Growth factor messenger ribonucleic acid expression during differentiation of porcine embryonic myogenic cells

Notch signaling leads to a slower progression of embryonic myogenic differentiation in Landrace than in Langtang pigs

Delving into porcine embryonic myogenesis is the key to elucidate the complex regulation of breed-specific differences in growth performance and meat production. Increasing evidence proves that pigs with less meat production show earlier embryonic myogenesis, but little is known about the underlying mechanisms. In this study, we examine the longissimus dorsi muscle (LDM) by immunohistochemistry and confirm that the differentiation of myogenic progenitors is increased ( P<0.05) in Lantang (LT, fatty) pigs compared with that in Landrace (LR, lean) pigs, which results in more ( P<0.001) differentiated myoblasts (Pax7 ^-/MyoD ⁺) and less ( P<0.001) myogenic progenitors (Pax7 ⁺/MyoD ^-) in LT pigs at 35 days post-conception (35dpc). Additionally, embryonic myogenic progenitors isolated from LT pigs show greater ( P<0.001) differentiation capacity with earlier expression of MyoD compared with those from LR pigs. Moreover, Notch signaling is more active ( P<0.05) in LR pig myogenic progenitors than in LT pig myogenic progenitors. Inhibition of Notch signaling in LR myogenic progenitors suppresses Pax7 expression and increases MyoD expression, thus promoting myogenic differentiation. Consistently, the process of myogenic progenitors differentiating into myoblasts in ex vivo embryo limbs is accelerated when Notch signaling is inhibited. These results indicate that Notch signaling facilitates the maintenance of myogenic progenitors and antagonizes myogenic differentiation by promoting Pax7 expression and preventing MyoD expression in LR pigs.

Impact of genotype, body weight and sex on the prenatal muscle transcriptome of Iberian pigs

Growth is dependent on genotype and diet, even at early developmental stages. In this study, we investigated the effects of genotype, sex, and body weight on the fetal muscle transcriptome of purebred Iberian and crossbred Iberian x Large White pigs sharing the same uterine environment. RNA sequencing was performed on 16 purebred and crossbred fetuses with high body weight (340±14g and 415±14g, respectively) and 16 with low body weight (246±14g and 311±14g, respectively), on gestational day 77. Genotype had the greatest effect on gene expression, with 645 genes identified as differentially expressed (DE) between purebred and crossbred animals. Functional analysis showed differential regulation of pathways involved in energy and lipid metabolism, muscle development, and tissue disorders. In purebred animals, fetal body weight was associated with 35 DE genes involved in development, lipid metabolism and adipogenesis. In crossbred animals, fetal body weight was associated with 60 DE genes involved in muscle development, viability, and immunity. Interestingly, the results suggested an interaction genotype*weight for some DE genes. Fetal sex had only a modest effect on gene expression. This study allowed the identification of genes, metabolic pathways, biological functions and regulators related to fetal genotype, weight and sex, in animals sharing the same uterine environment. Our findings contribute to a better understanding of the molecular events that influence prenatal muscle development and highlight the complex interactions affecting transcriptional regulation during development.

Increased expressions of genes and proteins involved in mitochondrial oxidation and antioxidant pathway in adipose tissue of pigs selected for a low residual feed intake

