Gene expression profiling in the Cynomolgus macaque Macaca fascicularis shows variation within the normal birth range

The human genetic variant rs6190 unveils Foxc1 and Arid5a as novel pro-metabolic targets of the glucocorticoid receptor in muscle

Genetic variations in the glucocorticoid receptor (GR) gene NR3C1 can impact metabolism. The single nucleotide polymorphism (SNP) rs6190 (p.R23K) has been associated in humans with enhanced metabolic health, but the SNP mechanism of action remains completely unknown. We generated a transgenic knock-in mice genocopying this polymorphism to elucidate how the mutant GR impacts metabolism. Compared to non-mutant littermates, mutant mice showed increased muscle insulin sensitivity and strength on regular chow and high-fat diet, blunting the diet-induced adverse effects on weight gain and exercise intolerance. Overlay of RNA-seq and ChIP-seq profiling in skeletal muscle revealed increased transactivation of Foxc1 and Arid5A genes by the mutant GR. Using adeno-associated viruses for in vivo overexpression in muscle, we found that Foxc1 was sufficient to transcriptionally activate the insulin response pathway genes Insr and Irs1. In parallel, Arid5a was sufficient to transcriptionally repress the lipid uptake genes Cd36 and Fabp4, reducing muscle triacylglycerol accumulation. Collectively, our findings identify a muscle-autonomous epigenetic mechanism of action for the rs6190 SNP effect on metabolic homeostasis, while leveraging a human nuclear receptor coding variant to unveil Foxc1 and Arid5a as novel epigenetic regulators of muscle metabolism.

Unveiling the mechanisms of neuropathic pain suppression: perineural resiniferatoxin targets Trpv1 and beyond

Neuropathic pain arises from damage or disorders affecting the somatosensory system. In rats, L5 nerve injury induces thermal and mechanical hypersensitivity/hyperalgesia. Recently, we demonstrated that applying resiniferatoxin (RTX) directly on uninjured L3 and L4 nerves alleviated thermal and mechanical hypersensitivity resulting from L5 nerve injury. Herein, using immunohistochemistry, Western blot, and qRT-PCR techniques, we reveal that perineural application of RTX (0.002%) on the L4 nerve substantially downregulated the expression of its receptor (Trpv1) and three different voltage-gated ion channels (Nav1.9, Kv4.3, and Cav2.2). These channels are found primarily in small-sized neurons and show significant colocalization with Trpv1 in the dorsal root ganglion (DRG). However, RTX treatment did not affect the expression of Kv1.1, Piezo2 (found in large-sized neurons without colocalization with Trpv1), and Kir4.1 (localized in satellite cells) in the ipsilateral DRGs. Furthermore, RTX application on L3 and L4 nerves reduced the activation of c-fos in the spinal neurons induced by heat stimulation. Subsequently, we investigated whether applying RTX to the L3 and L4 nerves 3 weeks before the L5 nerve injury could prevent the onset of neuropathic pain. Both 0.002 and 0.004% concentrations of RTX produced significant analgesic effects, while complete prevention of thermal and mechanical hypersensitivity required a concentration of 0.008%. Importantly, this preventive effect on neuropathic manifestations was not associated with nerve degeneration, as microscopic examination revealed no morphological changes. Overall, this study underscores the mechanisms and the significance of perineural RTX treatment applied to adjacent uninjured nerves in entirely preventing nerve injury-induced neuropathic pain in humans and animals.

DNA methylation in the pathogenesis of type 2 diabetes

Type 2 diabetes (T2D) is a metabolic disease characterized by the development of β-cell dysfunction with hepatic, muscular and adipose tissue insulin resistance. Although the molecular mechanisms leading to its development are not entirely known, investigations of its causes reveal a multifactorial contribution to its development and progression in most cases. In addition, regulatory interactions mediated by epigenetic modifications such as DNA methylation, histone tail modifications and regulatory RNAs have been found to play a significant role in the etiology of T2D. In this chapter, we discuss the role of DNA methylation and its dynamics in the development of the pathological features of T2D.

