Intracerebroventricular Leptin Research Articles

Chronic central nervous system leptin administration attenuates kidney dysfunction and injury in a model of ischemia/reperfusion-induced acute kidney injury.

In the present study, we examined whether chronic intracerebroventricular (ICV) leptin administration protects against ischemia/reperfusion (I/R)-induced acute kidney injury (AKI). Twelve-week-old male rats were implanted with an ICV cannula into the right lateral ventricle, and 8-10 days after surgery, leptin (0.021 µg/h, n = 8) or saline vehicle (0.5 µL/h, n = 8) was infused via osmotic minipump connected to the ICV cannula for 12 days. On day 8 of leptin or vehicle infusion, rats were submitted to unilateral ischemia/reperfusion (UIR) by clamping the left pedicle for 30 min. To control for leptin-induced reductions in food intake, the vehicle-treated group was pair-fed (UIR-PF) to match the same amount of food consumed by leptin-treated (UIR-Leptin) rats. On the 12th day of leptin or vehicle infusion (fourth day after AKI), single-left kidney glomerular filtration rate (GFR) was measured, blood samples were collected to quantify white blood cells, and kidneys were collected for histological assessment of injury. UIR-Leptin-treated rats showed reduced right and left kidney weights (right: 1,040 ± 24 vs. 1,281 ± 36 mg; left: 1,127 ± 71 vs. 1,707 ± 45 mg, for UIR-Leptin and UIR-PF, respectively). ICV leptin infusion improved GFR (0.50 ± 0.06 vs. 0.13 ± 0.03 mL/min/g kidney wt) and reduced kidney injury scores. ICV leptin treatment also attenuated the reduction in circulating adiponectin levels that was observed in UIR-PF rats and increased the circulating white blood cells count compared with UIR-PF rats (16.3 ± 1.3 vs. 9.8 ± 0.6 k/µL). Therefore, we show that leptin, via its actions on the central nervous system, confers significant protection against major kidney dysfunction and injury in a model of ischemia/reperfusion-induced AKI.NEW & NOTEWORTHY A major new finding of this study is that chronic activation of leptin receptors in the CNS markedly attenuates acute kidney injury and protects against severe renal dysfunction after ischemia/reperfusion, independently of leptin's anorexic effects.

Chronic central leptin administration attenuates kidney dysfunction and injury in a model of ischemia/reperfusion-induced acute kidney injury

Kidney disease occurs in approximately 15% of the adult population, accounting for 37 million people in the US alone. Lack of blood flow is a major driver of kidney injury and no therapeutic modalities have shown substantial effcacy in treating ischemia-induced acute kidney injury (AKI). We recently demonstrated that activation of the brain leptin-melanocortin system dramatically improves cardiomyocyte mitochondrial function, energy metabolism and contractility, preserving cardiac function and preventing progression of heart failure following myocardial infarction and ischemia/reperfusion injury. In the present study we examined whether chronic intracerebroventricular (ICV) leptin administration protects the kidney against ischemia/reperfusion (I/R)-induced AKI. Twelve-week old male rats were implanted with an ICV cannula into the right lateral ventricle and 8-10 days after surgery, leptin (0.021 mg/hr, n=8) or saline vehicle (0.5 ml/h, n=8) was infused via osmotic minipump connected to the ICV cannula for 12 days. On day 8 of leptin or vehicle infusion, rats were submitted to unilateral ischemia/reperfusion (UIR) by clamping the left pedicle for 30 min. To control for leptin-induced reductions in food intake, the vehicle group was pair-fed (UIR-PF) to match the same amount of food consumed by leptin-treated (UIR-Leptin) rats. On the 12th day of leptin or vehicle infusion (i.e. 4th day after AKI), single-left kidney glomerular filtration rate (GFR) was measured, blood samples were collected to quantify white blood cells, and kidneys were collected for histological assessment of injury. Chronic leptin infusion reduced body weight by 20±1% compared to only 10±1% reduction in UIR-PF. UIR-Leptin rats also showed reduced right and left kidney weights (right: 1040±24 vs. 1281±36 and left: 1127±71 vs. 1707±45 mg, for UIR-Leptin and UIR-PF, respectively). Leptin infusion improved GFR (0.50±0.06 vs. 0.13±0.03 ml/min/g KW) and reduced kidney injury scores. Leptin treatment also increased circulating white blood cells count compared to UIR-PF rats (16.3±1.3 vs. 9.8±0.6 k/mL). Thus, leptin, via its actions on the central nervous system, confers significant protection against major kidney dysfunction and damage in a model of ischemia/reperfusion-induced AKI. NIH grants: (1R0DK1121411 (do Carmo), 1R0HL1630376 (da Silva/do Carmo), P20GM104357 (Hall), P30GM149404 (Hall) and U54GM115428 (Hall)). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract 14283: Brain-Mediated Cardioprotective Actions of Leptin: Potential Role of Brown Adipose Tissue and Its Release of Extracellular Vesicles

