Morphometric analysis of obesity (ob/ob)- and diabetes (db/db)-associated hypothalamic neuronal degeneration in C57BL/KsJ mice

Neurog2 Acts as a Classical Proneural Gene in the Ventromedial Hypothalamus and Is Required for the Early Phase of Neurogenesis

The tuberal hypothalamus is comprised of the dorsomedial, ventromedial, and arcuate nuclei, as well as parts of the lateral hypothalamic area, and it governs a wide range of physiologies. During neurogenesis, tuberal hypothalamic neurons are thought to be born in a dorsal-to-ventral and outside-in pattern, although the accuracy of this description has been questioned over the years. Moreover, the intrinsic factors that control the timing of neurogenesis in this region are poorly characterized. Proneural genes, including Achate-scute-like 1 (Ascl1) and Neurogenin 3 (Neurog3) are widely expressed in hypothalamic progenitors and contribute to lineage commitment and subtype-specific neuronal identifies, but the potential role of Neurogenin 2 (Neurog2) remains unexplored. Birthdating in male and female mice showed that tuberal hypothalamic neurogenesis begins as early as E9.5 in the lateral hypothalamic and arcuate and rapidly expands to dorsomedial and ventromedial neurons by E10.5, peaking throughout the region by E11.5. We confirmed an outside-in trend, except for neurons born at E9.5, and uncovered a rostrocaudal progression but did not confirm a dorsal-ventral patterning to tuberal hypothalamic neuronal birth. In the absence of Neurog2, neurogenesis stalls, with a significant reduction in early-born BrdU⁺ cells but no change at later time points. Further, the loss of Ascl1 yielded a similar delay in neuronal birth, suggesting that Ascl1 cannot rescue the loss of Neurog2 and that these proneural genes act independently in the tuberal hypothalamus. Together, our findings show that Neurog2 functions as a classical proneural gene to regulate the temporal progression of tuberal hypothalamic neurogenesis.SIGNIFICANCE STATEMENT Here, we investigated the general timing and pattern of neurogenesis within the tuberal hypothalamus. Our results confirmed an outside-in trend of neurogenesis and uncovered a rostrocaudal progression. We also showed that Neurog2 acts as a classical proneural gene and is responsible for regulating the birth of early-born neurons within the ventromedial hypothalamus, acting independently of Ascl1 In addition, we revealed a role for Neurog2 in cell fate specification and differentiation of ventromedial -specific neurons. Last, Neurog2 does not have cross-inhibitory effects on Neurog1, Neurog3, and Ascl1 These findings are the first to reveal a role for Neurog2 in hypothalamic development.

Amylin and Leptin interaction: Role During Pregnancy, Lactation and Neonatal Development

Amylin is co-secreted with insulin by pancreatic β-cells in response to a meal and produced by neurons in discrete hypothalamic brain areas. Leptin is proportionally secreted by the adipose tissue. Both hormones control food intake and energy homeostasis post-weaning in rodents. While amylin's main site of action is located in the area postrema (AP) and leptin's is located in the mediobasal hypothalamus, both hormones can also influence the other's signaling pathway; amylin has been shown enhance hypothalamic leptin signaling, and amylin signaling in the AP may rely on functional leptin receptors to modulate its effects. These two hormones also play major roles during other life periods. During pregnancy, leptin levels rise as a result of an increase in fat depot resulting in gestational leptin-resistance to prepare the maternal body for the metabolic needs during fetal development. The role of amylin is far less studied during pregnancy and lactation, though amylin levels seem to be elevated during pregnancy relative to insulin. Whether amylin and leptin interact during pregnancy and lactation remains to be assessed. Lastly, during brain development, amylin and leptin are major regulators of cell birth during embryogenesis and act as neurotrophic factors in the neonatal period. This review will highlight the role of amylin and leptin, and their possible interaction, during these dynamic time periods of pregnancy, lactation, and early development.

Emerging Signaling Pathway in Arcuate Feeding-Related Neurons: Role of the Acbd7

The understanding of the mechanisms whereby energy balance is regulated is essential to the unraveling of the pathophysiology of obesity. In the last three decades, focus was put on the metabolic role played by the hypothalamic neurons expressing proopiomelanocortin (POMC) and cocaine and amphetamine regulated transcript (CART) and the neurons co-localizing agouti-related peptide (AgRP), neuropeptide Y (NPY), and gamma-aminobutyric acid (GABA). These neurons are part of the leptin-melanocortin pathway, whose role is key in energy balance regulation. More recently, the metabolic involvement of further hypothalamic uncharacterized neuron populations has been suggested. In this review, we discuss the potential homeostatic implication of hypothalamic GABAergic neurons that produce Acyl-Coa-binding domain containing protein 7 (ACBD7), precursor of the nonadecaneuropeptide (NDN), which has recently been characterized as a potent anorexigenic neuropeptide capable of relaying the leptin anorectic/thermogenic effect via the melanocortin system.

Embryonic development of the hypothalamic feeding circuitry: Transcriptional, nutritional, and hormonal influences

Background

Embryonic neurogenesis and differentiation in the hypothalamic feeding circuitry is under the control of a variety of diffused morphogens and intrinsic transcription factors, leading to the unique structural and functional characteristics of each nucleus.

Scope of review

The transcriptional regulation of the development of feeding neuroendocrine systems during the period of embryonic neurogenesis and differentiation will be reviewed here, with a special emphasis on genetic and environmental manipulations that yield an adverse metabolic phenotype.

Major conclusions

Emerging data suggest that developmental mechanisms can be perturbed not only by genetic manipulation, but also by manipulations to maternal nutrition during the gestational period, leading to long-lasting behavioral, neurobiological, and metabolic consequences. Leptin is neurotrophic in the embryonic brain, and given that it varies in proportion to maternal energy balance, may mediate these effects through an interaction with the mechanisms of hypothalamic development.

