Metabolic syndrome: is equine disease comparable to what we know in humans?

Adiposity in mares induces insulin dysregulation and mitochondrial dysfunction which can be mitigated by nutritional intervention

Obesity is a complex disease associated with augmented risk of metabolic disorder development and cellular dysfunction in various species. The goal of the present study was to investigate the impacts of obesity on the metabolic health of old mares as well as test the ability of diet supplementation with either a complex blend of nutrients designed to improve equine metabolism and gastrointestinal health or L-carnitine alone to mitigate negative effects of obesity. Mares (n = 19, 17.9 ± 3.7 years) were placed into one of three group: normal-weight (NW, n = 6), obese (OB, n = 7) or obese fed a complex diet supplement for 12 weeks (OBD, n = 6). After 12 weeks and completion of sample collections, OB mares received L-carnitine alone for an additional 6 weeks. Obesity in mares was significantly associated with insulin dysregulation, reduced muscle mitochondrial function, and decreased skeletal muscle oxidative capacity with greater ROS production when compared to NW. Obese mares fed the complex diet supplement had better insulin sensivity, greater cell lipid metabolism, and higher muscle oxidative capacity with reduced ROS production than OB. L-carnitine supplementation alone did not significantly alter insulin signaling, but improved lipid metabolism and muscle oxidative capacity with reduced ROS. In conclusion, obesity is associated with insulin dysregulation and altered skeletal muscle metabolism in older mares. However, dietary interventions are an effective strategy to improve metabolic status and skeletal muscle mitochondrial function in older mares.

Sex hormone-binding globulin improves lipid metabolism and reduces inflammation in subcutaneous adipose tissue of metabolic syndrome-affected horses

Equine metabolic syndrome (EMS) is a steadily growing endocrine disorder representing a real challenge in veterinary practice. As a multifactorial condition, EMS is characterized by three main metabolic abnormalities including insulin resistance, increased adiposity or obesity and hoof laminitis. Adipose tissue dysfunction is recognized as a core pathophysiological determinant of EMS, as it strongly participates to lipotoxicity and systemic metaflammation, both of which have been closely linked to the development of generalized insulin resistance. Besides, sex hormone binding globulin (SHBG) is an important sex steroids transporters that has been recently proposed as an important metabolic mediator. Therefore, the aim of this study was to verify whether SHBG treatment may ameliorate subcutaneous adipose tissue metabolic failure under EMS condition in terms of lipidome homeostasis, lipid metabolism programs, insulin signalling and local inflammation. Subcutaneous adipose tissue (SAT) biopsies were collected post-mortem from healthy (n = 3) and EMS (n = 3) slaughtered horses. SHBG protein has been applied to SAT samples from EMS horses for 24 h at a final concentration of 50 nM, while control groups (healthy and untreated EMS) were cultured in the presence of SHBG-vehicle only. Tissues from all groups were afterwards secured for downstream analysis of gene expression using RT-qPCR, protein levels by Western blot and ELISA assay and lipidomics through GC-MS technique. Obtained results showcased that SHBG intervention efficiently normalized the altered fatty acids (FAs) profiles by lowering the accumulation of saturated and trans FAs, as well as the pro-inflammatory arachidonic and linoleic acids. Moreover, SHBG showed promising value for the regulation of adipocyte lipolysis and engorgement by lowering the levels of perilipin-1. SHBG exerted moderated effect toward SCD1 and FASN enzymes expression, but increased the LPL abundance. Interestingly, SHBG exhibited a negative regulatory effect on pro-adipogenic stimulators and induced higher expression of KLF3, IRF3 and β-catenin, known as strong adipogenesis repressors. Finally, SHBG protein showed remarkable ability in restoring the insulin signal transduction, IR/IRS/Pi3K/AKT phosphorylation events and GLUT4 transporter abundance, and further attenuate pro-inflammatory response by lowering IL-6 tissue levels and targeting the PDIA3/ERK axis. Overall, the obtained data clearly demonstrate the benefice of SHBG treatment in the regulation of adipose tissue metabolism in the course of EMS and provide new insights for the development of molecular therapies with potential translational application to human metabolic disorders.

