Vascular access dysfunction underlies much of the morbidity and mortality in ESRD and its healthcare costs. The arteriovenous fistula (AVF) is the favored access because of its lower risk for infection and thrombosis, and its greater functionality. AVF outcomes, however, are grim as 50% or more may never mature and function, and increasing numbers of once functional AVFs may, thereafter, cease to do so. Promoting AVF maturation and functionality is thus a dominant unmet need in CKD and ESRD. For more than 15 years, the PI's laboratory has investigated AVF rodent models and delineated vasculopathic and vasoprotective species in the AVF. For the past 2 years, this laboratory sought the basis for the range of maladaptive responses and observed that the AVF exhibits a senescence phenotype as assessed by multiple biomarkers and drivers of senescence. These findings, along with this lab's published data demonstrating marked upregulation of PAI-1, MCP-1, IL-6, MMPs, and other mediators, indicate that senescence is prematurely induced in the AVF. Using the murine AVF-CKD model introduced by this laboratory, three aims are proposed:
Aim I : Define the role of specific stressors in initiating AVF senescence and impairing AVF outcomes. Hypothesis: The AVF imposes hemodynamic and other stress which veins were never designed to bear; such stress causes AVF senescence. Approach:
This aim examines pathologic shear stress and the relative imbalance of vasculopathic (eg, NF-kB) over vasoprotective (eg, Klf2, Klf4, and Nrf2) transcription factors; oxidative stress; uremia; and age-related stress.
Aim II : Define the roles of p16Ink4a and p21cip1 expressing cells in AVF senescence and impairing AVF outcomes. Hypothesis: p16Ink4a-expressing and p21cip1-expressing cells drive senescence, and deletion of senescent cells (SCs) improves the AVF. Approach: p16Ink4a-expressing cells will be deleted in the AVF using the INK-ATTAC mouse which enables the removal of p16-expressing SCs but not non-SCs; a conditional endothelial-specific INK-ATTAC mouse provides an added approach. The role of p21cip1-expressing SCs will be examined using p21+/+ and p21-/- mice and p21-ER-Cre mice which enable deletion of p21-expressing SCs.
Aim III : Define the efficacy of senolytics, inhibitors of senescence-associated secretory phenotype (SASP), and inhibitors of specific SASP factors in improving AVF outcomes. Hypothesis: Interrupting senescence improves AVF maturation and function. Approach: SCs survive because of upregulated anti-apoptotic pathways. Inducing SC apoptosis (senolytics) provides a novel therapeutic approach, as do SASP-inhibitory agents.
This aim examines the efficacy of senolytics, SASP inhibitors, and inhibitors of specific SASP factors (MCP-1 and IL-6) upregulated in human and rodent AVFs. In sum, this new R01 application examines a novel mechanism of AVF failure, namely, senescence; stressors that may cause it; mechanisms that may drive it; and therapeutic approaches that are part of the groundswell of interest in the therapeutic frontier of senolytics, the latter now entering clinical trials.
A dialysis arteriovenous fistula connects a vein to an artery and, once developed and matured, such a fistula is the preferred dialysis access for purification of the blood by dialysis in patients suffering from kidney failure. Many dialysis fistulas, however, do not adequately develop and mature such that they can be used for effective hemodialysis. A major hypothesis of this grant is that fistulas fail because they develop accelerated aging, and this grant application will test this hypothesis and how such aging can be prevented.