This work was supported by NIH R21 AG072011 to OL.

The procedures have been reviewed and approved by the University of Florida IACUC (#202200000227). Male C57BL/6J mice, 17 weeks old, with a body mass ranging from 27 g to 34 g, were used for the present study. The experimental procedures and timeline outlined in this protocol are depicted in Figure 1. As indicated, the protocol spans a total of 11 days. Animals undergo survival surgery (CLP/Sham) on Day 0, followed by four days of fluid and analgesic support. On Day 4, animals begin HLS for a duration of 7 days. Terminal experiments are conducted on Day 11. The details of the reagents and the equipment used are listed in the Table of Materials.
1. Cecal ligation and puncture (CLP)
<ol>
	<li>After obtaining the animals from the commercial source, let them acclimate in the animal facility for at least 1 week before conducting CLP (or sham) surgeries. This will help minimize the stress associated with transportation.</li>
	<li>Group-house the mice, adhering to local IACUC guidelines. 
	NOTE: As a general direction, the animals are housed in a maximum of 5 mice per cage until the day of surgery. Standard cages, measuring 7.25 inches in width, 11.75 inches in length, and 5 inches in height, are utilized and furnished with corncob bedding. A 12h : 12h light-dark cycle is maintained, with lights on at 7 AM and off at 7 PM. The housing temperature is kept at 20-22 &#176;C, and the relative humidity (RH) is maintained between 30% and 60%. Ad libitum access to standard chow diet and water is ensured.</li>
	<li>To perform CLP, anesthetize the animal with isoflurane (2.5%, 500 mL/min) in an induction chamber. Confirm anesthesia by pinching the paw with tweezers. Once in deep anesthesia, as confirmed by the absence of reflex withdrawal from paw pinching, transfer the animal to continued anesthesia using a nose cone (2.5%, 100-125 mL/min). 
	NOTE: Aseptic techniques should be employed throughout the whole procedure.</li>
	<li>Apply veterinary eye lubricant ointment to safeguard the animal&#39;s eyes from potential nosecone-induced damage or injury during surgery.</li>
	<li>To clean the surgical site, use commercially available hair remover. Remove the fur from the lower abdomen only, avoiding overexposure of the skin. 
	NOTE: Alternatively, animal hair clippers can be used, but care must be taken to avoid skin damage.</li>
	<li>Once the surgical site is exposed, cleanse the area with three applications of povidone-iodine (or an equivalent germicidal scrub), followed by a rinse with 70% alcohol in between each application.</li>
	<li>Administer a single dose of 3.25 mg/kg of sustained-release buprenorphine or equivalent, according to the analgesic treatment approved by your local IACUC.</li>
	<li>Transfer the mouse to the surgical area. Isolate the surgical site using an adhesive drape. Under deep anesthesia, make a ventral midline incision (~2 cm) in the skin using a scalpel blade.
	<ol>
		<li>Use scissors to separate the skin from the muscle layer. Using the scalpel blade, make a smaller incision (~1 cm) in the muscle layer. Once the bowels are visualized, using blunt forceps, locate the cecum and exteriorize it.</li>
	</ol>
	</li>
	<li>Once exteriorized, ligate the cecum using a sterile 5-0 polyglactin absorbable suture. Consider the area of the ligated cecum, defined as the distance from the distal end of the cecum to the ligation point, as it will contribute to the severity of the infection. To reproduce the results presented here, tie the cecum 1 cm from its distal point. 
	NOTE: Ligating a larger cecum area will result in increased severity10.</li>
	<li>Using a 27 G needle, perforate the cecum through and through, allowing the fecal content to leak. With caution, gently squeeze the cecum to externalize the fecal content. To perform sham surgery, follow the same steps exposing the animal cecum. However, do not ligate nor puncture the cecum. 
	NOTE: The needle gauge directly affects the severity of the infection. To produce a low-grade infection, 26 G to 28 G needles are recommended. Please note that using thicker needle gauges will result in an increased mortality rate, and animals may not tolerate the subsequent hindlimb suspension phase of the protocol.</li>
	<li>Relocate the cecum into the abdominal cavity. Close the muscle layer with a sterile 5-0 absorbable suture. Close the skin with a 5-0 nylon, nonabsorbable suture. After the skin suture is complete, provide sterile saline (1&#160;mL&#160;for males and 0.5&#160;mL&#160;for females) via subcutaneous injection in the back of the animal. 
