Name: isolation of primary mouse hepatocytes for nascent protein synthesis analysis by non-radioactive l-azidohomoalanine labeling method
Uploaded: 2018-10-23T13:30:00
Description: Watch this Scientific Journal Video about Isolation of Primary Mouse Hepatocytes for Nascent Protein Synthesis Analysis by Non-radioactive L-azidohomoalanine Labeling Method at JoVE.com

We thank Drs. Joonbae Seo and Vivian Hwa for their scientific input and discussion. This work was supported by National Institute of Health (NIH) (R01DK107530). T.N. was supported by the PRESTO from the Japan Science and Technology Agency. A part of this study was supported by a grant from NIH (P30DK078392) for the Digestive Disease Research Core Center in Cincinnati.

This protocol contains the use of laboratory mice. Animal care and experimental procedures were performed according to procedures approved by the animal care committees of Cincinnati Children Hospital Medical Center.
1. Isolation of Primary Mouse Hepatocytes
<ol>
	<li>Pre-isolation preparations
	<ol>
		<li>Prepare 450 mL of 40% density gradient buffer as described in Table 1 and keep at 4 &#176;C (15 mL/mouse).</li>
		<li>Prepare 500 mL of Williams&#8217; Medium as described...

Although several immortalized hepatic cell lines have been proposed and used to investigate liver functions49,50,51,52, these cells generally lack the important and fundamental functions of normal hepatocytes, such as the expression of albumin (Figure 3). It is widely recognized, therefore, that utilizing primary hepatocytes is a valuable option for examining liver...

