A recent study investigated the roles of brown adipose tissue and a lipid-controlling hormone, 12,13-diHOME, in cardiac health. The researchers examined the molecular mechanisms behind 12,13-diHOME’s effects on the hearts of aged mice [1].
The aging heart
Aging leads to many cardiovascular system-related changes, which are connected to disruptions in Ca2+ metabolism [2]. Similarly, brown adipose tissue (BAT), which protects against metabolic and cardiovascular diseases [3], also decreases with age.
Previous work from this group linked BAT to improved calcium signaling and cardiac function in mice and identified a molecule, 12,13-diHOME, a lipid-controlling hormone (lipokine) that mediates this connection in young, healthy mice [4]. In this study, those researchers investigated this relationship during aging and its connection to the age-related decline in cardiovascular health.
Transplanting fat
The age-dependent decline in the BAT’s thermogenic function is well documented [3], but the BAT’s endocrine function is less explored. To investigate this, the researchers measured circulating lipids in the plasma of human participants aged 65-90, young people aged 18-35, and aged and young male mice. Unsurprisingly, age affected lipid signaling in both humans and mice, with some overlap between the two species, including seven oxylipins that were decreased in both aged mice and humans compared to young controls. One of them is 12,13-diHOME, a molecule that is released by BAT and has a positive impact on cardiac function [4].
Transplanting BAT from young mice to the visceral cavities of sex-matched aged mice led to improvements in many metrics of cardiac function and health in these mice, suggesting that BAT transplantation ameliorated their age-related cardiac problems. This was judged to be through the release of 12,13-diHOME, as BAT transplantation increased circulating 12,13-diHOME in aged mice. Such beneficial effects were not observed when white adipose tissue was transplanted, suggesting that these effects are specific to BAT.
A non-viral gene therapy approach
Since transplanting fat from young donors to the elderly would be quite a cumbersome procedure to apply in a clinical setting, the researchers tested whether acute 12,13-diHOME treatment would have the same effect. Injecting male and female aged mice with 12,13-diHOME improved cardiac functions in male but not female mice.
12,13-diHOME has a short half-life. Just 30 minutes after injection, the researchers did not observe increased plasma levels of 12,13-diHOME. To remedy this, the researchers turned to a non-viral gene therapy approach: tissue nanotransfection (TNT), which allowed them to test the impact of sustained 12,13-diHOME increase. They inserted all the genes necessary to produce 12,13-diHOME on a string of circular DNA, which was delivered to mouse skin cells with a short electric pulse once a week for 6 weeks. This allowed for 12,13-diHOME overexpression in those cells and increased its levels in circulation, leading to improvements in cardiovascular health and function in both male and female aged mice.
“In just six weeks, we were able to really negate a lot of the effects of cardiovascular aging by using TNT to increase 12,13-diHOME. The results were quite striking with improvements to ejection fraction and the heart’s pumping cycles,” said Daniel Gallego-Perez, Ph.D., professor and Edgar C. Hendrickson Chair in Biomedical Engineering at The Ohio State University.
Male-specific mechanism
To understand the observed changes at the molecular level, the researcher compared the gene expression in the heart tissues of young mice, BAT-transplanted aged mice, and an aged control group; all of these mice were male. Gene expression analysis showed increased ER stress markers in the aged control group, while BAT-transplant mice had levels akin to the young mice. The same was found to be true for male mice given the gene therapy.
Surprisingly, the researchers didn’t observe any changes in ER stress among female mice, possibly because of lower baseline ER stress levels in females.
Further explorations of the mechanism involved experiments in mice lacking neuronal nitric oxide synthase (nNOS), an enzyme that produces a nitric oxide signaling molecule. The same group showed before that nNOS was necessary for 12,13-diHOME’s beneficial effects on cardiac function [4]. This study found that ER stress and cardiac function didn’t improve following the 12,13-diHOME gene therapy in the nNOS-deficient mice, suggesting the beneficial effect on cardiac function is mediated by 12,13-diHOME.
The researchers also showed the critical role of Ca2+/calmodulin-dependent protein kinase II (CaMKII). CaMKII is known to be a mediator of ER stress, has been linked to cardiac dysfunction, and increases in the heart with aging [5, 6].