	NOTE: For closing the muscle layer, a continuous suture technique is recommended, whereas for the skin layer, an interrupted suture technique is recommended. Consult and conform with your local IACUC guidelines for suturing in survival surgery.</li>
	<li>After the surgery, single house the animals in a clean cage on top of a heating mattress or a heating pad set at 35 &#176;C. Observe the mouse every 15 min throughout the initial hour following anesthesia recovery, after which it can be returned to the housing facility. 
	NOTE: Provide a minimum amount of chow on the cage floor to allow animals ad libitum food without affecting the surgical site. After returning to the facility, animals are checked twice a day following the septic animal assessment (step 3).</li>
	<li>Provide sterile saline and analgesic support over the following four days to allow the surgical incision to heal. 
	NOTE: Monitoring xiphoid surface temperature and body weight daily helps to keep accurate records of the sepsis severity11.</li>
</ol>
2. Hindlimb suspension (HLS)
<ol>
	<li>To perform the HLS, investigators must follow the local IACUC ethics guidelines. This includes ensuring the usage of appropriate cage dimensions and flooring, which are crucial aspects for accommodating animal locomotion, eating, and drinking habits in HLS conditions. 
	NOTE: 4 days of recovery after CLP is recommended for wound healing.</li>
	<li>Following 4 days of recovery from CLP or sham surgery, anesthetize the animal under light isoflurane flow (2.5%, 100-125 mL/min). Attach the mouse tail to a short metal chain using foam tape. Place the metal chain parallel to the tail while the foam tape firmly embraces the tail and chain together.</li>
	<li>To ensure the suspension of the hindlimbs, attach the metal chain to a hook connected to a crossbar along the center of the cage. Additionally, affix a second small bar that can move along the crossbar to allow greater movement ability for the animal. 
	NOTE: Animals must be able to move via their forelimbs by utilizing the metal grid on the cage floor.</li>
	<li>Adjust the height of the suspended limbs to prevent the contact of the paws with the chow pellets. Monitor the animals and clean the shaved area around the sutured skin by hand with a water-soaked cotton swab at least twice daily during the suspension period. 
	NOTE: Cleaning is crucial to avoid infection at the surgery site, especially from urine scalding due to the raised body position.</li>
	<li>To reproduce the results, ensure that the animals undergo 7 days of hindlimb suspension. The duration was determined based on previous time course studies showing the minimum time required for hindlimb suspension to elicit meaningful effects on skeletal muscles in non-septic conditions12,13. 
	NOTE: Animal survival, discomfort, or distress will increase according to the severity of the infection.</li>
</ol>
3. Septic animal assessment
NOTE: Assessing the clinical condition of the animal is a key aspect of keeping track of severity post CLP/sham surgeries. Also, as required by IACUC, humane endpoints must be established for animal welfare. To address these concerns and provide standards for daily animal care, directions for performing animal assessment using the Modified Murine Sepsis Score (MMSS) were used14.
<ol>
	<li>Use the MMSS (Supplementary File 1) to assess the animal. Note that for each category, a score of 0 represents a healthy animal. Score the animal twice a day from 0 to 3 according to the severity of the infection.</li>
	<li>To enhance accuracy, measure xiphoid surface temperature and body weight twice per day11,15 and record along with the MMSS score sheet. 
	NOTE: Typical xiphoid surface temperature and body weight fluctuations are provided in Supplementary Figure 1.</li>
	<li>Consult the local IACUC for humane endpoints. 
	NOTE: To reproduce the results, the following criteria were used as endpoints: (1) Body weight loss &#62;40% from baseline. (2) Temperature &#60;30 &#176;C or reduction of &#62;5 &#176;C from previous value. (3) A score of 3 in the following: Response to stimulus, level of consciousness, or respiration quality. (4) Total daily MSSS &#8805;17. The assessment described here is designed to be performed post-surgery and in animals undergoing normal ambulation. It is recommended to refrain from handling animals undergoing HLS to prevent contact between their hindlimbs and surfaces. After the final assessment, euthanize the animal as per local animal ethics committee recommendations.</li>
</ol>

