Espíndola‐Netto, Jair Machado

ABSTRACT Background and Aims Cellular senescence is a hallmark of several liver diseases, including primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC). Senescent cholangiocytes exhibit a senescence‐associated secretory phenotype (SASP), characterized by profibroinflammatory mediator release. Current cost‐effective biomarkers predicting disease progression, particularly for PSC, are limited and often lack mechanistic relevance. We sought to define a plasma biomarker signature for PSC and PBC. Methods Plasma from early‐ and late‐stage PSC and PBC, alcoholic liver disease (ALD), inflammatory bowel disease (IBD) patients, and healthy controls was analyzed. Seventy‐one analytes were quantified using Luminex Multiplex Immunoassay or enzyme‐linked immunosorbent assay (ELISA). Principal component analysis (PCA) identified key patterns. Findings from the PSC cohort were then applied to additional cohorts. Results Second principal component (PC2) (17 analytes, 17.1% variability) best separated PSC from controls. ANOVA showed significant differences in PC2 between early PSC vs. controls ( p = 0.0001), late PSC vs. controls ( p < 0.0001), and early vs. late PSC ( p < 0.0001). PC2 analytes also distinguished early PBC vs. controls ( p < 0.0332), late PBC ( p < 0.0001), and ALD ( p < 0.0001), and early vs. late PBC ( p < 0.0001), but not IBD vs. controls ( p = 0.119). Logistic regression using PC2 demonstrated strong discrimination of early‐ and late‐stage PSC (AUC = 0.86) and control vs. early‐stage PSC (AUC = 0.83). Conclusion This is the first study to define a plasma SASP biomarker signature associated with cholestatic liver disease. These analytes track disease stage and represent both mechanistic indicators and potential clinical trial endpoints.

Abstract Senescent cells drive tissue dysfunction through the senescence-associated secretory phenotype (SASP). We uncovered a central role for mitochondria in the epigenetic regulation of the SASP, where mitochondrial-derived metabolites, specifically citrate and acetyl-CoA, fuel histone acetylation at SASP gene loci, promoting their expression. We identified the mitochondrial citrate carrier (SLC25A1) and ATP-citrate lyase (ACLY) as critical for this process. Inhibiting these pathways selectively suppresses SASP without affecting cell cycle arrest, highlighting their potential as therapeutic targets for age-related inflammation. Notably, SLC25A1 inhibition reduces systemic inflammation and extends healthspan in aged mice, establishing mitochondrial metabolism as pivotal to the epigenetic control of aging.

Abstract Chronic conditions associated with aging have proven difficult to prevent or treat. Senescence is a cell fate defined by loss of proliferative capacity and the development of a pro‐inflammatory senescence‐associated secretory phenotype comprised of cytokines/chemokines, proteases, and other factors that promotes age‐related diseases. Specifically, an increase in senescent peripheral blood mononuclear cells (PBMCs), including T cells, is associated with conditions like frailty, rheumatoid arthritis, and bone loss. However, it is unknown if the percentage of senescent PBMCs associated with age‐associated orthopedic decline could be used for potential diagnostic or prognostic use in orthopedics. Here, we report senescent cell detection using the fluorescent compound C 12 FDG to quantify PBMCs senescence across a large cohort of healthy and osteoarthritic patients. There is an increase in the percent of circulating C 12 FDG + PBMCs that is commensurate with increases in age and senescence‐related serum biomarkers. Interestingly, C 12 FDG + PBMCs and T cells also were found to be elevated in patients with mild to moderate osteoarthritis, a progressive joint disease that is strongly associated with inflammation. The percent of C 12 FDG + PBMCs and age‐related serum biomarkers were decreased in a small subgroup of study participants taking the senolytic drug fisetin. These results demonstrate quantifiable measurements in a large group of participants that could create a composite score of healthy aging sensitive enough to detect changes following senolytic therapy and may predict age‐related orthopedic decline. Detection of peripheral senescence in PBMCs and subsets using C 12 FDG may be clinically useful for quantifying cellular senescence and determining how and if it plays a pathological role in osteoarthritic progression.

Abstract Senescent cell accumulation contributes to the progression of age-related disorders including Alzheimer’s disease (AD). Clinical trials evaluating senolytics, drugs that clear senescent cells, are underway, but lack standardized outcome measures. Our team recently published data from the first open-label trial to evaluate senolytics (dasatinib plus quercetin) in AD. After 12-weeks of intermittent treatment, we reported brain exposure to dasatinib, favorable safety and tolerability, and modest post-treatment changes in cerebrospinal fluid (CSF) inflammatory and AD biomarkers using commercially available assays. Herein, we present more comprehensive exploratory analyses of senolytic associated changes in AD relevant proteins, metabolites, lipids, and transcripts measured across blood, CSF, and urine. These analyses included mass spectrometry for precise quantification of amyloid beta (Aß) and tau in CSF; immunoassays to assess senescence associated secretory factors in plasma, CSF, and urine; mass spectrometry analysis of urinary metabolites and lipids in blood and CSF; and transcriptomic analyses relevant to chronic stress measured in peripheral blood cells. Levels of Aß and tau species remained stable. Targeted cytokine and chemokine analyses revealed treatment-associated increases in inflammatory plasma fractalkine and MMP-7 and CSF IL-6. Urinary metabolites remained unchanged. Modest treatment-associated lipid profile changes suggestive of decreased inflammation were observed both peripherally and centrally. Blood transcriptomic analysis indicated downregulation of inflammatory genes including FOS, FOSB, IL1β, IL8, JUN, JUNB, PTGS2. These data provide a foundation for developing standardized outcome measures across senolytic studies and indicate distinct biofluid-specific signatures that will require validation in future studies. ClinicalTrials.gov: NCT04063124.

