Frederik J. Steyn

Gender differences in autoimmune disease

Autoimmune diseases are a range of diseases in which the immune response to self-antigens results in damage or dysfunction of tissues. Autoimmune diseases can be systemic or can affect specific organs or body systems. For most autoimmune diseases there is a clear sex difference in prevalence, whereby females are generally more frequently affected than males. In this review, we consider gender differences in systemic and organ-specific autoimmune diseases, and we summarize human data that outlines the prevalence of common autoimmune diseases specific to adult males and females in countries commonly surveyed. We discuss possible mechanisms for sex specific differences including gender differences in immune response and organ vulnerability, reproductive capacity including pregnancy, sex hormones, genetic predisposition, parental inheritance, and epigenetics. Evidence demonstrates that gender has a significant influence on the development of autoimmune disease. Thus, considerations of gender should be at the forefront of all studies that attempt to define mechanisms that underpin autoimmune disease.

Pregnancy‐Induced Adaptation in the Neuroendocrine Control of Prolactin Secretion

During pregnancy, neuroendocrine control of prolactin secretion is markedly altered to allow a state of hyperprolactinaemia to develop. Prolactin secretion is normally tightly regulated by a short‐loop negative‐feedback mechanism, whereby prolactin stimulates activity of tuberoinfundibular dopamine (TIDA) neurones to increase dopamine secretion into the pituitary portal blood. Dopamine inhibits prolactin secretion, thus reducing prolactin concentrations in the circulation back to the normal low level. Activation of this feedback secretion by placental lactogen during pregnancy maintains relatively low levels of prolactin secretion during early and mid‐pregnancy. Despite the continued presence of placental lactogen, however, dopamine secretion from TIDA neurones is reduced during late pregnancy. Moreover, the neurones become completely unresponsive to endogenous or exogenous prolactin at this time, allowing a large nocturnal surge of prolactin to occur from the maternal pituitary gland during the night before parturition. In this review, we describe the changing patterns of prolactin secretion during pregnancy in the rat, and discuss the neuroendocrine mechanisms controlling these changes. The loss of response to prolactin is an important maternal adaptation to pregnancy, allowing the prolonged period of hyperprolactinaemia required for mammary gland development and function and for maternal behaviour immediately after parturition, and possibly also contributing to a range of other adaptive responses in the mother.

Development of a Method for the Determination of Pulsatile Growth Hormone Secretion in Mice

Measures of pulsatile GH secretion require frequent collection and analysis of blood samples at regular intervals. Due to blood volume constraints, repeat measures of circulating levels of GH in mice remain challenging. Consequently, few observations exist in which the pulsatile pattern of GH secretion in mice have been characterized. To address this, we developed a technique for the collection and analysis of circulating levels of GH at regular and frequent intervals in freely moving mice. This was achieved through the development of a sensitive assay for the detection of GH in small (2 μl) quantities of whole blood. The specificity and accuracy of this assay was validated following guidelines established for single-laboratory validation as specified by the International Union of Pure and Applied Chemistry. We incorporated an established method for tail-clip blood sample collection to determine circulating levels of GH secretion in 36 whole blood samples collected consecutively over a period of 6 h. Resulting measures were characterized by peak secretion periods and interpulse stable baseline secretion periods. Periods characterized by elevated whole blood GH levels consisted of multicomponent peaks. Deconvolution analysis of resulting measures confirmed key parameters associated with pulsatile GH secretion. We show a striking decrease in pulsatile GH secretion in mice after 12-18 h of fasting. This model is necessary to characterize the pulsatile profile of GH secretion in mice and will significantly contribute to current attempts to clarify mechanisms that contribute to the regulation of GH secretion.

Development of a methodology for and assessment of pulsatile luteinizing hormone secretion in juvenile and adult male mice.

Current methodology to monitor pulsatile LH release in mice is limited by inadequate assay sensitivity, resulting in the need for collection of large blood volumes. Thus, assessment of pulsatile LH secretion in mice remains highly challenging, and observations are limited to adult mice. To address this, we developed a highly sensitive ELISA for assessment of mouse LH concentrations in small fractions of whole blood. We demonstrate that this assay is capable of reliably detecting LH down to a theoretical limit of 0.117 ng/mL in a 2-μL fraction of whole blood. Using an established frequent blood collection procedure, we validated the accuracy of this method by determining the pulsatile LH secretion in early-adult (10 weeks old) C57BL6/J male mice. Data demonstrate regular pulsatile release of LH, with peaks in LH secretion rarely exceeding 3 ng/mL. Moreover, assessment of LH release in Gpr54 knockout mice demonstrates the lack of pulsatile LH release after the loss of kisspeptin-mediated pubertal maturation. We next determined age-associated changes in pulsatile LH secretion by assessment of LH secretion in prepubertal (28 days old) C57BL6/J male mice and repeated assessment in the same mice in adulthood (120 days old). Data demonstrate that the rise in total LH secretion in mice after pubertal maturation occurs along with an overall rise in the pulsatile LH secretion rate. This was coupled with a significant increase in the number of LH secretory events (number of pulses). In addition, we observed a decrease in the clearance (increased half-life) and a decrease in the regularity (approximate entropy) of LH release. This method will be of wide general utility within the field of reproductive biology.

