Comparative three-dimensional genome architectures of adipose tissues provide insight into human-specific regulation of metabolic homeostasis.

Elucidating the regulatory mechanisms of human adipose tissues (ATs) evolution is essential for understanding human-specific metabolic regulation, but the functional importance and evolutionary dynamics of three-dimensional (3D) genome organizations of ATs are not well defined. Here, we compared the 3D genome architectures of anatomically distinct ATs from humans and six representative mammalian models. We recognized evolutionarily conserved and human-specific chromatin conformation in ATs at multiple scales, including compartmentalization, topologically associating domain (TAD), and promoter-enhancer interactions (PEI), which have not been described previously. We found PEI are much more evolutionarily dynamic with respect to compartmentalization and topologically associating domain. Compared to conserved PEIs, human-specific PEIs are enriched for human-specific sequence, and the binding motifs of their potential mediators (transcription factors) are less conserved. Our data also demonstrated that genes involved in the evolutionary dynamics of chromatin organization have weaker transcriptional conservation than those associated with conserved chromatin organization. Furthermore, the genes involved in energy metabolism and the maintenance of metabolic homeostasis are enriched in human-specific chromatin organization, while housekeeping genes, health-related genes, and genetic variations are enriched in evolutionarily conserved compared to human-specific chromatin organization. Finally, we showed extensively divergent human-specific 3D genome organizations among one subcutaneous and three visceral ATs. Together, these findings provide a global overview of 3D genome architecture dynamics between ATs from human and mammalian models and new insights into understanding the regulatory evolution of human ATs.

Incidence of serum antibodies to xenoantigens on triple-knockout pig cells in different human groups.

BACKGROUND: Xenoantigens other than Gal, Neu5Gc, and Sda may be playing a role in pig graft rejection. We investigated the incidence of antibodies to unknown pig xenoantigen in different human groups. METHODS: We collected blood from TKO/hCD55 pigs (n = 3), and isolated PBMCs and RBCs. Serum samples were collected from (i) healthy human volunteers (n = 43), (ii) patients with end-stage renal disease (ESRD) (n = 87), (iii) the same patients after kidney allotransplantation (n = 50), and (iv) renal allotransplant recipients experiencing T cell-mediated rejection (allo-TCMR, n = 10). The sera were initially incubated with TKO/hCD55 pRBCs (1 × 108 cells) for 1 h to absorb anti-pig antibodies (except against SLA and possibly other antigens not expressed on pRBCs) and then the serum (absorbed or unabsorbed) was tested for antibody binding and complement-dependent cytotoxicity (CDC) to TKO/hCD55 pig PBMCs. RESULTS: A significant reduction in IgM/IgG binding and CDC was observed in the absorbed sera. Serum obtained before and after renal allotransplantation showed no significant difference in IgM or IgG binding to, or in CDC of, TKO/hCD55 pig cells. IgM antibodies (but rarely IgG) against unknown xenoantigens expressed on TKO/hCD55 PBMCs, possibly against swine leukocyte antigens, were documented in healthy humans, patients with ESRD, and those with renal allografts undergoing acute T cell rejection. IgM (but not CDC) was higher in patients experiencing allo-TCMR. CONCLUSION: Human sera contain IgM antibodies against unknown pig xenoantigens expressed on TKO/hCD55 pPBMCs. Although not confirmed in the present study, the targets for these antibodies may include swine leukocyte antigens.

Porcine ZBED6 regulates growth of skeletal muscle and internal organs via multiple targets.

ZBED6 (zinc finger BED domain containing protein 6) is a transcription factor unique to placental mammals and its interaction with the IGF2 (insulin-like growth factor 2) locus plays a prominent role in the regulation of postnatal skeletal muscle growth. Here, we generated lean Bama miniature pigs by generating ZBED6-knockout (ZBED6-/-) and investigated the mechanism underlying ZBED6 in growth of muscle and internal organs of placental mammals. ZBED6-/- pigs show markedly higher lean mass, lean mass rate, larger muscle fiber area and heavier internal organs (heart and liver) than wild-type (WT) pigs. The striking phenotypic changes of ZBED6-/- pigs coincided with remarkable upregulation of IGF2 mRNA and protein expression across three tissues (gastrocnemius muscle, longissimus dorsi, heart). Despite a significant increase in liver weight, ZBED6-/- pigs show comparable levels of IGF2 expression to those of WT controls. A mechanistic study revealed that elevated methylation in the liver abrogates ZBED6 binding at the IGF2 locus, explaining the unaltered hepatic IGF2 expression in ZBED6-/- pigs. These results indicate that a ZBED6-IGF2-independent regulatory pathway exists in the liver. Transcriptome analysis and ChIP-PCR revealed new ZBED6 target genes other than IGF2, including cyclin dependent kinase inhibitor 1A (CDKN1A) and tsukushi, small leucine rich proteoglycan (TSKU), that regulates growth of muscle and liver, respectively.