Adipose tissue is a primary sensor for nutrient availability and regulates many functions including feed intake and energy homeostasis. This study was undertaken to determine the molecular responses of adipose tissue to differences in feed intake and feed efficiency. Subcutaneous adipose tissue was collected from two lines of pigs divergently selected for residual feed intake (RFI), a measure of feed efficiency defined as the difference between actual and expected feed intake, and from a subset of high-RFI pigs that were feed-restricted at the level of the voluntary feed intake of low-RFI pigs during the growing-finishing period. Transcriptomics analyses indicated that the number of genes that were differentially expressed ( < 0.01) between low- and high-RFI pigs ( = 8 per group at each stage) in adipose tissue was much lower when pigs were considered at 19 kg (postweaning) than at 115 kg BW (market weight). Extended investigations were performed at 115 kg BW to compare low-RFI ( = 8), high-RFI ( = 8), and feed-restricted high-RFI ( = 8) pigs. They included in silico pathway analyses of the differentially expressed (DE) genes ( < 0.01) and a complementary proteomic investigation to list adipose proteins with a differential abundance ( < 0.10). Only 23% of the DE genes were affected by both RFI and feed restriction. This indicates that the responses of adipose tissue to RFI difference shared only some common mechanisms with feed intake modulation, notably the regulation of cell cycle (including ) and transferase activity pathway. Two carboxylesterase genes (, ) involved in lipolysis, were among the most overexpressed genes in the low-RFI pigs; they were also affected by feed restriction within the high-RFI line. About 60% of the molecular changes between low- and high-RFI pigs were specific to genetic divergence in feed efficiency, independently of feed intake. Different genes and proteins known to be associated with mitochondrial oxidative metabolism were overexpressed in adipose tissue of low-RFI pigs compared with high-RFI pigs; other proteins participating in the generation of energy were also affected by feed restriction within the high-RFI line. Finally, mitochondrial antioxidant genes were upregulated in low-RFI pigs vs. high-RFI pigs. Altogether, increased oxidative and antioxidant processes in adipose tissue might be associated with improved feed efficiency.

Allogeneic CD4+CD25high T cells regulate obliterative bronchiolitis of heterotopic bronchus allografts in both porcinized and humanized mouse models

BACKGROUND

Bronchiolitis obliterans syndrome is caused by a fibroproliferative process in lung allografts resulting in irreversible damage. In this study, we induced obliterative bronchiolitis and studied the contribution of regulatory T cells to its development in immune-deficient mice receiving heterotopic porcine bronchus transplants, and major histocompatibility complex-mismatched porcine peripheral blood mononuclear cell. Furthermore, we aimed to corroborate our findings in a humanized mouse model.

METHODS

Heterotopic bronchus transplantation was performed in 33 NOD.rag(−/−)γc(−/−) mice, using miniature pigs as tissue donors.The recipient mice then either received saline (negative control), unsorted MHC-mismatched PBMC (positive control), PBMC enriched with CD4(+)CD25(high) cells or PBMC depleted of CD4(+)CD25(high) cells for reconstitution. The results were validated in 28 NOD.rag(−/−)γc(−/−) mice undergoing heterotopic human bronchus transplantation and reconstitution with allogeneic human PBMC.

RESULTS

Histological lesions similar to those typical for obliterative bronchiolitis developed in vivo after reconstitution with allogeneic PBMC and were more severe in animals engrafted with PBMC depleted of CD4(+)CD25(high) cells. In contrast, the group reconstituted with PBMC enriched with CD4(+)CD25(high) cells showed well-preserved histology. The results of the humanized model confirmed those obtained in the porcinized model.

CONCLUSIONS

In conclusion, both porcinized and humanized mouse models of heterotopic subcutaneous bronchus transplantation imitate the in vivo development of bronchiolitis obliterans syndrome-like lesions and reveal its sensitivity to T-cell regulation.

Lean and obese pig breeds exhibit differences in prenatal gene expression profiles of muscle development

Muscle development in domesticated animals is important for meat production. Furthermore, intramuscular fat content is an important trait of meat intended for consumption. Here, we examined differences in the expression of factors related to myogenesis, adipogenesis and skeletal muscle growth during fetal muscle development of lean (Yorkshire) and obese (Chenghua) pig breeds. At prenatal days 50 (d50) and 90 (d90), muscles and sera were collected from pig fetuses. Histology revealed larger diameters and numbers of myofibers in Chenghua pig fetuses than those in Yorkshire pig fetuses at d50 and d90. Yorkshire fetuses had higher serum concentrations of myostatin (d90), a negative regulator for muscle development, and higher mRNA expression of the growth hormone receptor Ghr (d90), myogenic MyoG (d90) and adipogenic LPL (d50). By contrast, Chenghua fetuses exhibited higher serum concentration of growth hormone (d90), and higher mRNA expression of myogenic MyoD (d90) as well as adipogenic PPARG and FABP4 (d50). Our results revealed distinct expression patterns in the two pig breeds at each developmental stage before birth. Compared with Chenghua pigs, development and maturation of fetal skeletal muscles may occur earlier in Yorkshire pigs, but the negative regulatory effects of myostatin may suppress muscle development at the later stage.

