Circulating levels of white blood cells (WBCs) are one of the 10 variables used to quantify biological age with PhenoAge (https://michaellustgarten.com/2019/09/09/quantifying-biological-age). The reference range for WBCs is 4.5 – 11 *10⁹ cells/L, but within that range, what’s optimal?

Several studies have reported that WBCs greater than 5 are associated with an increased all-cause mortality risk (Ahmadi-Abhari et al. 2013, Samet et al. 2005, Weijenberg et al. 1996). While observational studies are important for identifying associations with mortality risk, stronger evidence is obtained when the data from the same subjects are tracked for a time period. Perhaps the best evidence for the association between WBCs with mortality risk comes from the Baltimore Longitudinal Study on Aging (BLSA), which studied 2803 men and women over a period of 44 years (Ruggiero et al. 2007). As shown below, subjects that had circulating WBCs between 3.5 – 6 had the best survival, whereas WBCs below 3.5, between 6 – 10, and 10+ each had successively higher risk. The 0.5 point on the y-axis of the curve (survival) is defined as 50% mortality, and is the point where half of the study subjects died, whereas the remaining 50% were still alive.

Aim: Aging in humans is associated with a 10–40-fold greater incidence of sudden cardiac death from malignant tachyarrhythmia. We have reported that thiol oxidation of ryanodine receptors (RyR2s) by mitochondria-derived reactive oxygen species (mito-ROS) contributes to defective Ca²⁺ homeostasis in cardiomyocytes (CMs) from aging rabbit hearts. However, mechanisms responsible for the increase in mito-ROS in the aging heart remain poorly understood. Here we test the hypothesis that age-associated decrease in autophagy is a major contributor to enhanced mito-ROS production and thereby pro-arrhythmic disturbances in Ca²⁺ homeostasis.

Methods and Results: Ventricular tissues from aged rabbits displayed significant downregulation of proteins involved in mitochondrial autophagy compared with tissues from young controls. Blocking autophagy with chloroquine increased total ROS production in primary rabbit CMs and mito-ROS production in HL-1 CMs. Furthermore, chloroquine treatment of HL-1 cells depolarized mitochondrial membrane potential (Δψm) to 50% that of controls. Blocking autophagy significantly increased oxidation of RyR2, resulting in enhanced propensity to pro-arrhythmic spontaneous Ca²⁺ release under β-adrenergic stimulation. Aberrant Ca²⁺ release was abolished by treatment with the mito-ROS scavenger mito-TEMPO. Importantly, the autophagy enhancer Torin1 and ATG7 overexpression reduced the rate of mito-ROS production and restored both Δψm and defective Ca²⁺ handling in CMs derived from aged rabbit hearts.

Conclusion: Decreased autophagy is a major cause of increased mito-ROS production in the aging heart. Our data suggest that promoting autophagy may reduce pathologic mito-ROS during normal aging and reduce pro-arrhythmic spontaneous Ca²⁺ release via oxidized RyR2s.

Back in January, we were joined by Dr. Aubrey de Grey, Dr. Amutha Boominathan, Dr. Matthew O’Conner, and Michael Rae from the SENS Research Foundation for a webinar discussion panel focused on MitoSENS, the mitochondrial repair program. During the webinar, a number of points were discussed, and the Lifespan Heroes in the audience got to ask the researchers questions about MitoSENS and about the work of the SENS Foundation in general.

In 2015, the MitoSENS team raised funding on Lifespan.io to launch a study testing if they could create mitochondrial DNA copies in the cell nucleus, and they were successful in doing so as a result of the funds they received. In October 2019, the MitoSENS team launched a new follow-up project called MitoMouse, which aims to bring its mitochondrial repair therapy to mammals as a proof of concept on the road to translation to human use.