RÉSUMÉ
Intrauterine growth-restricted (IUGR) fetuses exhibit systemic inflammation that contributes to programmed deficits in myoblast function and muscle growth. Thus, we sought to determine if targeting fetal inflammation improves muscle growth outcomes. Heat stress-induced IUGR fetal lambs were infused with eicosapentaenoic acid (IUGR+EPA; n = 9) or saline (IUGR; n = 8) for 5 days during late gestation and compared to saline-infused controls (n = 11). Circulating eicosapentaenoic acid was 42% less (p < 0.05) for IUGR fetuses but was recovered in IUGR+EPA fetuses. The infusion did not improve placental function or fetal O2 but resolved the 67% greater (p < 0.05) circulating TNFα observed in IUGR fetuses. This improved myoblast function and muscle growth, as the 23% reduction (p < 0.05) in the ex vivo differentiation of IUGR myoblasts was resolved in IUGR+EPA myoblasts. Semitendinosus, longissimus dorsi, and flexor digitorum superficialis muscles were 24-39% lighter (p < 0.05) for IUGR but not for IUGR+EPA fetuses. Elevated (p < 0.05) IL6R and reduced (p < 0.05) ß2 adrenoceptor content in IUGR muscle indicated enhanced inflammatory sensitivity and diminished ß2 adrenergic sensitivity. Although IL6R remained elevated, ß2 adrenoceptor deficits were resolved in IUGR+EPA muscle, demonstrating a unique underlying mechanism for muscle dysregulation. These findings show that fetal inflammation contributes to IUGR muscle growth deficits and thus may be an effective target for intervention.
RÉSUMÉ
Background: Intrauterine growth restriction (IUGR) is associated with reduced ß2 adrenergic sensitivity, which contributes to poor postnatal muscle growth. The objective of this study was to determine if stimulating ß2 adrenergic activity postnatal would rescue deficits in muscle growth, body composition, and indicators of metabolic homeostasis in IUGR offspring. Methods: Time-mated ewes were housed at 40°C from day 40 to 95 of gestation to produce IUGR lambs. From birth, IUGR lambs received daily IM injections of 0.8 µg/kg clenbuterol HCl (IUGR+CLEN; n = 11) or saline placebo (IUGR; n = 12). Placebo-injected controls (n = 13) were born to pair-fed thermoneutral ewes. Biometrics were assessed weekly and body composition was estimated by ultrasound and bioelectrical impedance analysis (BIA). Lambs were necropsied at 60 days of age. Results: Bodyweights were lighter (p ≤ 0.05) for IUGR and IUGR+CLEN lambs than for controls at birth, day 30, and day 60. Average daily gain was less (p ≤ 0.05) for IUGR lambs than controls and was intermediate for IUGR+CLEN lambs. At day 58, BIA-estimated whole-body fat-free mass and ultrasound-estimated loin eye area were less (p ≤ 0.05) for IUGR but not IUGR+CLEN lambs than for controls. At necropsy, loin eye area and flexor digitorum superficialis muscles were smaller (p ≤ 0.05) for IUGR but not IUGR+CLEN lambs than for controls. Longissimus dorsi protein content was less (p ≤ 0.05) and fat-to-protein ratio was greater (p ≤ 0.05) for IUGR but not IUGR+CLEN lambs than for controls. Semitendinosus from IUGR lambs had less (p ≤ 0.05) ß2 adrenoreceptor content, fewer (p ≤ 0.05) proliferating myoblasts, tended to have fewer (p = 0.08) differentiated myoblasts, and had smaller (p ≤ 0.05) muscle fibers than controls. Proliferating myoblasts and fiber size were recovered (p ≤ 0.05) in IUGR+CLEN lambs compared to IUGR lambs, but ß2 adrenoreceptor content and differentiated myoblasts were not recovered. Semitendinosus lipid droplets were smaller (p ≤ 0.05) in size for IUGR lambs than for controls and were further reduced (p ≤ 0.05) in size for IUGR+CLEN lambs. Conclusion: These findings show that clenbuterol improved IUGR deficits in muscle growth and some metabolic parameters even without recovering the deficit in ß2 adrenoreceptor content. We conclude that IUGR muscle remained responsive to ß2 adrenergic stimulation postnatal, which may be a strategic target for improving muscle growth and body composition in IUGR-born offspring.