Negative auto-regulation of myostatin expression is mediated by Smad3 and microRNA-27

Growth factors, such as myostatin (Mstn), play an important role in regulating post-natal myogenesis. In fact, loss of Mstn has been shown to result in increased post-natal muscle growth through enhanced satellite cell functionality; while elevated levels of Mstn result in dramatic skeletal muscle wasting through a mechanism involving reduced protein synthesis and increased ubiquitin-mediated protein degradation. Here we show that miR-27a/b plays an important role in feed back auto-regulation of Mstn and thus regulation of post-natal myogenesis. Sequence analysis of Mstn 3' UTR showed a single highly conserved miR-27a/b binding site and increased expression of miR-27a/b was correlated with decreased expression of Mstn and vice versa both in vitro and in mice in vivo. Moreover, we also show that Mstn gene expression was regulated by miR-27a/b. Treatment with miR-27a/b-specific AntagomiRs resulted in increased Mstn expression, reduced myoblast proliferation, impaired satellite cell activation and induction of skeletal muscle atrophy that was rescued upon either blockade of, or complete absence of, Mstn. Consistent with this, miR-27a over expression resulted in reduced Mstn expression, skeletal muscle hypertrophy and an increase in the number of activated satellite cells, all features consistent with impaired Mstn function. Loss of Smad3 was associated with increased levels of Mstn, concomitant with decreased miR-27a/b expression, which is consistent with impaired satellite cell function and muscular atrophy previously reported in Smad3-null mice. Interestingly, treatment with Mstn resulted in increased miR-27a/b expression, which was shown to be dependent on the activity of Smad3. These data highlight a novel auto-regulatory mechanism in which Mstn, via Smad3 signaling, regulates miR-27a/b and in turn its own expression. In support, Mstn-mediated inhibition of Mstn 3' UTR reporter activity was reversed upon miR-27a/b-specific AntagomiR transfection. Therefore, miR-27a/b, through negatively regulating Mstn, plays a role in promoting satellite cell activation, myoblast proliferation and preventing muscle wasting.

Expression of the insulin-like growth factor system in skeletal muscle during embryonic and postnatal development in the first filial generation pigs from Erhualian and Yorkshire reciprocal crosses

In this study, we detected the expression of IGF-I, IGF-II, IGF-IR, IGF-IIR, and IGFBP-3 mRNA at 50 (E50), 70 (E70), and 90 (E90) days of gestation, and 1 (D1), 20 (D20), 70 (D70), 120 (D120), and 180 (D180) days of age in the longissimus dorsi (LD) and the semitendinosus (ST) of pigs from a Yorkshire boar×Erhualian sow (YE) cross as well as a Erhualian boar×Yorkshire sow (EY) cross. We found that the expression of IGF-I and IGF-II mRNA in skeletal muscle tissues differed based on developmental age and reciprocal cross type (P<0.05). The expression of IGF-I mRNA exhibited a fluctuant ascending trend. In contrast, IGF-II showed a fluctuant descending trend after birth. The levels of IGF-IR mRNA were higher before birth compared with after birth except for the ST of EY pigs at D120 (P<0.05). The expression of IGF-IIR and IGFBP-3 mRNA remarkably changed with age and reciprocal cross type (P<0.05). IGF-I, IGF-II, and IGFBP-3 mRNA were positively correlated with IGF-IR from 50E to 180D. These data suggest that the expression of IGF-system genes exhibits specific developmental patterns in the skeletal muscle tissues of pigs from reciprocal crosses at different developmental stages and may show linked expression during certain periods of development. Our results may provide a valuable resource for the molecular breeding of pigs.