Omega-3 fatty acids: a review of the effects on adiponectin and leptin and potential implications for obesity management

An increase in adiposity is associated with altered levels of biologically active proteins. These include the hormones adiponectin and leptin. The marked change in circulating concentrations of these hormones in obesity has been associated with the development of insulin resistance and metabolic syndrome. Variations in dietary lipid consumption have also been shown to impact obesity. Specifically, omega-3 fatty acids have been correlated with the prevention of obesity and subsequent development of chronic disease sequalae. This review explores animal and human data relating to the effects of omega-3 fatty acids (marine lipids) on adiponectin and leptin, considering plausible mechanisms and potential implications for obesity management. Current evidence suggests a positive, dose-dependent relationship between omega-3 fatty acid intake and circulating levels of adiponectin. In obese subjects, this may translate into a reduced risk of developing cardiovascular disease, metabolic syndrome and diabetes. In non-obese subjects, omega-3 is observed to decrease circulating levels of leptin; however, omega-3-associated increases in leptin levels have been observed in obese subjects. This may pose benefits in the prevention of weight regain in these subjects following calorie restriction.

Hormonal Regulation of Suppressors of Cytokine Signaling (SOCS) Messenger Ribonucleic Acid in the Arcuate Nucleus during Late Pregnancy

Prolactin stimulates tuberoinfundibular dopamine neurons in the arcuate nucleus of the hypothalamus, mediated by signal transducer and activator of transcription 5b (STAT5b). During late pregnancy, these neurons become unresponsive to prolactin, with a loss of prolactin-induced activation of STAT5b and decreased dopamine secretion. Suppressors of cytokine signaling (SOCS) proteins inhibit STAT-mediated signaling, and SOCS mRNAs are specifically elevated in the arcuate nucleus during late pregnancy. We hypothesized that changes in circulating ovarian steroids during late pregnancy might induce expression of SOCS mRNAs, thus disrupting STAT5b-mediated prolactin signaling. Rats were ovariectomized on d 18 of pregnancy and treated with ovarian steroids to simulate an advanced, normal, or delayed decline in progesterone. Early progesterone withdrawal caused an early increase in prolactin secretion, and increased SOCS-1 and -3 and cytokine-inducible SH2-containing protein (CIS) mRNA levels in the arcuate nucleus. Prolonged progesterone treatment prevented these changes. To determine whether ovarian steroids directly alter SOCS mRNA levels, estrogen- and/or progesterone-treated ovariectomized nonpregnant rats were acutely injected with prolactin (300 microg sc) or vehicle. SOCS-1 and -3 and CIS mRNA levels in the arcuate nucleus were significantly increased by estrogen or prolactin, whereas progesterone treatment reversed the effect of estrogen. Results demonstrate that estrogen and prolactin can independently induce SOCS mRNA in the arcuate nucleus and that this effect is negatively regulated by progesterone. This is consistent with the hypothesis that declining progesterone and high levels of estrogen during late pregnancy induce SOCS in the tuberoinfundibular dopamine neurons, thus contributing to their insensitivity to prolactin at this time.

Adiponectin Regulate Growth Hormone Secretion Via Adiponectin Receptor Mediated Ca2+ Signalling in Rat Somatotrophs In Vitro

Obesity is associated with reduced levels of growth hormone (GH) and the disruption of pulsatile GH secretion. This results in relative GH deficiency. It is likely that a regulatory relationship between GH secretion and adipose tissue exists as the secretion of GH recovers to normal levels after a reduction in body weight. This report characterise the expression and interaction of adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2) and adiponectin, respectively, in regulating the activity of GH secreting cells. Polymerase chain reaction analysis of the GH3 cell line, rat anterior pituitary gland and isolated somatotroph cells from transgenic GFP expressing mice confirmed the expression of both AdipoR1 and AdipoR2 in GH secretory cells. Because GH cells expressed both receptors, it is likely that the measured increase in GH secretion, observed in primary cultured rat pituitary cells after 30 min of incubation with full‐length murine adiponectin, was mediated by a direct receptor regulated process. Adiponectin induced an increase in intracellular Ca2+ through both the influx of extracellular Ca2+ and the release of intracellular Ca2+ stores resulting in the secretion of GH. Furthermore, results confirm that this increase in GH secretion depended mainly on an increase in Ca2+ influx through L‐type Ca2+ channels. It is concluded that adiponectin directly regulates GH secretion from somatotrophs by binding to either adiponectin receptor, and that this is mediated via a similar process observed after the stimulation of GH secretion by GH‐releasing hormone.

