Early Life Effects on Hypothalamic Circuitry. By: The Mystery Gang

Transcription

1 Early Life Effects on Hypothalamic Circuitry By: The Mystery Gang

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3 Hypothalamic Circuits Controlling Energy Balance ARH (Arcuate nucleus of the Hypothalamus) Subgroup of Neurons 1: coexpress Neuropeptide Y (NPY) and agouti-related peptide (AgRP) Subgroup of Neurons 2: expresses Proopiomelanocortin (POMC) derived peptides like alpha-melanocyte stimulating hormones PVH, DMH, and LHA Other areas implicated in the control of feeding Glucose Regulation and the Hypothalamus Reduction of hepatic gluconeogenesis

4 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hypothalamic Nuclei Figure 12.13b

5 Development of Hypothalamic Feeding Circuits Initiated by cell proliferation in the neuroepithelium of the third ventricle Generation of neuronal progenitors that produce postmitotic neurons Those neurons migrate to their location in all parts of the Hypothalamus

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7 Development of Hypothalamic Feeding Circuits Human/Non-Human Primate Studies: Rodent Studies: Neuronal Birthdating Hypothalamic Neurogenesis Studies Development of HFC Early Production of in utero NPY in the DMH and Early Production of the LHA NPY immunoreactive NPY and obesity in fibers (21 weeks of animals gestation) TAKEAWAY: There are 2 major critical periods (midgestation and early postnatal life) when alterations can affect hypothalamic neurogenesis. This can have long term consequences to nutrition and metabolism

8 Leptin and Hypothalamic Development Important for the Formation of Hypothalamic Feeding Circuits Too little Leptin The formation of ARH circuits Axonal Formation in the ARH NPY/AgRP, and POMC Takeaway: Critical Periods exist! Too much Leptin/ The Leptin Surge Earlier leptin surges Altered hypothalamic responses The effects of a blunted postnatal surge Takeaway: leptin surges are important at the right times

9 Insulin and Hypothalamic Development Important for development of hypothalamic circuits that regulate energy homeostasis Hyperinsulinism Induced obesity, increased hypothalamic norepinephrine and the density of norepinephrine -containing fibers in the PVH Decreased brain NPY mrna and protein expression, altered neural morphology in the ARH in the fetus Morphological changes in the VMH Takeaway: hyperinsulinism during pregnancy could induce alterations in hypothalamic organization

10 Hyperinsulinism and Pregnancy Hypertrophic myocardiopathy: hypertrophy of the septum and ventricular walls that can in some cases obstruct blood flow. Rizzo G, Arduini D, Romanini C. Accelerated cardiac growth and abnormal cardiac flow in fetuses of diabetic mothers. Obstet Gynecol. 1992;80:

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12 Embryonic Birthdate of Hypothalamic Leptin- Activated Neurons in Mice Terminology/ Recap E0- the day of conception P0- the day of birth BrdU: 5-Bromo-2-deoxyuridine A marker of dividing cells/proliferation synthetic nucleoside, gets incorporated into new DNA ARH- arcuate nucleus DMH- dorsomedial nucleus PVH- paraventricular nucleus LHA- lateral hypothalamic nucleus POMC - A precursor protein; a precursor to alpha MSH, an agonist for MC4R - Mutations in either POMC or MC4R leads to severe obesity - In CNS, concentrated mainly in ARH, an area with strong functional ties to appetite and food intake

13 Embryonic Birthdate of Hypothalamic LeptinActivated Neurons in Mice The Study - Used BrdU, as well as HuC/D (which is a marker for cell differentiation) to examine the birth of neurons that transmit leptin signaling - Pregnant dams (female parent of an animal) were injected with BrdU at P 10, 12, 14, 16 0r 18 to evaluate the birthdate of cells in key hypothalamic nuclei that are involved in energy balance regulation

14 Embryonic Birthdate of Hypothalamic Leptin- Activated Neurons in Mice Materials, Methods and Immunohistochemistry - - Bred wild type mice, were provided food and water ad libitum (as they saw fit, is often shortened to ad lib) 12-hour light and 12 hour dark cycle, temperature controlled environment Litter size 6-8 pups (after culling average litter size was 7 pups) Only male offspring were studied Pregnant mice were administered a single intraperitoneal injection of BrdU Later, once brains were removed and immersed in 20% sucrose in a 0.02 M potassium PBS (a buffer solution) solution at 4 C overnight, frozen coronal sections were cut and stored in antifreeze at -20 C until put to use Used double labeling of both BrdU and HuC/D to monitor the proliferation and differentiation of cells

15 Embryonic Birthdate of Hypothalamic Leptin- Activated Neurons in Mice Results: Birthdate of neurons in the ARH,VMH, DMH, PVH and of leptin-activated neurons in the hypothalamus - In the ARH, BrdU injection on E12 showed the highest numbers of BrdU-labeled cells and decreased by about 4-to-5 fold between E From double labeling (BrdU and HuC/D) found that peak of neurogenesis occurred at E12 - In VMH, similar results to ARH results - Double labeling experiments found that neurogenesis peak also occurred at E12 - In DMH,double labeling experiments found that majority of neurons in DMH were born between E12-E14 - In PVH, animals that were given BrdU injection on E12 showed highest numbers of BrdU labeled cells - Double labeling experiments showed that neurogenesis also peaked at E12 - In conclusion, double staining experiments showed that 30-50% of leptin sensitive neurons in adult hypothalamus were born during a particularly short developmental period- namely, E12. At most, only 10% were born during a later embryonic stage.