Effects of heat stress on proliferation, protein turnover, and abundance of heat shock protein messenger ribonucleic acid in cultured porcine muscle satellite cells

It is well established that heat stress (HS) negatively affects growth rate in swine. Although reduced feed intake undoubtedly plays a significant role in this reduction, studies in laboratory animals and other nonswine species indicate muscle growth also is affected by HS-related alterations in muscle physiology. Evidence is now emerging that heat shock proteins (Hsp), produced in response to HS and other types of cellular stress, may play an important role in regulating the rate and efficiency of muscle growth. Because muscle satellite cells play a crucial role in postnatal muscle growth, the effects of HS on rates of satellite cell proliferation, protein synthesis, and protein degradation play an important role in determining the rate and extent of muscle growth. Consequently, in the current study we have examined the effects of mild HS (40.5°C for 48 h) on the rates of proliferation, protein synthesis, and protein degradation and on quantities of Hsp90, Hsp70, and Hsp25/27 mRNA and protein in cultured porcine muscle satellite cells (PSC). Mild HS of PSC cultures resulted in 2.5-, 1.4-, and 6.5-fold increases (P < 0.05) in the abundance of Hsp90, Hsp70, and Hsp25/27 mRNA, respectively, relative to control cultures. Abundance of Hsp 90, 70, and 25/27 proteins was also increased in HS PSC cultures compared with those in control cultures. Proliferation rates in HS PSC cultures were 35% less (P < 0.05) than those in control cultures. Protein synthesis rates in HS-fused PSC cultures were 85% greater (P < 0.05) than those in control cultures, and protein degradation rates in HS-fused PSC were 23% less (P < 0.05) than those in control cultures. In light of the crucial role satellite cells play in postnatal muscle growth, the HS-induced changes we have observed in rates of proliferation, protein turnover, and abundance of Hsp mRNA and Hsp protein in PSC cultures indicate that mild HS affects the physiology of PSC in ways that could affect muscle growth in swine.

Developmental changes and the impact of isoflavones on mRNA expression of IGF-I receptor, EGF receptor and related growth factors in porcine skeletal muscle cell cultures

OBJECTIVE

Soy that is widely used in human nutrition and in livestock production is a rich source of isoflavones. In addition to the estrogenic or antiestrogenic effects, isoflavones are suggested to affect cell growth via inhibition of protein tyrosine kinases (e.g. growth factor receptors). Therefore, the present in vitro-study was undertaken to determine, whether genistein and daidzein affect the mRNA expression of growth factor receptors (IGF-I receptor and EGF receptor) and their related growth factors in porcine skeletal muscle cell cultures.

DESIGN

First, we investigated the basal mRNA expression of IGF-I, IGF-II, EGF, IGF-I receptor, and EGF receptor in proliferating and differentiating porcine skeletal muscle cell cultures using real-time PCR. Secondly, we measured the changes in the mRNA expression in these cell cultures treated with 0 (control), 1, 10, 100 microM genistein or daidzein over 26 h in serum-free medium (n=3).

RESULTS

The mRNA expression of IGF-I was slightly decreased, whereas transcript concentrations of IGF-II and EGF were increased during differentiation compared with the proliferating stage of porcine muscle cell cultures. IGF-I receptor transcripts tended to be increased, whereas EGF receptor mRNA expression remained unchanged from proliferation to differentiation. Genistein and daidzein at 1 microM and 10 microM showed no effects on the mRNA expression of these genes, neither in proliferating nor in differentiating cells. However, high-concentrated isoflavones (100 microM) decreased the mRNA expression of IGF-I receptor and of the growth factors examined.

