Jianqun Yan

Maternal High-Fat Diet During Gestation or Suckling Differentially Affects Offspring Leptin Sensitivity and Obesity

Maternal high-fat (HF) diet throughout gestation and suckling has long-term consequences on the offspring’s metabolic phenotype. Here we determine the relative contribution of pre- or postnatal maternal HF diet on offspring’s metabolic phenotype. Pregnant Sprague-Dawley rats were maintained on normal chow or HF diet throughout gestation and suckling. All litters were cross-fostered to chow or HF dams on postnatal day (PND)1, resulting in four groups. Body weight, body composition, and glucose tolerance were measured at weaning and in adulthood. Leptin sensitivity was assessed by signal transducer and activator of transcription (STAT)3 activation on PND10 and PND21. Pups cross-fostered to HF dams gained more body weight than chow pups by PND7 and persisted until weaning. Postnatal HF pups had greater adiposity, higher plasma leptin concentration, impaired glucose tolerance, and reduced phosphorylated STAT3 in response to leptin in the arcuate nucleus at weaning. After weaning, male offspring cross-fostered to HF dams were hyperphagic and maintained greater body weight than postnatal chow pups. Postnatal HF diet during suckling continued to impair glucose tolerance in male and female offspring in adulthood. Maternal HF diet during suckling has a greater influence in determining offspring’s metabolic phenotype than prenatal HF diet exposure and could provide insight regarding optimal perinatal nutrition for mothers and children.

Nutritional status alters saccharin intake and sweet receptor mRNA expression in rat taste buds.

Sweet taste usually signifies the presence of caloric food. It is commonly accepted that a close association exists among sweet taste perception, preference, and nutritional status. However, the mechanisms involved remain unknown. To investigate whether nutritional status affects the preference for palatable solutions and alters sweet taste receptor gene expression in rats, we measured saccharin intake and preference using a two-bottle preference test, and changes in body weight, plasma leptin levels, and gene expression for the sweet taste receptor in taste buds in high-fat diet-induced obese rats and chronically diet-restricted rats. We found that the consumption and preference ratios for 0.01 and 0.04 M saccharin were significantly lower in the high-fat diet-induced obese rats than in the normal diet rats, while the serum leptin levels were markedly increased in obese rats. Consistent with the changes in saccharin intake, the gene expression level of the sweet taste receptor T1R3 was significantly decreased in the high-fat diet-induced obese rats compared with the control rats. By contrast, the chronically diet-restricted rats showed remarkably enhanced consumption and preference for 0.04 M saccharin. The serum leptin concentration was decreased, and the gene expression of the leptin receptor was markedly increased in the taste buds. In conclusion, our results suggest that nutritional status alters saccharin preference and the expression of T1R3 in taste buds. These processes may be involved in the mechanisms underlying the modulation of peripheral sweet taste sensitivity, in which leptin plays a role.

LRRK2 kinase activity mediates toxic interactions between genetic mutation and oxidative stress in a Drosophila model: Suppression by curcumin

Parkinsons disease (PD) is a neurodegenerative disorder characterized by selective loss of dopaminergic neurons and the presence of Lewy bodies. The pathogenesis of PD is believed to involve both genetic susceptibility and environmental factors. Mutations in Leucine-rich repeat kinase 2 (LRRK2) cause genetic forms of PD, and the LRRK2 locus contributes to sporadic PD. Environmental toxins are believed to act in part by causing oxidative stress. Here we employed cell and Drosophila models to investigate the interaction between LRRK2 genetic mutations and oxidative stress. We found that H(2)O(2) increased LRRK2 kinase activity and enhanced LRRK2 cell toxicity in cultured cells and mouse primary cortical neurons. Furthermore, a sub-toxic dose of H(2)O(2) significantly shortened the survival of LRRK2 transgenic flies and augmented LRRK2-induced locomotor defects and dopamine neuron loss. Treatment with a LRRK2 kinase inhibitor (GW5074) or an anti-oxidant (curcumin) significantly suppressed these PD-like phenotypes in flies. Moreover, curcumin significantly reduced LRRK2 kinase activity and the levels of oxidized proteins, and thus acted as not only an antioxidant but also a LRRK2 kinase inhibitor. These results indicate that LRRK2 genetic alterations can interact with oxidative stress, converging on a pathogenic pathway that may be related to PD. These studies also identified curcumin as a LRRK2 kinase inhibitor that may be a useful candidate for LRRK2-linked PD intervention.

Characterization of cold-induced remodelling reveals depot-specific differences across and within brown and white adipose tissues in mice.

Brown and beige adipose tissues dissipate energy in the form of heat via mitochondrial uncoupling protein 1, defending against hypothermia and potentially obesity. The latter has prompted renewed interest in understanding the processes involved in browning to realize the potential therapeutic benefits. To characterize the temporal profile of cold‐induced changes and browning of brown and white adipose tissues in mice.