Deficiency of ASGR1 in pigs recapitulates reduced risk factor for cardiovascular disease in humans.

Genetic variants in the asialoglycoprotein receptor 1 (ASGR1) are associated with a reduced risk of cardiovascular disease (CVD) in humans. However, the underlying molecular mechanism remains elusive. Given the cardiovascular similarities between pigs and humans, we generated ASGR1-deficient pigs using the CRISPR/Cas9 system. These pigs show age-dependent low levels of non-HDL-C under standard diet. When received an atherogenic diet for 6 months, ASGR1-deficient pigs show lower levels of non-HDL-C and less atherosclerotic lesions than that of controls. Furthermore, by analysis of hepatic transcriptome and in vivo cholesterol metabolism, we show that ASGR1 deficiency reduces hepatic de novo cholesterol synthesis by downregulating 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), and increases cholesterol clearance by upregulating the hepatic low-density lipoprotein receptor (LDLR), which together contribute to the low levels of non-HDL-C. Despite the cardioprotective effect, we unexpectedly observed mild to moderate hepatic injury in ASGR1-deficient pigs, which has not been documented in humans with ASGR1 variants. Thus, targeting ASGR1 might be an effective strategy to reduce hypercholesterolemia and atherosclerosis, whereas further clinical evidence is required to assess its hepatic impact.

Meeting report: Xenotransplantation Development Conference in Neijiang, China.

A conference on progress in the development of xenotransplantation in China was held in Neijiang, Sichuan, in May 2023, and was attended by approximately 100 established researchers and trainees. Progress in xenotransplantation research was reviewed by both Chinese and foreign experts. The topics discussed ranged from genetic engineering of pigs and the results of pig-to-nonhuman primate organ transplantation to the requirements for designated pathogen-free (DPF) pig facilities and regulation of xenotransplantation. This conference served as an opportunity to collectively advance the development of xenotransplantation in China and pave the way for its clinical application.

Advances and applications of genetically modified pig models in biomedical and agricultural field.

Compared with rodents, pigs are closer to humans in terms of anatomy, metabolism and physiology, so they are ideal animal models of human diseases and xenotransplantation donors. In addition, as one of the most important livestock in China, pigs are closely related to our lives in terms of breeding improvement, disease prevention and animal welfare. In this review, we mainly summarize the research progress and future application of genetically modified pig models in the fields of xenotransplantation, molecular breeding and human disease models. We wish to take this opportunity to raise the awareness of researchers in related fields on cutting-edge technologies such as gene editing and understand the significance of genetically modified pig models in life science research.

Comprehensive analysis of lncRNAs involved in skeletal muscle development in ZBED6-knockout Bama pigs.

