Name: experimental approach to examine leptin signaling in the carotid bodies and its effects on control of breathing
Uploaded: 2019-10-25T13:30:00
Description: Watch this Scientific Journal Video about Experimental Approach to Examine Leptin Signaling in the Carotid Bodies and its Effects on Control of Breathing at JoVE.com

R01HL138932, RO1HL133100, RO1HL128970, AHACDA34700025

All experimental protocols have been approved by the Institutional Animal Care and Use Committee (MO18M211).
1. Leptin Infusion
NOTE: In order to examine the effect of leptin on breathing, we infused leptin subcutaneously in lean C57BL/6J mice by an osmotic pump to raise circulating leptin levels to those observed in obese mice.
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	<li>Osmotic pump preparation
	<ol>
		<li>Weigh the empty pump to check the net weight of the solu...

<ol>
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C., Shin, M. K., Yao, Q., Devera, R., Fonti-Bevans, S., Polotsky, V. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermoneutrality+modifies+the+impact+of+hypoxia+on+lipid+metabolism.">Thermoneutrality modifies the impact of hypoxia on lipid metabolism.</a> American Journal of Physiology Endocrinology and Metabolism. 304, 424-435 (2012).</li><li>Polotsky, V. 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The main focus of our study was to examine respiratory effects of leptin signaling in the CB. Several protocols have been developed to assess the role of leptin in a mechanistic fashion. First, specific contribution of CB to the HVR was analyzed by careful quantification of the HVR during the first 2 min of hypoxic exposure. Second, the relevance of CB in leptin-mediated up-regulation of control of breathing was examined by two complementary approaches. In lean wild-type mice with low leptin levels, the HVR was measured ...

An adipocyte produced hormone leptin acts in the hypothalamus to suppress food intake and increase metabolic rate. Studies performed in our laboratory1,2 and by other investigators3,4 showed that leptin increases the hypercapnic ventilatory response (HVR) preventing obesity hypoventilation in leptin deficient obesity. However, a majority of obese individuals have high plasma leptin levels and demonstrate resistance to the metabolic and respiratory effects of the hormone5,6,7,8. Resistance to leptin is multifactorial, but limited permeability of the blood-brain barrier (BBB) to leptin plays a major role. We propose that leptin acts below BBB in a key organ of peripheral hypoxic sensitivity, the carotid bodies (CB), to defend breathing in obese individuals. CBs express the long functional isoform of leptin receptor, LepRb, but the role of CB in respiratory effects of leptin has not been sufficiently elucidated9,10.
The goal of our method was to examine the effect of leptin signaling in the CB on HVR. Our rationale was to perform (a) loss of function experiments infusing leptin in mice with intact carotid bodies and denervated carotid bodies followed by HVR measurements; (b) gain of function experiments in db/db mice lacking LepRb, in which we measured the HVR at baseline and after expression of LepRb exclusively in CB. The advantage of our techniques was that we performed all our experiments in unrestrained unanesthetized mice during sleep and wakefulness. Previous investigators either performed their experiments under anesthesia9 or did not measure effects of leptin during sleep10. In addition, our study is the first to utilize a unique gain of function approach with selective LepRb expression in CB described above.
In the broad context, our approach can be generalized to other receptors expressed in CB and their role in hypoxic sensitivity. Investigators can infuse a ligand to a receptor of interest and measure the HVR at baseline and after CB denervation. As a complementary approach, a receptor of interest can be overexpressed in CB and HVR measurements can be performed before and after overexpression using our technology described in this manuscript.