Mice with overexpressed 12,13-diHOME had reduced pCaMKII (activated CaMKII) in the hearts of male but not female mice. The authors suggest that reduced baseline pCaMKII levels in aged female but not aged male mice might be why this is ineffective in female mice.
Hyperactivation of CaMKII in primary murine fibroblasts led to reduced mitochondrial respiration and increased ER stress; however, adding 12,13-diHOME to the cells reversed those CaMKII-induced effects. Similar effects were observed in human fibroblasts. The authors concluded that “these data provide a mechanism for 12,13-diHOME to modulate CaMKII activity and ER stress in a model of aging.”
Overcoming limitations
Kristin Stanford, Ph.D., the leader of the group who conducted the study and a professor at the Department of Surgery at the Ohio State University College of Medicine and associate director of the Dorothy M. Davis Heart and Lung Research Institute, summarized: “One of the biggest things we see with aging is cardiovascular disease, which increases dramatically in patients who are over 65. Now we’re correlating it to a decrease in the lipokine 12,13-diHOME, and we’re showing directly that when we increase this lipokine that we can essentially rescue cardiac function.”
The results obtained in this study align with previous data showing significantly decreased levels of circulating 12,13-diHOME in male and female patients with cardiovascular disease compared to age-matched healthy people [4]. However, previous studies did not explore 12,13-diHOME’s therapeutic potential due to its short half-life. This study overcame this obstacle by using a non-viral gene therapy approach.
While it successfully improved cardiovascular health and function in both male and female aged mice, the mechanism behind 12,13-diHOME’s positive impact is sex-specific, and the researchers were only able to identify the mechanisms and molecular processes at play in males; future investigation into understanding its mechanics in females is necessary. Also, while current research showed promising results, it was done in mice; therefore, there is still a need for human testing.
Literature
[1] Nirengi, S., Buck, B., Das, D., Peres Valgas da Silva, C., Calyeca, J., Baer, L. A., Huang, H. L., Vidal, P., Dewal, R. S., Pinckard, K. M., Félix-Soriano, E., Hernandez-Saavedra, D., Gerea, A., Dathathreya, K., Duarte-Sanmiguel, S., Saldana, T. A., Hookfin, H. L., Gorr, M. W., Bussberg, V., Aristizabal-Henao, J. J., … Stanford, K. I. (2025). 12,13-diHOME protects against the age-related decline in cardiovascular function via attenuation of CaMKII. Nature communications, 16(1), 7088.
[2] Janczewski, A. M., & Lakatta, E. G. (2010). Modulation of sarcoplasmic reticulum Ca(2+) cycling in systolic and diastolic heart failure associated with aging. Heart failure reviews, 15(5), 431–445.
[3] Becher, T., Palanisamy, S., Kramer, D. J., Eljalby, M., Marx, S. J., Wibmer, A. G., Butler, S. D., Jiang, C. S., Vaughan, R., Schöder, H., Mark, A., & Cohen, P. (2021). Brown adipose tissue is associated with cardiometabolic health. Nature medicine, 27(1), 58–65.
[4] Pinckard, K. M., Shettigar, V. K., Wright, K. R., Abay, E., Baer, L. A., Vidal, P., Dewal, R. S., Das, D., Duarte-Sanmiguel, S., Hernández-Saavedra, D., Arts, P. J., Lehnig, A. C., Bussberg, V., Narain, N. R., Kiebish, M. A., Yi, F., Sparks, L. M., Goodpaster, B. H., Smith, S. R., Pratley, R. E., … Stanford, K. I. (2021). A Novel Endocrine Role for the BAT-Released Lipokine 12,13-diHOME to Mediate Cardiac Function. Circulation, 143(2), 145–159.
[5] Timmins, J. M., Ozcan, L., Seimon, T. A., Li, G., Malagelada, C., Backs, J., Backs, T., Bassel-Duby, R., Olson, E. N., Anderson, M. E., & Tabas, I. (2009). Calcium/calmodulin-dependent protein kinase II links ER stress with Fas and mitochondrial apoptosis pathways. The Journal of clinical investigation, 119(10), 2925–2941.
[6] McCluskey, C., Mooney, L., Paul, A., & Currie, S. (2019). Compromised cardiovascular function in aged rats corresponds with increased expression and activity of calcium/calmodulin dependent protein kinase IIδ in aortic endothelium. Vascular pharmacology, 118-119, 106560.
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