Hypercytolipidemia-induced nuclear lipoapoptosis: cytochemical analysis and integrated review of hypogonadal, diabetes-obesity syndrome-induced female reproductive axis disruption

Expression of the diabetes (db/db) mutation (i.e., leptin receptor defect) in C57BL/KsJ mice results in the functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian lipocytoatrophy. The current studies define the cytostructural, metabolic and endocrine disturbances associated with hypercytolipidemia and coincident nuclear lipoapoptosis following expression of the db/db-mutation. Adult, female C57BL/KsJ control (+/+ and +/? genotypes) and db/db mutant littermates were monitored for systemic alterations in blood glucose, insulin, luteinizing hormone (LH) and 17-B-estradiol (E2) concentrations associated with db/db-enhanced cytolipid depositions and TUNEL-labeled 3'-DNA fragmentation indexed nuclear lipoapoptosis. Obesity, hyperglycemia and hyperinsulinemia, in addition to depressed LH and E2 concentrations, characterized all db/db-mutants relative to control indices. Structural and cytochemical analysis of basophilic gonadotroph cells, ovarian follicular granulosa cells and uterine endometrial epithelial layers indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to control cytoarchitecture profiles. Vasolipidemia and interstitial cytoadiposity were prominent in all db/db tissue compartments. In each affected cell type within the db/db pituitary-reproductive tract axis, hypercytolipidemia was localized with pronounced nuclear lipo-infiltration and 3'-DNA TUNEL-labeled fragmentation. These data indicate that coincident cytostructural, endocrine and metabolic disturbances associated with hypogonadal pituitary-reproductive tract hypercytolipidemia are functional manifestations of the expressed diabetes-obesity syndrome in db/db-mutants. The progressive vaso-, interstitial-, and cyto-lipidemic alterations in cytoarchitecture correlated with the coincident nuclear lipoapoptotic dissolution and pronounced organo-involution, alterations which contributed to the functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Obesity-dependent cannabinoid modulation of proliferation in adult neurogenic regions

Endocannabinoid signalling participates in the control of neurogenesis, especially after brain insults. Obesity may explain alterations in physiology affecting neurogenesis, although it is unclear whether cannabinoid signalling may modulate neural proliferation in obese animals. Here we analyse the impact of obesity by using two approaches, a high-fat diet (HFD, 60% fat) and a standard/low-fat diet (STD, 10% fat), and the response to a subchronic treatment with the cannabinoid receptor type 1 (CB1) inverse agonist AM251 (3 mg/kg) on cell proliferation of two relevant neurogenic regions, namely the subventricular zone in the striatal wall of the lateral ventricle (SVZ) and the subgranular zone of the dentate gyrus (SGZ), and also in the hypothalamus given its role in energy metabolism. We found evidence of an interaction between diet-induced obesity and CB1 signalling in the regulation of cell proliferation. AM251 reduced caloric intake and body weight in obese rats, as well as corrected plasma levels of cholesterol and triglycerides. AM251 is shown, for the first time, to modulate cell proliferation in HFD-obese rats only. We observed an increase in the number of 5-bromo-2-deoxyuridine-labelled (BrdU+) cells in the SGZ, but a decrease in the number of BrdU+ cells in the SVZ and the hypothalamus of AM251-treated HFD rats. These BrdU+ cells expressed the neuron-specific βIII-tubulin. These results suggest that obesity may impact cell proliferation in the brain selectively, and provide support for a role of CB1 signalling regulation of neurogenesis in response to obesity.

The Cdk5/p35 kinases modulate leptin-induced STAT3 signaling

Cyclin-dependent kinase (Cdk) 5 is ubiquitously expressed in the brain and plays an essential role in central nervous system development and synaptic plasticity. The p35 kinase is a neuronal specific activator of Cdk5. Here, we show for the first time that Cdk5 activation modulates leptin signaling. P35 and its metabolite p25 were colocalized with the leptin receptor ObR in selective neurons in the hypothalamus. Overexpression of p35 alone was sufficient to induce the transcriptional activation of signal transducer and activator of transcription 3 (STAT3) in a cellular model. In retinoic acid-differentiated SH-SY5Y neuronal cells where ObRb was induced, leptin increased the expression of Cdk5, p35, and p25 kinases. The time course of induction coincided with that of phosphorylated (p)-STAT3. When Cdk5 activity was inhibited, either by roscovitine or overexpression of dominant negative Cdk5, there was a reduction of pSTAT3 activation. The results show that the activation of Cdk5 by p35 sustained leptin-induced pSTAT3 at 3-6 h. Thus, p35 is a novel modulator of leptin-induced STAT3 signaling.

Hypothalamic substrates of metabolic imprinting

The mammalian brain develops according to intrinsic genetic programs that are influenced by a variety of environmental factors. Developing neural circuits take shape in two major environments: one in utero and a second during postnatal life. Although an abundance of epidemiological and experimental evidence indicates that nutritional variables during perinatal life have a lasting effect on metabolic phenotype, the underlying mechanisms remain unclear. Peripheral hormones are widely regarded as effective signals that reflect the state of peripheral environments and can directly influence the development of a variety of functional neural systems. Recent findings suggest that the adipocyte-derived hormone leptin may play an important role in directing formation of hypothalamic neural pathways that control body weight. The arcuate nucleus of the hypothalamus (ARH) is a key site for the regulatory actions of leptin in adults, and this same hormone is required for the normal development of ARH projections to other parts of the hypothalamus. In this review, the neurobiological role of leptin is considered within the context of hypothalamic development and the possibility that variations in both prenatal and postnatal nutritional environments may impact development of neural circuits that control energy metabolism through an indirect action on leptin secretion, or signaling, during key developmental critical periods.

