Characteristics of glucose and lipid metabolism and the interaction between gut microbiota and colonic mucosal immunity in pigs during cold exposure

Abstract

Background: Cold regions have long autumn and winter seasons and low ambient temperatures. When pigs are unable to adjust to the cold, oxidative damage and inflammation may develop. However, the differences between cold and non-cold adaptation regarding glucose and lipid metabolism, gut microbiota and colonic mucosal immunological features in pigs are unknown. This study revealed the glucose and lipid metabolic responses and the dual role of gut microbiota in pigs during cold and non-cold adaptation. Moreover, the regulatory effects of dietary glucose supplements on glucose and lipid metabolism and the colonic mucosal barrier were evaluated in cold-exposed pigs.

Results: Cold and non-cold-adapted models were established by Min and Yorkshire pigs. Our results exhibited that cold exposure induced glucose overconsumption in non-cold-adapted pig models (Yorkshire pigs), decreasing plasma glucose concentrations. In this case, cold exposure enhanced the ATGL and CPT-1α expression to promote liver lipolysis and fatty acid oxidation. Meanwhile, the two probiotics (Collinsella and Bifidobacterium) depletion and the enrichment of two pathogens (Sutterella and Escherichia-Shigella) in colonic microbiota are not conducive to colonic mucosal immunity. However, glucagon-mediated hepatic glycogenolysis in cold-adapted pig models (Min pigs) maintained the stability of glucose homeostasis during cold exposure. It contributed to the gut microbiota (including the enrichment of the Rikenellaceae RC9 gut group, [Eubacterium] coprostanoligenes group and WCHB1-41) that favored cold-adapted metabolism.

Conclusions: The results of both models indicate that the gut microbiota during cold adaptation contributes to the protection of the colonic mucosa. During non-cold adaptation, cold-induced glucose overconsumption promotes thermogenesis through lipolysis, but interferes with the gut microbiome and colonic mucosal immunity. Furthermore, glucagon-mediated hepatic glycogenolysis contributes to glucose homeostasis during cold exposure.

Keywords: Cold exposure; Colonic mucosal immunity; Fatty acid oxidation; Glucose and lipid metabolism; Gut microbiota; Pig model.

Fig. 1

Effects of cold exposure on glucose and lipid metabolism, colonic microbiota and colonic mucosal immunity in Min pigs and Yorkshire pigs

Fig. 2

Development of cold-adaptive and non-cold-adaptive models, and plasma metabolic parameters during cold exposure. A Plasma glucose of Min pig models. n = 6. B Plasma glucose of Yorkshire pig models. n = 6. C Plasma hormones in Min pig models. n = 6. D Plasma hormones in Yorkshire pig models. n = 6. E Volcanic map of metabolic differences in positive ion mode of Min pigs. n = 5. F Volcanic map of metabolic differences in negative ion mode of Min pigs. n = 5. G KEGG analysis of plasma metabolites of Min pigs. ^*P < 0.05. Other factors without significant changes are shown in Fig. S1

Fig. 3

Large amounts of glucose are consumed during cold exposure. A–C Pyruvate kinase (PK), pyruvate carboxylase (PC) and glucose-6-phosphate kinase (G6PC) concentration in the liver of Min pigs. n = 6. D Glycogen phosphorylase (PYGL) activity in the liver of Min pigs. n = 6. E–G PK, PC and G6PC concentration in the liver of Yorkshire pigs. n = 6. H PYGL activity in the liver of Yorkshire pigs. n = 6. I Glucose transport and glycolysis in the longissimus dorsi muscle of Min pigs. n = 6. J GLUT1 protein expression in the longissimus dorsi muscle of Min pigs. n = 4. K Glucose transport and glycolysis in the longissimus dorsi muscle of Yorkshire pigs. n = 6. L GLUT1 protein expression in the longissimus dorsi muscle of Yorkshire pigs. n = 4. ^*P < 0.05. Other factors without significant changes are shown in Fig. S2