Mouse Model for Studying Sepsis-Induced Myopathy with Hindlimb Suspension

<ol><li>Prescott, H. C., Angus, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Enhancing+recovery+from+sepsis%5BTitle%5D)+AND+%22JAMA%22%5BJournal%5D)">Enhancing recovery from sepsis.</a> JAMA. 319 (1), 62-75 (2018).</li>
<li>Stortz, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Benchmarking+clinical+outcomes+and+the+immunocatabolic+phenotype+of+chronic+critical+illness+after+sepsis+in+surgical+intensive+care+unit+patients%5BTitle%5D)+AND+%22J+Trauma+Acute+Care+Surg%22%5BJournal%5D)">Benchmarking clinical outcomes and the immunocatabolic phenotype of chronic critical illness after sepsis in surgical intensive care unit patients.</a> J Trauma Acute Care Surg. 84 (2), 342-349 (2018).</li>
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<li>Callahan, L. A., Supinski, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Sepsis-induced+myopathy%5BTitle%5D)+AND+%22Crit+Care+Med%22%5BJournal%5D)">Sepsis-induced myopathy.</a> Crit Care Med. 37, 10 Suppl S354-S367 (2009).</li>
<li>Cuthbertson, B. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mortality+and+quality+of+life+in+the+five+years+after+severe+sepsis%5BTitle%5D)+AND+%22Crit+Care%22%5BJournal%5D)">Mortality and quality of life in the five years after severe sepsis.</a> Crit Care. 17 (2), R70(2013).</li>
<li>Schmitt, R. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Muscle+stem+cells+contribute+to+long-term+tissue+repletion+following+surgical+sepsis%5BTitle%5D)+AND+%22J+Cachexia+Sarcopenia+Muscle%22%5BJournal%5D)">Muscle stem cells contribute to long-term tissue repletion following surgical sepsis.</a> J Cachexia Sarcopenia Muscle. 14 (3), 1424-1440 (2023).</li>
<li>Owen, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Chronic+muscle+weakness+and+mitochondrial+dysfunction+in+the+absence+of+sustained+atrophy+in+a+preclinical+sepsis+model%5BTitle%5D)+AND+%22eLife%22%5BJournal%5D)">Chronic muscle weakness and mitochondrial dysfunction in the absence of sustained atrophy in a preclinical sepsis model.</a> eLife. 8, e49920(2019).</li>
<li>Chen, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cellular+senescence+implicated+in+sepsis-induced+muscle+weakness+and+ameliorated+with+metformin%5BTitle%5D)+AND+%22Shock%22%5BJournal%5D)">Cellular senescence implicated in sepsis-induced muscle weakness and ameliorated with metformin.</a> Shock. 59 (4), 646(2023).</li>
<li>Granger, J. I., Ratti, P. L., Datta, S. C., Raymond, R. M., Opp, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Sepsis-induced+morbidity+in+mice%3A+effects+on+body+temperature%2C+body+weight%2C+cage+activity%2C+social+behavior+and+cytokines+in+brain%5BTitle%5D)+AND+%22Psychoneuroendocrinology%22%5BJournal%5D)">Sepsis-induced morbidity in mice: effects on body temperature, body weight, cage activity, social behavior and cytokines in brain.</a> Psychoneuroendocrinology. 38 (7), 1047-1057 (2013).</li>
<li>Ruiz, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Sepsis+modeling+in+mice%3A+ligation+length+is+a+major+severity+factor+in+cecal+ligation+and+puncture%5BTitle%5D)+AND+%22Intensive+Care+Med+Exp%22%5BJournal%5D)">Sepsis modeling in mice: ligation length is a major severity factor in cecal ligation and puncture.</a> Intensive Care Med Exp. 4 (1), 22(2016).</li>
<li>Laitano, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Xiphoid+surface+temperature+predicts+mortality+in+a+murine+model+of+septic+shock%5BTitle%5D)+AND+%22Shock+%28Augusta%2C+Ga%29%22%5BJournal%5D)">Xiphoid surface temperature predicts mortality in a murine model of septic shock.</a> Shock (Augusta, Ga). 50 (2), 226-232 (2018).</li>
<li>Park, S., Brisson, B. K., Liu, M., Spinazzola, J. M., Barton, E. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mature+IGF-I+excels+in+promoting+functional+muscle+recovery+from+disuse+atrophy+compared+with+pro-IGF-IA%5BTitle%5D)+AND+%22J+App+Physiol%22%5BJournal%5D)">Mature IGF-I excels in promoting functional muscle recovery from disuse atrophy compared with pro-IGF-IA.</a> J App Physiol. 116 (7), 797-806 (2013).</li>
<li>Spradlin, R. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Deletion+of+muscle+Igf1+exacerbates+disuse+atrophy+weakness+in+mice%5BTitle%5D)+AND+%22J+App+Physiol%22%5BJournal%5D)">Deletion of muscle Igf1 exacerbates disuse atrophy weakness in mice.</a> J App Physiol. 131 (3), Bethesda, Md. 881-894 (2021).</li>