Sphingolipid therapy in myocardial ischemia-reperfusion injury

Sphingolipids are known to play a significant physiological role in cell growth, cell differentiation, and critical signal transduction pathways. Recent studies have demonstrated a significant role of sphingolipids and their metabolites in the pathogenesis of myocardial ischemia-reperfusion injury. Our laboratory has investigated the cytoprotective effects of N,N,N-trimethylsphingosine chloride (TMS), a stable N-methylated synthetic sphingolipid analogue on myocardial and hepatic ischemia-reperfusion injury in clinically relevant in vivo murine models of ischemia-reperfusion injury. TMS administered intravenously at the onset of ischemia reduced myocardial infarct size in the wild-type and obese (ob/ob) mice. Following myocardial I/R, there was an improvement in cardiac function in the wild-type mice. Additionally, TMS also decreased serum liver enzymes following hepatic I/R in wild-type mice. The cytoprotective effects did not extend to the ob/ob mice following hepatic I/R or to the db/db mice following both myocardial and hepatic I/R. Our data suggest that although TMS is cytoprotective following I/R in normal animals, the cytoprotective actions of TMS are largely attenuated in obese and diabetic animals which may be due to altered signaling mechanisms in these animal models. Here we review the therapeutic role of TMS and other sphingolipids in the pathogenesis of myocardial ischemia-reperfusion injury and their possible mechanisms of cardioprotection.

Cytoprotective effects of N,N,N-trimethylsphingosine during ischemia- reperfusion injury are lost in the setting of obesity and diabetes

N,N,N-trimethylsphingosine chloride (TMS), a stable N-methylated synthetic sphingolipid analog, has been shown to modulate protein kinase C (PKC) activity and exert a number of important biological effects, including inhibition of tumor cell growth and metastasis, inhibition of leukocyte migration and respiratory burst, and inhibition of platelet aggregation. We hypothesized that TMS would be cytoprotective in clinically relevant in vivo murine models of myocardial and hepatic ischemia-reperfusion (I/R) injury. Wild-type, obese (ob/ob), and diabetic (db/db) mice were subjected to 30 min of left coronary artery occlusion followed by 24 h of reperfusion in the myocardial I/R model. In additional studies, mice were subjected to 45 min of hepatic artery occlusion followed by 5 h of reperfusion. TMS was administered intravenously at the onset of ischemia. Myocardial infarct size, cardiac function, and serum liver enzymes were measured to assess the extent of tissue injury. TMS attenuated myocardial infarct size by 66% in the wild type and by 36% in the ob/ob mice. Furthermore, TMS reduced serum alanine transaminase levels by 43% in wild-type mice. These benefits did not extend to the ob/ob mice following hepatic I/R or to the db/db mice following both myocardial and hepatic I/R. A likely mechanism is the failure of TMS to inhibit PKC-delta translocation in the diseased heart. These data suggest that although TMS is cytoprotective following I/R in normal animals, the cytoprotective actions of TMS are largely attenuated in obese and diabetic animals.

Early developmental expression of leptin receptor gene and [125I]leptin binding in the rat forebrain

Leptin, via leptin receptors (Ob-R), regulates appetite and energy balance. Of the six isoforms of the receptor identified, so far, only the long form (Ob-Rb) can fully activate downstream signal transduction pathways. Although the expression and function of leptin receptors is well described in the adult brain, little is known about the ontogeny of leptin receptor system around the time of birth. In this study, the mRNA expression patterns of total leptin receptor, Ob-R, and the long signalling form of the receptor, Ob-Rb, were investigated in the brain of embryonic and newborn rats using in situ hybridisation and [125I]leptin binding. On embryonic day 18 (E18), Ob-R mRNA was detected in the choroid plexus and the ependymal layer of the third ventricle by in situ hybridisation. At E21, Ob-Rb mRNA was first observed in the arcuate and the ventral premammillary hypothalamic nuclei while at P3, receptor expression was also found in the dorsomedial nucleus. Other leptin target areas identified were the trigeminal ganglion, the thalamus and the hippocampus. Using quantitative receptor autoradiography specific [125I]leptin binding sites on the choroid plexus were found to increase with age in contrast to the ependymal layer of the third ventricle where levels decreased with age. Together these findings demonstrate that the leptin receptor system is differentially regulated during late gestation and early postnatal life in the rat.

Influences of diabetes (db/db), obese (ob/ob) and dystrophic (dy/dy) genotype mutations on hind limb bone maturation: a morphometric, radiological and cytochemical indices analysis

The influences of single-gene missense mutations expressing diabetes (db/db), obese (ob/ob) or dystrophia (dy/dy) dysregulated metabolic syndromes on hind limb bone maturation and cytodevelopment in C57BL/KsJ mice were evaluated by radiological, macro- and cytomorphometric analysis of the resulting variances in os coxae, femur and tibia osteodevelopment indices relative to control parameters between 8 and 16 weeks of age. Associated with obesity and hyperglycaemic/hyperinsulinaemic states, both db/db and ob/ob mutants demonstrated significant suppression of hind limb maturation (length) and cytodensity indices relative to control growth parameters. By contrast, skeletal growth suppression induced by dy/dy mutation expression was associated with lean body mass and normoglycaemic/hypoinsulinaemic systemic endometabolic indices. In both db/db and ob/ob mutation syndromes, osteovascular, -interstitial and -cytolipidaemia were prominent cytochemical aberrations of the osteopaenic states relative to the dyslipidaemia/fibrodysplasia characteristic of dy/dy osteomaturation. Between 8 and 16 weeks of age, both ob/ob and db/db groups demonstrated extensive cortical interstitial (laminal) osteolipidaemia and suppressed cytodensities compared to control indices. These data demonstrate that the abnormal hyperglycaemic/hyperinsulinaemic endometabolic states associated with the expression of db/db and ob/ob genomutations promote extensive lipidaemia-induced osteopaenia, compromising hind limb osteomaturation and cytodensity indices, as compared to the hyperfibritic osteopaenia characteristic of dy/dy mutation syndromes. Recognized therapeutic modulation of the hypercytolipidaemic component of diabetes-obesity syndromes may prove to be effective towards amelioration of the deleterious influences of these expressed hyperglycaemic, dysregulated lipometabolic conditions on osteomaturation and cytodevelopment.

