# High-intensity intermittent training promotes adipose tissue browning via the IL-27/p38 MAPK–PGC-1α signaling pathway in diet-induced obese rats

## TL;DR

High-intensity intermittent training (HIIT) activates a specific signaling pathway in obese rats, promoting fat tissue transformation and improving metabolic health better than moderate exercise.

## Contribution

This study reveals that HIIT activates the IL-27/p38 MAPK–PGC-1α pathway to induce adipose tissue browning more effectively than moderate-intensity training.

## Key findings

- HIIT significantly reduced plasma triglyceride levels and adipose mass compared to moderate-intensity training.
- HIIT increased browning-related genes and UCP1 in adipose tissue more than moderate-intensity training.
- HIIT elevated IL-27 signaling and p38 MAPK–PGC-1α pathway activation in both plasma and adipose tissue.

## Abstract

This study investigated the effects of high-intensity intermittent training (HIIT) versus moderate-intensity aerobic training (MAIT) on IL-27 signalling and adipose tissue browning in obese rats.

Forty male Sprague–Dawley rats were randomly divided into two groups: standard diet (C, n = 10) and high-fat diet (HFD, n = 30). After 8 weeks of HFD feeding, 24 obese rats were further randomised into three subgroups: HFD (H, n = 8), HFD + moderate-intensity training (HMT, n = 8), and HFD + HIIT (HHT, n = 8). The HMT and HHT groups underwent 8 week training interventions (six sessions/week). The HMT protocol included a 10 min warm-up (treadmill speed: 10 m/min), a 40 min moderate-intensity aerobic phase (60%–70% of maximum speed), and a 10 min recovery (10 m/min). The HHT protocol featured 10 min warm-up and recovery phases (10 m/min), with 40 min of alternating treadmill training: 3 min at 50% maximum speed followed by 3 min at 90% maximum speed.

No significant differences in body weight were observed between the HHT and HMT groups. HHT rats displayed significantly lower plasma triglyceride levels than H and HMT rats. Compared with HMT, HHT reduced adipose mass and adipocyte size and increased mitochondrial succinate dehydrogenase and cytochrome c oxidase (COX) activities in adipose tissue. However, HHT rats displayed lower COX activity in visceral white adipose tissue than HMT rats. Training upregulated browning-related genes and uncoupling protein 1 (UCP1) in adipose tissue, with stronger effects in HHT than in HMT. Plasma and adipose tissue IL-27 levels, as well as p38 MAPK–PGC-1α signalling pathway activation, were significantly elevated in both training groups, with greater increases in HHT.

HIIT promotes adipose tissue browning by activating the IL-27 signalling pathway and ameliorates obesity-associated metabolic disorders more effectively than MAIT, supporting its potential as a therapeutic strategy for obesity.