BACKGROUND: The mutation of insulin-like growth factor 2 (IGF2 mutation) that a single-nucleotide substitution (G→A) in the third intron of IGF2 abrogates the interaction with zinc finger BED-type containing 6 (ZBED6) and leads to increased muscle mass in pigs. IGF2 mutation knock-in (IGF2 KI) and ZBED6 knockout (ZBED6 KO) lead to changes in IGF2 expression and increase muscle mass in mice and pigs. Long noncoding RNAs (lncRNAs) may participate in numerous biological processes, including skeletal muscle development. However, the role of the ZBED6-lncRNA axis in skeletal muscle development is poorly characterized. RESULTS: In this study, we assembled transcriptomes using RNA-seq data published in previous studies by our group and identified 11,408 known lncRNAs and 2269 potential lncRNAs in seven tissues, heart, longissimus dorsi, gastrocnemius muscle, liver, spleen, lung and kidney, of ZBED6 KO (lean mass model) and WT Bama pigs. ZBED6 affected the expression of 1570 lncRNAs (differentially expressed lncRNAs [DE-lncRNAs]; log2-fold change ≥ 1, nominal p-value ≤ 0.05) in the seven examined tissues. The expressed lncRNAs (FPKM > 0.1) exhibited tissue-specific patterns in WT pigs. Specifically, 3410 lncRNAs were expressed exclusively in only one tissue. Potential functions of lncRNAs were indirectly predicted by searching their target cis- and trans-regulated protein-coding genes. LncRNAs with tissue-specific expression influence numerous genes related to tissue functions. Weighted gene coexpression network analysis (WGCNA) of 1570 DE-lncRNAs between WT and ZBED6 KO pigs was used to define the following six lncRNA modules specific to different tissues: skeletal muscle, heart, lung, spleen, kidney and liver modules. Furthermore, by conjoint analysis of longissimus dorsi data (tissue-specific expression, muscle module and DE-lncRNAs) and ChIP-PCR revealed NONSUSG002145.1 (adjusted p-values = 0.044), which is coexpressed with the IGF2 gene and binding with ZBED6, may play important roles in ZBED6 KO pig skeletal muscle development. CONCLUSIONS: These findings indicate that the identified lncRNAs may play essential roles in tissue function and regulate the mechanism of ZBED6 action in skeletal muscle development in pigs. To our knowledge, this is the first study describing lncRNAs in ZBED6 KO pigs. These results may open new research directions leading to a better understanding of the global functions of ZBED6 and of lncRNA functions in skeletal muscle development in pigs.

FcRn is not the receptor mediating the transfer of serum IgG to colostrum in pigs.

In contrast to humans or rabbits, in which maternal IgG is transmitted to offspring prenatally via the placenta or the yolk sac, large domestic animals such as pigs, cows and sheep transmit IgG exclusively through colostrum feeding after delivery. The extremely high IgG content in colostrum is absorbed by newborns via the small intestine. Although it is widely accepted that the neonatal Fc receptor, FcRn, is the receptor mediating IgG transfer across both the placenta and small intestine, it remains unclear whether FcRn also mediates serum IgG transfer across the mammary barrier to colostrum/milk, especially in large domestic animals. In this study, using a FcRn knockout pig model generated with a CRISPR-Cas9-based approach, we clearly demonstrate that FcRn is not responsible for the IgG transfer from serum to colostrum in pigs, although like in other mammals, it is involved in IgG homeostasis and mediates IgG absorption in the small intestine of newborns.

Silencing of retrotransposon-derived imprinted gene RTL1 is the main cause for postimplantational failures in mammalian cloning.

Substantial rates of fetal loss plague all in vitro procedures involving embryo manipulations, including human-assisted reproduction, and are especially problematic for mammalian cloning where over 90% of reconstructed nuclear transfer embryos are typically lost during pregnancy. However, the epigenetic mechanism of these pregnancy failures has not been well described. Here we performed methylome and transcriptome analyses of pig induced pluripotent stem cells and associated cloned embryos, and revealed that aberrant silencing of imprinted genes, in particular the retrotransposon-derived RTL1 gene, is the principal epigenetic cause of pregnancy failure. Remarkably, restoration of RTL1 expression in pig induced pluripotent stem cells rescued fetal loss. Furthermore, in other mammals, including humans, low RTL1 levels appear to be the main epigenetic cause of pregnancy failure.

Immortalization of porcine hepatocytes with a α-1,3-galactosyltransferase knockout background.