<li>Shrum, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+robust+scoring+system+to+evaluate+sepsis+severity+in+an+animal+model%5BTitle%5D)+AND+%22BMC+Res+Notes%22%5BJournal%5D)">A robust scoring system to evaluate sepsis severity in an animal model.</a> BMC Res Notes. 7 (1), 233(2014).</li>
<li>Mai, S. H. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Body+temperature+and+mouse+scoring+systems+as+surrogate+markers+of+death+in+cecal+ligation+and+puncture+sepsis%5BTitle%5D)+AND+%22Intensive+Care+Med+Exp%22%5BJournal%5D)">Body temperature and mouse scoring systems as surrogate markers of death in cecal ligation and puncture sepsis.</a> Intensive Care Med Exp. 6 (1), 20(2018).</li>
<li>Vankrunkelsven, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+muscle+weakness+in+a+mouse+model+of+critical+illness%3A+does+fibroblast+growth+factor+21+play+a+role%5BTitle%5D)+AND+%22Skelet+Muscle%22%5BJournal%5D)">Development of muscle weakness in a mouse model of critical illness: does fibroblast growth factor 21 play a role.</a> Skelet Muscle. 13 (1), 12(2023).</li>
<li>Supinski, G., Stofan, D., Nethery, D., Szweda, L., DiMarco, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Apocynin+improves+diaphragmatic+function+after+endotoxin+administration%5BTitle%5D)+AND+%22J+Appl+Physiol%22%5BJournal%5D)">Apocynin improves diaphragmatic function after endotoxin administration.</a> J Appl Physiol. 87 (2), Bethesda, Md. 776-782 (1999).</li>
<li>Li, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Sepsis+leads+to+impaired+mitochondrial+calcium+uptake+and+skeletal+muscle+weakness+by+reducing+the+micu1%3Amcu+protein+ratio%5BTitle%5D)+AND+%22Shock+%28Augusta%2C+Ga%29%22%5BJournal%5D)">Sepsis leads to impaired mitochondrial calcium uptake and skeletal muscle weakness by reducing the micu1:mcu protein ratio.</a> Shock (Augusta, Ga). 60 (5), 698-706 (2023).</li>
<li>Wang, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Targeting+NAT10+protects+against+sepsis-induced+skeletal+muscle+atrophy+by+inhibiting+ROS%2FNLRP3%5BTitle%5D)+AND+%22Life+Sci%22%5BJournal%5D)">Targeting NAT10 protects against sepsis-induced skeletal muscle atrophy by inhibiting ROS/NLRP3.</a> Life Sci. 330, 121948(2023).</li>
<li>Mankowski, R. T., Laitano, O., Clanton, T. L., Brakenridge, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Pathophysiology+and+treatment+strategies+of+acute+myopathy+and+muscle+wasting+after+sepsis%5BTitle%5D)+AND+%22J+Clinical+Med%22%5BJournal%5D)">Pathophysiology and treatment strategies of acute myopathy and muscle wasting after sepsis.</a> J Clinical Med. 10 (9), 1874(2021).</li>
<li>Oliveira, J. R. S., Mohamed, J. S., Myers, M., Brooks, M. J., Alway, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+hindlimb+suspension+and+reloading+on+gastrocnemius+and+soleus+muscle+mass+and+function+in+geriatric+mice%5BTitle%5D)+AND+%22Exp+Gerontol%22%5BJournal%5D)">Effects of hindlimb suspension and reloading on gastrocnemius and soleus muscle mass and function in geriatric mice.</a> Exp Gerontol. 115, 19-31 (2019).</li>
<li>Ashare, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Insulin-like+growth+factor-1+improves+survival+in+sepsis+via+enhanced+hepatic+bacterial+clearance%5BTitle%5D)+AND+%22Am+J+Respir+Crit+Care+Med%22%5BJournal%5D)">Insulin-like growth factor-1 improves survival in sepsis via enhanced hepatic bacterial clearance.</a> Am J Respir Crit Care Med. 178 (2), 149-157 (2008).</li>
<li>Starr, M. E., Saito, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Age-related+increase+in+food+spilling+by+laboratory+mice+may+lead+to+significant+overestimation+of+actual+food+consumption%3A+implications+for+studies+on+dietary+restriction%2C+metabolism%2C+and+dose+calculations%5BTitle%5D)+AND+%22J+Gerontol+A+Biol+Sci+Med+Sci%22%5BJournal%5D)">Age-related increase in food spilling by laboratory mice may lead to significant overestimation of actual food consumption: implications for studies on dietary restriction, metabolism, and dose calculations.</a> J Gerontol A Biol Sci Med Sci. 67 (10), 1043-1048 (2012).</li>
<li>Crowell, K. T., Soybel, D. I., Lang, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Restorative+mechanisms+regulating+protein+balance+in+skeletal+muscle+during+recovery+from+sepsis%5BTitle%5D)+AND+%22Shock%22%5BJournal%5D)">Restorative mechanisms regulating protein balance in skeletal muscle during recovery from sepsis.</a> Shock. 47 (4), 463-473 (2017).</li>
</ol>