Thromboelastography in obese horses with insulin dysregulation compared to healthy controls

BACKGROUND

Both obesity and metabolic syndrome are associated with hypercoagulability in people, increasing the risk of cardiovascular disease and thromboembolic events. Whether hypercoagulability exists in obese, insulin-dysregulated horses is unknown.

HYPOTHESIS/OBJECTIVES

To determine if coagulation profiles differ between healthy horses and those with obesity and insulin dysregulation.

ANIMALS

Fifteen healthy horses (CON) and 15 obese, insulin-dysregulated horses (OBID). Individuals were university or client owned.

METHODS

Case-control study. Obesity was defined as a body condition score (BCS) ≥7.5/9 (modified Henneke scale). Insulin dysregulation status was assessed by an oral sugar test (OST). Kaolin-thromboelastography and traditional coagulation variables were compared between groups. The direction and strength of the association between coagulation variables and BCS and OST results were determined using Spearman's correlation.

RESULTS

Thromboelastography variables MA (OBID: 69.5 ± 4.5 mm; CON: 64.8 ± 4.3 mm; P = .007) and G-value (OBID: 11749 ± 2536 dyn/m2 ; CON: 9319 ± 1650 dyn/m2 ; P = .004) were higher in OBID compared to CON. Positive correlations between MA and BCS (R = 0.45, P = .01) and serum insulin (T0 : R = 0.45, P = .01; T60 : R = 0.39, P = .03), and G-value and BCS (R = 0.46, P = .01), and serum insulin (T0 : R = 0.48, P = .007; T60 : R = 0.43, P = .02; T90 : R = 0.38, P = .04) were present.

CONCLUSIONS AND CLINICAL IMPORTANCE

Obese, insulin-dysregulated horses are hypercoagulable compared to healthy controls.

Measurement of Plasma Resistin Concentrations in Horses with Metabolic and Inflammatory Disorders

Simple Summary

Obesity and its associated complications, such as metabolic syndrome, are an increasing problem in both humans and horses in the developed world. Adipose tissue is a key endocrine organ that communicates with other organs by multiple endocrine substances called adipokines. There is evidence to suggest that adipokines may contribute to the regulation of biological processes, such as metabolism, immunity, and inflammation. The aim of this study was to investigate the usefulness of one of these adipokines in horses, resistin, and its relationship with insulin dysregulation (ID) and inflammation. Seventy-two horses, included in one of the four following groups, were studied: healthy controls, horses with inflammatory conditions, horses with mild, and horses with severe ID. Plasma resistin concentrations were significantly different between groups, and the highest values were recorded in the inflammatory and severe ID groups. The lack of correlation of resistin with basal insulin concentration and the significant correlation of resistin with the inflammatory marker serum amyloid A suggest that, as is the case in humans, plasma resistin concentrations in horses are predominantly related to inflammatory conditions and not to ID.

Abstract

Obesity and its associated complications, such as metabolic syndrome, are an increasing problem in both humans and horses in the developed world. The expression patterns of resistin differ considerably between species. In rodents, resistin is expressed by adipocytes and is related to obesity and ID. In humans, resistin is predominantly produced by inflammatory cells, and resistin concentrations do not reflect the degree of obesity, although they may predict cardiovascular outcomes. The aim of this study was to investigate the usefulness of resistin and its relationship with ID and selected indicators of inflammation in horses. Seventy-two horses, included in one of the four following groups, were studied: healthy controls (C, n = 14), horses with inflammatory conditions (I, n = 21), horses with mild ID (ID1, n = 18), and horses with severe ID (ID2, n = 19). Plasma resistin concentrations were significantly different between groups and the higher values were recorded in the I and ID2 groups (C: 2.38 ± 1.69 ng/mL; I: 6.85 ± 8.38 ng/mL; ID1: 2.41 ± 2.70 ng/mL; ID2: 4.49 ± 3.08 ng/mL). Plasma resistin was not correlated with basal insulin concentrations. A significant (r = 0.336, p = 0.002) correlation was found between resistin and serum amyloid A. Our results show that, as is the case in humans, plasma resistin concentrations in horses are predominantly related to inflammatory conditions and not to ID. Horses with severe ID showed an elevation in resistin that may be secondary to the inflammatory status associated with metabolic syndrome.