Background: We recently demonstrated that leptin has powerful central nervous system (CNS) actions that dramatically improve cardiac function following ischemia/reperfusion (IR) injury. How the brain communicates with the heart during CNS leptin infusion to improve cardiac function is unknown. One potential mechanism is activation of brown adipose tissue (BAT) which may be an important source of extracellular vesicles (EVs) carrying cardioprotective microRNAs (miR), including miR-125b-5p. Hypothesis: We investigated whether BAT contributes to the cardioprotective effect of CNS leptin infusion and the potential role of EVs carrying the miR-125b-5p in this protection. Methods: Male Sprague-Dawley rats were submitted to interscapular BAT ablation (iBATx) and instrumented with an intracerebroventricular (ICV) cannula in the brain lateral ventricle. After recovery and baseline assessment of cardiac function by echocardiography (ECHO), myocardial IR was induced by temporary ligation of the left anterior descending coronary artery. Vehicle (saline, 0.5 μL/hr) or leptin (0.62 μg/hr) was infused ICV chronically for 28 days using osmotic pumps. Cardiac function was assessed weekly by ECHO. Another set of animals with intact iBAT was treated with ICV leptin or vehicle for 4 weeks and had their iBAT collected for EVs isolation and quantification. Expression of the miR-125b-5p was measured in the heart of leptin treated rats with intact iBAT or iBATx. Results: Compared to vehicle-treated animals, ICV leptin infusion increased iBAT-derived EVs and removal of iBAT prevented leptin’s CNS-mediated cardioprotective effects after IR injury as indicated by a lack of improvement in ejection fraction (26±6 vs 41±3%) and stroke volume (162±31 vs 275±19μL) at week 4 post-IR. Expression of the mature miR-125b-5p was increased in the heart of ICV leptin treated rats and iBATx abolished this effect. Conclusion: These results indicate that the BAT plays an important role in mediating the cardioprotective effect of CNS leptin administration after IR injury and suggest that iBAT-derived EVs may be involved in delivering the miR-125b-5p to the heart during central leptin infusion. AHA 835218, 1R01HL163076, P20GM104357, and P20GM104320-07

Abstract 10134: Role of Cardiac Sympathetic Nerves in Mediating the Central Nervous System Cardioprotective Effects of Leptin After Ischemia/Reperfusion Injury

We previously demonstrated that central nervous system (CNS) administration of leptin improves left ventricular (LV) function after myocardial infarction through mechanisms that are poorly understood. Increased cardiac sympathetic activity is an important compensatory mechanism to maintain cardiac output after ischemic injury, and previous studies showed that centrally-administered leptin increases sympathetic outflow to various tissues. In the present study, we tested the hypothesis that leptin’s CNS-mediated cardioprotective effects are mediated via cardiac sympathetic nerves. Male and female Wistar rats (~8 weeks of age) were submitted to cervical ganglia denervation (CGx) and instrumented with an intracerebroventricular (ICV) cannula in the brain lateral ventricle. After recovery and baseline assessment of cardiac function by echocardiography (ECHO) and an exercise performance test (Vmax), myocardial ischemia/reperfusion (I/R) was induced by temporary (60 min) ligation of the left anterior descending coronary artery. Vehicle (saline, 0.5 μL/hr) or leptin (0.62 μg/hr) was infused chronically for 28 days starting 20 min after reperfusion using osmotic pumps implanted subcutaneously in the scapular region and connected to the ICV cannula. Cardiac function was assessed weekly by ECHO. At the end of week 4, a final Vmax was performed and +dP/dt max was accessed by LV catheterization using a Millar catheter. Despite ~70% reduction in cardiac tyrosine hydroxylase positive fibers compared to sham, CGx did not prevent leptin’s CNS-mediated cardioprotective effects as indicated by improved ejection fraction (55±1 vs. 29±3 %), global longitudinal strain (-19±2 vs. -3±2 %), +dP/dt max (10214±614 vs. 7174±716 mmHg/s) and exercise performance (1.3±14 vs. -46.3±14 Δ% compared to baseline before I/R) when compared with CGx vehicle-treated animals. CGx also did not prevent the effect of ICV leptin to reduce septal collagen deposition and heart weight/tibia length post-I/R. These results suggests that leptin, via its CNS actions, improves cardiac function and remodeling after I/R injury independent of cardiac sympathetic innervation.

Central Nervous System Actions of Leptin Improve Cardiac Function After Ischemia-Reperfusion: Roles of Sympathetic Innervation and Sex Differences.

Background Therapeutic strategies for preventing paradoxical reperfusion injury after myocardial ischemia are limited. We tested whether central nervous system actions of leptin induce important protective effects on cardiac function and metabolism after myocardial ischemia/reperfusion (I/R) injury, the role of cardiac sympathetic innervation in mediating these effects, and whether there are major sex differences in the cardioprotective effects of chronic central nervous system leptin infusion. Methods and Results Myocardial I/R was induced by temporary ligation of the left descending coronary artery in male and female Wistar rats instrumented with intracerebroventricular cannula in the lateral ventricle. Vehicle or leptin (0.62 μg/h) infusion was started immediately after reperfusion and continued for 28 days using osmotic minipumps connected to the intracerebroventricular cannula. Cardiac function was assessed by echocardiography, ventricular pressures, and exercise performance. Intracerebroventricular leptin treatment markedly attenuated cardiac dysfunction post-I/R as evidenced by improved ejection fraction (56.7±1.9 versus 22.6%±1.1%), maximal rate of left ventricle rise (11 680±2122 versus 5022±441 mm Hg) and exercise performance (-4.2±7.9 versus -68.2±3.8 Δ%) compared with vehicle-treated rats. Intracerebroventricular leptin infusion reduced infarct size in females, but not males, when compared with ad-lib fed or pair-fed saline-treated rats. Intracerebroventricular leptin treatment also increased cardiac NAD+/NADH content (≈10-fold) and improved mitochondrial function when compared with vehicle treatment. Cervical ganglia denervation did not attenuate the cardiac protective effects of leptin after I/R injury. Conclusions These data indicate that leptin, via its central nervous system actions, markedly improves overall heart function and mitochondrial metabolism after I/R injury regardless of sex, effects that are largely independent of cardiac sympathetic innervation.