The authors have no conflicts of interest to disclose.

The current protocol provides technical guidelines for the implementation of a new preclinical model of sepsis-induced myopathy. All materials and important steps are described in detail for the reproduction of the model. This approach can reproduce the skeletal muscle dysfunction observed in septic patients, highlighting the role of disuse as a crucial component in worsening myopathy. Thus far, the majority of the preclinical studies addressing sepsis-induced myopathy did not include the disuse as an active component of...

Sepsis is a life-threatening condition due to an overactive immune response that adversely affects multiple organ systems, resulting in a major burden to health systems worldwide1. More recently, the in-hospital mortality linked to sepsis has decreased due to improved intensity care unit (ICU) management1,2. However, approximately 75% of the patients surviving the initial septic insult develop skeletal muscle atrophy (e.g., reductions in cross-sectional area) and weakness (e.g., reductions in force production capacity)3,4. This phenomenon has been characterized as sepsis-induced myopathy, highly linked to impaired physical activity and lack of independence to perform daily living tasks, leading to re-hospitalization and mortality within five years of the initial episode5.
Due to an aggressive and generalized infection, septic patients are exposed to prolonged periods of bed rest while recovering in the ICU. In this context, the skeletal muscle undergoes severe disuse, which likely exacerbates muscle atrophy and weakness3,4. Currently, no treatment has effectively addressed sepsis-induced myopathy. The available preclinical models designed to address the myopathy have used cecal ligation and puncture (CLP)6, cecal slurry7, or injection of purified lipopolysaccharide (LPS), which is a component of the cellular wall in gram-negative bacteria8. Although these models succeed in delivering infection, they do not properly reproduce the muscle disuse observed in septic hosts beyond a natural reduction in physical activity observed in septic animals9. 
The main objective of this study is to provide a detailed description of how to properly execute the model of sepsis-induced myopathy with disuse in mice. We demonstrate the feasibility of combining CLP as a model of sepsis with hindlimb suspension (HLS) as a model of disuse to study sepsis-induced myopathy in mice3. Furthermore, representative results of muscle mechanics and typical morphological changes in response to the model are also provided.

<table><tbody><tr><td>4-0 Ethicon Coated Vicryl</td><td>Ethicon</td><td>D5792</td><td>Absorbable suture used for closure of muscle layer and for ligation of the cecum.</td></tr><tr><td>4-0 Ethilon Black 18&quot;&amp;nbsp;</td><td>Ethicon</td><td>662G</td><td>Non absorbable suture for closure of the skin layer.</td></tr><tr><td>BD&amp;nbsp; PrecisionGlide Needle 26-28 G</td><td>BD</td><td>305136 for 27g needle</td><td>Needle for puncturing the cecum.</td></tr><tr><td>C57BL/6J mice&amp;nbsp;</td><td>Jackson Laboratory&amp;nbsp;</td><td>strain #000664</td><td></td></tr><tr><td>Cotton Tipped Applicators</td><td>Puritan</td><td>S-18991</td><td>Swabs for topical application of iodine.</td></tr><tr><td>Cryostat</td><td>(Leica CM1950)</td><td></td><td></td></tr><tr><td>Dynarex Povidone Iodine Prep Solution</td><td>Dynarex</td><td>1415</td><td>Topical Antiseptic Liquid for Skin and Mucosa</td></tr><tr><td>Ethanol 200 Proof (100%)</td><td>Fisher Scientific</td><td></td><td>To make 70% ethanol for cleaning skin.</td></tr><tr><td>Hindlimb Suspension Cages</td><td>Custom Made</td><td>N/A</td><td>These custom made cages will be highlighted in the video recordings of the MS.</td></tr><tr><td>Optixcare Eye Lube</td><td>Optixcare</td><td></td><td>Eye lube for protection during survival surgery.</td></tr><tr><td>Scalpel blades #11</td><td>Fine Science</td><td></td><td>Blade used to make incisions on skin and muscle.</td></tr><tr><td>Skin-Trac</td><td>Zimmer</td><td>736579</td><td>Foam tape for fixing the tail to the suspension apparatus.</td></tr><tr><td>SomnoSuite Low-Flow Digital Vaporizer</td><td>Kent Scientific Corporation</td><td>SS-01</td><td>Vaporizer for Isoflurane Anesthesia</td></tr><tr><td>Tissue bath apparatus&amp;nbsp;</td><td>Aurora Scientific</td><td>Model 800A, Dual Mode Muscle Lever 300C</td><td></td></tr></tbody></table>