Expression of Ovarian Steroid Hormone Receptors in Tuberoinfundibular Dopaminergic Neurones During Pregnancy and Lactation

During late‐pregnancy, tuberoinfundibular dopaminergic (TIDA) neurones, a critical component of the negative‐feedback loop regulating prolactin secretion, become unresponsive to the stimulatory effects of prolactin. The change in TIDA responsiveness to prolactin at this time results in a decrease in dopamine secretion and a prolactin surge. As the onset of parturition and the antepartum prolactin surge depend on the withdrawal of progesterone in the presence of oestrogen, it is likely that ovarian steroid hormones mediate this change in TIDA responsiveness. To determine whether ovarian steroids can directly modulate TIDA activity, and whether changes of receptor numbers might contribute to overall steroid‐regulation of these neurones, we investigated the level of oestrogen receptor alpha (ERα) and progesterone receptor (PR) expression within TIDA neurones during pregnancy and lactation. Animals were sacrificed on dioestrous, days 12, 19 and 21 of pregnancy and day 5 of lactation, and the proportion of TIDA neurones expressing ERα or PR, as well as the total number of PR expressing cells within the arcuate nucleus, was determined. Approximately 75% and 55% of tyrosine hydroxylase neurones expressed ERα and PR, respectively. Levels of steroid receptor expression within TIDA neurones remained fairly constant, except for an increase in ERα on days 12 and 19 of pregnancy compared to dioestrous and lactation day 5. The presence of steroid receptors on TIDA neurones during pregnancy and lactation supports the concept of a direct effect of steroid hormones on these neurones at this time. Thus, steroid hormones may directly act on TIDA neurones to regulate maternal prolactin secretion. The relatively stable level of expression during late pregnancy suggests that a shift in steroid receptor expression during late pregnancy does not contribute to the change in TIDA responsiveness to prolactin at this time.

Body mass index and dietary intervention: Implications for prognosis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult onset, neurodegenerative disease that is characterized by the loss of upper (corticospinal) and lower motor neurons. ALS is a multifactorial disease whereby a combination of genetic and environmental factors may contribute to disease pathogenesis. While the majority of studies indicate that the underlying causes for ALS pathology may be due to multiple defects at the cellular level, factors that have recently been identified to be associated with survival could lead to the development of beneficial interventions. In ALS, a higher pre-morbid body mass index (BMI) and the maintenance of BMI and nutritional state is associated with improved outcome. This review will focus on the associations between body composition and adiposity relative to disease duration and risk, and will discuss current evidence that supports the benefits of improving energy balance, and the maintenance of body mass through nutritional intervention in ALS.

17α-Estradiol Alleviates Age-related Metabolic and Inflammatory Dysfunction in Male Mice Without Inducing Feminization

Aging is associated with visceral adiposity, metabolic disorders, and chronic low-grade inflammation. 17&agr;-estradiol (17&agr;-E2), a naturally occurring enantiomer of 17&bgr;-estradiol (17&bgr;-E2), extends life span in male mice through unresolved mechanisms. We tested whether 17&agr;-E2 could alleviate age-related metabolic dysfunction and inflammation. 17&agr;-E2 reduced body mass, visceral adiposity, and ectopic lipid deposition without decreasing lean mass. These declines were associated with reductions in energy intake due to the activation of hypothalamic anorexigenic pathways and direct effects of 17&agr;-E2 on nutrient-sensing pathways in visceral adipose tissue. 17&agr;-E2 did not alter energy expenditure or excretion. Fasting glucose, insulin, and glycosylated hemoglobin were also reduced by 17&agr;-E2, and hyperinsulinemic-euglycemic clamps revealed improvements in peripheral glucose disposal and hepatic glucose production. Inflammatory mediators in visceral adipose tissue and the circulation were reduced by 17&agr;-E2. 17&agr;-E2 increased AMPK&agr; and reduced mTOR complex 1 activity in visceral adipose tissue but not in liver or quadriceps muscle, which is in contrast to the generalized systemic effects of caloric restriction. These beneficial phenotypic changes occurred in the absence of feminization or cardiac dysfunction, two commonly observed deleterious effects of exogenous estrogen administration. Thus, 17&agr;-E2 holds potential as a novel therapeutic for alleviating age-related metabolic dysfunction through tissue-specific effects.