BACKGROUND: In vivo pig liver xenotransplantation preclinical trials appear to have poor efficiency compared to heart or kidney xenotransplantation because of xenogeneic rejection, including coagulopathy, and particularly thrombocytopenia. In contrast, ex vivo pig liver (wild type) perfusion systems have been proven to be effective in "bridging" liver failure patients until subsequent liver allotransplantation, and transgenic (human CD55/CD59) modifications have even prolonged the duration of pig liver perfusion. Despite the fact that hepatocyte cell lines have also been proposed for extracorporeal blood circulation in conditions of acute liver failure, porcine hepatocyte cell lines, and the GalT-KO background in particular, have not been developed and applied in this field. Herein, we established immortalized wild-type and GalT-KO porcine hepatocyte cell lines, which can be used for artificial liver support systems, cell transplantation, and even in vitro studies of xenotransplantation. METHODS: Primary hepatocytes extracted from GalT-KO and wild-type pigs were transfected with SV40 LT lentivirus to establish immortalized GalT-KO porcine hepatocytes (GalT-KO-hep) and wild-type porcine hepatocytes (WT). Hepatocyte biomarkers and function-related genes were assessed by immunofluorescence, periodic acid-Schiff staining, indocyanine green (ICG) uptake, biochemical analysis, ELISA, and RT-PCR. Furthermore, the tumorigenicity of immortalized cells was detected. In addition, a complement-dependent cytotoxicity (CDC) assay was performed with GalT-KO-hep and WT cells. Cell death and viability rates were assessed by flow cytometry and CCK-8 assay. RESULTS: GalT-KO and wild-type porcine hepatocytes were successfully immortalized and maintained the characteristics of primary porcine hepatocytes, including albumin secretion, ICG uptake, urea and glycogen production, and expression of hepatocyte marker proteins and specific metabolic enzymes. GalT-KO-hep and WT cells were confirmed as having no tumorigenicity. In addition, GalT-KO-hep cells showed less apoptosis and more viability than WT cells when exposed to complement and xenogeneic serum. CONCLUSIONS: Two types of immortalized cell lines of porcine hepatocytes with GalT-KO and wild-type backgrounds were successfully established. GalT-KO-hep cells exhibited higher viability and injury resistance against a xenogeneic immune response.

Progress in multiple genetically modified minipigs for xenotransplantation in China.

Pig-to-human organ transplantation provides an alternative for critical shortage of human organs worldwide. Genetically modified pigs are promising donors for xenotransplantation as they show many anatomical and physiological similarities to humans. However, immunological rejection including hyperacute rejection (HAR), acute humoral xenograft rejection (AHXR), immune cell-mediated rejection, and other barriers associated with xenotransplantation must be overcome with various strategies for the genetic modification of pigs. In this review, we summarize the outcomes of genetically modified and cloned pigs achieved by Chinese scientists to resolve the above-mentioned problems in xenotransplantation. It is now possible to knockout several porcine genes associated with the expression of sugar residues, antigens for (naturally) existing antibodies in humans, including GGTA1, CMAH, and ß4GalNT2, and thereby preventing the antigen-antibody response. Moreover, insertion of human complement- and coagulation-regulatory transgenes, such as CD46, CD55, CD59, and hTBM, can further overcome effects of the humoral immune response and coagulation dysfunction, while expression of regulatory factors of immune responses can inhibit the adaptive immune rejection. Furthermore, transgenic strategies have been developed by Chinese scientists to reduce the potential risk of infections by endogenous porcine retroviruses (PERVs). Breeding of multi-gene low-immunogenicity pigs in China is also presented in this review. Lastly, we will briefly mention the preclinical studies on pig-to-non-human primate xenotransplantation conducted in several centers in China.

Downregulation of Gabarapl1 significantly attenuates antibody binding to porcine aortic endothelial cells.

After hyperacute rejection in pig-to-primate xenotransplantation had been overcome by the introduction of α1,3-galactosyltransferase gene-knockout (GTKO) pigs, acute and chronic antibody-mediated rejection became one of the major barriers to long-term graft survival. This was associated with exposure of non-Gal antigens to the recipient's immune system and indicated that further genetic engineering of the pigs would be necessary. We here report that Gabarapl1, a regulator of tumorigenesis, plays a role in the regulation of immunogenicity of porcine aortic endothelial cells (PAECs). Knockdown of Gabarapl1 in PAECs results in a remarkable reduction in binding of serum antibody from PAEC-immunized monkeys, associated with decreased serum cytotoxicity of pig cells. Expression of swine leukocyte antigens (SLA) II DR was downregulated by Gabarapl1 knockdown. However, suppression of expression of SLA II is associated with less reduction of antibody binding than achieved by Gabarapl1 knockdown, suggesting that other Gabarapl1-regulated xenoantigens may be more important. These findings indicate a hitherto unknown relationship between Gabarapl1 and xenoimmunogenicity, suggesting a potential new strategy to reduce rejection initiated by the presence of non-Gal antigens.

Generation of chimeric minipigs by aggregating 4- to 8-cell-stage blastomeres from somatic cell nuclear transfer with the tracing of enhanced green fluorescent protein.