Protein is an important nutritional element and approximately 50% of the dry weight of a human body is composed of proteins which have several biological traits and functions1. Consequently, protein synthesis is one of the most energy consuming events and an alteration in protein metabolism is highly associated with the development of diseases, including metabolic diseases2,3,4. In the liver, protein biosynthesis accounts for approximately 20&#8211;30% of total energy consumption5,6. In addition, proteins function as not only passive or building blocks of the liver, but also active signal-mediating factors intracellularly or extracellularly to regulate the systemic metabolism7. For instance, reduced levels of serum albumin, which is synthesized and secreted by the liver and the most abundant protein in the plasma8, increases the risk of type 2 diabetes development9,10,11, whereas a higher concentration of serum albumin is protective against developing metabolic syndrome12. Furthermore, disturbed or disruption of secretory or membrane-bound hepatic proteins, which modulate cholesterol homeostasis, including lipoproteins, LDLR, and LRP1, can lead to the development of insulin resistance, hyperlipidemia, or atherosclerosis13. Therefore, the identification of molecular pathophysiological mechanisms that are involved in protein metabolism disturbance in the liver and its associated metabolic complications might be useful for discovering novel pharmacological approaches to retard onset or treat metabolic diseases such as insulin resistance, diabetes, and non-alcoholic fatty liver.
Protein synthesis is tightly linked to the cellular energy status (e.g., the formation of one peptide bond during the elongation step of protein synthesis requires 4 phosphodiester bonds14) and is regulated by molecular pathways that sense inter- and intra-cellular nutrient availability15,16. AMP-activated protein kinase (AMPK) is one of the intracellular energy sensors that maintain energy homeostasis17. Once AMPK is activated when cellular energy levels become lower, AMPK and its targeted substrates function to stimulate catabolic pathways and inhibit anabolic processes including protein synthesis18,19. The regulation of protein synthesis is mediated by phosphorylation of multiple translation factors and ribosomal proteins20. Of note, the mammalian target of rapamycin complex 1 (mTORC1), a major driver of protein synthesis, is one of the main targets of AMPK21. Activation of the mTORC1 pathway enhances the cell growth and proliferation by stimulating protein translation and autophagy20,21. Therefore, it is logical that activation of AMPK can inhibit mTORC1-mediated protein synthesis22. Indeed, activation of AMPK counteracts and directly phosphorylates mTORC1 on threonine residue 2446 (Thr2446) leading to its inactivation23 and suppression of protein biosynthesis24. Moreover, AMPK can indirectly inhibit mTORC1 function by phosphorylation and activation of tuberous sclerosis complex 2 (TSC2)25 which is the upstream regulator of mTORC1 signaling cascade. In short, dysregulation of these pathways in the liver is often linked to the development of metabolic diseases and therefore there is a critical need to establish effective experimental tools to investigate the role of these pathways in the regulation of energy and protein metabolism in hepatocytes.
There is a stronger similarity between the functional properties of isolated primary hepatocytes and in vivo hepatocytes than with in vitro liver-derived cell lines26,27,28. It has been shown that primary human hepatocytes share 77% similarity with that of liver biopsies, whereas HepG2 cells, which are well-differentiated hepatic cancerous cells and widely used to investigate hepatic functions, display less than 48% in the context of gene expression profiles29. Therefore, utilization of primary hepatocytes, rather than immortalized culture cells, is of vital importance in investigating hepatic function and physiology, and several protocols are available for the isolation and culture of primary hepatocytes especially from rats30,31. While the rat hepatocytes are useful with a relatively higher yield of cells, mouse hepatocytes have a greater potential in many scientific aspects because of the wide availability of genetically modulated mice. However, there are several technical challenges in isolating healthy and abundant primary hepatocytes from mice for cellular- and molecular-based assessments: first, cannula insertion to perfuse the liver with buffer reagents is very difficult to handle because of the small and thin mouse portal vein or inferior vena cava; second, a longer manipulation time of cells during the isolation can cause reduction in cell quantity and quality; third, non-enzymatic mechanical separation methods can result in severe damage and produce a low yield of viable isolated primary hepatocytes32,33. In the 1980s, collagenase perfusion technique was introduced for isolating hepatocytes from the livers of animals34. This method is based on collagenase perfusion of the liver35,36,37, infusion of the liver with calcium chelator solution38,39, enzymatic digestion and mechanical dissociation of the hepatic parenchyma35. In the first step, a mouse liver is perfused with a calcium [Ca2+] free buffer containing a [Ca2+] chelator (ethylenediamine tetraacetic acid, EDTA). In the second step, the mouse liver is perfused with a collagenase-containing buffer to hydrolyze the cellular-extracellular matrix interactions. Unlike the buffer used in step one, the presence of [Ca2+] ions in the buffer of the second step is required for effective collagenase activity, after which the digested liver has to be further gently and mechanically separated using forceps between the hepatic capsule and parenchymatous tissue. Finally, connective tissue is removed by filtering, and subsequent centrifugation separates viable hepatocytes from both non-parenchymal cells and non-living hepatocyte with the use of density gradient buffer40,41,42. In the present study, we show a modified two-step collagenase perfusion technique to isolate primary hepatocytes from a mouse liver for the analysis of protein synthesis.
The radiolabeling of proteins is widely used to quantify the expression levels, turnover rates, and determine the biological distribution of proteins43 due to the high sensitivity of detection of radioactivity44. However, the use of radioactive isotopes requires highly controlled research circumstances and procedures45. Alternative non-radioactive methods have been developed and have increasingly gained in popularity. The chemo-selective ligation reaction with a Tetramethylrhodamine (TAMRA) protein detection method is one of them and is based on the chemo-selective reaction between an azide and alkyne groups46, which can be utilized to analyze cellular events such as detecting nascent protein synthesis and subclasses of glycoproteins modified with an azide group. For nascent protein synthesis, L-Azidohomoalanine (L-AHA, an azide-modified amino acid) can be metabolically incorporated into proteins and detected by using the TAMRA protein detection method47. By using this assay in primary mouse hepatocytes, we show that the nascent protein synthesis rate is tightly linked to the availability of ATP from mitochondrial and AMPK activation (Figure 1).
In summary, utilization of primary mouse hepatocytes is crucial to investigating the protein and energy metabolism and quantifying nascent protein synthesis is valuable for gaining insights into the physiological role of pathways relevant to the development and cure of hepatocyte-related diseases.

