype (SASP). Sturmlechner et al . report that the cell cycle regulator p21 directs an early form of the SASP, which they call the p21-activated secretory phenotype (PASP) (see the Perspective by Reen and Gil). As part of the PASP, the chemokine CXCL14 attracts macrophages, which monitor stressed cells expressing elevated p21. If stressed cells recuperate and p21 levels return to normal within 4 days, then macrophages disengage from their targets. Otherwise, macrophages recruit cytotoxic T cells that facilitate target cell removal. Other cell cycle regulators such as p16 can induce many factors overlapping with the PASP, but p21 uniquely drives this CXCL14-mediated “timer” mechanism of senescent cell immunosurveillance. —STS

High plasma cholesterol levels increase the risk of cardiovascular disease (CVD). Transintestinal Cholesterol Excretion (TICE) is a recently emerged pathway of cholesterol removal and has the potential to lower plasma cholesterol levels and confer protection against CVD. Under control conditions, TICE accounts for about 30% of fecal cholesterol loss in mice. Using a panel of knock-out and transgenic mice as well as pharmacological manipulations we show that in mice TICE is regulated by intestinal activation of the Farnesoid X Receptor (FXR), via its target Fibroblast Growth Factor 15/19 (FGF15/19). Activation of FXR by the agonist PX20606 (PX) resulted in a >10-fold increased fecal cholesterol excretion as well as TICE and 40% reduced plasma cholesterol levels. The induction of fecal cholesterol excretion and TICE was absent in PX-treated intestine-specific FXR-null mice but was regained when those mice were co-treated with FGF19. Moreover, FGF19 treatment alone was sufficient to induce fecal cholesterol loss to a similar extend as was observed in PX-treated wild-type mice. PX treatment resulted in an increased muricholate/cholate-ratio and thereby induced a more hydrophilic bile salt pool. Not surprisingly, cholesterol absorption was reduced in PX-treated mice. However, experiments in which mice were co-treated with PX and the cholesterol absorption inhibitor ezetimibe revealed that the stimulating effect of PX on fecal neutral sterol excretion and TICE were completely independent of differences in cholesterol absorption. Of note, treatment of mice with a combination of PX and ezetimibe stimulated fecal cholesterol loss and TICE so strongly that those mice lost about 60% of their entire estimated body cholesterol content each day. The stimulation of fecal cholesterol loss and TICE by PX and PX/ezetimibe treatment was severely blunted in Abcg8-KO mice and this could not be restored by hepatic reintroduction of Abcg8, indicating a decisive role for intestinal ABCG5/G8 in PX-induced fecal cholesterol loss and TICE. Our data strongly suggest that hydrophilic bile acids stimulate ABCG5/G8 activity in the intestine, leading to an increased flux of cholesterol from the body into the intestinal lumen that is subsequently excreted with the feces.

Abstract One of the greatest barriers to curative treatment of neuroblastoma is its frequent metastatic outgrowth prior to diagnosis, especially in cases driven by amplification of the MYCN oncogene. However, only a limited number of regulatory proteins that contribute to this complex MYCN-mediated process have been elucidated. Here we show that the growth arrest-specific 7 (GAS7) gene, located at chromosome band 17p13.1, is preferentially deleted in high-risk MYCN-driven neuroblastoma. GAS7 expression was also suppressed in MYCN-amplified neuroblastoma lacking 17p deletion. GAS7 deficiency led to accelerated metastasis in both zebrafish and mammalian models of neuroblastoma with overexpression or amplification of MYCN. Analysis of expression profiles and the ultrastructure of zebrafish neuroblastoma tumors with MYCN overexpression identified that GAS7 deficiency led to (i) downregulation of genes involved in cell–cell interaction, (ii) loss of contact among tumor cells as critical determinants of accelerated metastasis, and (iii) increased levels of MYCN protein. These results provide the first genetic evidence that GAS7 depletion is a critical early step in the cascade of events culminating in neuroblastoma metastasis in the context of MYCN overexpression. Significance: Heterozygous deletion or MYCN-mediated repression of GAS7 in neuroblastoma releases an important brake on tumor cell dispersion and migration to distant sites, providing a novel mechanism underlying tumor metastasis in MYCN-driven neuroblastoma. See related commentary by Menard, p. 2815