Chronic Central Nervous System Leptin Infusion Improves Cardiac Function and Metabolism after Ischemia/Reperfusion Injury

Important adverse changes in cardiac energy metabolism occur after ischemia/reperfusion injury (I/R), contributing to the worsening of cardiac function and development of heart failure. We recently showed that leptin, via its actions on the central nervous system (CNS), improves left ventricular (LV) function in a model of heart failure induced by permanent ligation of the left anterior descending coronary artery (LAD). In the present study, we examined whether the CNS‐ effects of leptin protect against myocardial I/R injury, and if chronic intracerebroventricular (ICV) leptin infusion improves cardiac substrate utilization, assessed by markers of myocardial fatty acid (FA) and glucose oxidation, NAD+/NADH redox state and plasma levels of β‐hydroxybutyrate (β‐HOB). Male Wistar rats were instrumented with an ICV cannula in the brain lateral ventricle. After recovery and baseline assessment of cardiac function by echocardiography (ECHO), myocardial I/R was induced by temporary (60 min) ligation of the LAD. Vehicle (saline, 0.5 µL/hr) or leptin (0.62 µg/hr) was infused chronically for 28 days starting 20 min after reperfusion using osmotic minipumps connected to the ICV cannula. ECHO assessment of cardiac function was performed weekly. At the end of week 4, +dP/dtmax was accessed by LV catheterization. Hearts and plasma samples were collected for evaluation of CD36, PPAR‐δ, PDK4 and p‐PDH1/PDH1 by western blot and cardiac NAD+/NADH ratio and plasma levels of β‐OHB were measured by ELISA. Our results showed that ICV leptin treatment improved cardiac function as evidenced by increased ejection fraction 4 weeks after I/R (46±3 vs. 26±3 %) and +dP/dtmax (10387±1686 vs. 5022±442 mmHg/s) when compared with vehicle‐treated rats. ICV leptin infusion also significantly increased cardiac protein expression of CD36 (1.4±0.1 vs. 1.0±0.1 au), PPAR‐δ (1.8±0.1vs. 1.0±0.01 au), PDK4 (1.8±0.1 vs. 1.0±0.1 au) and p‐PDH1/PDH1 (2.2±0.3 vs. 1.0±0.2 au) when compared with vehicle‐treated animals. In addition, ICV leptin infusion increased cardiac NAD+/NADH ratio (6.8±2 vs. 1.02±0.3 pmol/µL) and reduced plasma levels of β‐OHB (18.2±3 vs. 62.8±7.0 nmol/µL). These results demonstrate that chronic ICV leptin infusion improves cardiac function following I/R injury and suggest that leptin’s CNS‐mediated cardioprotective effects may involve improved myocardial FA oxidation and NAD+/NADH redox state, reducing the reliance on ketone bodies (β‐OHB) as an energy source.

Abstract P321: Chronic Central Nervous System Leptin Infusion Increases Cardiomyocyte Mitochondrial Function And Biogenesis And Improves Cardiac Function After Ischemia-reperfusion Injury.

Mitochondrial (MT) dysfunction plays an important role in the pathophysiology of myocardial ischemia/reperfusion injury (I/R). We recently showed that leptin, via its actions in the central nervous system (CNS), improves left ventricular (LV) function in a model of heart failure induced by permanent ligation of the left anterior descending coronary artery (LAD). In the present study, we examined if the CNS effects of leptin protect against myocardial ischemia/reperfusion (I/R) injury, and whether chronic intracerebroventricular (ICV) leptin infusion increases MT function and biogenesis in the non-infarcted area of the LV that is at risk but still viable. Male Wistar rats were instrumented with an ICV cannula in the brain lateral ventricle. After recovery and baseline assessment of cardiac function by echocardiography (ECHO), myocardial I/R was induced by temporary (60 min) ligation of the LAD. Vehicle (saline, 0.5 μL/hr) or leptin (0.62 μg/day) was infused chronically for 28 days starting 20 min after reperfusion using osmotic minipumps connected to the ICV cannula. ECHO assessment of cardiac function was performed every week. At the end of week 4, +dP/dt max and Tau were accessed by LV catheterization. Hearts were then collected for evaluation of MT function in isolated cardiac fibers using Oroboros oxygraphy-2k respirometer. ICV leptin treatment improved systolic and diastolic function as evidenced by increased ejection fraction 4 weeks after I/R (46±3 vs. 26±3 %), stroke volume (353±19 vs. 193±27 μL), +dP/dt max (10387±1686 vs. 5022±442 mmHg/s) and reduced Tau (6.5±0.3 vs. 8±0.3 ms) when compared with vehicle-treated rats. In addition, ICV leptin infusion significantly increased ATP-linked respiration (55±3 vs. 39±1 %), reduced proton leak (45±3 vs. 61±1 %), and improved MT reserve capacity (42±5 vs. 27±2 %). Improved MT function was associated with increased MT Complex I- mediated respiration (47±6 vs. 26±1 pmolO 2 /s - mg). ICV leptin treatment also increased PGC1 α protein expression and COX3 gene expression, indicating enhanced MT biogenesis. These results demonstrate that chronic ICV leptin infusion improves cardiac function following I/R injury and suggests that leptin’s CNS-mediated cardioprotective effects may involve improved myocardial MT function and biogenesis.