a preclinical model of sepsis-induced myopathy with disuse in mice

Sepsis is a major cause of in-hospital deaths. Improvements in treatment result in a greater number of sepsis survivors. Approximately 75% of the survivors develop muscle weakness and atrophy, increasing the incidence of hospital readmissions and mortality. However, the available preclinical models of sepsis do not address skeletal muscle disuse, a key component for the development of sepsis-induced myopathy. Our objective in this protocol is to provide a step-by-step guideline for a mouse model that reproduces the clinical setting experienced by a bedridden septic patient. Male C57Bl/6 mice were used to develop this model. Mice underwent cecal ligation and puncture (CLP) to induce sepsis. Four days post-CLP, mice were subjected to hindlimb suspension (HLS) for seven days. Results were compared with sham-matched surgeries and/or animals with normal ambulation (NA). Muscles were dissected for in vitro muscle mechanics and morphological assessments. The model results in marked muscle atrophy and weakness, a similar phenotype observed in septic patients. The model represents a platform for testing potential therapeutic strategies for the mitigation of sepsis-induced myopathy.

For the representative data shown in the results, male C57BL/6J mice, 17 weeks old, with a body mass ranging from 27 to 34 g, were used. The entire protocol takes eleven days to complete and consists of the surgery intervention (CLP or sham), saline and analgesic support (days 0 to 4), and the HLS disuse (days 4 to 11). Terminal experiments can be performed at any point over the suspension phase. To better understand the impact of the model on skeletal muscle function, the results are compiled from several experiments ac...

Author Spotlight: Advanced Integrated Model for Sepsis-Induced Myopathy and Single-Cell Metabolic Analysis

This murine model combines a septic insult with hindlimb muscle disuse to recapitulate the bedridden feature of the typical septic patient. The model represents a significant departure from previous models to study muscle dysfunction in sepsis and is a reproducible approach to addressing therapeutic strategies to treat this condition.

A Preclinical Model of Sepsis-Induced Myopathy with Disuse in Mice

Sepsis is a major cause of in-hospital deaths. Improvements in treatment result in a greater number of sepsis survivors. Approximately 75% of the ...

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682 Views.  University of Florida. This murine model combines a septic insult with hindlimb muscle disuse to recapitulate the bedridden feature of the typical septic patient. The model represents a significant departure from previous models to study muscle dysfunction in sepsis and is a reproducible approach to addressing therapeutic strategies to treat this condition.

Video: Author Spotlight: Advanced Integrated Model for Sepsis-Induced Myopathy and Single-Cell Metabolic Analysis

Assessing Functional Performance in the Mdx Mouse Model

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder for which no cure is available. Nevertheless, several potential pharmaceutical compounds and gene therapy approaches have progressed into clinical trials. With improvement in muscle function being the most important end point in these trials, a lot of emphasis has been placed on setting up reliable, reproducible, and easy to perform functional tests to pre clinically assess muscle function, strength, condition, and coordination in the mdx mouse model for DMD. Both invasive and noninvasive tests are available. Tests that do not exacerbate the disease can be used to determine the natural history of the disease and the effects of therapeutic interventions (e.g. forelimb grip strength test, two different hanging tests using either a wire or a grid and rotarod running). Alternatively, forced treadmill running can be used to enhance disease progression and/or assess protective effects of therapeutic interventions on disease pathology. We here describe how to perform these most commonly used functional tests in a reliable and reproducible manner. Using these protocols based on standard operating procedures enables comparison of data between different laboratories.

Assessing Functional Performance in the Mdx Mouse Model

The primary outcome measure in clinical trials for neuromuscular disorders is generally improved muscle function. Therefore, assessing the effect of potential therapeutic compounds on muscle performance pre clinically in mouse models is of great importance. We here describe several functional tests to address this.

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder for which no cure is available. Nevertheless, several potential ...

Behavior

Electrophysiological Motor Unit Number Estimation (MUNE) Measuring Compound Muscle Action Potential (CMAP) in Mouse Hindlimb Muscles