The Hepatic Stellate Cells (HSTCs) and Adipose-derived Mesenchymal Stem Cells (ASCs) Axis as a Potential Major Driver of Metabolic Syndrome - Novel Concept and Therapeutic Implications

Abstract

Herein, we would like to introduce a novel concept for the prevention and treatment of metabolic syndrome, which is based on molecular relationship between liver and adipose tissue. Particularly, we believe, that unravelling the molecular crosstalk between hepatokines and adipokines will allow to better understand the pathophysiology of metabolic diseases and allow to develop novel, effective therapeutic solutions against obesity and metabolic syndrome.

Graphical Abstract

Inter-organ communication on the level of stem progenitor cells-hepatic stellate cells (HSTCs) and adipose-derived progenitors (ASCs) could represents a key mechanism involved in controlling glucose tolerance as well as insulin sensitivity.

Sex Hormone Binding Globulin (SHBG) Mitigates ER Stress in Hepatocytes In Vitro and Ex Vivo

Despite multiple research studies regarding metabolic syndrome and diabetes, the full picture of their molecular background and pathogenies remains elusive. The latest studies revealed that sex hormone-binding globulin (SHBG)-a serum protein released mainly by the liver-may participate in metabolic dysregulation, as its low serum level correlates with a risk for obesity, metabolic syndrome, and diabetes. Yet, the molecular phenomenon linking SHBG with these disorders remains unclear. In the presented study, we investigate how exogenous SHBG affects metabolically impaired hepatocytes with special attention to endoplasmic reticulum stress (ER stress) and lipid metabolism both in vitro and ex vivo. For that reason, palmitate-treated HepG2 cells and liver tissue samples collected post mortem were cultured in the presence of 50 nM and 100 nM SHBG. We found that SHBG protects against ER stress development and its progression. We have found that SHBG decreased the expression levels of inositol-requiring enzyme 1 (IRE1α), activating transcription factor 6 (ATF6), DNA damage-inducible transcript 3 (CHOP), and immunoglobulin heavy chain-binding protein (BIP). Furthermore, we have shown that it regulates lipolytic gene expression ex vivo. Additionally, herein, we deliver a novel large-animal model to study SHBG in translational research. Our data provide new insights into the cellular and molecular mechanisms by which SHBG modulates hepatocyte metabolism and offer a new experimental approach to study SHBG in human diseases.

MSI-1436 improves EMS adipose derived progenitor stem cells in the course of adipogenic differentiation through modulation of ER stress, apoptosis, and oxidative stress

BACKGROUND

Protein tyrosine phosphatase 1B (PTP1B) is one of the major negative regulators of leptin and insulin signaling, and has been strongly implicated in insulin resistance development in the course of obesity and metabolic syndrome conditions; however, its exact role in controlling adipose tissue biogenesis is still poorly understood.

OBJECTIVES

This investigation aimed to elucidate whether selective inhibition of PTP1B using MSI-1436 compound may improve and restore the defective adipogenicity of ASCs isolated from EMS-affected horses.

METHODS

Equine ASC EMS cells were cultured under adipogenic conditions in the presence of PTP1B inhibitor and were subsequently tested for expression of the main adipogenic-related genes using RT-qPCR, changes in free fatty acid profiles by means of GC-MS technique, and for mitochondrial dynamics improvement through the analysis of mitochondrial transmembrane potential and oxidative stress.

RESULTS

Selective inhibition of PTP1B in equine ASC EMS cells improved substantially adipogenic differentiation by promoting cellular proliferation and normalizing expression of C/EBPalpha, PPARγ, and Adipoq markers that are critical for proper adipogenesis. Levels of secreted adiponectin and PPARγ were also shown to be increased in MSI-1436-conditioned cells, while total leptin levels markedly dropped under the same conditions. Moreover, MSI-1436 treatment enabled the regulation of metabolic-related transcripts that are crosslink to adipogenesis, namely Akt1, Akt2, and SHBG. The obtained results demonstrated also an obvious reduction in intracellular accumulated ROS and NO, as well as mitigated ER stress through the downregulation of Chop, Perk, Atf6, Ire1, and Xbp1 transcripts upon PTP1B inhibition. Furthermore, general fluctuations in FFA composition of all differentiated groups have been highlighted, where palmitic acid, palmitoleic acid, stearic acid, and linolelaidic acid that are known to be associated with the development of metabolic disorders were found to be normalized upon PTP1B inhibition during adipogenic differentiation.