Megalin mediates the transport of leptin across the blood-CSF barrier

Leptin, a peptide hormone secreted by adipose tissue, exhibits a large range of central and peripheral actions. It has been proposed that the participation of leptin in diseases such as obesity is due to, at least in part, its impaired transport across the blood-brain barrier (BBB). Since, the mechanisms by which brain takes up leptin remain unclear, we set out to study how leptin may cross the BBB. We have used different immunoassays and lentiviral vectors to analyze the role of megalin in the transport of leptin in rodents and humans. We demonstrate that circulating leptin is transported into the brain by binding to megalin at the choroid plexus epithelium. Indeed, the downregulation of megalin expression in physiological and pathological situations such as aging and Alzheimer's disease was correlated with poor entry of leptin into the brain. Moreover, amyloid beta (Abeta) deposits of choroid plexus could be disturbing megalin function. The present data indicate that leptin represents a novel megalin ligand of importance in the levels and therapeutic actions of leptin into the brain.

Hypercytolipidemia-induced cellular lipoapoptosis: Cytostructural and endometabolic basis of progressive organo-involution following expression of diabetes (db/db) and obese (ob/ob) mutation syndromes

Onset expression of Type 2 (NIDDM) diabetes and obesity metabolic syndromes (DOS) are characterized by premature, progressive cytoatrophy and organo-involution induced by dysregulated cellular gluco- and lipo-metabolic cascades. The consequential systemic, interstitial and intracellular hyperlipidemia disrupts normal cytointegrity and metabolic responsivity to the established hypercaloric pericellular environments. The sequential cytostructural, metabolic and endocrine disturbances associated with the development of progressive DOS-associated hypercytolipidemia compromises cellular metabolic response cascades and promotes cytochemical disturbances which culminate with nuclear lipoapoptosis and cytoatrophy. The dramatic alterations in interstitial glucose and lipid (free fatty acids/triglycerides) concentrations are recognized to influence interstitial and cytoplasmic microchemical environments, which markedly alter cellular nutrient diffusion and active trans-membrane flux rates. The progressive exacerbation of interstitial and cytoplasmic lipid imbibition has been demonstrated to be associated with DNA fragmentation by lipo-infiltration into the chromatin matrix, inducing structural disruption and physical dissolution, indexed as nuclear lipoapoptosis. Therapeutic reduction of the severity of hypercytolipidemia-induced structural and cytochemical compromise promotes the restoration of homeostatic metabolic support for normalized cytostructural indices and supportive cellular gluco- and lipo-metabolic cascades. The re-establishment of a homeostatic interstitial microenvironment moderates the severity of cytolipidemic compromise within affected cell types, reduces nuclear lipo-infiltration and DNA lipo-dissolution, resulting in the preservation of cytostructural integrity. Through the therapeutic restoration of extra- and intra-cellular microchemical environments in genetically dysregulated metabolic syndrome models, the coincident cytochemical, endocrine and metabolic disturbances associated with progressive hypercytolipidemia, resulting from the expressed systemic hypercaloric environmental and hepato-pancreatic endometabolic disturbances which characterize Type 2 (NIDDM) diabetes-obesity and metabolic (X) syndromes, may be ameliorated.

Influences of obese (ob/ob) and diabetes (db/db) genotype mutations on lumber vertebral radiological and morphometric indices: skeletal deformation associated with dysregulated systemic glucometabolism

Background

Both diabetes and obesity syndromes are recognized to promote lumbar vertebral instability, premature osteodegeneration, exacerbate progressive osteoporosis and increase the propensity towards vertebral degeneration, instability and deformation in humans.

Methods

The influences of single-gene missense mutations, expressing either diabetes (db/db) or obese (ob/ob) metabolic syndromes on vertebral maturation and development in C57BL/KsJ mice were evaluated by radiological and macro-morphometric analysis of the resulting variances in osteodevelopment indices relative to control parameters between 8 and 16 weeks of age (syndrome onset @ 4 weeks), and the influences of low-dose 17-B-estradiol therapy on vertebral growth expression evaluated.

Results

Associated with the indicative genotypic obesity and hyper-glycemic/-insulinemic states, both db/db and ob/ob mutants demonstrated a significant (P ≤ 0.05) elongation of total lumbar vertebrae column (VC) regional length, and individual lumbar vertebrae (LV1-5) lengths, relative to control VC and LV parameters. In contrast, LV1-5 width indices were suppressed in db/db and ob/ob mutants relative to control LV growth rates. Between 8 and 16 weeks of age, the suppressed LV1-5 width indices were sustained in both genotype mutant groups relative to control osteomaturation rates. The severity of LV1-5 width osteosuppression correlated with the severe systemic hyperglycemic and hypertriglyceridemic conditions sustained in ob/ob and db/db mutants. Low-dose 17-B-estradiol therapy (E2-HRx: 1.0 ug/ 0.1 ml oil s.c/3.5 days), initiated at 4 weeks of age (i.e., initial onset phase of db/db and ob/ob expressions) re-established control LV 1–5 width indices without influencing VC or LV lengths in db/db groups.

Conclusion

These data demonstrate that the abnormal systemic endometabolic states associated with the expression of db/db and ob/ob genomutation syndromes suppress LV 1–5 width osteomaturation rates, but enhanced development related VC and LV length expression, relative to control indices in a progressive manner similar to recognized human metabolic syndrome conditions. Therapeutic E2 modulation of the hyperglycemic component of diabetes-obesity syndrome protected the regional LV from the mutation-induced osteopenic width-growth suppression. These data suggest that these genotype mutation models may prove valuable for the evaluation of therapeutic methodologies suitable for the treatment of human diabetes- or obesity-influenced, LV degeneration-linked human conditions, which demonstrate amelioration from conventional replacement therapies following diagnosis of systemic syndrome-induced LV osteomaturation-associated deformations.