16 Embryonic Birthdate of Hypothalamic Leptin- Activated Neurons in Mice - Results: Birthdate of neurons in the ARH, PVH, DMH, and of leptin activated neurons in the hypothalamus

17 Discussion The majority of hypothalamic nuclei that control energy homeostasis were born between E12 and E14. - What does this timing of the proliferation of leptin activated neurons in the hypothalamus implicate? The paper found that cells in the hypothalamus were derived from precursors in the lower portion of the third ventricle. The paper also found that the development of the hypothalamus had two parts: A portion in-utero which determined the cell number in the hypothalamus, and an extra-utero portion which established neuronal connections Hypothalamic neurogenesis is not restricted to neonatal periods and can be enhanced by external cues (3665)

18 Discussion cont. Environmental changes can affect the development of the hypothalamus between E12 and E14 Maternal nutrition affects hypothalamic cellular proliferation - Maternal high-fat feeding increases cellular proliferation in rats...which yields higher numbers of neurons that contain orexigenic neuropeptides in the PVH and LHA (3665) - Maternal malnutrition reduces orexigenic neurons in the hypothalamus, as well as reducing NPY neurons in the ARH (3665)

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20 Discussion cont. What is this paper trying to prove? This paper aims to show the significance of the time period of the production of leptin receptor neurons in the hypothalamus, and what external stimuli can affect the nature of the hypothalamus in this critical period. Maternal actions have a tremendous influence on the cognitive development of a fetus, especially in the hypothalamus.

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22 Background Knowledge The brain may be particularly vulnerable to the effects of obesogenic diets during early life periods of rapid growth, maturation, and brain development

23 What can early life exposure to obesogenic diets do? How does it affect the future generations?

24 Factors Reviewed 1) Varying levels of HFD : 40%, 60%, 25%... %kcal derived from fat 2) Different ratios of fats : sugars : %kcal from sugar? Independent? With HFD? 3) Timing of Exposure: Perinatal period vs Juvenile/adolescent Period 4) Duration of Exposure: # of weeks exposed

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27 Rodent Model Findings Maternal Consumption of HFD beginning before mating and ending before weaning : 1) Caused evident hippocampal-dependent spatial learning deficits in offspring at 4 weeks of age 2) Detrimental effects are more pronounced during early life 3) Progeny performed worse in the MWM during adulthood relative to offspring born from dams on standard chow 4) Animals that were switched to standard chow at weaning were equally impaired in learning the learning task compared to animals weaned on the HFD

28 Contrasting Results A) Under some conditions, prenatal and perinatal exposure to a HFD does not impair hippocampal dependent learning and memory. (No change between experiment and control) a) One study showed that HFD induced memory deficits may be overcome by switching the pups to standard chow at weaning B) Other reports indicate that pre-weaning HFD exposure confers cognitive deficits that persist into adulthood, even when the animals were fed a standard chow diet post weaning a) Progeny born from dams fed a HFD performed worse in the MWM How do we interpret these differing results?

29 Possible Explanation: % of fat and sugar in the diet A) MWM deficit study despite weaning on chow utilized HFD with 45% kcal from fat a) Page et al. utilized 45% HFD with a considerably higher proportion of kcal from sugar compared with HFD used by others b) Page et al. had 17% sugar in HFD B) Recovery of Function results utilized HFD with 60% kcal from fat a) White et al. study had 7% sugar in HFD It is possible that the combined impact of high sugar and fat in the diet is greater than the impact of fat alone.

30 What developmental processes does it interrupt? What do we know? What SHOULD we know?

31 Extension of HFD Diet Duration Goal: To study the impact of perinatal through childhood and/or early adulthood consumption of an obesogenic diet on learning and memory and function

32 Results A) Progeny of dams maintained on HFD(60-65% kcal from fat) who were fed the HFD for over 2 months post weaning exhibited impaired performance in MWM a) When HFD was fed throughout both pre- and post-natal development as well as post-weaning, the offspring had deficits in spatial learning capabilities (MWM) during adulthood (Lepinay et al. 2015) B) HFD(39%kcal from fat) diet when confined exclusively to either the prenatal or postnatal phase, HFD-feeding had no effect on spatial memory in MWM (Lepinay et al. 2015) Similar findings using Novel Context Mismatch task**