Abstract Accurate biomarkers for predicting COVID‐19 severity have remained an unmet need due to an incomplete understanding of virus pathogenesis and heterogeneity among patients. Cellular senescence and its pro‐inflammatory phenotype are suggested to be a consequence of SARS‐CoV‐2 infection and potentially drive infection‐dependent pathological sequelae. Senescence‐associated markers in infected individuals have been identified primarily in the lower respiratory tract, while little is known about their presence in more easily accessible bio‐specimens. Here, we measured the abundance of senescence‐associated signatures in whole blood, plasma and peripheral blood mononuclear cells (PBMCs) of COVID‐19 patients and patients without an infection. Bulk transcriptomic and targeted proteomic assays revealed that the level of senescence‐associated markers, including the senescence‐associated secretory phenotype (SASP), is predictive of SARS‐CoV‐2 infection. Single‐cell RNA‐sequencing data demonstrated that a senescence signature is particularly enriched in monocytes of COVID‐19 patients, partially correlating with disease severity. Our findings suggest that monocytes are prematurely induced to senescence by SARS‐CoV‐2 infection, might contribute to exacerbating a SASP‐like inflammatory response and can serve as markers and predictors for COVID‐19 and its sequelae.

Abstract Decreased α-Klotho, a geroprotective factor, and increased senescent cell burden are both associated with early onset of physical disability, cognitive impairment, and premature all-cause mortality. It has been demonstrated that eliminating senescent cells can enhance physical function, cognition, and survival in mice, as does overexpressing α-Klotho. Mice with low α-Klotho exhibit accelerated senescent cell accumulation, recombinant α-Klotho decreases senescent cell burden and restores lifespan in these mice, and senescent epidermal cells are reduced in mice overexpressing α-Klotho. Here, we tested the hypothesis that senescent cells cause decreased α-Klotho and hence that reducing senescent cells can increase α-Klotho. Senescent cell conditioned medium (CM) reduced α-Klotho in cultured non-senescent human umbilical vein endothelial cells (HUVECs), renal tubular endothelial cells, and astrocytes. These effects of senescent CM were partially attenuated by neutralizing antibodies against the senescence-associated secretory phenotype (SASP) factors, activin A and IL-1α. Transplanting senescent cells into younger mice caused decreased urine and brain α-Klotho. Genetically reducing highly p16Ink4a-expressing cells in old INK-ATTAC mice or administering the senolytics, Dasatinib plus Quercetin (D+Q) or Fisetin (F), to young mice transplanted with senescent cells, young diet-induced obese (DIO) mice, or naturally-aged mice increased urine, kidney, and/or brain α-Klotho. Treating patients with idiopathic pulmonary fibrosis (IPF), a cellular senescence-related disease, with D+Q led to increased urinary α-Klotho. Thus, targeting senescent cells causes increases in the geroprotective factor α-Klotho, potentially amplifying the beneficial effects of senolytic drugs.

Abstract Senescent cells drive age-related tissue dysfunction partially via the induction of a chronic senescence-associated secretory phenotype (SASP). Mitochondria are major regulators of the SASP; however, the underlying mechanisms have not been elucidated. Mitochondria also control apoptosis, a cell fate generally perceived as distinct from cellular senescence, which is apoptosis resistant. Here, we show that mitochondrial outer membrane permeability (MOMP) occurring in a small subset of mitochondria is a feature of cellular senescence. This process, called minority MOMP (miMOMP), depends on the formation of BAX and BAK macropores and results in release of mitochondrial DNA (mtDNA) into the cytosol, which in turn activates the cGAS/STING pathway, a major regulator of the SASP. Importantly, we found that inhibition of MOMP in vivo decreases inflammatory markers and improves healthspan parameters in aged mice. Our results propose the novel concept that apoptosis and senescence are regulated by similar mitochondrial-dependent mechanisms, and that sub-lethal mitochondrial apoptotic stress is a major driver of the SASP. We also provide proof-of-concept that inhibition of miMOMP may be a new therapeutic avenue to improve healthspan.

Senescent cells exacerbate COVID-19 Cellular senescence is a state elicited in response to stress signals and is associated with a damaging secretory phenotype. The number of senescent cells increases with advanced age and this in turn drives age-related diseases. Camell et al. show that senescent cells have an amplified inflammatory response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (see the Perspective by Cox and Lord). This response is communicated to nonsenescent cells, suppressing viral defense mechanisms and increasing the expression of viral entry proteins. In old mice infected with a SARS-CoV-2–related virus, treatment with senolytics to reduce the senolytic cell burden reduced mortality and increased antiviral antibodies. Science , abe4832, this issue p. eabe4832 ; see also abi4474, p. 281