BACKGROUND: Blastocyst complementation is an important technique for generating chimeric organs in organ-deficient pigs, which holds great promise for solving the problem of a shortage of organs for human transplantation procedures. Porcine chimeras have been generated using embryonic germ cells, embryonic stem cells, and induced pluripotent stem cells; however, there are no authentic pluripotent stem cells for pigs. In previous studies, blastomeres from 4- to 8-cell-stage parthenogenetic embryos were able to generate chimeric fetuses efficiently, but the resulting fetuses did not produce live-born young. Here, we used early-stage embryos from somatic cell nuclear transfer (SCNT) to generate chimeric piglets by the aggregation method. Then, the distribution of chimerism in various tissues and organs was observed through the expression of enhanced green fluorescent protein (EGFP). METHODS: Initially, we determined whether 4- to 8- or 8- to 16-cell-stage embryos were more suitable to generate chimeric piglets. Chimeras were produced by aggregating two EGFP-tagged Wuzhishan minipig (WZSP) SCNT embryos and two Bama minipig (BMP) SCNT embryos. The chimeric piglets were identified by coat color and microsatellite and swine leukocyte antigen analyses. Moreover, the distribution of chimerism in various tissues and organs of the piglets was evaluated by EGFP expression. RESULTS: We found that more aggregated embryos were produced using 4- to 8-cell-stage embryos (157/657, 23.9%) than 8- to 16-cell-stage embryos (100/499, 20.0%). Thus, 4- to 8-cell-stage embryos were used for the generation of chimeras. The rate of blastocysts development after aggregating WZSP with BMP embryos was 50.6%. Transfer of 391 blastocysts developed from 4- to 8-cell-stage embryos to five recipients gave rise to 18 piglets, of which two (11.1%) were confirmed to be chimeric by their coat color and microsatellite examination of the skin. One of the chimeric piglets died at 35 days and was subsequently autopsied, whereas the other piglet was maintained for the following observations. The heart and kidneys of the dead piglet showed chimerism, whereas the spinal cord, stomach, pancreas, intestines, muscle, ovary, and brain had no chimerism. CONCLUSIONS: To our knowledge, this is the first report of porcine chimeras generated by aggregating 4- to 8-cell-stage blastomeres from SCNT. We detected chimerism only in the skin, heart, and kidneys. Collectively, these results indicate that aggregation using 4- to 8-cell-stage SCNT embryos offers a practical approach for producing chimeric minipigs. Furthermore, it also provides a potential platform for generating interspecific chimeras between pigs and non-human primates for xenotransplantation.

Angiopoietin-1 and angiopoietin-2 protect porcine iliac endothelial cells from human antibody-mediated complement-dependent cytotoxicity through phosphatidylinositide 3-kinase/AKT pathway activation.

Cytokines play crucial roles in inflammation, but their role in xenotransplantation remains elusive. We assessed the role of several cytokines using an in vitro model of human antibody-mediated complement-dependent cytotoxicity (CDC). Recombinant human angiopoietin-1 (Ang-1) protected porcine iliac endothelial cells (PIECs) from human antibody-mediated CDC. Interestingly, human angiopoietin-2 (Ang-2) had a similar protective effect on PIECs. By flow cytometry analysis, the extent of human IgM and IgG binding to PIECs did not decrease when PIECs were exposed to Ang-1/Ang-2. The mRNA level of complement regulators (CD46, CD55, CD59) was not upregulated in PIECs treated with Ang-1/Ang-2, both of which activated the PI3K/AKT pathway in PIECs. Wortmannin, which inhibits phosphatidylinositide 3-kinase (PI3K), suppressed Ang-1/Ang-2-induced AKT phosphorylation and consequent Ang-1/Ang-2-mediated protection of PIECs in human antibody-mediated CDC model. Moreover, dominant negative AKT also suppressed Ang-1/Ang-2-mediated protection of PIECs in this model. In conclusion, our data suggest that human Ang-1/Ang-2 induces the protection of PIECs from human antibody-mediated CDC by activating the PI3K/AKT pathway. Ang-1/Ang-2 is likely to protect porcine endothelial cells and may be beneficial in xenotransplantation research.

Klotho attenuated antibody-mediated porcine endothelial cell activation and injury.