Cytochemical analysis of pancreatic islet lipoapoptosis: hyperlipidemia-induced cytoinvolution following expression of the diabetes (db/db) mutation

The diabetes (db/db) genotype mutation induces a hyperglycemic-hyperinsulinemic endometabolic state in C57BL/KsJ mice, manifesting a type II NIDDM diabetes-obesity syndrome (DOS) associated with intrinsic leptin receptor expression defects. The severity of the DOS-induced premature pancreatic dysfunction and cytoatrophic involution has been linked to the severity of hypercytolipidemia which develops in pancreatic islets following systemic lipoidosis. The current studies define the cytochemical changes associated with pancreatic islet and acinar vesicular degranulation (deproteinization), cytoinvolution and B-cell dysfunction relative to the onset of cellular (nuclear DNA fragmentation) apoptosis in 20- to 26-week-old chronic db/db mutants relative to control (+/?) indices. The db/db mutation induced dramatic increases in body weights, blood glucose as well as serum and tissue triglyceride concentrations relative to +/? parameters. In contrast, pancreatic tissue weights and insulin concentrations were significantly decreased in db/db groups in association with premature islet cytoatrophy relative to +/? indices. Concurrent elevations in db/db tissue triglyceride concentrations and islet cytolipid depositions accompanied the progressive pancreatic cytoatrophic alterations. Diminished B-cell vesicular (insulin) granulation was pronounced in atrophic pancreatic islets, which were also characterized by hyperplasic acinar cellular intrusion and subsequent proteolytic B-cell dissolution coincident with 3'-DNA fragmentation-indexed (TUNEL-labeled) nuclear apoptosis. The chronic expression of the db/db mutation exacerbated these pancreatic islet B-cell atrophy indices, characterized by insulin vesicular degranulation, suppressed systemic insulin concentrations, invasive hypercytolipidemia, progressive cellular atrophy and hyperplasic acinar proteolytic dissolution, culminating in islet volume/mass reduction and chronic db/db-related pancreatic involution. The results of these studies indicate that pancreatic islet B-cell apoptosis is coincident with the progressive hypercytolipidemia component of the type II DOS promoted by the db/db genotypic mutation. These data suggest that the severity of progressive pancreatic lipoapoptosis disrupts regulatory cellular metabolic cascades, resulting in nuclear fragmentation, organelle dissolution and the subsequent promotion of a nonhomeostatic cytochemical milieu which ultimately renders islet B-cell populations susceptible to acinar proteolytic dissolution and progressive pancreatic involution.

Structural, metabolic and endocrine analysis of the diabetes (db/db) hypogonadal syndrome: relationship to hypophyseal hypercytolipidemia

Expression of the diabetes (db/db) mutation in C57BL/KsJ mice results in functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian cytolipoatrophy. Cellular gluco- and lipo-metabolic disturbances promoted by the db/db systemic hyperglycemic-hyperinsulinemic state suppress pituitary gonadotropin release in response to gonadotropin-releasing hormone and gonadal steroid stimulation and results in a hypogonadal-infertility syndrome. Adult female C57BL/KsJ control (+/+ and +/? genotypes) and db/db littermates were monitored for associations in systemic and cellular alterations in luteinizing hormone (LH), follicle-stimulating hormone (FSH), gonadal steroid (binding) levels, and pituitary glucometabolic indices associated with db/db-enhanced lipid imbibition and cytostructural disruption. Obesity, hyperglycemia, and hyperinsulinemia characterized all db/db mutants relative to controls. Serum and pituitary progesterone and estradiol concentrations were suppressed in db/db mutants, in association with serum LH and FSH levels, but not with pituitary LH and FSH concentrations, which were comparable between groups. Pituitary insulin receptor binding and glucose utilization rates were suppressed in db/db groups relative to +/? indices. Structural and cytochemical analysis of anterior (AP), intermediate (IL), and neuro-(NP) hypophyseal lobes demonstrated prominent hypercytolipidemia in db/db mutants relative to controls. Prominent cytolipidemia was localized within well-granulated basophilic gonadotrophs and within IL and NP pituicytes. Vasolipidemia and interstitial cytoadiposity were prominent throughout all db/db pituitary lobes. Thus, disturbances associated with pituitary hypercytolipidemia are functional components of the expressed diabetes-associated hypogonadal syndrome in db/db mutants. Progressive alterations in hypophyseal cytoarchitecture are correlated with suppression of pituitary metabolic and endocrine indices, alterations that contribute to functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Estrogenic restoration of functional pancreatic islet cytoarchitecture in diabetes (db/db) mutant C57BL/KsJ mice: relationship to estradiol localization, systemic glycemia, and persistent hyperinsulinemia

The diabetes (db/db) genotype mutation induces a hyperglycemic-hyperinsulinemic endometabolic state in C57BL/KsJ mice, manifesting a type 2 NIDDM diabetes-obesity syndrome (DOS) in this hyperphagic, leptin receptor (lf) defective model. The severity of the DOS induced by the single gene, homozygous-recessive mutation may be therapeutically moderated by gonadal steroids and pre-steroidal metabolites. The current studies define the estradiol (E2)-modulated phenotypic, systemic, cytochemical, and cellular metabolic responses to db/db mutation expression as compared to littermate control (+/?) indices. The db/db mutation induced dramatic age- and DOS severity-related increases in body weights, blood glucose, and serum insulin concentrations relative to +/? indices between 4-week-old (i.e., initial onset stage of DOS phenotype) and 16-week-old (i.e., chronic stage of DOS) groups. Chronic, low-dose (0.1 microg/3.5 days) E2 treatment (E2-HRx) significantly reduced the obesity mass and blood glucose levels of db/db mutants relative to oil-HRx groups. Similarly, E2-HRx maintained pancreatic glucose utilization rates and pancreatic tissue weights in db/db mutants to near +/? indices. Concurrent amelioration of db/db-enhanced pancreatic lipogenesis and islet hypercytolipidemia occurred following E2-HRx. Pancreatic islet lipo-deposition was markedly reduced in db/db mutants following E2-HRx, and the restoration of islet size and cellular insulin concentrations correlated with beta-cell cytoplasmic regranulation of insulin secretory vesicles. In chronic E2-HRx db/db groups, autoradiographic localization of (3)H-E2 was demonstrated in the nuclear compartments of regranulated, nonhypertrophic islet cell populations, including insulin-containing beta-cells. In chronic E2-HRx db/db mutants, beta-cell insulin granulation was prominent in mildly hypertrophic pancreatic islets, with cytodistribution patterns and concentrations comparable to normal +/? indices. In contrast, E2-HRx maintained the systemic hyperinsulinemia characteristic of oil-HRx db/db mutants. The results of these studies indicate that the severity of the type 2 NIDDM endometabolic syndrome induced by the db/db genotypic mutation may be influenced by E2-HRx, including reduction of the islet hypercytolipidemia and hypertrophic atrophy which are indicators of impending pancreatic involution in this mutant model. The hypercytolipidemia-induced demise of beta-cell cytoarchitecture was reduced by E2-HRx, including the reestablishment of islet beta-cell cytogranulation. These data suggest that the severity of genomic db/db-mutation expression may be modified by E2-HRx, with the gonadal steroid probably acting as a nuclear-specific stimulatory transcriptional modulator of cellular glucometabolic cascades in the absence of leptin-directed homeostatic influences.