Fig. 4

Effects of chronic cold exposure on colonic microbiota of Min pigs. A Colonic microbiota diversity index of Min pigs. B PCoA analysis of colonic microbiota in Min pigs. C Phylum level of colonic microbiota in Min pigs. D Firmicutes, Bacteroidetes and Verrucomicrobiota abundance in Min pigs. E Genus level of colonic microbiota in Min pigs. n = 6. ^*P < 0.05. ^**P < 0.05

Fig. 5

Effects of chronic cold exposure on colonic microbiota of Yorkshire pigs. A Phylum level of colonic microbiota in Yorkshire pigs. B PCoA analysis of colonic microbiota in Yorkshire pigs. C Heat map of genus level abundance. D Colonic microbiota diversity index of Yorkshire pigs. E Genus level of colonic microbiota in Yorkshire pigs. F Two genera depletion in Actinobacteria of Yorkshire pigs. G Two genera of Proteobacteria are enriched. n = 6. ^*P < 0.05, ^**P < 0.01

Fig. 6

Chronic cold exposure induces colonic barrier injury and mitochondrial dysfunction in Yorkshire pigs. A Pathological sections and ultrastructure of the colon of Yorkshire pigs. The arrows show the infiltration of inflammatory cells. B The mRNA expression of inflammatory cytokines and antimicrobial peptides in colon mucosa of Yorkshire pigs. n = 6. C The mRNA expression of tight junction proteins, inflammatory pathways, apoptosis and mitophagy related genes in colon mucosa of Yorkshire pigs. n = 6. D Protein expression in the colon mucosa of Yorkshire pigs. n = 4. E Correlation coefficients between mucus layer, inflammatory response, and epithelial barrier. Correlation coefficients > 0.5 or ≤ 0.5. Orange and blue colors denote positive and negative correlations, respectively. Color intensity is proportional to Spearman’s rank correlation values. n = 6. ^*P < 0.05. Other factors without significant changes are shown in Fig. S4

Fig. 7

Excessive glucose consumption induced by cold exposure promotes lipolysis and fatty acid oxidation. A The mRNA expression of fat metabolism related genes in the liver of Min pigs. B The mRNA expression of fat metabolism related genes in the liver of Yorkshire pigs. C and D CPT-1α and ATGL protein expression in the liver of Yorkshire pigs. E Correlation coefficients between plasma glucose, mucus layer, inflammatory response, epithelial barrier and microbiota. Correlation coefficients > 0.5 or ≤ 0.5. Pink and blue colors denote positive and negative correlations, respectively. Color intensity is proportional to Spearman’s rank correlation values. n = 6. ^*P < 0.05. ^**P < 0.01

Fig. 8

Provide adequate glucose during cold exposure regulated glucose metabolism, lipid metabolism and colonic mucosal immunity in Yorkshire pigs. A–C Plasma hormone levels, n = 6. D Glycogen phosphorylase (PYGL) activity in the liver, n = 6. E Glycolysis and gluconeogenesis in the liver, n = 6. F Fat metabolism in the liver, n = 6. G Colonic mucosal immunity and mitochondrial function, n = 6. H Pathological sections of the colonic mucosa of a Yorkshire pig (n = 3). I ATGL and CPT-1α protein expression in the liver, n = 4. J Mature-IL-1β, Bax and Bcl2 protein expression in the colonic mucosa, n = 4. ^*P < 0.05, ^**P < 0.01

Fig. 9

Cold-induced glucose overconsumption drives lipolysis but interferes with the gut microbiota. We delineate the importance of glucagon-mediated hepatic glycogenolysis for glucose homeostasis during cold exposure by using Min pig (cold-adapted) models and Yorkshire pig (non-cold-adapted) models. Moreover, we reveal that lipolysis and fatty acid oxidation under chronic cold exposure result from excessive glucose consumption. It should be particularly emphasized that cold-induced glucose overconsumption is detrimental to colonic microbiota and mucosal immunity, although lipolysis and fatty acid oxidation contribute to thermogenesis to maintain a stable internal body temperature