Chronic Antidiabetic Actions of Leptin: Evidence From Parabiosis Studies for a CNS-Derived Circulating Antidiabetic Factor.

We used parabiosis to determine whether the central nervous system (CNS)-mediated antidiabetic effects of leptin are mediated by release of brain-derived circulating factors. Parabiosis was surgically induced at 4 weeks of age, and an intracerebroventricular (ICV) cannula was placed in the lateral cerebral ventricle at 12 weeks of age for ICV infusion of leptin or saline vehicle. Ten days after surgery, food intake, body weight, and blood glucose were measured for 5 consecutive days, and insulin-deficiency diabetes was induced in all rats by a single streptozotocin (STZ) injection (40 mg/kg). Five days after STZ injection, leptin or vehicle was infused ICV for 7 days, followed by 5-day recovery period. STZ increased blood glucose and food intake. Chronic ICV leptin infusion restored normoglycemia in leptin-infused rats while reducing blood glucose by ∼27% in conjoined vehicle-infused rats. This glucose reduction was caused mainly by decreased hepatic gluconeogenesis. Chronic ICV leptin infusion also reduced net cumulative food intake and increased GLUT4 expression in skeletal muscle in leptin/vehicle compared with vehicle/vehicle conjoined rats. These results indicate that leptin's CNS-mediated antidiabetic effects are mediated, in part, by release into the systemic circulation of leptin-stimulated factors that enhance glucose utilization and reduce liver gluconeogenesis.

Leptin receptor expression in the dorsomedial hypothalamus stimulates breathing during NREM sleep in db/db mice.

Obesity leads to obstructive sleep apnea (OSA), which is recurrent upper airway obstruction during sleep, and obesity hypoventilation syndrome (OHS), hypoventilation during sleep resulting in daytime hypercapnia. Impaired leptin signaling in the brain was implicated in both conditions, but mechanisms are unknown. We have previously shown that leptin stimulates breathing and treats OSA and OHS in leptin-deficient ob/ob mice and leptin-resistant diet-induced obese mice and that leptin's respiratory effects may occur in the dorsomedial hypothalamus (DMH). We hypothesized that leptin receptor LepRb-deficient db/db mice have obesity hypoventilation and that restoration of leptin signaling in the DMH will increase ventilation during sleep in these animals. We measured arterial blood gas in unanesthetized awake db/db mice. We subsequently infected these animals with Ad-LepRb or control Ad-mCherry virus into the DMH and measured ventilation during sleep as well as CO2 production after intracerebroventricular (ICV) infusions of phosphate-buffered saline or leptin. Awake db/db mice had elevated CO2 levels in the arterial blood. Ad-LepRb infection resulted in LepRb expression in the DMH neurons in a similar fashion to wildtype mice. In LepRb-DMH db/db mice, ICV leptin shortened REM sleep and increased inspiratory flow, tidal volume, and minute ventilation during NREM sleep without any effect on the quality of NREM sleep or CO2 production. Leptin had no effect on upper airway obstruction in these animals. Leptin stimulates breathing and treats obesity hypoventilation acting on LepRb-positive neurons in the DMH.

Effects of intracerebroventricular leptin and orexin-A on the baroreflex control of renal sympathetic nerve activity in conscious rats fed a normal or high-fat diet.

This study examined the effect of leptin and orexin-A on autonomic baroreflex control in conscious Wistar rats exposed to high-fat (45% fat) or normal (3.4%) diet for 4weeks. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were monitored during the generation of baroreflex gain curves and acute volume expansion (VEP). Intracerebroventricular (ICV) leptin (1μg/min) increased RSNA in the normal diet group (0.31±0.04 vs 0.23±0.03mV/s) and MAP in the high-fat diet group (115±5 vs 105±5mm Hg, P<.05). Orexin-A (50ng/min) increased RSNA, HR and MAP in the high-fat diet group (0.26±0.03 vs 0.22±0.02mV/s, 454±8 vs 417±12beats/min, 117±1 vs 108±1mm Hg) and the normal diet group (0.18±0.05 vs 0.17±0.05mV/s, 465±10 vs 426±6beats/min, 116±2 vs 104±3 mmHg). Baroreflex sensitivity for RSNA was increased during ICV leptin by 50% in the normal diet group, compared to 14% in the high-fat diet group (P<.05). Similarly, orexin-A increased baroreflex sensitivity by 56% and 50% in the high-fat and normal diet groups, respectively (all P<.05). During ICV saline, VEP decreased RSNA by 31±5% (P<.05) after 10minutes and the magnitude of this response was blunted during ICV infusion of leptin (17±2%, P<.05) but not orexin-A in the normal diet group. RSNA response to VEP was not changed during ICV leptin or orexin-A in the high-fat diet group. These findings indicate possible central roles for leptin and orexin-A in modulating the baroreflexes under normal or increased fat intake in conscious rats and potential therapeutic approaches for obesity associated hypertension.