Long-term success in pig-to-primate xenotransplantation is currently hampered by acute vascular rejection (AVR), characterized by endothelial cell (EC) activation and injury. Klotho has anti-apoptotic, anti-inflammatory effects on EC and protects EC against reactive oxygen species, rendering klotho a promising molecule to control AVR. In this study, porcine ECs were pre-incubated with klotho and then exposed to xenoreactive antibodies and complement. Real-time PCR revealed that klotho suppressed antibody-induced pro-inflammatory gene expression of VCAM-1 and IL-1α. NF-κB activation, IκBα phosphorylation, was also attenuated by klotho administration. Furthermore, klotho induced in porcine EC resistance against complement-dependent cytotoxicity. Accompanying this change, the binding of IgG and IgM xenoreactive antibodies to porcine EC was decreased and the expression of anti-inflammatory gene HO-1 was upregulated. These findings indicated that klotho protein protected porcine EC from activation and injury caused by binding of xenoreactive antibodies and was a promising candidate molecule in a multitransgenic pig strategy for xenotransplantation.

Cytokine profiles in Tibetan macaques following α-1,3-galactosyltransferase-knockout pig liver xenotransplantation.

BACKGROUND: Pig-to-nonhuman primate orthotopic liver xenotransplantation is often accompanied by thrombocytopenia and coagulation disorders. Furthermore, the release of cytokines can trigger cascade reactions of coagulation and immune attacks within transplant recipients. To better elucidate the process of inflammation in liver xenograft recipients, we utilized a modified heterotopic auxiliary liver xenotransplantation model for xeno-immunological research. We studied the cytokine profiles and the relationship between cytokine levels and xenograft function after liver xenotransplantation. METHODS: Appropriate donor and recipient matches were screened using complement-dependent cytotoxicity assays. Donor liver grafts from α1,3-galactosyltransferase gene-knockout (GTKO) pigs or GTKO pigs additionally transgenic for human CD47 (GTKO/CD47) were transplanted into Tibetan macaques via two different heterotrophic auxiliary liver xenotransplantation procedures. The cytokine profiles, hepatic function, and coagulation parameters were monitored during the clinical course of xenotransplantation. RESULTS: Xenograft blood flow was stable in recipients after heterotopic auxiliary transplantation. A Doppler examination indicated that the blood flow speed was faster in the hepatic artery (HA) and hepatic vein (HV) of xenografts subjected to the modified Sur II (HA-abdominal aorta+HV-inferior vena cava) procedure than in those subjected to our previously reported Sur I (HA-splenic artery+HV-left renal vein) procedure. Tibetan macaques receiving liver xenografts did not exhibit severe coagulation disorders or immune rejection. Although the recipients did suffer from a rapid loss of platelets, this loss was mild. In blood samples dynamically collected after xenotransplantation (post-Tx), dramatic increases in the levels of monocyte chemoattractant protein 1, interleukin (IL)-8, granulocyte-macrophage colony-stimulating factor, IL-6, and interferon gamma-induced protein 10 were observed at 1 hour post-Tx, even under immunosuppression. We further confirmed that the elevation in individual cytokine levels was correlated with the onset of graft damage. Finally, the release of cytokines might contribute to leukocyte infiltration in the xenografts. CONCLUSION: Here, we established a modified auxiliary liver xenotransplantation model resulting in near-normal hepatic function. Inflammatory cytokines might contribute to early damage in liver xenografts. Controlling the systemic inflammatory response of recipients might prevent early post-Tx graft dysfunction.

Production of α1,3-galactosyltransferase and cytidine monophosphate-N-acetylneuraminic acid hydroxylase gene double-deficient pigs by CRISPR/Cas9 and handmade cloning.

Gene-knockout pigs hold great promise as a solution to the shortage of organs from donor animals for xenotransplantation. Several groups have generated gene-knockout pigs via clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) and somatic cell nuclear transfer (SCNT). Herein, we adopted a simple and micromanipulator-free method, handmade cloning (HMC) instead of SCNT, to generate double gene-knockout pigs. First, we applied the CRISPR/Cas9 system to target α1,3-galactosyltransferase (GGTA1) and cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) genes simultaneously in porcine fetal fibroblast cells (PFFs), which were derived from wild-type Chinese domestic miniature Wuzhishan pigs. Cell colonies were obtained by screening and were identified by Surveyor assay and sequencing. Next, we chose the GGTA1/CMAH double-knockout (DKO) cells for HMC to produce piglets. As a result, we obtained 11 live bi-allelic GGTA1/CMAH DKO piglets with the identical phenotype. Compared to cells from GGTA1-knockout pigs, human antibody binding and antibody-mediated complement-dependent cytotoxicity were significantly reduced in cells from GGTA1/CMAH DKO pigs, which demonstrated that our pigs would exhibit reduced humoral rejection in xenotransplantation. These data suggested that the combination of CRISPR/Cas9 and HMC technology provided an efficient and new strategy for producing pigs with multiple genetic modifications.