CONCLUSION

The presented data provides the evidence that the use of PTP1B inhibitor may be successful in controlling and enhancing adipogenic differentiation of impaired equine ASCs affected by metabolic syndrome, and thus offers new insights for the management of obesity through the regulation of adipose tissue dynamics.

Effects of equine metabolic syndrome on inflammation and acute-phase markers in horses

Obesity and metabolic disorders are associated with systemic low-grade chronic inflammation, both in humans and animals. The aim of the study is to assess the effects of obesity and hyperinsulinemia on individual components of the acute-phase reaction in equine metabolic syndrome (EMS) horses. Eight mixed-breed EMS and six control, age-matched horses of both sexes were included in the study. Animals were classified as EMS or control based on the assessment of BCS, cresty neck score, and basal insulin >50 μU/mL and/or insulin responses to the oral sugar test (OST) >60 μU/mL. Peripheral venous blood was collected. The expression of proinflammatory cytokines, the concentration of circulating cytokines, and acute-phase proteins (serum amyloid A, C-reactive protein, haptoglobin, activin A, and procalcitonin) were measured. The data were analyzed using the Mann-Whitney test, whereas correlations were examined using Spearman's correlation coefficient. The tests were statistically significant if P ≤ 0.05. There were no differences in cytokine gene expression, circulating cytokine concentrations, or concentrations of acute-phase proteins between the EMS and the control groups. There was a strong correlation between the basal concentration of insulin and the serum concentrations of IL-6 (r = 0.71, P < 0.05). Activin A was positively correlated with post-OST insulin concentrations (r = 0.707, P = 0.05), indicating that this marker of inflammation could warrant further investigation in horses with EMS.

Pododermal angioarchitecture in the equine hoof wall: A light and scanning electron microscopic study of the wall proper

BACKGROUND

Blood supply is an important factor for the normal function of the equine hoof, but earlier studies present conflicting data on functional characteristics of its angioarchitecture.

OBJECTIVE

Emphasis was laid on demonstration of the microvascularisation in the different hoof wall regions, aiming at assessment of specialised vascular structures, e.g. vascular sphincter mechanisms and arteriovenous anastomoses.

METHODS

The angioarchitecture of the adult pododerma in the equine hoof wall was examined by scanning electron microscopy of micro-corrosion casts assisted by exemplary histological and immuno-histochemical characterisation of the pododermal vasculature.

RESULTS

The microvasculature of the lamellae and terminal papillae in all hoof wall regions was described in detail. Focal dilations and microvascular sphincters were a common feature. In contrast to former investigations, true arteriovenous anastomoses were detected at the base of the primary lamellae and the terminal papillae only, while thoroughfare channels proved a regular element within the microvasculature of the wall proper. Bicuspid venous valves were detected as regular feature. For the first time, the alpha-smooth muscle actin-reactivity of the microvascularisation in the hoof wall was systematically assessed, verifying its specialised vasomotor devices.

CONCLUSIONS

The vasculature of the hoof wall displays specific angio-adaptations to high pressure and tensile load.

Association of uncoupling protein (Ucp) gene polymorphisms with cardiometabolic diseases

The hereditary aspect of obesity is a major focus of modern medical genetics. The genetic background is known to determine a higher-than-average prevalence of obesity in certain regions, like Oceania. There is evidence that dysfunction of brown adipose tissue (BAT) may be a risk factor for obesity and type 2 diabetes (T2D). A significant number of studies in the field focus on the UCP family. The Ucp genes code for electron transport carriers. UCP1 (thermogenin) is the most abundant protein of the UCP superfamily and is expressed in BAT, contributing to its capability of generating heat. Single nucleotide polymorphisms (SNPs) of Ucp1-Ucp3 were recently associated with risk of cardiometabolic diseases. This review covers the main Ucp SNPs A-3826G, A-1766G, A-112C, Met229Leu, Ala64Thr (Ucp1), Ala55Val, G-866A (Ucp2), and C-55 T (Ucp3), which may be associated with the development of obesity, disturbance in lipid metabolism, T2D, and cardiovascular diseases.