Cytochemical Analysis of Pancreatic Islet Hypercytolipidemia following Diabetes (db/db) and Obese (ob/ob) Mutation Expression: Influence of Genomic Background

Both diabetes (db/db) and obese (ob/ob) genotype mutations induce a hyperglycemic-hyperinsulinemic endometabolic state in C57BL mice, manifesting a type II NIDDM diabetes-obesity syndrome (DOS) in these leptin ligand/receptor-deficient models. The severity of the DOS induced by these single gene, homozygous-recessive mutations may be moderated by the background genome on which the mutation is expressed. The current studies define the phenotypic, systemic, cytochemical and cellular metabolic responses to db/db and ob/ob mutation expression when modified by /KsJ (severe DOS expression) or /6 (modified DOS expression) background strain influences as compared to littermate control (+/?) indices. Both db/db and ob/ob mutations induced dramatic increases in body weights, blood glucose and serum insulin concentrations relative to +/? indices when expressed on either the C57BL/KsJ (-/KsJ) or C57BL/6 (-/6) backgrounds. However, the -/KsJ background enhanced the severity of expression of these DOS indices relative to the -/6 strain. Similarly, the -/KsJ genome suppressed cellular glucose uptake rates, pancreatic tissue weights and insulin concentrations in both db/db and ob/ob mutants relative to /6 background strain influences or +/? indices. Concurrent enhancement of tissue and cellular lipogenic metabolism and islet cytolipid depositions were exaggerated when the mutations were expressed on the -/KsJ background relative to the -/6 genome. Pancreatic islet B-cell lipodeposition was markedly enhanced in ob/ob and db/db mutants expressed on either the -/KsJ or -/6 background. In both ob/ob and db/db models, B-cell insulin granulation was prominent in mildly hypertrophic pancreatic islets when the mutations were expressed on the -/6 background. In contrast, the severity of the DOS state expressed on the -/KsJ background resulted in pronounced B-cell atrophy, characterized by insulin degranulation, cellular hypertrophy and hypercytolipidemia associated with tissue involution, in both ob/ob and db/db mutants. Dramatic alterations in tissue norephinephrine (NE) and alpha-1-receptor populations in ob/ob and db/db mutants were exaggerated by the -/KsJ genome as compared to -/6 or control indices. The influences of the -/KsJ genome on the progressive expression of tissue NE counter-regulatory responses to enhanced cytolipidemic indices were inversely related, with cytochemical lipodeposition occurring under conditions of diminished adrenergic responses to the DOS indices. The results of these studies indicate that the severity of the type-II diabetes endometabolic syndrome induced by the ob/ob or db/db genotypic mutations is modified by the existing genome on which the mutations are expressed. These data suggest that the severity of genomic mutation expression may be modified depending on the capability of the background genome to counter-regulate the systemic, cellular or metabolic consequences of these mutations.

Ultrastructural analysis of progressive endometrial hypercytolipidemia induced by obese (ob/ob) and diabetes (db/db) genotype mutations: structural basis of female reproductive tract involution

The diabetes (db/db) and obese (ob/ob) genotype mutations induce a progressive, hypercytolipidemic condition within the endometrium of the female reproductive tract that promotes sterility and premature organ involution in C57BL/KsJ mice. The current studies focus on the ultrastructural changes that occur within the epithelial and stromal layers of the uterine endometrium during the progressive expression of these mutations, which induce a hyperglycemic-hyperinsulinemic metabolic state and promote tissue cytolipidemia and organoinvolution. Control (normal: +/-), diabetes (db/db) and obese (ob/ob) genotype groups were prepared for high resolution light (LM) and transmission (TEM) microscopic analysis of endometrial tissue samples collected from 4 (young)- to 20 (aged)-week-old mice, allowing for the progressive influences of the mutational aberrations on uterine structure to be evaluated. Compared to controls, both (ob/ob) and (db/db) mutations induced a dramatic increase in endometrial epithelial cytolipid vacuole accumulation, which increased in density between 4 and 20 weeks of age. Lipid vacuoles aggregated at the baso-polar regions of epithelial cells in response to the hyperglycemic-hyperlipidemic conditions typical of both (ob/ob) and (db/db) groups. Progressive cytoplasmic movement of the lipid pools induced a perinuclear isolation from surrounding cytoplasmic organelles. Apical lipid accumulations forced cytoplasmic organelles into peripheral cell compartments and altered the periepithelial stromal cell profile relative to controls. These studies define the progressive, intracellular accumulation of hypercytolipidemic pools which induce a transformation of normal endometrial cell types into adipocyte-like entities. The lipidemia-induced alterations in cell structure disrupt normal tissue continuity and function, culminating in organoinvolution and overt female reproductive sterility.