The nutrient sensing pathways FoxO1/3 and mTOR in the heart are coordinately regulated by central leptin through PPARβ/δ. Implications in cardiac remodeling

BackgroundCardiovascular disease in obese individuals with type 2 diabetes is often associated with hyperleptinemia and leptin resistance, while other studies support that leptin has cardioprotective effects. Besides, the role of leptin in regulating cardiac atrophy or hypertrophy remains to be clearly defined. In fact, in rats with normal leptin sensitivity, the molecular underpinnings of the effects of central leptin regulating cardiac structural pathways remain poorly understood. ObjectiveHence, we assessed the effects of intracerebroventricular (icv) leptin infusion on cardiac remodeling analyzing FOXO1/3 and mTORC1 pathways, focusing special attention to PPARβ/δ as mediator of central leptin's effects on cardiac metabolism. MethodsMale 3-months-old Wistar rats, infused with icv leptin (0.2 μg/day) for 7 days, were daily co-treated intraperitoneally with the specific PPARβ/δ antagonist GSK0660, at 1 mg/kg per day along leptin treatment. ResultsCentral leptin regulated dynamically, in an opposite manner, the network between FOXOs and mTORC1 and induced an atrophy-related gene program in cardiac tissue. Leptin activated the anti-hypertrophic kinase GSK3β and increased the protein levels of muscle-specific ubiquitin ligases, muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx)/Atrogin-1 involved in limiting cardiac hypertrophy. FOXO1 activity and the expression of their target genes, Sod2 and Lpl, were also increased in the heart upon central leptin infusion. Besides, Beclin-1 and LC3B-II, gene products of the autophagic pathway response, were upregulated, while the content and expression levels of phenotypic markers of cardiac hypertrophy as ANP and β-myosin heavy chain, gene product of Myh7 were significantly decreased. On the other hand, mTORC1 activity and OXPHOS protein levels were decreased suggesting a key role of central leptin preventing cardiac oxidative stress. In fact, the content of carbonylated proteins, TBARS and ROS/RSN were not increased in cardiac tissue in response to central leptin infusion. Finally, the pharmacological inhibition of PPARβ/δ, via in vivo administration of the selective antagonist GSK0660, blunted the induction of FOXO1/3, Atrogin-1, MuRF1 and GSK3β in the heart mediated by icv leptin infusion. ConclusionsOur results demonstrate that, in lean rats with normal leptin sensitivity, central leptin regulates nutrient sensing pathways in heart contributing to balance cardiac remodeling through the anti- and pro-hypertrophic programs, and in this process is involved PPARβ/δ.

Chronic CNS-mediated cardiometabolic actions of leptin: potential role of sex differences.

Previous studies using male rodents showed the adipocyte-derived hormone leptin acts in the brain to regulate cardiovascular function, energy balance, and glucose homeostasis. The importance of sex differences in cardiometabolic responses to leptin, however, is still unclear. We examined potential sex differences in leptin's chronic central nervous system (CNS)-mediated actions on blood pressure (BP), heart rate (HR), appetite, and glucose homeostasis in normal and type 1 diabetic rats. Female and male Sprague-Dawley (SD) rats were instrumented with intracerebroventricular cannulas for continuous 7-day leptin infusion (15 µg/day), and BP and HR were measured by telemetry 24 h/day. At baseline, females had lower mean arterial pressure (MAP) (96 ± 3 vs. 104 ± 4 mmHg, P < 0.05) but higher HR (375 ± 5 vs. 335 ± 5 beats/min, P < 0.05) compared with males. After leptin treatment, we observed similar increases in BP (∼3 mmHg) and HR (∼25 beats/min) in both sexes. Females had significantly lower body weight (BW, 283 ± 2 vs. 417 ± 7 g, P < 0.05) and caloric intake (162 ± 20 vs. 192 ± 9 kcal/kg of body wt, P < 0.05) compared with males, and leptin infusion reduced BW (-10%) and caloric intake (-62%) similarly in both sexes. In rats with streptozotocin-induced diabetes (n = 5/sex), intracerebroventricular leptin treatment for 7 days completely normalized glucose levels. The same dose of leptin administered intraperitoneally did not alter MAP, HR, glucose levels, or caloric intake in normal or diabetic rats. These results show that leptin's CNS effects on BP, HR, glucose regulation, and energy homeostasis are similar in male and female rats. Therefore, our results provide no evidence for sex differences in leptin's brain-mediated cardiovascular or metabolic actions.

Abstract 16200: Chronic Central Nervous System Actions of Leptin Protect Against Myocardial Ischemia/reperfusion Injury