Compound muscle action potential (CMAP) and motor unit number estimation (MUNE) are electrophysiological techniques that can be used to monitor the functional status of a motor unit pool in vivo. These measures can provide insight into the normal development and degeneration of the neuromuscular system. These measures have clear translational potential because they are routinely applied in diagnostic and clinical human studies. We present electrophysiological techniques similar to those employed in humans to allow recordings of mouse sciatic nerve function. The CMAP response represents the electrophysiological output from a muscle or group of muscles following supramaximal stimulation of a peripheral nerve. MUNE is an electrophysiological technique that is based on modifications of the CMAP response. MUNE is a calculated value that represents the estimated number of motor neurons or axons (motor control input) supplying the muscle or group of muscles being tested. We present methods for recording CMAP responses from the proximal leg muscles using surface recording electrodes following the stimulation of the sciatic nerve in mice. An incremental MUNE technique is described using submaximal stimuli to determine the average single motor unit potential (SMUP) size. MUNE is calculated by dividing the CMAP amplitude (peak-to-peak) by the SMUP amplitude (peak-to-peak). These electrophysiological techniques allow repeated measures in both neonatal and adult mice in such a manner that facilitates rapid analysis and data collection while reducing the number of animals required for experimental testing. Furthermore, these measures are similar to those recorded in human studies allowing more direct comparisons.

Electrophysiological Motor Unit Number Estimation MUNE Measuring Compound Muscle Action Potential CMAP in Mouse Hindlimb Muscles

We present refined protocols that allow in vivo monitoring of motor unit function in the mouse. Techniques to measure compound muscle action potential (CMAP) and motor unit number estimation (MUNE) in the mouse hind limb muscles innervated by the sciatic nerve are described.

Compound muscle action potential (CMAP) and motor unit number estimation (MUNE) are electrophysiological techniques that can be used to monitor the ...

A Murine Model of Muscle Training by Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) is a common clinical modality that is widely used to restore1, maintain2 or enhance3-5 muscle functional capacity. Transcutaneous surface stimulation of skeletal muscle involves a current flow between a cathode and an anode, thereby inducing excitement of the motor unit and the surrounding muscle fibers. 
NMES is an attractive modality to evaluate skeletal muscle adaptive responses for several reasons. First, it provides a reproducible experimental model in which physiological adaptations, such as myofiber hypertophy and muscle strengthening6, angiogenesis7-9, growth factor secretion9-11, and muscle precursor cell activation12 are well documented. Such physiological responses may be carefully titrated using different parameters of stimulation (for Cochrane review, see 13). In addition, NMES recruits motor units non-selectively, and in a spatially fixed and temporally synchronous manner14, offering the advantage of exerting a treatment effect on all fibers, regardless of fiber type. Although there are specified contraindications to NMES in clinical populations, including peripheral venous disorders or malignancy, for example, NMES is safe and feasible, even for those who are ill and/or bedridden and for populations in which rigorous exercise may be challenging. 
Here, we demonstrate the protocol for adapting commercially available electrodes and performing a NMES protocol using a murine model. This animal model has the advantage of utilizing a clinically available device and providing instant feedback regarding positioning of the electrode to elicit the desired muscle contractile effect. For the purpose of this manuscript, we will describe the protocol for muscle stimulation of the anterior compartment muscles of a mouse hindlimb.

A murine model of neuromuscular electrical stimulation (NMES), a safe and inexpensive clinical modality, to the anterior compartment muscles is described. This model has the advantage of modifying a readily available clinical device for the purpose of eliciting targeted and specific muscle contractions in mice.

Neuromuscular electrical stimulation (NMES) is a common clinical modality that is widely used to restore1, maintain2 or enhance3-5 muscle functional ...

Use of Animal Model of Sepsis to Evaluate Novel Herbal Therapies

Sepsis refers to a systemic inflammatory response syndrome resulting from a microbial infection. It has been routinely simulated in animals by several techniques, including infusion of exogenous bacterial toxin (endotoxemia) or bacteria (bacteremia), as well as surgical perforation of the cecum by cecal ligation and puncture (CLP)1-3. CLP allows bacteria spillage and fecal contamination of the peritoneal cavity, mimicking the human clinical disease of perforated appendicitis or diverticulitis. The severity of sepsis, as reflected by the eventual mortality rates, can be controlled surgically by varying the size of the needle used for cecal puncture2. In animals, CLP induces similar, biphasic hemodynamic cardiovascular, metabolic, and immunological responses as observed during the clinical course of human sepsis3. Thus, the CLP model is considered as one of the most clinically relevant models for experimental sepsis1-3.
Various animal models have been used to elucidate the intricate mechanisms underlying the pathogenesis of experimental sepsis. The lethal consequence of sepsis is attributable partly to an excessive accumulation of early cytokines (such as TNF, IL-1 and IFN-&gamma;)4-6 and late proinflammatory mediators (e.g., HMGB1)7. Compared with early proinflammatory cytokines, late-acting mediators have a wider therapeutic window for clinical applications. For instance, delayed administration of HMGB1-neutralizing antibodies beginning 24 hours after CLP, still rescued mice from lethality8,9, establishing HMGB1 as a late mediator of lethal sepsis. The discovery of HMGB1 as a late-acting mediator has initiated a new field of investigation for the development of sepsis therapies using Traditional Chinese Herbal Medicine. In this paper, we describe a procedure of CLP-induced sepsis, and its usage in screening herbal medicine for HMGB1-targeting therapies.