Early postweaning exercise improves central leptin sensitivity in offspring of rat dams fed high-fat diet during pregnancy and lactation

Maternal high-fat (HF) diet has long-term consequences on the metabolic phenotype of the offspring. Here, we determined the effects of postweaning exercise in offspring of rat dams fed HF diet during gestation and lactation. Pregnant Sprague-Dawley rats were maintained on chow or HF diet throughout gestation and lactation. All pups were weaned onto chow diet on postnatal day (PND) 21. At 4 wk of age, male pups were given free access to running wheels (RW) or remained sedentary (SED) for 3 wk, after which all rats remained sedentary, resulting in four groups: CHOW-SED, CHOW-RW, HF-SED, and HF-RW. Male HF offspring gained more body weight by PND7 compared with CHOW pups and maintained this weight difference through the entire experiment. Three weeks of postweaning exercise did not affect body weight gain in either CHOW or HF offspring, but reduced adiposity in HF offspring. Plasma leptin was decreased at the end of the 3-wk running period in HF-RW rats but was not different from HF-SED 9 wk after the exercise period ended. At 14 wk of age, intracerebroventricular injection of leptin suppressed food intake in CHOW-SED, CHOW-RW, and HF-RW, while it did not affect food intake in HF-SED group. At death, HF-RW rats also had higher leptin-induced phospho-STAT3 level in the arcuate nucleus than HF-SED rats. Both maternal HF diet and postweaning exercise had effects on hypothalamic neuropeptide and receptor mRNA expression in adult offspring. Our data suggest that postweaning exercise improves central leptin sensitivity and signaling in this model.

Adiponectin potentiates the acute effects of leptin in arcuate Pomc neurons

Objective Adiponectin receptors (AdipoRs) are located on neurons of the hypothalamus involved in metabolic regulation – including arcuate proopiomelanocortin (Pomc) and Neuropeptide Y/Agouti-related peptide (NPY/AgRP) neurons. AdipoRs play a critical role in regulating glucose and fatty acid metabolism by initiating several signaling cascades overlapping with Leptin receptors (LepRs). However, the mechanism by which adiponectin regulates cellular activity in the brain remains undefined. Methods In order to resolve this issue, we utilized neuron-specific transgenic mouse models to identify Pomc and NPY/AgRP neurons which express LepRs for patch-clamp electrophysiology experiments. Results We found that leptin and adiponectin synergistically activated melanocortin neurons in the arcuate nucleus. Conversely, NPY/AgRP neurons were inhibited in response to adiponectin. The adiponectin-induced depolarization of arcuate Pomc neurons occurred via activation of Phosphoinositide-3-kinase (PI3K) signaling, independent of 5′ AMP-activated protein kinase (AMPK) activity. Adiponectin also activated melanocortin neurons at various physiological glucose levels. Conclusions Our results demonstrate a requirement for PI3K signaling in the acute adiponectin-induced effects on the cellular activity of arcuate melanocortin neurons. Moreover, these data provide evidence for PI3K as a substrate for both leptin and adiponectin to regulate energy balance and glucose metabolism via melanocortin activity.

TrpC5 Mediates Acute Leptin and Serotonin Effects via Pomc Neurons

The molecular mechanisms underlying acute leptin and serotonin 2C receptor-induced hypophagia remain unclear. Here, we show that neuronal and pro-opiomelanocortin (Pomc)-specific loss of transient receptor potential cation 5 (TrpC5) subunits is sufficient to decrease energy expenditure and increase food intake resulting in elevated body weight. Deficiency of Trpc5 subunits in Pomc neurons is also sufficient to block the anorexigenic effects of leptin and serotonin 2C receptor (Ht2Cr) agonists. The loss of acute anorexigenic effects of these receptors is concomitant with a blunted electrophysiological response to both leptin and Ht2Cr agonists in arcuate Pomc neurons. We also demonstrate that the Ht2Cr agonist lorcaserin-induced improvements in glucose and insulin tolerance are blocked by TrpC5 deficiency in Pomc neurons. Together, our results link TrpC5 subunits in the brain with leptin- and serotonin 2C receptor-dependent changes in neuronal activity, as well as energy balance, feeding behavior, and glucose metabolism.