While myocardial reperfusion is the most effective therapy to reduce mortality after myocardial infarction, it can paradoxically exacerbate ischemic injury. We recently showed that leptin, via its actions on the central nervous system (CNS), improved left ventricular function in a model of heart failure induced by permanent ligation of the left anterior coronary artery (LAD). To investigate whether leptin also protects the heart against ischemia/reperfusion (I/R) injury via its actions in the CNS, we instrumented female Wistar rats (15 weeks of age) with an intracerebroventricular (ICV) cannula into the lateral ventricle, and after 7 days of recovery and baseline assessment of cardiac function by echocardiography (VisualSonics VEVO-3100®), myocardial I/R was induced by temporary LAD ligation (60 min). Vehicle (saline, 0.5 μL/hr, n=6) or leptin (15 μg/day, n=7) were infused ICV for 28 consecutive days starting 20 min after reperfusion using osmotic minipump connected to the ICV cannula. Echocardiographic assessment of cardiac function was performed every week and at the end of the 4 th week of treatment, the heart was collected and processed for protein analysis and histological evaluation of infarct size and collagen deposition. Compared to vehicle treatment, chronic ICV leptin infusion significantly reduced infarcted area (21±2 vs. 37±4 %), septal collagen deposition (2.2±0.2 vs. 4.0±0.7 %), and markedly attenuated systolic dysfunction as evidenced by increased ejection fraction 4 weeks post I/R (59±1 vs. 30±2%), stroke volume (296±19 vs. 159±8 μL) and cardiac output (108±5 vs.63±4 μL/min). ICV leptin infusion also prevented the increase in left atrium to aorta diameter ratio (1.5±0.1 vs. 2±0.1 mm), an index of cardiac congestion. In addition, we found a 2-fold increase in the ratio of phospho-acetyl-CoA carboxylase (p-ACC) to total ACC protein expression, a marker of fatty acid oxidation, in hearts of leptin-treated rats compared with vehicle infusion. These results indicate that leptin exerts powerful beneficial CNS-mediated effects on the heart that improve systolic function and protect the myocardium against I/R injury. Our results also suggest that these beneficial actions may involve improved myocardial bioenergetics.

SUN-570 The Crosstalk Between Central Leptin and PPARbeta/delta Protects the Heart Against Oxidative Stress Damage and the Development of Hypertrophy

Cardiovascular disease is a common cause of morbidity and mortality in obese people with type 2 diabetes, which is often associated with increased levels of leptin. While many studies hint at the existence of important roles for both hyperleptinemia and leptin resistance in obesity and diabetes-associated cardiovascular disease, others support that leptin has cardioprotective effects. Leptin action comprises direct effects on cardiac tissue and indirect effects mediated via the sympathetic nervous system. Since the molecular underpinnings of leptin-regulated pathways in cardiac tissue in normoleptinemic animals remain less well defined, we addressed the effects of central leptin infusion on cardiac function and remodeling analyzing FOXO1/3 and mTORC1 pathways, paying special attention to PPARβ/δ as a key leptin signal regulator. We found that central leptin regulated dynamically the network between PPARβ/δ, FOXOs, and mTORC1 in cardiac tissue, through antioxidant, thermogenic and autophagy programs. Intracerebroventricular (ICV) leptin infusion (0.2µg/day) for 7 days in male 3-months-old Wistar rats induced protection from hypertrophy without increasing TBARS and protein carbonylation nor ROS/RSN cardiac levels. These effects were further supported by both increased of Sod2 and Ucp1 expression and reduced Tnf-α. Atrophy-related ubiquitin ligase Atrogin-1, accompanied by Beclin-1 and LC3II, gene products of the autophagic pathway response, were all upregulated by central leptin. In addition, mTORC1 activity and OXPHOS protein levels were decreased without affecting cellular function. Moreover, the content of carbonylated proteins did not increase upon the central leptin treatment, suggesting a key role of leptin in preventing cardiac oxidative stress. Finally, the pharmacological inhibition of PPARβ/δ, via in vivo administration of the selective antagonist GSK0660, blunted the induction of FOXO1/3 and Atrogin-1 in the heart mediated by icv leptin infusion. Together these data support that PPARβ/δ may act as a mediator of central leptin effects on cardiac cellular reprogramming through the activation of FOXO1/3 and the inactivation of mTORC1 pathways, and the upregulation of Atrogin-1 and the genes involved in energy uncoupling.

Chronic Intracerebroventricular Leptin Infusion Attenuates Cardiac Dysfunction After Myocardial Infarction

Leptin is an important regulator of energy balance and substrate utilization in various tissues including the heart. In the present study we tested whether activation of leptin receptors in the central nervous system (CNS) confers protection against cardiac dysfunction after myocardial infarction (MI) induced by permanent ligation of the left anterior descending coronary artery (LAD). Male Sprague‐Dawley rats at 12 weeks of age were implanted with BP telemetry transmitters and an intracerebroventricular (ICV) cannula was inserted into the lateral ventricle. After 10 days of recovery, mean arterial pressure (MAP) and heart rate (HR) were measured 24‐hrs/day by telemetry and cardiac function was assessed by echocardiography (VisualSonics‐VEVO3100®). After stable baseline measurements for 4 days, the LAD was permanently ligated and saline vehicle (0.5 μL/hr, n=6) or leptin (15 μg/day, n=7) were infused ICV via osmotic minipump for 28 consecutive days. Compared to vehicle treatment, chronic ICV leptin infusion for 4 weeks markedly attenuated cardiac dysfunction caused by MI as evidenced by normalization of global cardiac radial strain (39±4 to 36±5 vs. 37±4 to 25±3 %), cardiac output (92±5 to 110±10 vs. 105±6 to 83±9 ml/min) and left atrium to aorta ratio, an index of cardiac congestion, (1.6±0.1 to 1.6±0.1 vs. 1.7±0.1 to 2.3±0.1). Central leptin administration also significantly improved ejection fraction (from 35±3 to 49±2 %) and fractional shortening (from 12.4±0.8 to 18.6±1.4 %, for week 1 and week 4 post‐MI, respectively), whereas no improvement was observed in vehicle‐treated rats (from 36±4 to 30±2 %, and from 12.2±1.7 to 10.1±1.3 %, respectively). In addition, ICV leptin infusion prevented the bradycardia observed in vehicle‐treated rats (354±3 to 370±6 vs. 360±7 to 323±6 bpm) but did not attenuate the reduction in MAP evoked by MI (101±4 to 94±3 vs. 102±3 to 97±2 mmHg). There was no difference in infarcted area between groups (30±3 vs. 29±5 %). These results indicate that leptin can improve cardiac function and attenuate progression of heart failure after MI via a CNS‐mediated mechanism.Support or Funding InformationNHLBI PO1HL51971, NIGMS P20GM104357 and NIGMS U54GM115428This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Differential Regulation of Cardiac Substrate Utilization in Response to Chronic Central Nervous System Administration of Leptin and Melanotan II in Rats with Myocardial Infarction