CONCLUSIONS

The present study confirms the role of the IGF and EGF system in proliferation and differentiation of skeletal muscle cell culture especially under serum-free culture conditions. Furthermore, the results of this in vitro-study suggest that there is no effect of isoflavones at concentrations resulting from dietary consumption (1 and 10 microM) on IGF- and EGF-associated gene expression in porcine skeletal muscle tissue. Genistein and daidzein at high concentration (100 microM) reduced the mRNA expression of the IGF-I receptor and the growth factors examined, and therefore, may modify their autocrine and paracrine actions in skeletal muscle tissue.

Decreased expression of the IGF-II gene during porcine adipose cell differentiation

IGF-I and IGF-II are known to regulate cell development and recent data suggest a possible role of IGF-II on adipose tissue development. This study was undertaken to examine the IGF system gene expression in porcine differentiating adipocytes. Both adipocytes and stromal-vascular (s/v) cells were isolated from subcutaneous adipose tissue collected from 7-day-old piglets. s/v cells were cultured in chemically defined medium. Compared with isolated adipocytes, IGF-II and IGFBP-5 mRNA levels were very high in freshly isolated s/v cells, whereas IGF-I mRNA levels were lower in s/v cells than in adipocytes. Between day 0 and day 6 of culture, IGF-II and IGFBP-5 gene expression decreased whereas expression levels of late markers of adipocyte differentiation were up-regulated. Cell differentiation was also associated with an increase in the expression of IGF-I, insulin and IGF receptor genes. The current findings suggest that IGF-I and IGF-II have different effects on porcine adipose cell development.

Clinical, agricultural, and evolutionary biology of myostatin: a comparative review

The discovery of myostatin and our introduction to the "Mighty Mouse" over a decade ago spurred both basic and applied research and impacted popular culture as well. The myostatin-null genotype produces "double muscling" in mice and livestock and was recently described in a child. The field's rapid growth is by no means surprising considering the potential benefits of enhancing muscle growth in clinical and agricultural settings. Indeed, several recent studies suggest that blocking myostatin's inhibitory effects could improve the clinical treatment of several muscle growth disorders, whereas comparative studies suggest that these actions are at least partly conserved. Thus, neutralizing myostatin's effects could also have agricultural significance. Extrapolating between studies that use different vertebrate models, particularly fish and mammals, is somewhat confusing because whole genome duplication events have resulted in the production and retention of up to four unique myostatin genes in some fish species. Such comparisons, however, suggest that myostatin's actions may not be limited to skeletal muscle per se, but may additionally influence other tissues including cardiac muscle, adipocytes, and the brain. Thus, therapeutic intervention in the clinic or on the farm must consider the potential of alternative side effects that could impact these or other tissues. In addition, the presence of multiple and actively diversifying myostatin genes in most fish species provides a unique opportunity to study adaptive molecular evolution. It may also provide insight into myostatin's nonmuscle actions as results from these and other comparative studies gain visibility in biomedical fields.

Cellular and molecular regulation of muscle growth and development in meat animals1,2

Although in vivo and in vitro studies have established that anabolic steroids, transforming growth factor-beta (TGF-beta), and myostatin affect muscle growth in meat-producing animals, their mechanisms of action are not completely understood. Anabolic steroids have been widely used as growth promoters in feedlot cattle for over 50 yr. A growing body of evidence suggests that increased muscle levels of IGF-I and increased muscle satellite cell numbers play a role in anabolic steroid enhanced muscle growth. In contrast to anabolic steroids, the members of the TGF-beta-myostatin family suppress muscle growth in vivo and suppress both proliferation and differentiation of cultured myogenic cells. Recent evidence suggests that IGFBP-3 and IGFBP-5 play a role in mediating the proliferation-suppressing actions of both TGF-beta and myostatin on cultured myogenic cells. Consequently, this review will focus on the roles of IGF-I and IGFBP in the cellular and molecular mechanisms of action of anabolic steroids and TGF-beta and myostatin, respectively.