Abstract Defining the epigenetic mechanisms (e.g. chromatin modifications) that underlie T cell fate decisions is a major challenge. The transcriptional coactivators CREB binding protein (CBP) and the closely related p300 comprise a two-member family of histone/protein acetyltransferases that interact with over 50 T lymphocyte-essential transcriptional regulators. Rather than having distinct regulatory roles, CBP and p300 are often thought to confer utilitarian transactivation and histone modifying functions to transcription factors that mediate T cell fate. In contrast to this view, we show here that CBP acts uniquely in conventional T cell development. Inactivation of CBP, but not p300, starting at the double negative stage of T cell development yielded thymocytes with partial activation of an effector/memory- or innate-T cell program. CD8SP thymocytes from CBP mutant mice expressed genes that define professional CD8 cells such as Il-2/Il-15 receptor β chain, granzyme A, interferon γ (Ifnγ), Fas ligand, perforin, and the chemokine receptors Ccr5, and Cxcr3. CD4SP thymocytes from CBP mutant mice also expressed effector genes such as Ifnγ, Il-4, and Ccr5. In addition, CD8SP and CD4SP thymocytes from CBP mutant mice produced Ifnγ protein when the cells were stimulated with phorbol ester and ionomycin. Mechanistically, loss of CBP acted cell non-autonomously to induce the expression of the CD8 T cell master regulatory transcription factor eomesodermin (Eomes). This suggests that CBP in thymocytes or T cells controls an extracellular factor that helps demarcate conventional naïve T cell development in the thymus from effector/memory T cell differentiation in the periphery.

Background and Aims Up‐regulation of the E2F‐dependent transcriptional network has been identified in nearly every human malignancy and is an important driver of tumorigenesis. Two members of the E2F family, E2F7 and E2F8, are potent repressors of E2F‐dependent transcription. They are atypical in that they do not bind to dimerization partner proteins and are not controlled by retinoblastoma protein. The physiological relevance of E2F7 and E2F8 remains incompletely understood, largely because tools to manipulate their activity in vivo have been lacking. Approach and Results Here, we generated transgenic mice with doxycycline‐controlled transcriptional activation of E2f7 and E2f8 and induced their expression during postnatal development, in adulthood, and in the context of cancer. Systemic induction of E2f7 and, to lesser extent, E2f8 transgenes in juvenile mice impaired cell proliferation, caused replication stress, DNA damage, and apoptosis, and inhibited animal growth. In adult mice, however, E2F7 and E2F8 induction was well tolerated, yet profoundly interfered with DNA replication, DNA integrity, and cell proliferation in diethylnitrosamine‐induced liver tumors. Conclusion Collectively, our findings demonstrate that atypical E2Fs can override cell‐cycle entry and progression governed by other E2F family members and suggest that this property can be exploited to inhibit proliferation of neoplastic hepatocytes when growth and development have subsided during adulthood.

Abstract Chemotherapy is important for cancer treatment, however, toxicities limit its use. While great strides have been made to ameliorate the acute toxicities induced by chemotherapy, long-term comorbidities including bone loss remain a significant problem. Chemotherapy-driven estrogen loss is postulated to drive bone loss, but significant data suggests the existence of an estrogen-independent mechanism of bone loss. Using clinically relevant mouse models, we showed that senescence and its senescence-associated secretory phenotype (SASP) contribute to chemotherapy-induced bone loss that can be rescued by depleting senescent cells. Chemotherapy-induced SASP could be limited by targeting the p38MAPK-MK2 pathway, which resulted in preservation of bone integrity in chemotherapy-treated mice. These results transform our understanding of chemotherapy-induced bone loss by identifying senescent cells as major drivers of bone loss and the p38MAPK–MK2 axis as a putative therapeutic target that can preserve bone and improve a cancer survivor's quality of life. Significance: Senescence drives chemotherapy-induced bone loss that is rescued by p38MAPK or MK2 inhibitors. These findings may lead to treatments for therapy-induced bone loss, significantly increasing quality of life for cancer survivors.