Influence of Metabolic Status and Diet on Early Pregnant Equine Histotroph Proteome: Preliminary Findings

Insulin resistance (IR) is characterized by an increase in biomarkers of systemic inflammation and susceptibility to laminitis in horses. Impacts on reproduction include a lengthened interovulatory period in horses. Dietary omega-3 (docosahexaenoic acid [DHA]) promotes anti-inflammatory processes, has been implicated in health benefits, and can reduce cytokine secretion. This preliminary study investigated the impact of IR as well as the influence of dietary supplementation (DHA) on the uterine fluid proteome in early pregnant horses. Mares were artificially inseminated; uterine fluid and embryos were collected on d 12.5 after ovulation. Uterine fluid was pooled for metabolic and diet categories (n = 8; n = 2 per metabolic and dietary status) and concentrated, and the proteome was analyzed using tandem mass spectrometry (iTRAQ). Five proteins met differential abundance criteria (±1.5-fold change, P < .05) in all comparisons (Control C, IS vs. C, IR; C, IS vs. DHA, IS; C, IR vs. DHA, IR). Serum amyloid A, afamin, and serotransferrin were upregulated in C, IR mares but downregulated in DHA, IR mares when compared to C, IS and C, IR, respectively. Quantitative PCR supported mass spectrometry results. The presence of serum amyloid A and serotransferrin in histotroph of IR mares potentially indicates an inflammatory response not seen in IS counterparts. These preliminary findings provide novel evidence on the potential impact of insulin resistance and DHA supplementation on the secreted equine uterine proteome during early pregnancy.

Ultrasonographic measures of body fatness and their relationship with plasma levels and adipose tissue expression of four adipokines in Welsh pony mares

Obesity is responsible for metabolic dysregulations that alter fertility and induce pathologies. The objectives of the present study were to validate a reliable method for the evaluation of body fatness in mares and to associate the body fat estimation data to metabolic changes, including adipokines at the plasma and adipose tissue levels. To reach this purpose, animals were subjected to two extreme breeding conditions to study the variation of morphological, ultrasound, and physiological parameters. Twenty Welsh mares were followed up monthly from April to October before and after animals were moved outdoors to grasslands. Body weight (BW), body length (BL), height at the withers (HW), thoracic perimeter (TP), 5-point body condition score (BCS), and subcutaneous fat thickness (SFT) at the level of the shoulder, the lumbar region, and the rump, measured by ultrasonography, and plasma and adipose tissue metabolic indicators were assessed in parallel. Statistical analysis was performed using a linear mixed-effects model, whereas Pearson tests were used for the analysis of the correlations between the different parameters. Although mean BW did not increase significantly (P = 0.0940), TP (P = 0.0002) and BCS (P < 0.0001) increased during the study period. Ultrasonographic examination of subcutaneous adipose tissue showed an increase in SFT at the level of the shoulder (P < 0.0001), lumbar region (P < 0.0001), and rump (P < 0.0001). Plasma concentrations of nonesterified fatty acids (P < 0.0001), phospholipids (P < 0.0001), and cholesterol (P < 0.0001) increased significantly, whereas triglycerides (P < 0.0001) decreased significantly during the study period. Although both plasma concentrations and adipose tissue expression of leptin (P < 0.0001) and resistin (P < 0.0001) increased significantly, adiponectin (P < 0.0001) significantly decreased and visfatin remained unchanged (P = 0.8401). Expression of adipokine receptors studied showed the opposite pattern compared with their ligand. Ultrasonographic measurements of subcutaneous adipose tissue thickness at the shoulder, lumbar region, and rump are relevant indicators of fatness related with adipokine plasma concentrations and expression of adipokine-related receptors in adipose tissue, and particularly highlight seasonal effects.

