Biology subjects

Proulx, J.

Publications and source records attributed to Proulx, J..

8 recordsLinked to original sources

bioRxiv2026

Age-associated repression of HNF4α is a driver and potential therapeutic target in liver metabolic dysfunction

Aging is a major risk factors for metabolic dysfunction-associated steatotic liver disease (MASLD). However, the mechanisms by which aging disrupts hepatocyte transcriptional networks to drive metabolic dysfunction remain poorly understood. Hepatocyte nuclear factor 4 alpha (HNF4) is a master regulator of hepatocyte identity and metabolic homeostasis, but its role in liver aging has not been defined. Here, we perform a comprehensive multi-omic profiling of young and aged mouse livers combined with targeted HNF4 functional studies to define how aging remodels HNF4-dependent gene regulation and whether HNF4 can be a target to reverse age-associated liver dysfunction. Despite preserved HNF4 expression with age, aging was associated with reduced HNF4 chromatin occupancy and transcriptional activity, accompanied by epigenetic remodeling, including changes in histone acetylation, chromatin accessibility, and DNA methylation. Integration and comparison of HNF4 CUT&RUN with hepatocyte-specific Hnf4a deletion in young and aged livers identified high-confidence overlapping but distinct young- and old- specific HNF4 target gene networks. In young hepatocytes, HNF4 coordinates two complementary transcriptional programs: activation of genes governing hepatocyte identity, lipid metabolism, and metabolic function, while simultaneously inhibiting alternative developmental, proliferative, and inflammatory programs. Spatial transcriptomic analyses further revealed zone-specific specialization of HNF4-dependent gene programs. Aging selectively disrupted these regulatory networks, resulting in compromised liver identity and metabolic gene programs, de-repression of inflammatory pathways and alternative cellular identity programs and disrupted hepatocyte zonation, consistent with age-dependent lipidomic and metabolic changes, hepatic fat accumulation, and immune infiltration. Hepatocyte-specific Hnf4a deletion in young mice recapitulated key features of liver aging, including impaired hepatocyte identity, metabolic dysfunction, steatosis, inflammatory activation and altered hepatic immune-cell composition, while deletion in aged mice further exacerbated steatosis, inflammation, and hepatic dysfunction. Conversely, hepatocyte-specific HNF4 restoration in aged mice significantly reduced hepatic steatosis and lipid accumulation, restored fatty acid metabolic programs, and partially reversed age-associated transcriptional changes. However, inflammatory and interferon-associated programs were not uniformly reversed, revealing differential responsiveness of metabolic and inflammatory pathways to HNF4 restoration. Together, these findings identify age-associated impairment of HNF4 activity as a functional contributor to liver aging, linking dysregulation of hepatocyte identity, metabolic homeostasis, and inflammatory control to age-associated hepatic dysfunction. Importantly, the selective reversibility of metabolic defects following HNF4 restoration establishes HNF4 as a promising strategy for preserving hepatocyte homeostasis and reversing age-associated hepatic metabolic dysfunction.

molecular biology↗

bioRxiv2026

NAMPT activation uncovers a senescence-specific vulnerability and promotes healthy aging in combination with NAM

Aging is driven by multiple interacting processes, suggesting that effective strategies to promote healthy aging may require simultaneous targeting of more than one underlying mechanism. Here we identify a strategy that couples restoration of nicotinamide adenine dinucleotide (NAD+) homeostasis with selective targeting of senescent cells, two mechanistically linked features of aging. Senescent cells express elevated intracellular levels of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the nicotinamide (NAM) salvage pathway for NAD+ biosynthesis. Despite increased NAMPT abundance, isotope-tracing studies revealed decreased NAD+ biosynthesis and consumption, indicating that elevated NAMPT abundance was not accompanied by a corresponding increase in NAD+ metabolic flux. Treatment with the NAMPT activator SBI-0802162 engaged the spare enzymatic capacity of NAMPT in senescent cells and produced a marked rise in intracellular NAD+ that, when sustained, disrupted their transcriptional program and selectively reduced the viability of senescent cells but not proliferating cells. In mice, SBI-0802162 reduced circulating NAM levels, suggesting that sustained NAMPT activation may be limited by substrate availability. This observation prompted the development of a combination approach using SBI-0802162 together with dietary NAM supplementation. Co-administration of SBI-0802162 and NAM robustly increased tissue NAD+, suppressed select age-associated inflammatory signatures and markers of cellular senescence in a tissue-specific manner. These molecular effects occurred alongside preserved physical performance in aged mice and reductions in food intake and body weight, which were observed whether SBI-0802162 was present in the chow or administered by oral gavage. Together, these findings establish a mechanistically integrated approach to target two convergent features of aging, NAD+ dysregulation and senescent cell accumulation, and support combined NAMPT activation and NAM supplementation as a strategy to promote healthy aging.