Barriers for Deriving Transgene-Free Pig iPS Cells with Episomal Vectors.

To date no authentic embryonic stem cell (ESC) line or germline-competent-induced pluripotent stem cell (iPSC) line has been established for large animals. Despite this fact, there is an impression in the field that large animal ESCs or iPSCs are as good as mouse counterparts. Clarification of this issue is important for a healthy advancement of the stem cell field. Elucidation of the causes of this failure in obtaining high quality iPSCs/ESCs may offer essential clues for eventual establishment of authentic ESCs for large animals including humans. To this end, we first generated porcine iPSCs using nonintegrating replicating episomal plasmids. Although these porcine iPSCs met most pluripotency criteria, they could neither generate cloned piglets through nuclear transfer, nor contribute to later stage chimeras through morula injections or aggregations. We found that the reprogramming genes in iPSCs could not be removed even under negative selection, indicating they are required to maintain self-renewal. The persistent expression of these genes in porcine iPSCs in turn caused differentiation defects in vivo. Therefore, incomplete reprogramming manifested by a reliance on sustained expression of exogenous-reprogramming factors appears to be the main reason for the inability of porcine iPSCs to form iPSC-derived piglets.

Pig BMSCs Transfected with Human TFPI Combat Species Incompatibility and Regulate the Human TF Pathway in Vitro and in a Rodent Model.

BACKGROUND: The activation of tissue factor (TF) is one of the major reasons for coagulation dysregulation after pig-to-primate xenotransplantation. Tissue factor pathway inhibitor (TFPI) is the most important inhibitor of TF. Studies have demonstrated species incompatibility between pig TFPI and human TF. METHODS: A pig-to-macaque heterotopic auxiliary liver transplantation model was established to determine the origin of activated TF. Chimeric proteins of human and pig TFPI were constructed to assess the role of Kunitz domains in species incompatibility. Immortalised pig bone marrow mesenchymal stem cells transfected with human TFPI were tested for their ability to inhibit clotting in vitro. RESULTS: TF from recipient was activated early after liver xenotransplantation. Pig TFPI Kunitz domain 2 bound human FXa, but Kunitz domain 1 did not effectively inhibit human TF/FVIIa. Immortalised pig bone marrow mesenchymal cells (BMSCs) transfected with human TFPI showed a prolonged recalcification time in vitro and in a rodent model. CONCLUSION: Recipient TF is relevant to dysregulated coagulation after xenotransplantation. Kunitz domain 1 plays the most important role in species incompatibility between pig TFPI and human TF, and clotting can be inhibited by human TFPI-transfected pig BMSCs. Our study shows a possible way to resolve the incompatibility of pig TFPI.

[Expression analysis of green fluorescent protein in tissues and organs in α-1,3 galactosyltransferase knockout pigs].

The pig is an ideal source to provide organs because its organ size and physiology are similar to humans. However, an acute rejection will ensue after pig-to-human xenotransplantation. The α-1,3 galactosyltransferase gene knockout (GTKO) pigs were generated in recent years, and could solve the problem of hyperacute rejection. But due to lack of reporting genes, the rejection status of cells and organs post pig-to-human xenotransplantation cannot be visualized. In this study, we introduced the enhanced green fluorescent protein (EGFP) gene driven by the CAG promoter into GTKO porcine ear fibroblasts. Then we produced transgenic pigs expressing the EGFP gene by nuclear transfer technology. Expression levels of EGFP in different tissues and organs of the cloned pig were investigated by Nightsea DFP-1 Fluorescent Protein Flashlight, fluorescence microscope and quantitative PCR assays. The results showed that the protein and transcript of EGFP were expressed in all tissues and organs of the GTKO pig, but the expression was weak in the liver and central nervous system. In conclusion, we have successfully produced the transgenic GTKO pigs expressing EGFP in all tested tissues and organs, which builds up a good basis to track transplanted cells or tissues.