Roles of dorsomedial hypothalamic cholecystokinin signaling in the controls of meal patterns and glucose homeostasis

A role for dorsomedial hypothalamus (DMH) cholecystokinin (CCK) signaling in feeding control has been proposed. Administration of CCK into the DMH reduces food intake and OLETF rats lacking CCK1 receptors (CCK1R) become hyperphagic and obese. We hypothesized that site specific replenishment of CCK1R in the DMH of OLETF rats would attenuate aspects of their feeding deficits. Recombinant vectors of adeno-associated viral (AAV)-mediated expression of CCK1R (AAVCCK1R) were bilaterally delivered into the DMH of OLETF. OLETF rats with AAVCCK1R injections demonstrated a 65% replenishment of Cck1r mRNA expression in the DMH relative to lean LETO control rats. Although this level of replenishment did not significantly affect overall food intake or body weight through 14 weeks following viral injections, meal patterns were partially normalized in OLETF rats receiving AAVCCK1R with a significant decrease in dark cycle meal size and a small but significant decrease in daily food intake in the meal analysis chambers. Importantly, the elevation in blood glucose level of OLETF rats was attenuated by the AAVCCK1R injections (p=0.03), suggesting a role for DMH CCK signaling in glucose homeostasis. In support of this role, administration of CCK into the DMH of intact rats enhanced glucose tolerance, as this occurred through activation of CCK1R but not CCK2R signaling. In conclusion, partial replenishment of CCK1R in the DMH of OLETF rats, although insufficient for altering overall food intake and body weight, normalizes meal pattern changes and reduces blood glucose levels. Our study also shows a novel role of DMH CCK signaling in glucose homeostasis.

Activation of μ-opioid receptors in the central nucleus of the amygdala induces hypertonic sodium intake.

Opioid mechanisms are involved in the control of water and NaCl intake and opioid receptors (ORs) are present in the central nucleus of the amygdala (CeA), a site of important facilitatory mechanisms related to the control of sodium appetite. Therefore, in the present study we investigated the effects of the activation of μ-ORs in the CeA on 0.3 M NaCl and water intake in rats. Male Sprague-Dawley rats with stainless steel cannulas implanted bilaterally in the CeA were used. In rats submitted to water deprivation-partial rehydration, bilateral injections of the selective μ-OR agonist [D-Ala², N-Me-Phe⁴, Gly⁵-ol]-enkephalin (DAMGO) in the doses of 1, 2, and 4 nmol into the CeA induced a dose-related increase of 0.3M NaCl intake and water intake, and bilateral injections of the selective μ-OR antagonist D-Phe-Cys-Trp-Arg-Thr-Pen-Thr-NH₂ (CTAP) in the doses of 0.5, 1, and 2 nmol into the CeA produced a dose-related decrease of 0.3 M NaCl and water intake induced by DAMGO 2 nmol into the same site. In rats treated with the diuretic furosemide (10 mg/kg b.w.) combined with the angiotensin-converting enzyme inhibitor captopril (5 mg/kg b.w.) injected subcutaneously, bilateral injections of DAMGO 2 nmol into the CeA increased 0.3 M NaCl intake and water intake and the blockade of μ-ORs with CTAP 1 nmol injected into the CeA reduced the increase in 0.3 M NaCl intake and water intake induced by DAMGO 2 nmol into the same site. Bilateral injections of DAMGO into the CeA did not change urinary volume, sodium urinary excretion and mean arterial pressure, but increased activity. Thus stimulating μ-ORs in the CeA increases hypertonic sodium intake, whereas antagonizing these sites inhibits hypertonic sodium intake. Together, our results implicate μ-ORs in the CeA in a positive regulation of sodium intake.

Large litter rearing improves leptin sensitivity and hypothalamic appetite markers in offspring of rat dams fed high-fat diet during pregnancy and lactation

Maternal high-fat (HF) diet has long-term consequences on the offsprings metabolic phenotype. Here, we determined the effects of large litter (LL) rearing in offspring of rat dams fed HF diet during gestation and lactation. Pregnant Sprague-Dawley rats were maintained on standard chow (CHOW) or HF diet throughout gestation and lactation. Pups were raised in normal litters (NLs) (10 pups/dam) or LLs (16 pups/dam) during lactation, resulting in 4 groups: CHOW-NL, CHOW-LL, HF-NL, and HF-LL. The offspring were weaned onto to either CHOW or HF diet on postnatal day 21. Male and female pups with maternal HF diet (HF-NL) had greater body weight and adiposity, higher plasma leptin levels, impaired glucose tolerance, abnormal hypothalamic leptin signaling pathways (lower leptin receptor-b [OB-Rb] and signal transducer and activator of transcription 3, higher suppressor of cytokine signaling 3 mRNA expression) and appetite markers (lower neuropeptide Y and Agouti-related peptide mRNA expression), and reduced phospho-signal transducer and activator of transcription 3 level in response to leptin in the arcuate nucleus at weaning, whereas LL rearing normalized these differences. When weaned onto CHOW diet, adult male offspring from HF diet-fed dams continued to have greater adiposity, higher leptin levels, and lower hypothalamic OB-Rb, and LL rearing improved them. When weaned onto HF diet, both adult male and female offspring with maternal HF diet had greater body weight and adiposity, higher leptin levels, impaired glucose tolerance, lower OB-Rb, and higher suppressor of cytokine signaling 3 in hypothalamus compared with those of CHOW dams, whereas LL rearing improved most of them except male OB-Rb expression. Our data suggest that LL rearing improves hypothalamic leptin signaling pathways and appetite markers in an age- and sex-specific manner in this model.