Cutaneous Injection of Resiniferatoxin Completely Alleviates and Prevents Nerve-Injury-Induced Neuropathic Pain

Fifth lumbar (L5) nerve injury in rodent produces neuropathic manifestations in the corresponding hind paw. The aim of this study was to investigate the effect of cutaneous injection of resiniferatoxin (RTX), a TRPV1 receptor agonist, in the rat's hind paw on the neuropathic pain induced by L5 nerve injury. The results showed that intraplantar injection of RTX (0.002%, 100 µL) (1) completely reversed the development of chronic thermal and mechanical hypersensitivity; (2) completely prevented the development of nerve-injury-induced thermal and mechanical hypersensitivity when applied one week earlier; (3) caused downregulation of nociceptive pain markers, including TRPV1, IB4 and CGRP, and upregulation of VIP in the ipsilateral dorsal horn of spinal cord and dorsal root ganglion (DRG) immunohistochemically and a significant reduction in the expression of TRPV1 mRNA and protein in the ipsilateral DRG using Western blot and qRT-PCR techniques; (4) caused downregulation of PGP 9.5- and CGRP-immunoreactivity in the injected skin; (5) produced significant suppression of c-fos expression, as a neuronal activity marker, in the spinal neurons in response to a second intraplantar RTX injection two weeks later. This work identifies the ability of cutaneous injection of RTX to completely alleviate and prevent the development of different types of neuropathic pain in animals and humans.

Co-localization of nociceptive markers in the lumbar dorsal root ganglion and spinal cord of dromedary camel

Nociceptive markers in mice have been identified in two distinct peptidergic and nonpeptidergic neurons in the dorsal root ganglion (DRG) and distributed in different laminae of the dorsal horn of the spinal cord. Recently, however, a study in humans showed a significant overlapping in these two populations. In this study, we investigated the distribution of various nociceptive markers in the lumbar DRG and spinal cord of the dromedary camel. Immunohistochemical data showed a remarkable percentage of total neurons in the DRG expressed IB4 binding (54.5%), calcitonin gene-related peptide (CGRP; 49.5%), transient receptor potential vanilloid 1 (TRPV1; 48.2%), and nitric oxide synthase (NOS; 30.6%). The co-localization data showed that 89.6% and 74.0% of CGRP- and TRPV1-labeled neurons, respectively, were IB4 positive. In addition, 61.6% and 84.2% of TRPV1- and NOS-immunoreactive neurons, respectively, were also co-localized with CGRP. The distribution of IB4, CGRP, TRPV1, substance P, and NOS immunoreactivities in the spinal cord were observed in lamina I and outer lamina II (IIo). Quantitative data showed that 82.4% of IB4-positive nerve terminals in laminae I and IIo were co-localized with CGRP, and 86.0% of CGRP-labeled terminals were co-localized with IB4. Similarly, 85.1% of NOS-labeled nerve terminals were co-localized with CGRP. No neuropeptide Y (NPY) or cholecystokinin (CCK) immunoreactivities were detected in the DRG, and no co-localization between IB4, NPY, and CCK were observed in the spinal cord. Our results demonstrate marked convergence of nociceptive markers in the primary afferent neurons in camels, which is similar to humans rather than the mouse. The data also emphasizes the importance of interspecies differences when selecting ideal animal models for studying nociception and treating chronic pain.

