Peter S. Rabinovitch’s research while affiliated with University of Washington and other places

The mitochondrial-rich renal tubule cells are key regulators of blood homeostasis via excretion and reabsorption of metabolic waste. With age, tubules are subject to increasing mitochondrial dysfunction and declining nicotinamide adenine dinucleotide (NAD ⁺ ) levels, both hampering ATP production efficiency. We tested two mitochondrial interventions in young (6-mo) and aged (26-mo) adult male mice: (ELAM), a tetrapeptide in clinical trials that improves mitochondrial structure and function, and nicotinamide mononucleotide (NMN), an NAD ⁺ intermediate and commercially available oral supplement. Kidneys were analyzed from young and aged mice after eight weeks of treatment with ELAM (3 mg/kg/day), NMN (300 mg/kg/day), or from aged mice treated with the two interventions combined (ELAM+NMN). We hypothesized that combining pharmacologic treatments to ameliorate mitochondrial dysfunction and boost NAD ⁺ levels, would more effectively reduce kidney aging than either intervention alone. Unexpectedly, in aged kidneys, NMN increased expression of genetic markers of inflammation (IL-1β and Ccl2) and tubule injury (Kim-1). Metabolomics of endpoint sera showed that NMN-treated aged mice had higher circulating levels of uremic toxins than either aged controls or young NMN-treated mice. ELAM+NMN- treated aged mice accumulated uremic toxins like NMN-only aged mice, but reduced IL-1β and Ccl2 kidney mRNA. This suggests that pre-existing mitochondrial dysfunction in aged kidney underlies susceptibility to inflammatory signaling with NMN supplementation in aged, but not young, mice. These findings demonstrate age and tissue dependent effects on downstream metabolic accumulation from NMN and highlight the need for targeted analysis of aged kidneys to assess the safety of anti-aging supplements in older populations. Summary Statement Declining levels of NAD ⁺ and increasing mitochondrial dysfunction with age are functionally linked and are popular mechanistic targets of commercially available anti-aging therapeutics. Studies have focused on nicotinamide mononucleotide (NMN), nicotinamide riboside (NR) and nicotinamide (NAM) supplementation to boost cellular NAD ⁺ , but a consensus on the dosage and regimen that is beneficial or tolerable has not been reached. We show that although high levels of sustained NMN supplementation are beneficial to liver and heart in aged mice, the same dosing regimen carries age-associated signs of kidney inflammation. Our findings underscore a complex state of age- and tissue-specific metabolic homeostasis and raise questions not only about how much, and for how long, but at what age is NAD ⁺ boosting safe.

Changes in mitochondrial function play a critical role in the basic biology of aging and age-related disease. Mitochondria are typically thought of in the context of ATP production and oxidant production. However, it is clear that the mitochondria sit at a nexus of cell signaling where they affect metabolite, redox, and energy status, which influence many factors that contribute to the biology of aging, including stress responses, proteostasis, epigenetics, and inflammation. This has led to growing interest in identifying mitochondrial targeted interventions to delay or reverse age-related decline in function and promote healthy aging. In this review, we discuss the diverse roles of mitochondria in the cell. We then highlight some of the most promising strategies and compounds to target aging mitochondria in preclinical testing. Finally, we review the strategies and compounds that have advanced to clinical trials to test their ability to improve health in older adults.

The ability to respond to physical stress that disrupts normal physiological homeostasis at an older age embraces the concept of resilience to aging. A physical stressor could be used to induce physiological responses that are age-related, since resilience declines with increasing age. Increased fat and sugar intake is a nutritional stress with a high prevalence of obesity in older people. In order to determine the effect of this type of diet on resilience to aging, 18-month-old C57BL/6J male mice were fed a diet high in saturated fat (lard) and sucrose (HFS) for ten months. At the end of the 10-month study, mice fed the HFS diet showed increased cognitive impairment, decreased cardiac function, decreased strength and agility, and increased severity of renal pathology compared to mice fed a rodent chow diet low in saturated fat and sucrose (LFS). The degree of response aligned with decreased resilience to the long-term adverse effects of the diet with characteristics of accelerated aging. This observation suggests additional studies could be conducted to investigate the relationship between an accelerated decline in resilience to aging and enhanced resilience to aging under different dietary conditions.

Aging muscle experiences functional decline in part mediated by impaired mitochondrial ADP sensitivity. Elamipretide (ELAM) rapidly improves physiological and mitochondrial function in aging and binds directly to the mitochondrial ADP transporter ANT. We hypothesized that ELAM improves ADP sensitivity in aging leading to rescued physiological function. We measured the response to ADP stimulation in young and old muscle mitochondria with ELAM treatment, in vivo heart and muscle function, and compared protein abundance, phosphorylation, and S-glutathionylation of ADP/ATP pathway proteins. ELAM treatment increased ADP sensitivity in old muscle mitochondria by increasing uptake of ADP through the ANT and rescued muscle force and heart systolic function. Protein abundance in the ADP/ATP transport and synthesis pathway was unchanged, but ELAM treatment decreased protein s-glutathionylation incuding of ANT. Mitochondrial ADP sensitivity is rapidly modifiable. This research supports the hypothesis that ELAM improves ANT function in aging and links mitochondrial ADP sensitivity to physiological function. Graphical abstract ELAM binds directly to ANT and ATP synthase and ELAM treatment improves ADP sensitivity, increases ATP production, and improves physiological function in old muscles. ADP (adenosine diphosphate), ATP (adenosine triphosphate), VDAC (voltage-dependent anion channel), ANT (adenine nucleotide translocator), H ⁺ (proton), ROS (reactive oxygen species), NADH (nicotinamide adenine dinucleotide), FADH 2 (flavin adenine dinucleotide), O 2 (oxygen), ELAM (elamipretide), –SH (free thiol), –SSG (glutathionylated protein)