Expression of immune regulatory genes correlate with the abundance of specific Clostridiales and Verrucomicrobia species in the equine ileum and cecum

Billions of bacteria inhabit the gastrointestinal tract. Immune-microbial cross talk is responsible for immunological homeostasis, and symbiotic microbial species induce regulatory immunity, which helps to control the inflammation levels. In this study we aimed to identify species within the equine intestinal microbiota with the potential to induce regulatory immunity. These could be future targets for preventing or treating low-grade chronic inflammation occurring as a result of intestinal microbial changes and disruption of the homeostasis. 16S rRNA gene amplicon sequencing was performed on samples of intestinal microbial content from ileum, cecum, and colon of 24 healthy horses obtained from an abattoir. Expression of genes coding for IL-6, IL-10, IL-12, IL-17, 18 s, TNFα, TGFβ, and Foxp3 in the ileum and mesenteric lymph nodes was measured by qPCR. Intestinal microbiota composition was significantly different in the cecum and colon compared to the ileum, which contains large abundances of Proteobacteria. Especially members of the Clostridiales order correlated positively with the regulatory T-cell transcription factor Foxp3 and so did the phylum Verrucomicrobia. We conclude that Clostridiales and Verrucomicrobia have the potential to induce regulatory immunity and are possible targets for intestinal microbial interventions aiming at regulatory immunity improvement.

From Table to Stable: A Comparative Review of Selected Aspects of Human and Equine Metabolic Syndrome

Obesity data in people and companion animals are depicting a future of increasing morbidity, cost for society, and significant health and welfare concerns. Between 25 and 50% of cats, dogs, and horses in developed countries are overweight or obese, which mirrors the situation in humans. Equine metabolic syndrome (EMS) was named after human metabolic syndrome (MetS), which has about 30 years of lead in research efforts. Even though the complications of the two syndromes seem to grossly differ (cardiac vs. laminitis risk), a number of similar disease mechanisms are worthy of investigation. Since the first EMS consensus statement by the American College of Veterinary Internal Medicine in 2010, numerous studies have confirmed the link between insulin dysregulation and laminitis, even though the mechanisms are not fully understood. After the discovery of the role of adipokines in MetS, evidence about inflammatory mechanisms related to adiposity in rodent models, companion animals, horses, and humans is constantly increasing. Oxidative and dicarbonyl stress have been correlated with insulin dysregulation, obesity, and recently with laminitis. Vascular actions of insulin through nitric oxide, endothelin-1, and other mechanisms are being studied in horses and can provide a better understanding of laminitis pathophysiology. More research is needed on neuropathic mechanisms in insulin-dysregulated horses, which could be important in the pathogenesis of laminitis and laminitic pain. Human literature can provide viable material for novel studies in areas that have received limited attention, in addition to being valuable information for clients about the consequences of unhealthy management of their horses.

Lipid classes in adipose tissues and liver differ between Shetland ponies and Warmblood horses

Fatty acids, as key components of cellular membranes and complex lipids, may play a central role in endocrine signalling and the function of adipose tissue and liver. Thus, the lipid fatty acid composition may play a role in health status in the equine. This study aimed to investigate the fatty acid composition of different tissues and liver lipid classes by comparing Warmblood horses and Shetland ponies under defined conditions. We hypothesized that ponies show different lipid patterns than horses in adipose tissue, liver and plasma. Six Warmblood horses and six Shetland ponies were housed and fed under identical conditions. Tissue and blood sampling were performed following a standardized protocol. A one-step lipid extraction, methylation and trans-esterification method with subsequent gas chromatography was used to analyse the total lipid content and fatty acid profile of retroperitoneal, mesocolon and subcutaneous adipose tissue, liver and plasma. Fatty acids were grouped according to their degree of saturation and their conjugated double bond into the respective lipid classes. In the adipose tissues, saturated fatty acids (SFAs) and n-9 monounsaturated fatty acids (n-9 MUFAs) were most present in ponies and horses. N-6 polyunsaturated fatty acids (n-6 PUFAs), followed by SFAs, were most frequently found in liver tissue and plasma in all animals. Horses, in comparison to ponies, had significantly higher n-6 PUFA levels in all tissues and plasma. In liver tissue, horses had significantly lower hepatic iso-branched-chain fatty acids (iso-BCFAs) than ponies. The hepatic fatty acid composition of selected lipid classes was different between horses and ponies. In the polar PL fraction, horses had low n-9 MUFA and n-3 PUFA contents but higher n-6 PUFA contents than ponies. Furthermore, iso-BCFAs are absent in several hepatic lipid fractions of horses but not ponies. The differences in fatty acid lipid classes between horses and ponies provide key information on the species- and location-specific regulation of FA metabolism, thus affecting health status such as inflammatory responses.