<table>
	<tbody>
		<tr>
			<td>HEPES buffer</td>
			<td>Fisher Scientific</td>
			<td>BP310-500</td>
			<td></td>
		</tr>
		<tr>
			<td>D-glucose</td>
			<td>Fisher Scientific</td>
			<td>D16-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylene glycol-bis(&#946;-aminoethyl ether)-tetraacetic acid</td>
			<td>AmericanBio</td>
			<td>AB00505-00025</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic-Antimycotic (100X)</td>
			<td>Gibco</td>
			<td>15240-062</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS (10X) no calcium, magnesium, phenol red</td>
			<td>Gibco</td>
			<td>14185-052</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride Dihydrate (CaCl2.2H2O)</td>
			<td>Fisher Scientific</td>
			<td>C79-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Density gradient buffer</td>
			<td>GE Healthcare</td>
			<td>17-0891-02</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM (Dulbecco&#39;s Modified Eagle Medium) low glucose, pyruvate</td>
			<td>Gibco</td>
			<td>11885-084</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Hyclone</td>
			<td>SH30910.03</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (PBS) (1X)</td>
			<td>Gibco</td>
			<td>1897141</td>
			<td></td>
		</tr>
		<tr>
			<td>Williams medium E, no glutamine</td>
			<td>Gibco</td>
			<td>12551-032</td>
			<td></td>
		</tr>
		<tr>
			<td>L-alanyl-L-glutamine dipeptide supplement</td>
			<td>Gibco</td>
			<td>35050-061</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase Type X</td>
			<td>Wako Pure Chemical Industries</td>
			<td>039-17864</td>
			<td></td>
		</tr>
		<tr>
			<td>Perfusion pump</td>
			<td>Cole-Parmer</td>
			<td>Masterflex L/S</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>IV administration set</td>
			<td>EXELINT</td>
			<td>29081</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>A water bath</td>
			<td>REVSCI</td>
			<td>RS-PB-200</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Tube heater</td>
			<td>Fisher Scientific</td>
			<td>Isotemp</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Decon Lab, Inc</td>
			<td>0-39613</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>PHOENIX</td>
			<td>10250</td>
			<td></td>
		</tr>
		<tr>
			<td>Autoclaved Cotton Tips</td>
			<td>Fisherbrand</td>
			<td>23-400-124</td>
			<td></td>
		</tr>
		<tr>
			<td>100 mm Petri Dish</td>
			<td>TPP</td>
			<td>93100</td>
			<td></td>
		</tr>
		<tr>
			<td>Connector (Male Luer Lock Ring)</td>
			<td>Cole-Parmer instrument</td>
			<td>EW-4551807</td>
			<td></td>
		</tr>
		<tr>
			<td>24G catheters</td>
			<td>TERUMO</td>
			<td>Surflo 24Gx3/4&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>100 &#956;m Filter (CELL STRAINERS)</td>
			<td>VWR</td>
			<td>10199-658</td>
			<td></td>
		</tr>
		<tr>
			<td>15 ml conical-bottom centrifuge tubes</td>
			<td>VWR</td>
			<td>89039-666</td>
			<td></td>
		</tr>
		<tr>
			<td>50 ml conical-bottom centrifuge tubes</td>
			<td>VWR</td>
			<td>89039-658</td>
			<td></td>
		</tr>
		<tr>
			<td>Chemoselective ligation reaction PROTEIN ANALYSIS DETECTION KIT, TAMRA ALKYNE</td>
			<td>Invitrogen</td>
			<td>C33370</td>
			<td></td>
		</tr>
		<tr>
			<td>AHA (L-azidohomoalanine)</td>
			<td>Invitrogen</td>
			<td>C10102</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM (methionine free)</td>
			<td>Gibco</td>
			<td>21013024</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Cystine Dihydrochloride</td>
			<td>SIGMA</td>
			<td>C2526</td>
			<td></td>
		</tr>
		<tr>
			<td>Laemmli sample buffer</td>
			<td>BioRad</td>
			<td>161-0737</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease Inhibitor Cocktail</td>
			<td>SIGMA</td>
			<td>P9599</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS solution (20%)</td>
			<td>BioRad</td>
			<td>161-0418</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-HCL (1M)</td>
			<td>American Bioanalytical</td>
			<td>AB14044-01000</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphatase Inhibitor Cocktail</td>
			<td>SIGMA</td>
			<td>P5726</td>
			<td></td>
		</tr>
		<tr>
			<td>Protein concentration measuring Kit (Bovin Serum Albumin-BSA)</td>
			<td>BioRad</td>
			<td>500-0207</td>
			<td></td>
		</tr>
		<tr>
			<td>6-well tissue culture plate</td>
			<td>TPP</td>
			<td>92006</td>
			<td></td>
		</tr>
		<tr>
			<td>Digital Heatblock</td>
			<td>VWR</td>
			<td>12621-092</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Multi-Rotator</td>
			<td>Grant-bio</td>
			<td>PTR-60</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Ultrasonic Sonicator</td>
			<td>Cole-Parmer</td>
			<td>GE130PB</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Standard Heavy-Duty Vortex Mixer</td>
			<td>VWR</td>
			<td>97043-566</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>A variable mode laser scanner</td>
			<td>GE Healthcare Life Science</td>
			<td>FLA 9500</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Coomassie-dye reagent</td>
			<td>Thermo Scientific</td>
			<td>24594</td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted microscope</td>
			<td>Olympus</td>
			<td>CKX53</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Western Blotting apparatus</td>
			<td>BioRad</td>
			<td>1658004</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>5424R</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Automated cell counter</td>
			<td>BioRad</td>
			<td>TC20</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>FluorChem R system</td>
			<td>proteinsimple</td>
			<td>-</td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>p-Ampka (T172) antibody</td>
			<td>Cell signaling</td>
			<td>2535</td>
			<td></td>
		</tr>
		<tr>
			<td>Total-AMPK antibody</td>
			<td>Cell signaling</td>
			<td>5832</td>
			<td></td>
		</tr>
		<tr>
			<td>Albumin antibody</td>
			<td>Cell signaling</td>
			<td>4929</td>
			<td></td>
		</tr>
		<tr>
			<td>beta actin antibody</td>
			<td>Santa Cruz</td>
			<td>sc-130656</td>
			<td></td>
		</tr>
		<tr>
			<td>Fine scissors and forceps</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