Perineural application of resiniferatoxin on uninjured L3 and L4 nerves completely alleviates thermal and mechanical hypersensitivity following L5 nerve injury in rats

Fifth lumbar (L5) nerve injury in rats causes neuropathic pain manifested with thermal and mechanical hypersensitivity in the ipsilateral hind paw. This study aimed to determine whether the elimination of unmyelinated primary afferents of the adjacent uninjured nerves (L3 and L4) would alleviate peripheral neuropathic pain. Different concentrations of capsaicin or its analog, resiniferatoxin (RTX), were applied perineurally on either the left L4 or L3 and L4 nerves in Wistar rats whose left L5 nerves were ligated and cut. The application of both capsaicin and RTX on the L4 nerve significantly reduced both thermal and mechanical hypersensitivity. However, only the application of RTX on both L3 and L4 nerves completely alleviated all neuropathic manifestations. Interestingly, responses to thermal and mechanical stimuli were preserved, despite RTX application on uninjured L3, L4, and L5 nerves, which supply the plantar skin in rats. Perineural application of RTX caused downregulation of TRPV1, CGRP, and IB4 binding and upregulation of VIP in the corresponding dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. In comparison, VGLUT1 and NPY immunoreactivities were not altered. RTX application did not cause degenerative or ultrastructural changes in the treated nerves and corresponding DRGs. The results demonstrate that RTX induces neuroplasticity, rather than structural changes in primary afferents, that are responsible for alleviating hypersensitivity and chronic pain. Furthermore, this study suggests that treating uninjured adjacent spinal nerves may be used to manage chronic neuropathic pain following peripheral nerve injury.

The metabolic sensor PASK is a histone 3 kinase that also regulates H3K4 methylation by associating with H3K4 MLL2 methyltransferase complex

The metabolic sensor Per-Arnt-Sim (Pas) domain-containing serine/threonine kinase (PASK) is expressed predominantly in the cytoplasm of different cell types, although a small percentage is also expressed in the nucleus. Herein, we show that the nuclear PASK associates with the mammalian H3K4 MLL2 methyltransferase complex and enhances H3K4 di- and tri-methylation. We also show that PASK is a histone kinase that phosphorylates H3 at T3, T6, S10 and T11. Taken together, these results suggest that PASK regulates two different H3 tail modifications involving H3K4 methylation and H3 phosphorylation. Using muscle satellite cell differentiation and functional analysis after loss or gain of Pask expression using the CRISPR/Cas9 system, we provide evidence that some of the regulatory functions of PASK during development and differentiation may occur through the regulation of these histone modifications.

Identification of early indicators of altered metabolism in normal development using a rodent model system

Although the existence of a close relationship between the early maternal developmental environment, fetal size at birth and the risk of developing disease in adulthood has been suggested, most studies, however, employed experimentally induced intrauterine growth restriction as a model to link this with later adult disease. Because embryonic size variation also occurs under normal growth and differentiation, elucidating the molecular mechanisms underlying these changes and their relevance to later adult disease risk becomes important. The birth weight of rat pups vary according to the uterine horn positions. Using birth weight as a marker, we compared two groups of rat pups – lower birth weight (LBW, 5th to 25th percentile) and average birth weight (ABW, 50th to 75th percentile) – using morphological, biochemical and molecular biology, and genetic techniques. Our results show that insulin metabolism, Pi3k/Akt and Pparγ signaling and the genes regulating growth and metabolism are significantly different in these groups. Methylation at the promoter of the InsII (Ins2) gene and DNA methyltransferase 1 in LBW pups are both increased. Additionally, the Dnmt1 repressor complex, which includes Hdac1, Rb (Rb1) and E2f1, was also upregulated in LBW pups. We conclude that the Dnmt1 repressor complex, which regulates the restriction point of the cell cycle, retards the rate at which cells traverse the G1 or G0 phase of the cell cycle in LBW pups, thereby slowing down growth. This regulatory mechanism mediated by Dnmt1 might contribute to the production of small-size pups and altered physiology and pathology in adult life.

Summary: This study suggests an important link between the early embryonic environment and later adult physiology and pathology. At least one process by which this might be coordinated is through the regulatory mechanisms mediated by Dnmt1.

