Research highlights: Regulation of adipose tissue lipolysis by ghrelin is impaired with high-fat diet feeding and is not restored with exercise

Ghrelin, often referred to as the “hunger hormone,” is known for its role in stimulating appetite. However, recent research has expanded its profile, showing that ghrelin also influences how the body manages fat, particularly in white adipose tissue (WAT). A new study from the University of Guelph explores how high-fat diets (HFDs) affect ghrelin’s ability to regulate fat breakdown, or lipolysis, and whether exercise can restore this function. This research is particularly relevant for understanding obesity, metabolic health, and the hormonal regulation of fat metabolism.

Overview

The study aimed to determine whether short-term (5 days) or long-term (6 weeks) consumption of a high-fat diet impairs ghrelin’s ability to regulate lipolysis in WAT. Researchers also investigated whether a structured exercise program could reverse any observed impairments. Understanding these mechanisms could help clarify how dietary habits and physical activity influence fat metabolism and hormonal sensitivity.

Key findings

The researchers used an ex vivo adipose tissue organ culture (ATOC) model to isolate the effects of ghrelin on fat tissue. They focused on two forms of ghrelin: acylated ghrelin (AG) and unacylated ghrelin (UnAG). Both forms have been shown to reduce lipolysis under normal dietary conditions.

Key findings include:

In rats fed a low-fat diet for 5 days, AG significantly reduced lipolysis in inguinal WAT, as measured by glycerol and free fatty acid release.
This anti-lipolytic effect was lost in rats fed a high-fat diet for either 5 days or 6 weeks.
Exercise training over 4 weeks did not restore ghrelin’s ability to regulate lipolysis in WAT.
The loss of ghrelin sensitivity was not linked to changes in hormone-sensitive lipase (HSL) phosphorylation, a key enzyme in fat breakdown.
Ghrelin receptor (GHS-R1) expression was reduced in WAT after high-fat feeding but increased with exercise, although this did not translate into restored function.

These results suggest that high-fat diets can induce a form of ghrelin resistance in fat tissue, and that exercise alone may not be sufficient to reverse this effect.

Abcam's antibody ab16056 was used to measure COXIV protein levels, a marker of mitochondrial activity and exercise adaptation in muscle tissue.

Implications

This research provides new insights into how dietary fat intake can alter hormonal regulation of fat metabolism. The findings suggest that even short-term exposure to a high-fat diet can impair ghrelin’s ability to suppress lipolysis, potentially contributing to elevated circulating fatty acids and metabolic dysfunction. The inability of exercise to restore this function highlights the complexity of hormonal resistance and suggests that additional interventions may be needed to fully reverse diet-induced changes in fat tissue.

These insights could inform future strategies for managing obesity and metabolic diseases by targeting hormonal pathways in adipose tissue.

Future work

The study opens several avenues for future research:

Investigating the molecular mechanisms behind ghrelin resistance in WAT, including downstream signaling pathways beyond HSL.
Exploring whether dietary modifications, pharmacological agents, or longer-term exercise interventions can restore ghrelin sensitivity.
Examining the role of age and body weight in ghrelin function, as the study observed a loss of ghrelin’s effects even in older rats on a low-fat diet.
Studying how different macronutrient compositions, such as sugar content, influence ghrelin’s metabolic effects.

These directions could help develop more targeted approaches to improve metabolic health and hormonal regulation in individuals with obesity or insulin resistance.

References