isolation of primary mouse hepatocytes for nascent protein synthesis analysis by non-radioactive l-azidohomoalanine labeling method

Hepatocytes are parenchymal cells of the liver and engage multiple metabolic functions, including synthesis and secretion of proteins essential for systemic energy homeostasis. Primary hepatocytes isolated from the murine liver constitute a valuable biological tool to understand the functional properties or alterations occurring in the liver. Herein we describe a method for the isolation and culture of primary mouse hepatocytes by performing a two-step collagenase perfusion technique and discuss their utilization for investigating protein metabolism. The liver of an adult mouse is sequentially perfused with ethylene glycol-bis tetraacetic acid (EGTA) and collagenase, followed by the isolation of hepatocytes with the density gradient buffer. These isolated hepatocytes are viable on culture plates and maintain the majority of endowed characteristics of hepatocytes. These hepatocytes can be used for assessments of protein metabolism including nascent protein synthesis with non-radioactive reagents. We show that the isolated hepatocytes are readily controlled and comprise a higher quality and volume stability of protein synthesis linked to energy metabolism by utilizing the chemo-selective ligation reaction with a Tetramethylrhodamine (TAMRA) protein detection method and western blotting analyses. Therefore, this method is valuable for investigating hepatic nascent protein synthesis linked to energy homeostasis. The following protocol outlines the materials and methods for the isolation of high-quality primary mouse hepatocytes and detection of nascent protein synthesis.

Primary mouse hepatocytes isolation results in a yield of approximately 20 x 106 total cells/mouse. Histologically, live and attached primary hepatocytes appear polygonal or typical hexagonal in shape with clearly outlined membranous boundary after 24 h incubation (Figure 2).
To confirm whether isolated cells are primary hepatocytes, we compared expression levels of albumin protein in iso...

Watch this Scientific Journal Video about Isolation of Primary Mouse Hepatocytes for Nascent Protein Synthesis Analysis by Non-radioactive L-azidohomoalanine Labeling Method at JoVE.com

Isolation of Primary Mouse Hepatocytes for Nascent Protein Synthesis Analysis by Non-radioactive L-azidohomoalanine Labeling Method

Here, we present a protocol for the isolation of healthy and functional primary mouse hepatocytes. Instructions for detecting hepatic nascent protein synthesis by non-radioactive labeling substrate were provided to help understand the mechanisms underlying protein synthesis in the context of energy-metabolism homeostasis in the liver.

Hepatocytes are parenchymal cells of the liver and engage multiple metabolic functions, including synthesis and secretion of proteins essential for ...

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