molecular biology↗

bioRxiv2026

HIRA-mediated H3.3 deposition preserves hepatocyte cell identity during liver aging

Age-associated functional decline is partly driven by progressive chromatin degeneration. Maintenance of chromatin integrity preserves cell identity and promotes healthy aging, but through different mechanisms in proliferating and non-proliferating cells. However, specific mechanisms of chromatin maintenance and their compensatory capacity in proliferating and non-proliferating cells are undefined. The histone chaperone HIRA deposits the histone variant H3.3 in a DNA replication-independent manner, leading to its accumulation in aging, non-proliferating cells. Here, we show that hepatocyte-specific loss of HIRA causes loss of cell identity, metabolic dysfunction, and accelerated fibrotic pathology with age. Transcriptomic and epigenomic analyses indicate that HIRA-H3.3 preserves chromatin integrity and sustains transcription of highly expressed genes, including cell identity genes. Partial hepatectomy, associated with induced proliferation, restores identity of HIRA knockout livers with compensatory deposition of canonical histones H3.1/2. Together, these results demonstrate that HIRA-mediated H3.3 deposition is essential for safeguarding cell identity and tissue function during aging of non-proliferating cells, but this function can be rescued by tissue regeneration and associated cell proliferation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=124 SRC="FIGDIR/small/710643v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@a2a26aorg.highwire.dtl.DTLVardef@154e5aeorg.highwire.dtl.DTLVardef@b315a7org.highwire.dtl.DTLVardef@152bca4_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2025

Aging-induced hepatocyte CD44 drives IL6/STAT3 signaling and associates with impaired neighboring T cell function.

Liver cancer incidences increase dramatically beyond 55 years of age, suggesting that age-associated changes contribute critically to tumor initiation. However, the mechanisms linking liver aging and cancer initiation are not well defined. This study investigates the role of CD44, a marker of liver tumor-initiating cells (TIC), in age-associated liver pathophysiology. Aged livers showed accumulation of CD44-expressing hepatocytes exhibiting enrichment of immune modulatory genes and activation of the immunosuppressive IL6/JAK/STAT3 pathway. Indeed, in adoptive transfer assays, antigen-exposed CD8+ T cells mounted a lower IFN-{gamma} response in aged livers than in young livers, indicating an immunosuppressive aged milieu. Concordantly, spatial analyses showed that the proximal neighbourhoods of Cd44-expressing hepatocytes are enriched in T cells exhibiting reduced cytokine and chemokine gene expression. Finally, hepatocyte-specific knock out of Cd44 mitigated the IL6/JAK/STAT3 gene signature in aged livers. Overall, these findings suggest that CD44 expression in aged hepatocytes promotes activation of the immunosuppressive IL6/JAK/STAT3 pathway and this is associated with impaired T cell effector function.

cell biology↗

bioRxiv2025

Targeting CyclinD1-CDK6 to Mitigate Senescence-Driven Inflammation and Age-Associated Functional Decline

Cellular senescence contributes to aging and age-related diseases by driving chronic inflammation through the Senescence Associated Secretory Phenotype (SASP) and interferon-stimulated genes (ISGs). Cyclin D1 (CCND1), a key cell cycle regulator, is paradoxically upregulated in these non-proliferating cells. We show that CCND1 and its kinase partner CDK6 drive SASP and ISG expression in senescent cells by promoting DNA damage accumulation. This leads to the formation of cytoplasmic chromatin fragments (CCFs) that activate pro-inflammatory CGAS-STING signaling. The tumor suppressor p53 (TP53) and its target p21 (CDKN2A) antagonize this CCND1-CDK6-dependent DNA damage accumulation pathway to suppress the SASP. In aged mouse livers, senescent hepatocytes show increased Ccnd1 expression. Hepatocyte-specific Ccnd1 knockout or treatment with the Cdk4/6 inhibitor Palbociclib reduces DNA damage and ISGs in aged mouse liver. Notably, Palbociclib also suppresses frailty and improves physical performance of aged mice. These findings reveal a novel role for CCND1/CDK6 in regulating DNA damage and inflammation in senescence and aging, highlighting it as a promising therapeutic target.

cell biology↗

bioRxiv2025

Rapamycin Reverses the Hepatic Response to Diet-Induced Metabolic Stress That Is Amplified by Aging.