The brain leptin‐melanocortin system pathway plays an important role in regulating many physiological functions including energy homeostasis. We found that chronic intracerebroventricular (ICV) infusion of leptin or the melanocortin 4 receptor (MC4R) agonist Melanotan II, MTII, markedly attenuated cardiac dysfunction in rats with myocardial infarction (MI) induced by permanent left anterior descending coronary artery (LAD) ligation. In the present study we examined if activation of leptin‐MC4R axis in the central nervous system (CNS) alters cardiac substrate utilization in rats with MI. Male Sprague‐Dawley rats at 15 weeks of age were implanted with an ICV cannula into the lateral ventricle. After 10 days of recovery, the LAD was permanently ligated and saline vehicle (0.5 μL/hr, n=5), leptin (15 μg/day, n=5) or MTII (240 ng/day, n=3) was infused ICV via osmotic minipump for 14 consecutive days. On day 14 of treatment the hearts were quickly excised and perfused ex vivo in the working mode with glucose (5.5 mmol/L) and the fatty acid oleate (0.4 mmol/L). After a 5‐min baseline equilibration period the hearts were perfused for an additional 20 min and coronary flow samples were collected every 5 min to determine rates of substrate oxidation by quantitative measurement of [14C]O2 and [3H]2O using [U‐14C]glucose (0.08 μCi/ml) and [9,10‐3H]oleate (0.1 μCi/ml) as the radiolabeled tracers. Compared to vehicle treatment, chronic ICV leptin infusion for 2 weeks markedly increased glucose oxidation (0.60±0.04 vs. 0.27±0.02 μmol/min/g dry heart weight) without altering oleate oxidation (0.95±0.01 vs. 0.90±0.02 μmol/min/g dry heart weight). Chronic central MTII infusion did not alter glucose oxidation (0.25±0.03 vs. 0.27±0.02 μmol/min/g dry heart weight) but increased fatty acid oxidation compared to vehicle treatment (1.13±0.01 vs. 0.90±0.02 μmol/min/g dry heart weight). These results suggest the CNSmechanisms by which leptin and MC4R activation improve cardiac function post MI may involve increased myocardial bioenergetics by differential modulation of glucose and fatty acid utilization.Support or Funding InformationNHLBI PO1HL51971, NIGMS P20GM104357 and NIGMS U54GM115428This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

CPT1C in the ventromedial nucleus of the hypothalamus is necessary for brown fat thermogenesis activation in obesity

ObjectiveCarnitine palmitoyltransferase 1C (CPT1C) is implicated in central regulation of energy homeostasis. Our aim was to investigate whether CPT1C in the ventromedial nucleus of the hypothalamus (VMH) is involved in the activation of brown adipose tissue (BAT) thermogenesis in the early stages of diet-induced obesity. MethodsCPT1C KO and wild type (WT) mice were exposed to short-term high-fat (HF) diet feeding or to intracerebroventricular leptin administration and BAT thermogenesis activation was evaluated. Body weight, adiposity, food intake, and leptinemia were also assayed. ResultsUnder 7 days of HF diet, WT mice showed a maximum activation peak of BAT thermogenesis that counteracted obesity development, whereas this activation was impaired in CPT1C KO mice. KO animals evidenced higher body weight, adiposity, hyperleptinemia, ER stress, and disrupted hypothalamic leptin signaling. Leptin-induced BAT thermogenesis was abolished in KO mice. These results indicate an earlier onset leptin resistance in CPT1C KO mice. Since AMPK in the VMH is crucial in the regulation of BAT thermogenesis, we analyzed if CPT1C was a downstream factor of this pathway. Genetic inactivation of AMPK within the VMH was unable to induce BAT thermogenesis and body weight loss in KO mice, indicating that CPT1C is likely downstream AMPK in the central mechanism modulating thermogenesis within the VMH. Quite opposite, the expression of CPT1C in the VMH restored the phenotype. ConclusionCPT1C is necessary for the activation of BAT thermogenesis driven by leptin, HF diet exposure, and AMPK inhibition within the VMH. This study underscores the importance of CPT1C in the activation of BAT thermogenesis to counteract diet-induced obesity.