<table>
	<tbody>
		<tr>
			<td>1ml Insulin Syringes</td>
			<td>BD Biosciences</td>
			<td>309311</td>
			<td></td>
		</tr>
		<tr>
			<td>1x PBS (pH 7.4)</td>
			<td>Gibco</td>
			<td>10010-023</td>
			<td>500 ml</td>
		</tr>
		<tr>
			<td>Ad-Lacz</td>
			<td>Dr. Christopher Rhodes (University of Chicago)</td>
			<td></td>
			<td>1x1010 pfu/ml</td>
		</tr>
		<tr>
			<td>Ad-LepRb-GFP</td>
			<td>Vector Biolabs</td>
			<td>ADV-263380</td>
			<td>2-5x1010 pfu/ml</td>
		</tr>
		<tr>
			<td>Anesthetic cart</td>
			<td>Atlantic Biomedical</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Betadine</td>
			<td>Purdue Products Ltd.</td>
			<td>12496-0757-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Buprenorphine (Buprenex)</td>
			<td>Reckitt Benckiser Healthcare Ltd.</td>
			<td>12496-0757-5</td>
			<td>0.3mg/ml</td>
		</tr>
		<tr>
			<td>C57Bl/6J</td>
			<td>Jackson laboratory</td>
			<td>000664</td>
			<td>Mice Strain</td>
		</tr>
		<tr>
			<td>Cotton Gauze Sponges</td>
			<td>Fisherbrand</td>
			<td>22-362-178</td>
			<td></td>
		</tr>
		<tr>
			<td>db/db</td>
			<td>Jackson laboratory</td>
			<td>000697</td>
			<td>Mice Strain</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Pharmco-AAPER</td>
			<td>111000200</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Vetone</td>
			<td>502017</td>
			<td></td>
		</tr>
		<tr>
			<td>Lab Chart</td>
			<td>Data Science International (DSI)</td>
			<td></td>
			<td>Software</td>
		</tr>
		<tr>
			<td>Matrigel Matrix</td>
			<td>BD Biosciences</td>
			<td>356234</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Spring Scissors</td>
			<td>World Precision Instruments (WPI)</td>
			<td>14124</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse Ox Plus</td>
			<td>STARR Life Sciences Corp.</td>
			<td></td>
			<td>Software</td>
		</tr>
		<tr>
			<td>Mouse Ox Plus Collar Sensor</td>
			<td>STARR Life Sciences Corp.</td>
			<td>015022-2</td>
			<td>Medium Collar Clip Special 7&#8221;</td>
		</tr>
		<tr>
			<td>Mouse Whole Body Plethysmography Chamber</td>
			<td>Data Science International (DSI)</td>
			<td>PLY3211</td>
			<td></td>
		</tr>
		<tr>
			<td>Ohio Care Plus Incubator</td>
			<td>Ohmeda</td>
			<td>HCHD000173</td>
			<td></td>
		</tr>
		<tr>
			<td>Operating Scissors</td>
			<td>World Precision Instruments (WPI)</td>
			<td>501753-G</td>
			<td>Straight</td>
		</tr>
		<tr>
			<td>Osmotic Pump</td>
			<td>Alzet</td>
			<td>1003D</td>
			<td>1ul per hour, 3 days</td>
		</tr>
		<tr>
			<td>Phenol</td>
			<td>Sigma-Aldrich</td>
			<td>P4557</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Mouse Leptin protein</td>
			<td>R&#38;D systems</td>
			<td>498-OB-05M</td>
			<td>5mg</td>
		</tr>
		<tr>
			<td>Saline</td>
			<td>RICCA Chemical</td>
			<td>7210-16</td>
			<td>0.9% Sodium Chloride</td>
		</tr>
		<tr>
			<td>Sterile Surgical Suture</td>
			<td>DemeTech</td>
			<td>DT-639-1</td>
			<td>Silk, size 6-0</td>
		</tr>
		<tr>
			<td>Thermometer</td>
			<td>Innovative Calibration Solutions (INNOCAL)</td>
			<td>EW 20250-91</td>
			<td></td>
		</tr>
	</tbody>
</table>

experimental approach to examine leptin signaling in the carotid bodies and its effects on control of breathing

An adipocyte-produced hormone leptin is a potent respiratory stimulant, which may play an important role in defending respiratory function in obesity. The carotid bodies (CB), a key organ of peripheral hypoxic sensitivity, express the long functional isoform of leptin receptor (LepRb) but the role of leptin signaling in control of breathing has not been fully elucidated. We examined the hypoxic ventilatory response (HVR) (1) in C57BL/6J mice before and after leptin infusion at baseline and after CB denervation; (2) in LepRb-deficient obese db/db mice at baseline and after LepRb overexpression in CBs. In C57BL/6J mice, leptin increased HVR and effects of leptin on HVR were abolished by CB denervation. In db/db mice, LepRb expression in CB augmented the HVR. Therefore, we conclude that leptin acts in CB to augment responses to hypoxia.