Aging is associated with increased susceptibility to metabolic stress and chronic liver disease, yet the interactions between age and metabolic stressors and the potential for ameliorating interventions remain incompletely understood. Here, we examined the hepatic response of young (7-month-old) and old (25-month-old) C57BL/6 male mice to a 9-week high-fat diet (HFD) and assessed whether rapamycin, a well-established pro-longevity intervention, could mitigate age-exacerbated effects. While both age groups developed metabolic-associated steatohepatitis (MASH), older mice displayed more severe hepatic steatosis, inflammation, and transcriptional dysregulation. Transcriptomic profiling of whole livers and purified hepatocytes revealed that aging amplifies HFD-induced inflammatory and metabolic gene expression changes, including activation of immune pathways and suppression of metabolic pathways. Notably, treatment of aging mice with rapamycin reversed the majority of HFD-driven transcriptional alterations, including upregulation of pro-inflammatory regulators such as Stat1, and dysregulation of metabolic gene networks. Rapamycin also reduced hepatosteatosis, total body weight, and a tumorigenic transcriptomic signature associated with hepatocellular carcinoma risk. These findings demonstrate that aging intensifies hepatic sensitivity to metabolic stress and identify rapamycin as a promising therapeutic to counteract age-related liver dysfunction and MAFLD progression.

cell biology↗

bioRxiv2024

Activated Interferon Signaling Suppresses Age-Dependent Liver Cancer

Age is a major risk factor for liver cancer, as is the case for most adult human cancers. However, the underlying mechanisms are not well defined. A better understanding of the role of aging in liver and other cancers can facilitate approaches for risk assessment, early detection and prevention. We hypothesize that age-driven changes render aged liver more sensitive to oncogenic stress and hence tumorigenesis. To investigate how the liver changes with age, we documented the immune profile, transcriptome and epigenome of healthy livers from both young and aged mice, revealing pronounced alterations with aging. Notably, in aged hepatocytes, we identified heightened interferon (IFN) signaling, as well as simultaneous tumor suppressor and oncogene signaling at both bulk and single cell level, suggestive of an aged liver that is poised for neoplasia. To challenge this seemingly poised state, we employed adeno-associated virus (AAV)-mediated expression of a c-Myc oncogene in young and aged mouse liver hepatocytes in vivo. Analysis of aged hepatocytes expressing c-Myc revealed further elevated expression of IFN Stimulated Genes (ISGs). This ISG upregulation was evident in multiple models of oncogenic stress and transformation in older mice and also observed in aged humans with Metabolic dysfunction-Associated Steatohepatitis (MASH). We determined that Stat1 is both necessary and sufficient for the age specific elevated ISG expression in old wild type mice. Remarkably, inhibiting Jak/Stat signaling alongside ectopic c-Myc expression led to high-grade hepatocyte dysplasia and tumor formation, selectively in aged mice. Together, these results suggest that an aged liver is in a state of "precarious balance", due to concurrent activation of oncogenic and tumor suppressor pathways, but protected against neoplastic progression by IFN-signaling. Age-dependent activation of IFN signaling has been observed in many tissues and recent studies have demonstrated its detrimental consequences on aging, raising the question as to why IFN-signaling is activated during aging. We propose that aged tissues are intrinsically at higher risk of cancer and age-dependent activation of IFN-signaling is an adaptive process to protect from tumorigenesis, but one that also has maladaptive consequences.

cancer biology↗

bioRxiv2023

Histone chaperone HIRA, Promyelocytic Leukemia (PML) protein and p62/SQSTM1 coordinate to regulate inflammation during cell senescence and aging.

Cellular senescence, a stress-induced stable proliferation arrest associated with an inflammatory Senescence-Associated Secretory Phenotype (SASP), is a cause of aging. In senescent cells, Cytoplasmic Chromatin Fragments (CCFs) activate SASP via the anti-viral cGAS/STING pathway. PML protein organizes PML nuclear bodies (NBs), also involved in senescence and anti-viral immunity. The HIRA histone H3.3 chaperone localizes to PML NBs in senescent cells. Here, we show that HIRA and PML are essential for SASP expression, tightly linked to HIRAs localization to PML NBs. Inactivation of HIRA does not directly block expression of NF-{kappa}B target genes. Instead, an H3.3-independent HIRA function activates SASP through a CCF-cGAS-STING-TBK1-NF-{kappa}B pathway. HIRA physically interacts with p62/SQSTM1, an autophagy regulator and negative SASP regulator. HIRA and p62 co-localize in PML NBs, linked to their antagonistic regulation of SASP, with PML NBs controlling their spatial configuration. These results outline a role for HIRA and PML in regulation of SASP.

cell biology↗