Diastolic dysfunction is a key feature of the aging heart. We have shown that late-life treatment with mTOR inhibitor, rapamycin, reverses age-related diastolic dysfunction in mice but the molecular mechanisms of the reversal remain unclear. To dissect the mechanisms by which rapamycin improves diastolic function in old mice, we examined the effects of rapamycin treatment at the levels of single cardiomyocyte, myofibril and multicellular cardiac muscle. Compared to young cardiomyocytes, isolated cardiomyocytes from old control mice exhibited prolonged time to 90% relaxation (RT90) and time to 90% Ca2+ transient decay (DT90), indicating slower relaxation kinetics and calcium reuptake with age. Late-life rapamycin treatment for 10 weeks completely normalized RT90 and partially normalized DT90, suggesting improved Ca2+ handling contributes partially to the rapamycin-induced improved cardiomyocyte relaxation. In addition, rapamycin treatment in old mice enhanced the kinetics of sarcomere shortening and Ca2+ transient increase in old control cardiomyocytes. Myofibrils from old rapamycin-treated mice displayed increased rate of the fast, exponential decay phase of relaxation compared to old controls. The improved myofibrillar kinetics were accompanied by an increase in MyBP-C phosphorylation at S282 following rapamycin treatment. We also showed that late-life rapamycin treatment normalized the age-related increase in passive stiffness of demembranated cardiac trabeculae through a mechanism independent of titin isoform shift. In summary, our results showed that rapamycin treatment normalizes the age-related impairments in cardiomyocyte relaxation, which works conjointly with reduced myocardial stiffness to reverse age-related diastolic dysfunction.

Aims: Patients with primary sclerosing cholangitis (PSC) and inflammatory bowel disease (IBD, termed PSC-IBD) have a higher risk of harbouring nonconventional and/or invisible dysplasias, especially in the right/proximal colon, than those with IBD alone. We postulated that DNA content abnormality may be frequently detected in the right/proximal colon in PSC-IBD patients, even in the absence of dysplasia, and that this may predispose to progression to nonconventional and/or invisible dysplasias that are often associated with increased rates of aneuploidy and advanced neoplasia. Methods and results: DNA flow cytometry was performed on 96 morphologically benign colon biopsies taken throughout the colon from 25 PSC-IBD patients during the surveillance colonoscopy that preceded the next procedure that detected dysplasia. Thirty (31%) of the 96 benign colon biopsies in this dysplasia group demonstrated abnormal DNA content, with a propensity for the right/proximal colon (70%) (P < 0.001). In contrast, only one (1%) of 87 benign colon biopsies from 20 IBD patients without neoplasia (control group) demonstrated DNA content abnormality, and it was from the left colon. For analysis per patient, 48% (12 of 25) of the patients in the dysplasia group had abnormal DNA content compared with 5% (1 of 20) of the control group (P = 0.002). Of the 12 PSC-IBD patients with DNA content abnormality, invisible dysplasia was detected in 10 (83%) patients on follow-up, nine (75%) of whom had nonconventional dysplasia. Conclusion: PSC-IBD patients have an increased risk of developing abnormal DNA content in the right/proximal colon, predating the detection of dysplasia.

Age-associated diseases are becoming progressively more prevalent, reflecting the increased lifespan of the world’s population. However, the fundamental mechanisms of physiologic aging are poorly understood, and in particular, the molecular pathways that mediate cardiac aging and its associated dysfunction are unclear. Here, we focus on certain ion flux abnormalities of the mitochondria that may contribute to cardiac aging and age-related heart failure. Using oxidative phosphorylation, mitochondria pump protons from the matrix to the intermembrane space to generate a proton gradient across the inner membrane. The protons are returned to the matrix by the ATPase complex within the membrane to generate ATP. However, a portion of protons leak back to the matrix and do not drive ATP production, and this event is called proton leak or uncoupling. Accumulating evidence suggests that mitochondrial proton leak is increased in the cardiac myocytes of aged hearts. In this mini-review, we discuss the measurement methods and major sites of mitochondrial proton leak with an emphasis on the adenine nucleotide transporter 1 (ANT1), and explore the possibility of inhibiting augmented mitochondrial proton leak as a therapeutic intervention to mitigate cardiac aging.

The pathology of aging impacts multiple organ systems, including the kidney and skeletal and cardiac muscles. Long-term treatment with the mitochondrial-targeted peptide elamipretide has previously been shown to improve in vivo mitochondrial function in aged mice, which is associated with increased fatigue resistance and treadmill performance, improved cardiovascular diastolic function, and glomerular architecture of the kidney. However, elamipretide is a short tetrameric peptide that is not orally bioavailable, limiting its routes of administration. This study tested whether twice weekly intermittent injections of elamipretide could recapitulate the same functional improvements as continuous long-term infusion. We found that intermittent treatment with elamipretide for 8 months preserved exercise tolerance and left ventricular mass in mice with modest protection of diastolic function and skeletal muscle force production but did not affect kidney function as previously reported using continuous treatment.