Continuous infusion of leptin significantly increased HVR in lean C57BL/6J mice from 0.23 to 0.31 mL/min/g/&#916;FiO2 (P &#60; 0.001, Figure 2)11. CSND abolished the leptin-induced increase in HVR (Figure 2), while no attenuating effects of CSND on HVR were observed in sham surgery group after leptin infusion.
LepRb expression in the CB of LepRb-deficient obese...

Watch this Scientific Journal Video about Experimental Approach to Examine Leptin Signaling in the Carotid Bodies and its Effects on Control of Breathing at JoVE.com

Experimental Approach to Examine Leptin Signaling in the Carotid Bodies and its Effects on Control of Breathing

Our study focuses on the effects of leptin signaling in carotid body (CB) on the hypoxic ventilatory response (HVR). We performed &#39;loss of function&#39; experiments measuring the effect of leptin on HVR after CB denervation and &#39;gain of function&#39; experiments measuring HVR after overexpression of the leptin receptor in CB.

An adipocyte-produced hormone leptin is a potent respiratory stimulant, which may play an important role in defending respiratory function in obesity. The ...

Our protocol can be used to examine the respiratory effects of leptin on the carotid body in the peripheral chemoreflex breathing control, and physiological responses to hypoxia. We can also assess the effects of loss and gain of carotid body function using surgical and chemical denervation and adenovirus transfection respectively. Before beginning the procedure, measure the temperature inside a custom made whole body plasthemagrophy chamber, and measure the relative humidity of the lab.Next, measure the body weight and rectal temperature of the experimental mouse. Place the mouse inside the chamber and place an oximeter collar around the shaved neck of the animal. And be sure to completely seal the chamber to avoid air leakages.Wait approximately 30 minutes until the mouse is quiet and the chamber is at a constant volume. Before beginning to record the respiratory signals and peripheral oxygen saturation at normoxia. After 20 minutes of normoxia, expose the animal to a constant mixed gas flow of 10%oxygen and 3%carbon dioxide.And begin recording the first cycle of acute hypoxia in respiratory signals and peripheral oxygen saturation. During the first 30 seconds of hypoxia, open the two small side ports at the base of the chamber to allow in-plugs of the mix gases. After the initial 30 seconds, close one of the small side ports of the chamber and continue to record at a constant hypoxia at 10%of the fraction of inspired oxygen for five minutes.At the end of the hypoxia treatment, switch the in-flow source to re-expose the mouse to room air and allow the animal to recover at normoxia for at least 30 minutes before beginning the next analysis. At the end of the experiment, plug a syringe into one of the small side ports at the base of the chamber and inject one milliliter of room air into the whole blood plethysmography chamber three times to calibrate the chamber. After the third flush, measure the temperature in the chamber with the animal still inside and the chamber still closed.Then, open the chamber and measure the rectal temperature of the mouse before returning the animal to its home cage. For surgical denervation of the carotid sinus nerve, administer analgesia to the anesthetize mouse, and remove the hair at the ventral region of the neck. Disinfect the exposed skin with Betadine and alcohol and apply ointment to the animal's eyes.After making a midline incision, remove the connective and adipose tissues to expose the bifurcation of the common carotid arteries and identify the hypoglossal nerve. Lift up the hypoglossal nerve to expose the glossopharyngeal nerve immediately below and use micro-spring scissors to bilaterally dissect the carotid sinus nerves. When the carotid bodies have been exposed, gently suspend one microliter of the appropriate adenovirus in four microliters of liquid Matrigel matrix on ice, per side, and apply five microliters of the viral suspension to the carotid body area bilaterally.Wait two to three minutes until the liquid Matrigel matrix has solidified before closing the incision with 6-0 silk suture and administering one milliliter of normal saline subcutaneously. Then house the mouse in a recovery chamber with monitoring until sternal recumbency before returning the animal to its home cage. Continuous infusion of leptin significantly increases the hypoxic ventilatory response in lean C57BL/6 mice while carotid sinus nerve dissection abolishes this leptin induced increase.As expected, no attenuating effects of carotid sinus nerve dissection on the hypoxic ventilatory response are observed in the sham surgery group after leptin infusion. The induction of leptin receptor long isoform expression in the carotid bodies of leptin receptor long isoform deficient obese db/db mice results in a significant increase in the hypoxic ventilatory response. Whereas after transfection with control LacZ adenovirus, no change is observed.These techniques allow analysis of the role of carotid bodies in the peripheral chemoreflex and the effects of leptin on carotid bodies in the control of breathings.

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