Detection of endoplasmic reticulum stress and the unfolded protein response in naturally-occurring endocrinopathic equine laminitis

Background

Laminitis is often associated with endocrinopathies that cause hyperinsulinemia and is also induced experimentally by hyperinsulinemia, suggesting that insulin initiates laminitis pathogenesis. Hyperinsulinemia is expected to activate pro-growth and anabolic signaling pathways. We hypothesize that chronic over-stimulation of these pathways in lamellar tissue results in endoplasmic reticulum stress, contributing to tissue pathology, as it does in human metabolic diseases. We tested this hypothesis by asking whether lamellar tissue from horses with naturally-occurring endocrinopathic laminitis showed expression of protein markers of endoplasmic reticulum stress.

Results

Three markers of endoplasmic reticulum stress, spliced XBP1, Grp78/BiP and Grp94, were upregulated 2.5–9.5 fold in lamellar tissues of moderately to severely laminitic front limbs (n = 12) compared to levels in controls (n = 6–7) measured by immunoblotting and densitometry. Comparing expression levels between laminitic front limbs and less affected hind limbs from the same horses (paired samples from 7 to 8 individual horses) demonstrated significantly higher expression for both spliced XBP1 and Grp78/BiP in the laminitic front limbs, and a similar trend for Grp94. Expression levels of the 3 markers were minimal in all samples of the control (n = 6–7) or hind limb groups (n = 7–8). Immunofluorescent localizations were used to identify cell types expressing high levels of Grp78/BiP, as an indicator of endoplasmic reticulum stress. Grp78/BiP expression was highly elevated in suprabasal epidermal keratinocytes and only observed in laminitic front limbs (10/12 laminitic samples, compared to 0/7 in sections from the hind limbs and 0/5 of controls).

Conclusions

These data demonstrate that the endoplasmic reticulum stress pathway is active in naturally occurring cases of laminitis and is most active within a subset of epidermal keratinocytes. These data provide the rationale for further study of endoplasmic reticulum stress in experimental models of laminitis and the links between laminitis and human diseases sharing activation of this stress pathway. Pharmacological options to manipulate the endoplasmic reticulum stress pathway under investigation for human disease could be applicable to laminitis treatment and prevention should this pathway prove to be a driver of disease progression.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1748-x) contains supplementary material, which is available to authorized users.

Cell-Specific "Competition for Calories" Drives Asymmetric Nutrient-Energy Partitioning, Obesity, and Metabolic Diseases in Human and Non-human Animals

The mammalian body is a complex physiologic “ecosystem” in which cells compete for calories (i.e., nutrient-energy). Axiomatically, cell-types with competitive advantages acquire a greater number of consumed calories, and when possible, increase in size and/or number. Thus, it is logical and parsimonious to posit that obesity is the competitive advantages of fat-cells (adipocytes) driving a disproportionate acquisition and storage of nutrient-energy. Accordingly, we introduce two conceptual frameworks. Asymmetric Nutrient-Energy Partitioning describes the context-dependent, cell-specific competition for calories that determines the partitioning of nutrient-energy to oxidation, anabolism, and/or storage; and Effective Caloric Intake which describes the number of calories available to constrain energy-intake via the inhibition of the sensorimotor appetitive cells in the liver and brain that govern ingestive behaviors. Inherent in these frameworks is the independence and dissociation of the energetic demands of metabolism and the neuro-muscular pathways that initiate ingestive behaviors and energy intake. As we demonstrate, if the sensorimotor cells suffer relative caloric deprivation via asymmetric competition from other cell-types (e.g., skeletal muscle- or fat-cells), energy-intake is increased to compensate for both real and merely apparent deficits in energy-homeostasis (i.e., true and false signals, respectively). Thus, we posit that the chronic positive energy balance (i.e., over-nutrition) that leads to obesity and metabolic diseases is engendered by apparent deficits (i.e., false signals) driven by the asymmetric inter-cellular competition for calories and concomitant differential partitioning of nutrient-energy to storage. These frameworks, in concert with our previous theoretic work, the Maternal Resources Hypothesis, provide a parsimonious and rigorous explanation for the rapid rise in the global prevalence of increased body and fat mass, and associated metabolic dysfunctions in humans and other mammals inclusive of companion, domesticated, laboratory, and feral animals.