33 Juvenile and Adolescent Period

34 Methods Obesogenic Diets: High Fat Diet (HFD) - either 45% or 60% kcal from fat 11% High Fructose Corn Syrup (HFCS-55) 10% Sucrose solution Hippocampal Cognitive Tasks: Barnes Maze Morris Water Maze (MWM) Object-in-place Test Two-Stage Radial Maze Y Maze Novel Object Location Recognition Groton Maze Learning Task

35 Juvenile and Adolescent Period Animal Models: Obesogenic dietary factors negatively impact hippocampal function in juvenile/adolescents > adults HFD consumption impaired spatial memory retention and spatial reversal learning in juvenile/adolescents Impaired relational memory flexibility (two-stage radial arm maze) in rats exposed to HFD first 11 weeks post weaning, as opposed to those who began HFD at wk12 (Boitard et al) impaired in Novel Location Recognition task (hippocampal-dependent) in mice given HFD at wk5, compared to those given HFD at wk8 (Valladolid et al) Dietary sugars have particularly negative effects on hippocampus during juvenile/adolescent period (even in absence of elevated fat intake) Impaired hippocampal-dependent spatial learning and memory learning in juvenile rats fed 11% HFCS, compared to adult counterparts and control (H2O) conditions Intermittent sucrose access experiments: Study 1 (Kendig et al): Both adolescents and adults* reveal impaired Morris Water Maze performance Study 2 (Reichelt et al) : juvenile rats had impaired object-in-place task performance (episodic contextual memory)

36 Juvenile and Adolescent Period Dietary factors contribute more to memory impairments than do caloric intake or obesity Study 1 (Valladolid et al): Adolescent and adult mice fed HFD for 8 weeks or for 8 weeks followed by 5 weeks of food restriction Study 2 (Kaczmarczyk et al): short-term (1 week) HFD feeding of juvenile mice Adolescent mice: (-) Novel Object Recognition performance, even after 5 week food restriction Significant (-) spatial memory [Y maze] Noted before onset of weight gain or impaired glucose metabolism Study 3 (Hsu et al): 11% HFCS or control (H2O) given to adult and adolescent rats Adolescent rats: (-) spatial Barnes Maze performance Despite similar caloric intake and levels of body weight gain as control condition *Consideration for future studies: identify which specific dietary factors cause these early life obesogenic diet-induced cognitive defects

37 Juvenile and Adolescent Period Humans: Study 1 (Nyaradi et al): Western dietary pattern during early adolescence (14 y.o.) poor cognitive performance in late adolescence Study 2 (Baym et al): Cross-sectional study of 7-9 year olds Saturated fatty acid intake in children (-) performance in hippocampal-dependent relational and item memory tasks Independent of BMI

38 Neurobiological Mechanisms Inflammation/Cytokines: Obesity chronic low-grade inflammation levels of proinflammatory cytokines in brain (TNFα, IL-6) impaired hippocampal-dependent memory Maternal fat consumption and inflammation affects brain inflammation and behavior of offspring via IL-1β and IL-6 and microglial expression Hsu et al Study: IL-1β and IL-6 in adolescent rats fed 11% HFCS, not found in adults Reveals link between neuroinflammation and hippocampal function Boitard et al Study: Untreated animals: no change in TNFα and IL-1β Post LPS injection: significant in TNFα and IL-1β Reveals dietary manipulation affects neuroinflammatory signal pathways, which in turn affect hippocampal function

39 Neurobiological Mechanisms Neurotrophic Factors: Neurogenesis and Synaptic Plasticity Essential for hippocampal-dependent memory and learning Brain derived neurotrophic factor (BDNF) maternal HFD consumption = hippocampal BDNF expression in offspring = (-) impact on neurogenesis and synaptic plasticity in hippocampal neurons Insulin and Insulin-like growth factor-1 (IGF-1) Promote neurogenesis and synaptogenesis in dentate gyrus (Kuang et al) Maternal consumption of high sucrose Impaired spatial learning with IGF-1 and downstream PI3K and pakt in hippocampus of offspring Leptin Facilitates synaptic plasticity via AMPA receptor trafficking at synapses Peripheral and intra-hippocampal leptin injections into db/db rodents with cognitive deficits enhanced hippocampal-dependent spatial learning and memory performance (Valladolid et al) HFD-fed juvenile rats resistance of PI3K/AKT pathway in OBRb-expressing neurons in hippocampus impaired hippocampal-dep. Cognitive function

40 Conclusions Perinatal: Perinatal and Juvenile exposure to a chow diet supplemented with saturated fat, cholesterol, and sugar produces elevations in expression of Cytokines TNF-Alpha and IL-6 Juvenile/Adolescent: Particularly vulnerable to effects of obesogenic diet on hippocampal function due to increased expression of pro-inflammatory cytokines and changes in the expression of neurotrophic factors Sugar displays more negative effects on memory than high fat intake Future Research: identify the specific dietary factors that cause these early life obesogenic diet-induced cognitive deficits Look into epigenetic mechanisms of how diet may alter genes and neurotrophic factors crucial for learning and memory function

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