Minireview: Leptin and development of hypothalamic feeding circuits

The arcuate nucleus of the hypothalamus (ARH) is a critical component of the forebrain pathways that regulate energy homeostasis, and it plays a particularly important role in relaying leptin signal to other part of the hypothalamus. However, until recently, little was known about the development of these critical pathways. Recent work investigating the development of leptin-sensitive hypothalamic pathways suggests possible developmental mechanisms that may contribute to obesity later in life. Anatomic findings indicate that ARH circuits are structurally and functionally immature until the third week of postnatal life in mice. Recent data also suggest that leptin is required for normal development of ARH pathways and that this developmental activity of leptin is restricted to a neonatal window of maximum sensitivity that corresponds to a period of elevated leptin secretion. Thus, leptin may function to organize formation of hypothalamic circuitry in much the same way that sex steroids act on sexually dimorphic circuits. Perturbations in perinatal nutrition that alter leptin levels may, therefore, have enduring consequences for the formation and function of circuits regulating food intake and body weight.

Ovarian hypercytolipidemia induced by obese (ob/ob) and diabetes (db/db) mutations: basis of female reproductive tract involution II

The diabetes (db/db) and obese (ob/ob) genotype mutations induce a progressive, hypercytolipidemic condition within the ovarian compartments of the female reproductive tract that results in sterility and premature organ involution in C57BL/KsJ mice. The current studies focus on the ultrastructural changes that occur within the ovarian interstitial, thecal, and follicular granulosa cell layers during the progressive expression of these mutations which promote tissue cytolipidemia-induced organoinvolution. Control (normal: +/?), diabetes (db/db), and obese (ob/ob) genotype groups were prepared for high resolution light (HRLM) and transmission electron microscopic (TEM) analysis of ovarian tissue samples collected from 4 (young)- to 20 (aged)-week-old mice, allowing for the progressive influences of the mutational aberrations on tissue structure to be evaluated. Compared to controls, both (ob/ob) and (db/db) mutations induced a dramatic increase in ovarian interstitial, thecal and follicular granulosa cytolipid vacuole accumulations, which increased in density between 4 and 20 weeks of age. Initially, lipid vacuoles aggregated in the interstitial and thecal regions of ovarian follicles in response to the hyperglycemic-hypertriglyceridemic metabolic conditions typical of both (ob/ob) and (db/db) groups. Progressive cytoplasmic movement of the lipid pools established a perinuclear isolation from associated cytoplasmic organelles. Progressive lipid accumulations forced cytoplasmic organelles to peripheral cell compartments and altered the follicular cell profile towards that of adipocyte-like entities relative to controls. The progressive hypercytolipidemia-induced alterations in cell structure disrupted normal tissue continuity, which culminated in premature ovarian organo-involution and female reproductive sterility.

Hypophyseal lipoapoptosis: diabetes (db/db) mutation-associated cytolipidemia promotes pituitary cellular disruption and dysfunction

Expression of the diabetes (db/db) mutation in C57BL/KsJ mice suppresses the female pituitary-gonadal axis via progressive cytolipidemic disruption of hypophyseal gonadotropin release, culminating in premature involution of the reproductive tract and manifest infertility. The current studies define the systemic, endocrine, cytochemical and structural apoptotic changes that result from pituitary hypercytolipidemia induced by db/db mutation expression in this Type II diabetes-obesity syndrome (DOS) model. Adult female C57BL/KsJ control (+/? genotype) and db/db littermates were monitored for systemic and cellular alterations in LH-, FSH- and gonadal steroid-secretion, and coincident pituitary apoptosis, as indexed by TUNEL labeled 3' nuclear DNA-fragmentation, associated with cytolipid depositions. Obesity, hyperglycemia and hyperinsulinemia characterized all db/db-mutants relative to +/? groups. Serum progesterone (P) and estradiol (E2) concentrations were suppressed in db/db mutants coincident with decreased plasma LH and FSH concentrations relative to +/? values. Cytochemical analysis of anterior (AP) pituitary cell subtypes indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to +/? pituitary cytoarchitecture. Cytolipidemic vacuoles were localized within protein vesiculated db/db hypophyseal basophilic and acidophilic cell populations. Hypophyseal cytoadiposity in db/db AP cells was co-localized with prominent cellular apoptotic TUNEL labeling of nuclear 3'-DNA fragments in cells demonstrating vesicular depopulation and cytolytic vacuolization. These data represent the first demonstration of co-localized hypercytolipidemic and cytoapoptotic disruptive events occurring concurrently in a hypopituitary-hypogonadal syndrome model following expression of the Type II (NIDDM) diabetes-obesity syndrome in db/db-mutants. The coincident and progressive vascular-, interstitial- and cyto-lipidemic alterations in hypophyseal cytoarchitecture correlated with the concurrent apoptotic disruption of pituitary endocrine cytoarchitecture and supressed gonadal steroid synthesis, influences which collectively contribute to the premature involution of the pituitary-gonadal axis in C57BL/KsJ- db/db mice.

Lipoatrophic diabetes-associated utero-ovarian dysfunction: influence of cellular lipid deposition on norepinephrine indices

OBJECTIVE

Elucidation of the intracellular lipoatrophic diabetic state and the concomitant alterations in norepinephrine (NE) parameters characterizing female reproductive failure.

METHODS

Quantitation of intrinsic NE levels in utero-ovarian and pancreatic tissue samples of C57BL/KsJ (+/?) control and (db/db) diabetic littermate mice was by high performance liquid chromatography (HPLC) and compared with the microspectrofluorometric histofluorescent (HF) localization of cellular and parenchymal NE.

RESULTS

Diabetes-associated elevations in HPLC-detectable tissue NE concentrations occurred in all pancreatic and reproductive tract tissue samples as compared to control-matched samples, whereas concurrent HF analysis revealed suppressed perivascular and parenchymal NE depositions in diabetic mice.

CONCLUSIONS

These data suggest that progressive hypertriglyceridemia/lipidemia may suppress the effectiveness of intrinsic elevations in tissue NE concentrations from effectively counterregulating the deleterious effects of the hyperglycemic, type-2 diabetic condition.

