Lower Ceremide Levels in Aged GHRH Knockout Mice

GHRH knockout mice are one of the longest-lived lineages. It remains the case that disrupted growth hormone signaling extends life to a greater degree than any of the other interventions tested in mice. The equivalent Laron syndrome population in humans clearly doesn't experience the same sizable extension of life span, however. This should perhaps tell us that researchers must look elsewhere for approaches to the treatment of aging in long-lived mammals. The most well studied approaches to extend healthy life span in mice, meaning calorie restriction and disruption of growth hormone signaling, do not improve human life span to anywhere near the same degree.

Dysregulation of growth hormone (GH) signaling consistently leads to increased lifespan in laboratory rodents, yet the precise mechanisms driving this extension remain unclear. Understanding the molecular underpinnings of the beneficial effects associated with GH deficiency could unveil novel therapeutic targets for promoting healthy aging and longevity. In our pursuit of identifying metabolites implicated in aging, we conducted an unbiased lipidomic analysis of serum samples from growth hormone-releasing hormone knockout (GHRH-KO) female mice and their littermate controls.

Employing a targeted lipidomic approach, we specifically investigated ceramide levels in GHRH-KO mice, a well-established model of enhanced longevity. While younger GHRH-KO mice did not exhibit notable differences in serum lipids, older counterparts demonstrated significant reductions in over one-third of the evaluated lipids. In employing the same analysis in liver tissue, GHRH-KO mice showed pronounced downregulation of numerous ceramides and hexosylceramides, which have been shown to elicit many of the tissue defects that accompany aging (e.g., insulin resistance, oxidative stress, and cell death). Additionally, gene expression analysis in the liver tissue of adult GHRH-KO mice identified substantial decreases in several ceramide synthesis genes, indicating that these alterations are, at least in part, attributed to GHRH-KO-induced transcriptional changes.

These findings provide the first evidence of disrupted ceramide metabolism in a long-lived mammal. This study sheds light on the intricate connections between GH deficiency, ceramide levels, and the molecular mechanisms influencing lifespan extension.

Link: https://doi.org/10.1111/acel.14226

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