Gestational heat stress alters skeletal muscle gene expression profiles and vascularity in fetal pigs in a sexually dimorphic manner

Abstract

Background: There is evidence that sow heat stress (HS) during gestation affects fetal development with implications for impaired muscle growth. We have previously demonstrated that maternal HS during early to mid-gestation compromised muscle fibre hyperplasia in developing fetal pigs. Thus, we hypothesised these phenotypic changes are associated with a change in expression of genes regulating fetal skeletal muscle development and metabolism. To test this, at d 60 of gestation, RNA sequencing and immunohistochemistry were performed on fetal longissimus dorsi (LD) muscle biopsies collected from pregnant gilts that had experienced either thermoneutral control (CON, 20 °C, n = 7 gilts, 18 LD samples) or controlled HS (cyclic 28 to 33 °C, n = 8 gilts, 23 LD samples) conditions for 3 weeks.

Results: A total of 282 genes were differentially expressed between the HS and CON groups in female LD muscles (false discovery rate (FDR) ≤ 0.05), whereas no differentially expressed genes were detected in male LD muscles between the two groups (FDR > 0.05). Gestational HS increased the expression of genes associated with transcription corepressor activity, adipogenesis cascades, negative regulation of angiogenesis and pro-inflammatory signalling in female LD muscles. Immunohistochemical analyses revealed a decreased muscle vascularity density in fetuses from HS group for both sexes compared to those from the CON group (P = 0.004).

Conclusions: These results reveal gilt HS during early to mid-gestation altered gene expression profiles in fetal LD muscles in a sexually dimorphic manner. The molecular responses, including transcription and angiogenesis repressions and enhanced adipogenesis cascades, were exclusively observed in females. However, the associated reductions in muscle vascularity were observed independently of sexes. Collectively this may indicate female fetal pigs are more adaptive to gestational HS in terms of gene expression changes, and/or there may be sexually dimorphic differences with respect to the timing of muscle molecular responses to gestational HS.

Keywords: Adipogenesis; Angiogenesis; Fetal pig; Gestation; Heat stress; Sexual dimorphism; Skeletal muscle; Sows.

Fig. 1

Volcano plot of the differentially expressed genes (DEG) for the comparison of heat stress (HS, n =17) vs. control (CON, n = 10) in female fetal longissimus dorsi (LD) muscles at fetal d 60 age. Blue, red and grey dots denote downregulated (FDR (false discovery rate) ≤ 0.05), upregulated (FDR ≤ 0.05) and nondifferentially expressed (FDR > 0.05) genes in the HS group, respectively, compared to the CON group. The most up- and down-regulated genes by fold change are labelled

Fig. 2

Scatterplots of gene ontology (GO) terms significantly enriched (FDR ≤ 0.05) by the upregulated genes for the comparison of heat stress (HS, n = 17) vs. control (CON, n = 10) in female fetal longissimus dorsi (LD) muscles at fetal d 60 age for the GO domains of A biological process, B molecular function

Fig. 3

Scatterplots of gene ontology (GO: biological process) terms significantly enriched (FDR ≤ 0.05) by the downregulated genes for the comparison of heat stress (HS, n = 17) vs. control (CON, n = 10) in female fetal longissimus dorsi (LD) muscles at fetal d 60 age for the GO domain of biological process

Fig. 4

Photomicrographs of representative positive CD31 staining, the biomarker for blood vessel endothelium (examples indicated by red arrows), in fetal longissimus dorsi (LD) muscles of fetuses from the control (CON; A) or heat stress (HS; B) groups. CON: n = 14 LD samples, HS: n = 16 LD samples. Total magnification: 100×. Bars: 200 μm