RÉSUMÉ
Heat stress (HS) triggers oxidative stress, systemic inflammation, and disrupts growth efficiency of livestock. ß-adrenergic agonists supplemented to ruminant livestock improve growth performance, increase skeletal muscle mass, and decrease carcass fat. The objective of this study was to understand the independent and interacting effects of HS and zilpaterol hydrochloride (ZH) supplementation on the transcriptome of subcutaneous white adipose tissue and the longissimus dorsi muscle in steers. Twenty-four Red Angus-based steers were assigned to thermoneutral (TN; Temperature Humidity Index [THI] = 68) or HS (THI = 73-85) conditions and were not supplemented or supplemented with ZH (8.33 mg/kg/d) for 21 d in a 2 × 2 factorial. Steers in the TN condition were pair-fed to the average daily feed intake of HS steers. RNA was isolated from adipose tissue and skeletal muscle samples collected via biopsy on 3, 10, and 21 d and sequenced using 3' Tag-Seq to an achieved average depth of 3.6 million reads/sample. Transcripts, mapped to ARS-UCD1.2, were quantified. Differential expression (DE) analyses were performed in DESeq2 with a significance threshold for false discovery rate of 0.05. In adipose, 4 loci (MISP3, APOL6, SLC25A4, and S100A12) were DE due to ZH on day 3, and 2 (RRAD, ALB) were DE due to the interaction of HS and ZH on day 10 (Padj < 0.05). In muscle, 40 loci (including TENM4 and OAZ1) were DE due to ZH on day 10, and 6 loci (HIF1A, LOC101903734, PDZD9, HNRNPU, MTUS1, and TMCO6) were DE due to environment on day 21 (Padj < 0.05). To explore biological pathways altered by environment, supplement, and their interaction, loci with DE (Praw < 0.05) were evaluated in Ingenuity Pathway Analysis. In adipose, 509 pathways were predicted to be altered (P < 0.01): 202 due to HS, 126 due to ZH, and 181 due to the interaction; these included inflammatory pathways predicted to be upregulated due to HS but downregulated due to the interaction of HS and ZH. In muscle, 113 pathways were predicted to be altered (P < 0.01): 23 due to HS, 66 due to ZH, and 24 due to the interaction of HS and ZH. Loci and pathway data in muscle suggest HS induced oxidative stress and that the stress response was moderated by ZH. Metabolic pathways were predicted to be altered due to HS, ZH, and their interaction in both tissues. These data provide evidence that HS and ZH interact to alter expression of genes in metabolic and immune function pathways and that ZH moderates some adverse effects of HS.
Heat stress (HS) negatively impacts livestock health and carcass quality. Supplementation of livestock with ß-adrenergic agonists (ß-AA) increases muscle mass and decreases fat deposition. The purpose of this study was to understand how HS and zilpaterol hydrochloride (ZH), a ß-AA, alter gene expression in muscle and in adipose of cattle. Twenty-four steers were assigned to thermoneutral (TN) or HS conditions and were not supplemented (NS) or supplemented with ZH for 21 d. RNA was isolated from muscle and adipose collected on days 3, 10, and 21 to identify changes in gene expression. Several individual loci were differentially expressed (DE) due to HS or ZH in both tissues while the interaction of HS and ZH altered expression in adipose. A less stringent definition of DE used to explore biological pathways predicted that both treatments alter metabolism. Pathway analyses also supported that HS increased inflammation in adipose, but that these inflammatory pathways were downregulated by ZH. HS also was predicted to induce oxidative stress in muscle although ZH moderated this response. This study provides information on how HS and ß-AA act independently and interact to alter physiology, lending insight useful for the development of management and mitigation strategies for stress.