Why primate models matter

Research involving nonhuman primates (NHPs) has played a vital role in many of the medical and scientific advances of the past century. NHPs are used because of their similarity to humans in physiology, neuroanatomy, reproduction, development, cognition, and social complexity-yet it is these very similarities that make the use of NHPs in biomedical research a considered decision. As primate researchers, we feel an obligation and responsibility to present the facts concerning why primates are used in various areas of biomedical research. Recent decisions in the United States, including the phasing out of chimpanzees in research by the National Institutes of Health and the pending closure of the New England Primate Research Center, illustrate to us the critical importance of conveying why continued research with primates is needed. Here, we review key areas in biomedicine where primate models have been, and continue to be, essential for advancing fundamental knowledge in biomedical and biological research.

Baboons as a model to study genetics and epigenetics of human disease

A major challenge for understanding susceptibility to common human diseases is determining genetic and environmental factors that influence mechanisms underlying variation in disease-related traits. The most common diseases afflicting the US population are complex diseases that develop as a result of defects in multiple genetically controlled systems in response to environmental challenges. Unraveling the etiology of these diseases is exceedingly difficult because of the many genetic and environmental factors involved. Studies of complex disease genetics in humans are challenging because it is not possible to control pedigree structure and often not practical to control environmental conditions over an extended period of time. Furthermore, access to tissues relevant to many diseases from healthy individuals is quite limited. The baboon is a well-established research model for the study of a wide array of common complex diseases, including dyslipidemia, hypertension, obesity, and osteoporosis. It is possible to acquire tissues from healthy, genetically characterized baboons that have been exposed to defined environmental stimuli. In this review, we describe the genetic and physiologic similarity of baboons with humans, the ability and usefulness of controlling environment and breeding, and current genetic and genomic resources. We discuss studies on genetics of heart disease, obesity, diabetes, metabolic syndrome, hypertension, osteoporosis, osteoarthritis, and intrauterine growth restriction using the baboon as a model for human disease. We also summarize new studies and resources under development, providing examples of potential translational studies for targeted interventions and therapies for human disease.

Abruptio placentae in cynomolgus macaques (Macaca fascicularis): male bias

BACKGROUND

Abruptio placentae is a serious problem with a high rate of maternal and fetal mortality and documented sexual dimorphism in reoccurrence. Macaca fascicularis is a well-described reproductive model; however, there are no data available regarding sexual dimorphism in abruptio placentae in these species.

METHODS

A retrospective study of pathology and medical records in a large colony of M. fascicularis was performed. Placental specimens were analyzed.

RESULTS

The incidence of placenta abruptio in the colony was 15.7/1000 births. In the abruptio placentae group, male fetuses had lower placental disk length and increased femur length compared with female fetuses. The feto-pacental ratio and fetal weight were lower in the male fetuses in the abruption group compared with those in the stillbirth group without abruption placentae.

CONCLUSION

This is the first documentation of male bias in placental and fetal development in abruptio placentae in non-human primates.

Recurrent abruptio placentae in a cynomolgus monkey (Macaca fascicularis)

INTRODUCTION

Abruptio placentae, defined as premature separation of a normally implanted placenta, is a life threatening pregnancy complication with unknown pathophysiology. A history of abruptio placentae is the major risk factor for this pregnancy complication in humans. We describe the first case of recurrent abruptio placentae in a Macaca fascicularis.

MATERIAL AND METHODS

A pregnant M. fascicularis at term gestation was presented with weakness and hypothermia. Cesarean section revealed retroplacental hemorrhage with partial placental separation from the uterus.

RESULTS

The weight of the female fetus was within the lower birth weight range for these species. The maternal side of placenta contained necrotic tissue, occupying approximately 60% of the maternal surface. The placental implantation bed demonstrated neutrophil infiltration. Perivascular collections of lymphocytes were noticed in the uterine smooth muscle.

CONCLUSION

This case report underlines the importance of neutrophil infiltration and uterine venous drainage in the cascade of events leading to abruptio placentae.