Evidence for a circulating factor released by the brain that contributes to chronic antidiabetic actions of leptin

We previously demonstrated that leptin has powerful central nervous system (CNS)‐mediated antidiabetic actions that are independent of the autonomic nervous system (ANS) and the pituitary. In this study, we examined if a circulating factor released by the brain contributes to leptin's chronic antidiabetic actions in insulin deficient rats. Male inbred 4‐week‐old Lewis rats (n=14) were conjoined by attaching their skin to allow shared circulation. Six weeks later, the rats were implanted with an intracerebroventricular (ICV) cannula into the lateral ventricle to infuse leptin in one rat and vehicle in the other rat of each pair. Eight days after surgery, food intake, body weight and blood glucose concentration were measured for 5 consecutive days and then streptozotocin (STZ) was injected (40 mg/kg) to induce insulin‐deficient diabetes in both rats. Five days after STZ injection, leptin (15 mg/day) or vehicle (0.5 ml/h) was delivered ICV continuously for 7 days via osmotic minipumps. STZ injection significantly increased average blood glucose concentration (359±19 vs. 79±6 mg/dL) and food intake (49±2 vs. 39±3 g/day). Despite higher food intake, average body weight decreased after STZ injection (619±23 vs. 664±23 g). Chronic ICV leptin infusion restored normoglycemia (110±31 vs. 359±19 mg/dL) in leptin‐treated rats and reduced blood glucose by ~27% in the paired parabiotic rat infused with vehicle (269±20 vs. 366±41 mg/dL). Leptin treatment did not reduce food intake (53±20 vs. 49±23 g/day) or body weight (619±23 vs. 610±20 g) in the paired rats. After stopping leptin treatment, blood glucose concentration returned to diabetic values in leptin‐treated (305±44 vs. 110±31 mg/dL) as well as in vehicle‐treated rats (330±11 vs. 269±20 mg/dL), and food intake increased 37% (67±5 vs. 49±3 g/day). These results suggest that the chronic antidiabetic effects of leptin may involve release into the systemic circulation of a brain‐derived neuroendocrine factor that enhances glucose homeostasis in insulin deficient rats. (NHLBI‐PO1HL51971, NIGMS P20GM104357)Support or Funding InformationDepartment of Physiology and Biophysics and Mississippi Center for Obesity Research. University of Mississippi Medical Center.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

In Uncontrolled Diabetes, Hyperglucagonemia and Ketosis Result From Deficient Leptin Action in the Parabrachial Nucleus.

Growing evidence implicates neurons that project from the lateral parabrachial nucleus (LPBN) to the hypothalamic ventromedial nucleus (VMN) in a neurocircuit that drives counterregulatory responses to hypoglycemia, including increased glucagon secretion. Among LPBN neurons in this circuit is a subset that expresses cholecystokinin (LPBNCCK neurons) and is tonically inhibited by leptin. Because uncontrolled diabetes is associated with both leptin deficiency and hyperglucagonemia, and because intracerebroventricular (ICV) leptin administration reverses both hyperglycemia and hyperglucagonemia in this setting, we hypothesized that deficient leptin inhibition of LPBNCCK neurons drives activation of this LPBN→VMN circuit and thereby results in hyperglucagonemia. Here, we report that although bilateral microinjection of leptin into the LPBN does not ameliorate hyperglycemia in rats with streptozotocin-induced diabetes mellitus (STZ-DM), it does attenuate the associated hyperglucagonemia and ketosis. To determine if LPBN leptin signaling is required for the antidiabetic effect of ICV leptin in STZ-DM, we studied mice in which the leptin receptor was selectively deleted from LPBNCCK neurons. Our findings show that although leptin signaling in these neurons is not required for the potent antidiabetic effect of ICV leptin, it is required for leptin-mediated suppression of diabetic hyperglucagonemia. Taken together, these findings suggest that leptin-mediated effects in animals with uncontrolled diabetes occur through actions involving multiple brain areas, including the LPBN, where leptin acts specifically to inhibit glucagon secretion and associated ketosis.

Central leptin regulates heart lipid content by selectively increasing PPAR β/δ expression.

The role of central leptin in regulating the heart from lipid accumulation in lean leptin-sensitive animals has not been fully elucidated. Herein, we investigated the effects of central leptin infusion on the expression of genes involved in cardiac metabolism and its role in the control of myocardial triacylglyceride (TAG) accumulation in adult Wistar rats. Intracerebroventricular (icv) leptin infusion (0.2 µg/day) for 7 days markedly decreased TAG levels in cardiac tissue. Remarkably, the cardiac anti-steatotic effects of central leptin were associated with the selective upregulation of gene and protein expression of peroxisome proliferator-activated receptor β/δ (PPARβ/δ, encoded by Pparb/d) and their target genes, adipose triglyceride lipase (encoded by Pnpla2, herefater referred to as Atgl), hormone sensitive lipase (encoded by Lipe, herefater referred to as Hsl), pyruvate dehydrogenase kinase 4 (Pdk4) and acyl CoA oxidase 1 (Acox1), involved in myocardial intracellular lipolysis and mitochondrial/peroxisomal fatty acid utilization. Besides, central leptin decreased the expression of stearoyl-CoA deaturase 1 (Scd1) and diacylglycerol acyltransferase 1 (Dgat1) involved in TAG synthesis and increased the CPT-1 independent palmitate oxidation, as an index of peroxisomal β-oxidation. Finally, the pharmacological inhibition of PPARβ/δ decreased the effects on gene expression and cardiac TAG content induced by leptin. These results indicate that leptin, acting at central level, regulates selectively the cardiac expression of PPARβ/δ, contributing in this way to regulate the cardiac TAG accumulation in rats, independently of its effects on body weight.