IF aged C57BL/6J mice (20–24 months, both sexes) receive a sequential two-phase protocol in which Phase 1 consists of ruxolitinib (oral gavage, ~45 mg/kg/day, 4 weeks) to suppress JAK1/2-STAT3-driven SASP and block paracrine senescence spread, followed immediately by Phase 2 consisting of low-dose navitoclax (oral gavage, ~5 mg/kg/day, intermittent 3-days-on/4-days-off cycles for 4 weeks) as a senolytic, compared to navitoclax monotherapy at equivalent low dose, ruxolitinib monotherapy, vehicle control, and a concurrent (same-day) combination control in aged C57BL/6J mice,

THEN the sequential protocol will produce a significantly greater reduction in tissue senescent cell burden (≥40% reduction in p16INK4a/p21CIP1 double-positive cells by immunohistochemistry in liver, visceral adipose, kidney, and lung), lower circulating SASP cytokines (IL-6, IL-8, TNFα; ≥50% reduction by multiplex ELISA), improved healthspan metrics (grip strength, rotarod, gait speed), and critically, lower platelet toxicity (platelet counts >150×10³/μL) compared to standard-dose navitoclax monotherapy, while also demonstrating reduced new bystander senescence induction (fewer p21CIP1-positive non-p16-positive "recently converted" cells) during the senolytic phase,

BECAUSE the following causal chain operates:

1. Constitutive JAK1/2-STAT3 signaling in senescent cells drives robust transcription of SASP genes encoding IL-6, IL-8, TNFα, and CXCL1, which are secreted and induce paracrine/bystander senescence in neighboring cells via receptor-mediated signal transduction; JAK1/2 inhibition with momelotinib (a close ruxolitinib analogue) reduced the fraction of p21CIP1-positive bystander cells in vitro and in islet co-culture models, directly demonstrating that JAK inhibition curtails paracrine senescence spread (JAK1/2 inhibition suppresses paracrine senescence induction)[https://doi.org/10.1101/2025.05.07.648438]

2. Phospho-JAK1 and phospho-JAK2 levels are elevated in senescent cells, and treatment with a JAK inhibitor (1 μM, 72 h) suppressed key SASP transcripts and reduced the ability of conditioned medium from senescent cells to induce senescence in recipient cells, validating that JAK pathway blockade functionally interrupts paracrine transmission of the senescent phenotype (JAK inhibition suppresses SASP and paracrine spread)[https://doi.org/10.3389/fonc.2019.01576]

3. [SPECULATIVE] JAK1/2-STAT3 signaling in senescent cells does not exclusively drive inflammatory cytokine transcription — it co-regulates transcription of pro-survival Bcl-2 family members including Bcl-xL and Mcl-1 (which are known STAT3 transcriptional targets in cancer and immune cell biology); therefore, 4 weeks of ruxolitinib pretreatment is predicted to reduce Bcl-xL and Mcl-1 protein expression in senescent cells across tissues, lowering the apoptotic threshold and rendering these cells significantly more sensitive to BH3-mimetic navitoclax-mediated apoptosis at doses that would be subth...

SENS category: GlycoSENS

Key references: • doi.org/10.1101/2025.05.07.648438] • doi.org/10.3389/fonc.2019.01576] • doi.org/10.1111/acel.12931] • doi.org/10.1038/s41467-020-18039-x]; • doi.org/10.7554/elife.75492]