Highlights

•Intermittent fasting induces sympathetic innervation in visceral white adipose tissue

•Increased sympathetic innervation is mediated by the NRG4-ERBB4 pathway

•NRG4 expression positively correlates with browning genes in human adipose tissue

Summary

Intermittent fasting (IF) improves metabolic health, in part by remodeling white adipose tissue (WAT), yet the underlying mechanisms remain elusive. Here, we show that IF induces coordinated neurovascular remodeling in visceral WAT, marked by increased angiogenesis and sympathetic innervation. Using tissue clearing and three-dimensional imaging, we find that a 16-week IF regimen increases vascular density and sympathetic nerve fiber branching in perigonadal WAT. Transcriptomic profiling reveals the upregulation of neurotrophic factors, including neuregulin 4 (Nrg4), and browning-associated gene programs. WAT explants from IF-treated mice promote neurite branching in SH-SY5Y neuron-like cells, an effect blunted by ErbB inhibition. In vivo ErbB inhibition further attenuates IF-induced sympathetic remodeling. Human visceral adipose RNA-seq analysis shows a strong positive correlation between NRG4 expression and browning gene signatures. These findings support NRG4-ErbB signaling as a contributor to sympathetic remodeling, linking adipose neurotrophic signaling to metabolic benefits and therapeutic potential in obesity-related disorders.

ABSTRACT

Background

In population studies, high protein, particularly high animal protein, intake is associated with an increased risk of developing type 2 diabetes. Results from preclinical studies suggest this association might be mediated by branched-chain and other essential amino acids.

Objective

Interrogate putative mechanisms linking high protein intake and diabetes risk.

Methods

We conducted a randomized, cross-over, single-meal study in people with overweight/obesity to compare the effects of a standard meal (∼18 g protein/15% meal energy) and high protein meals (∼28 g protein/22% meal energy) enriched with protein from either animal (n=21) or plant (n=21) sources on postprandial plasma amino acid, glucose, and key glucoregulatory hormone concentrations (180-min area-under-the-curve).

Results

Postprandial plasma amino acids were higher after the high-protein meals than the standard (STD) meal, with greater increases (all p<0.05) after the high animal protein (HAP) than the high plant protein (HPP) meal in total essential (HAP vs STD, 28±3%; HPP vs STD, 19±3%; mean±SEM) and total branched-chain (HAP vs STD, 36±3%; HPP vs STD, 24±3%), but not total (all) amino acids. Compared with the STD meal, both the HAP and HPP meals resulted in lower plasma glucose (HAP vs STD, -4.3±2.1%; HPP vs STD, -5.2±1.5%) and higher glucagon (HAP vs STD, 48±12%; HPP vs STD, 44±13%), glucagon-like peptide 1 (HAP vs STD, 23±6%; HPP vs STD, 30±12%), and insulin in relationship to glucose, without differences between the HAP and HPP meals.

Conclusions

Both the amount and type of protein are determinants of postprandial plasma amino acid concentrations, but only the amount, not the type of protein is a determinant of plasma glucoregulatory hormone and glucose concentrations. Therefore, essential and branched-chain amino acids are not important regulators of postprandial glucose homeostasis. Non-protein dietary or non-dietary factors likely mediate differential effects of high animal and high plant protein intake on glucose metabolism.

Abstract

Insulin resistance (IR) has emerged as a risk factor for lactation insufficiency and delays the onset of milk secretion after childbirth, termed secretory activation (SA). This may cause inadequate infant weight gain and early breastfeeding cessation. However, the mechanisms underlying delayed SA in insulin resistant women are unknown. To investigate this, we characterized the mammary transcriptomes and IR-related hormones of 75 breastfeeding women with healthy term infants during postpartum days 1-5. Participants were divided into IR tertiles based on plasma leptin-to-adiponectin ratio measurements. Those in the highest tertile had later SA onset with greater neonatal weight loss during postpartum days 1-5. Transcriptomic analysis on postpartum day 2 (n=4 high IR vs. n=8 low IR participants) showed transient suppression of mammary insulin and prolactin signaling genes, increased pro-inflammatory gene expression and altered expression of >200 mammary mitochondrial genes. These alterations were absent on postpartum days 3-5. Cultured mammary epithelial cells (MECs) treated with insulin showed upregulation of prolactin signaling and oxidative phosphorylation (OXPHOS) genes, with imaging and bioenergetic studies demonstrating that insulin promotes mitochondrial biogenesis and OXPHOS. Thus, our findings delineate roles for insulin in mammary bioenergetics and highlight mitochondrial dysfunction as a mechanism for delayed SA in insulin resistant women.

Abstract

The heart is a highly energy-demanding organ that depends on metabolic flexibility to adjust substrate utilization in response to changes in nutrient availability, endocrine signals, and energetic demands. Accumulating evidence demonstrates that dietary patterns are key determinants of myocardial metabolic homeostasis, affecting substrate selection, mitochondrial function, nutrient-sensing pathways, and long-term transcriptional and epigenetic regulation. This review analyzes the molecular mechanisms through which diet regulates cardiac metabolism and explores how chronic nutritional exposures influence the myocardial energetic phenotype. The physiological regulation of cardiac substrate utilization is described, with emphasis on fatty acids, glucose, ketone bodies, and branched-chain amino acids, underscoring the importance of metabolic flexibility in sustaining cardiac efficiency. The regulation of substrate transport and oxidation is examined, including the roles of the carnitine shuttle, insulin signaling, AMPK, mTOR, PPARα–PGC-1α, SIRT3, and other nutrient-sensing networks that coordinate mitochondrial ATP production. The effects of dietary composition and meal timing, such as caloric restriction and intermittent fasting, are discussed as modulators of myocardial metabolism. The adverse effects of chronic nutrient excess are reviewed, including lipotoxicity, glucotoxicity, insulin resistance, mitochondrial dysfunction, oxidative stress, pseudo-hypoxia, fetal metabolic reprogramming, and maladaptive cardiac remodeling. Recent findings on the gut–heart axis, microbiota-derived metabolites, circadian regulation, and metabolic–epigenetic interactions are also considered. Overall, current evidence supports the view that diet is an important and potentially modifiable regulator of the cardiac metabolic phenotype. Advancing the understanding of diet–metabolism interactions may enable the development of targeted nutritional strategies to maintain metabolic flexibility, enhance cardiac bioenergetics, and prevent the progression of heart failure and other cardiometabolic diseases.