Estrogenic stimulation of hypothalamic-limbic system metabolism in ageing diabetic C57BL/KsJ mice

The therapeutic influences of estrogen treatment on age- and diabetes-related declines in regional brain glucose utilization (RBGU) rates were evaluated in 8- to 20-week-old female C57BL/KsJ normal (+/?) and diabetic (db/db) mice. Following either oil vehicle (oil: 0.1 ml) or estradiol (E: 1 microgram/3.5 days) treatments starting at 3 weeks of age, RBGU rates were subsequently determined at 8, 12, 16 and 20 weeks of age. A gradual decline in the basal rate of brain glucose utilization was observed in all control (oil- and E-treated) groups between 8 and 20 weeks. Expression of the hyperglycemic-obese diabetes syndrome in db/db mice resulted in a significant reduction in RBGU rates between 8 and 20 weeks relative to control values. In estrogen-sensitive hypothalamic, septal and amygdaloid regions, E therapy modulated RBGU rates in db/db mice relative to oil-treated diabetics, but did not significantly alter utilization rates in +/? mice. In cortical samples, E therapy had no significant influence on glucose utilization rates in either control or diabetic groups. A noticeable pattern of maturation-associated decline in CNS glucose utilization rates in all brain regions resulted in comparable regional metabolic indices being exhibited by all groups at 20 weeks of age, with the exception of the diabetes-associated exacerbation of RBGU rates in the oil-treated db/db group. These data demonstrate that the normal development-related decline in regional brain carbohydrate metabolism is accelerated by the diabetes syndrome, and that E therapy can modulate the syndrome-associated suppression of glucose utilization in steroid-sensitive CNS loci. These data suggest that the depressive influences of the diabetes syndrome on brain carbohydrate utilization rates may be therapeutically modified in recognized CNS regions possessing steroid-sequestering, metabolically responsive neurons.

Developmental and regional changes in brain norepinephrine levels in diabetic C57BL/KsJ mice: effects of estradiol and progesterone

Developmental and diabetes-associated changes in regional brain norepinephrine (NE) concentrations, and the influence of estradiol (E) and progesterone (P) on NE levels, were correlated with changes in blood glucose levels and body weight (obesity) in developing 4-16-week-old C57BL/KsJ (db/db) mice relative to corresponding age-matched control (+/?) parameters. Regional brain (i.e. amygdala, hypothalamus and medulla) NE levels were determined by high performance liquid chromatography. The (db/db) mice exhibited overt hyperglycemia and obesity relative to controls between 4 and 16 weeks of age. Hypothalamic NE levels in diabetics were chronically elevated as compared to those of age-matched controls by 8 weeks of age, and remained elevated through 16 weeks of age. Regional amygdaloid and medullary NE concentrations were comparable in (+/?) and (db/db) groups by 16 weeks. E-treatments normalized (db/db) hypothalamic NE concentrations to control levels between 8 and 16 weeks of age, but had no effect on amygdaloid or medullary values. In contrast, in 16 week old (db/db) mice, P-treatments elevated hypothalamic and medullary NE levels compared to controls and expected diabetic levels. These data demonstrate that a marked modification in regional brain NE concentrations occurs in association with the overt expression of the diabetes mutation during development in this species. Observed changes in adrenergic influences in specific CNS loci may be therapeutically modulated by ovarian steroid hormones, especially in the hypothalamic locus which is recognized to possess steroid-concentrating neurons. The observed normalization of regional brain NE concentrations by E-therapy may be causally related to the ovarian steroid-modulation of overt hyperglycemia and diabetes-associated neuronal degeneration in (db/db) mice.

Food deprivation and hypothalamic neuropeptide gene expression: effects of strain background and the diabetes mutation

We have used a novel method to identify genes expressed in the hypothalamus which may be potentially involved in controlling food intake and energy metabolism. We assumed that food deprivation, a powerful stimulus of food intake, would stimulate the activity of neural pathways involved in feeding behavior which should be reflected in an increase in the synthesis of any relevant neuropeptide and its messenger RNA. A study of 5 neuropeptides in 5 strains of mice has identified neuropeptide Y (NPY) as a gene whose expression in the hypothalamus is controlled by nutritional status, suggesting that hypothalamic NPY neurons are a link in the neural network regulating feeding behavior and energy metabolism. In addition, we have studied the effect of the diabetes mutation on neuropeptide gene expression during fasting and refeeding. Our findings suggest that abnormal NPY and enkephalin gene expression in the hypothalamus may be two important determinants of the expression of the diabetes mutation.

Reduced aminergic synthesis in the hypothalamus of the infertile, genetically diabetic (C57BL/KsJ-db/db) male mouse

Diabetes mellitus is commonly associated with reproductive neuroendocrinopathy in both humans and animal models for the disease. Diabetes-associated reproductive failure in the male is a result of multilevel dysfunction within the hypothalamo-pituitary-testicular axis. In view of the known effects of diabetes on hypothalamic gonadotropin-releasing hormone (GnRH) and gonadotropins in chemically-induced animal models for diabetes, we examined hypothalamic aminergic activities (important to the regulation of GnRH release), circulating gonadotropin levels and testicular morphology in the infertile, genetically diabetic (C57BL/KsJ-db/db) male mouse. Groups of 2-5 month old (average age: 3.4 months) and 6-11 month old (average age: 8.8 months) diabetic mice were compared with age-matched non-diabetic (C57BL/KsL(-)+/?) male mice. Diabetic mice in both age groups were markedly obese and hyperglycemic. Hypothalamic serotonin synthesis was inhibited in the preoptic area-anterior hypothalamus (POA-AH) in both 2-5 month old and 6-11 month old diabetic mice as well as in the mediobasal hypothalamus-median eminence (MBH-ME) of 6-11 month old diabetic mice. Catecholamine synthesis (norepinephrine and dopamine) was reduced in the POA-AH of 2-5 month old diabetic mice and in the MBH-ME of 6-11 month old mice. These aminergic changes were associated in 2-5 month old diabetic mice with reduced circulating levels of LH and in 6-11 month old diabetic mice, of both LH and FSH. In 6-11 month old diabetic mice, testes were characterized by a thickened tunica albuginea, numerous Sertoli cells and the near absence of any spermatogenic cells. The epididymis from these diabetic mice was devoid of spermatozoa.(ABSTRACT TRUNCATED AT 250 WORDS)