The Effect of Methyl-β-cyclodextrin on Apoptosis, Proliferative Activity, and Oxidative Stress in Adipose-Derived Mesenchymal Stromal Cells of Horses Suffering from Metabolic Syndrome (EMS)

Methyl-β-cyclodextrin (MβCD) is a cyclic oligosaccharide, commonly used as a pharmacological agent to deplete membrane cholesterol. In this study, we examined the effect of MβCD on adipose-derived mesenchymal stromal cells (ASCs) isolated form healthy horses (ASC_CTRL) and from horses suffering from metabolic syndrome (ASC_EMS). We investigated the changes in the mRNA levels of the glucose transporter 4 (GLUT4) and found that MβCD application may lead to a significant improvement in glucose transport in ASC_EMS. We also showed that MβCD treatment affected GLUT4 upregulation in an insulin-independent manner via an NO-dependent signaling pathway. Furthermore, the analysis of superoxide dismutase activity (SOD) and reactive oxygen species (ROS) levels showed that MβCD treatment was associated with an increased antioxidant capacity in ASC_EMS. Moreover, we indicated that methyl-β-cyclodextrin treatment did not cause a dysfunction of the endoplasmic reticulum and lysosomes. Thereby, we propose the possibility of improving the functionality of ASC_EMS by increasing their metabolic stability.

Determination of lipid profiles in serum of obese ponies before and after weight reduction by using multi-one-dimensional thin-layer chromatography

Obesity is a key component of equine metabolic syndrome, which is highly associated with laminitis. Feed restriction and/or exercise are known to alleviate the detrimental effects of insulin resistance in obese ponies. However, little is known about changes in the serum lipid patterns due to weight reduction and its association with disease outcomes. Therefore, the lipid patterns in the serum of 14 mature ponies before and after a 14-week body weight reduction program (BWRP) were investigated by multi-one-dimensional thin-layer chromatography (MOD-TLC). Additionally, sensitivity to insulin (SI), body condition scores (BCS) and cresty neck scores (CNS) were measured. A BWRP resulted in a significant loss of body weight (P<0.001), which was associated with beneficial decreases in BCS and CNS (both, P<0.001). Serum lipid compositions revealed significantly increased free fatty acid (FFA), sphingomyelin (SM; both P<0.001), total cholesterol (C) and cholesterol ester (CE) (both P<0.01) and triacylglycerol (TG; P<0.05) densities. Improvement of SI after the BWRP was associated with increases in neutral lipids (C, CE and TG, all P<0.01), FFA and the phospholipid SM (both, P<0.001). The results show that a BWRP in obese ponies was effective and associated with changes in the concentrations of neutral lipids and the phospholipid SM, indicating that SM may play a role in insulin signaling pathways and thus in the pathogenesis of insulin resistance and the progression of metabolic syndrome in obese ponies.

Endocrine, morphometric, and ultrasonographic characterization of neck adiposity in Andalusian horses

Equine metabolic syndrome (EMS) can be diagnosed by hormonal measurements; however, it would be important to find simpler measurements that allow easy identification of affected or at risk individuals. In horses, the dorsal neck region is one of the most frequent anatomical sites for fat deposition and neck obesity has been linked to EMS. The aim of this study was to evaluate the association of hormonal markers of obesity (leptin) and insulin resistance (insulin) with morphometric and ultrasonographic neck measurements in Andalusian horses. Plasma leptin and insulin concentrations were measured by RIA in 127 Andalusian horses. Neck circumferences (NC) were measured at 3 equidistant locations at 25%, 50%, and 75% of neck length (NC-25%, NC-50%, and NC-75%). At the same 3 locations, subcutaneous fat thickness (SFT-25%, SFT-50%, and SFT-75%) was measured ultrasonographically. In the population under study, a tendency to adiposity was confirmed by the elevated plasma leptin levels (7.47 ± 5.03 ng/mL). However, plasma insulin concentrations (4.05 ± 3.74 μIU/mL) were within normal range in most horses. Our results indicate that NC showed significant sexual dimorphism and did not correlate well with hormonal measurements. Ultrasonographic assessment of fat thickness at the base of the neck (SFT-75%) was significantly correlated with both plasma leptin and insulin and did not show differences between males and females. Thus, in the search for a single objective parameter which can be used in large populations, SFT-75% is a potential candidate and may be a meaningful parameter to predict EMS.