Sepsis refers to a systemic inflammatory response syndrome resulting from a microbial infection, and can be simulated by a surgical technique termed cecal ligation and puncture (CLP). Here we describe a method to use CLP-induced animal model to screen medicinal herbs for therapeutic agents.

Sepsis refers to a systemic inflammatory response syndrome resulting from a microbial infection. It has been routinely simulated in animals by several ...

Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of denervation-induced skeletal muscle atrophy in rodents. Although originally developed and used extensively in the rat due to its larger size, the tibial nerve in mice is big enough that it can be easily manipulated with either crush or transection, leaving the peroneal and sural nerve branches of the sciatic nerve intact and thereby preserving their target muscles. Thus, this model offers the advantages of inducing less morbidity and impediment of ambulation than the sciatic nerve transection model and also allows investigators to study the physiologic, cellular and molecular biologic mechanisms regulating the process of muscle atrophy in genetically engineered mice. The tibial nerve supplies the gastrocnemius, soleus and plantaris muscles, so its transection permits the study of denervated skeletal muscle composed of fast twitch type II fibers and/or slow twitch type I fibers. Here we demonstrate the tibial nerve transection model in the C57Black6 mouse. We assess the atrophy of the gastrocnemius muscle, as a representative muscle, at 1, 2, and 4 weeks post-denervation by measuring muscle weights and fiber type specific cross-sectional area on paraffin-embedded histologic sections immunostained for fast twitch myosin.

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of skeletal muscle atrophy. The model surgical protocol is described and demonstrated in C57Black6 mice. &#160;

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of denervation-induced skeletal muscle atrophy in rodents. ...

A Controlled Mouse Model for Neonatal Polymicrobial Sepsis

Neonatal sepsis remains a global burden. A preclinical model to screen effective prophylactic or therapeutic interventions is needed. Neonatal mouse polymicrobial sepsis can be induced by injecting cecal slurry intraperitoneally into day of life 7 mice and monitoring them for the following week. Presented here are the detailed steps necessary for the implementation of this neonatal sepsis model. This includes making a homogeneous cecal slurry stock, diluting it to a weight- and litter-adjusted dose, an outline of the monitoring schedule, and a definition of observed health categories used to define humane endpoints. The generation of a homogeneous cecal slurry stock from pooled donors allows for the administration into many litters over time, reducing the variation between donors, and preventing the use of potentially toxic glycerol. The monitoring strategy used allows for the anticipation of survival outcome and the identification of mice that would later progress to death, allowing for an earlier identification of the humane endpoint. Two main behavioral features are used to define the health scores, namely, the ability of the neonatal mice to right themselves when placed on their back and their level of mobility. These criteria could potentially be applied to address humane endpoints in other studies of neonatal disease in mice, as long as a pilot study is performed to confirm accuracy. In conclusion, this approach provides a standardized method to model newborn sepsis in mice, while providing resources to assess animal welfare used to define early humane endpoints for challenged animals.

This protocol provides the necessary steps to establish and evaluate neonatal sepsis in 7-day-old mice.

Neonatal sepsis remains a global burden. A preclinical model to screen effective prophylactic or therapeutic interventions is needed. Neonatal mouse ...

Immunology and Infection

Repeated Measurement of Respiratory Muscle Activity and Ventilation in Mouse Models of Neuromuscular Disease

Accessory respiratory muscles help to maintain ventilation when diaphragm function is impaired. The following protocol describes a method for repeated measurements over weeks or months of accessory respiratory muscle activity while simultaneously measuring ventilation in a non-anesthetized, freely behaving mouse. The technique includes the surgical implantation of a radio transmitter and the insertion of electrode leads into the scalene and trapezius muscles to measure the electromyogram activity of these inspiratory muscles. Ventilation is measured by whole-body plethysmography, and animal movement is assessed by video and is synchronized with electromyogram activity. Measurements of muscle activity and ventilation in a mouse model of amyotrophic lateral sclerosis are presented to show how this tool can be used to investigate how respiratory muscle activity changes over time and to assess the impact of muscle activity on ventilation. The described methods can easily be adapted to measure the activity of other muscles or to assess accessory respiratory muscle activity in additional mouse models of disease or injury.

This paper introduces a method for repeated measurements of ventilation and respiratory muscle activity in a freely behaving amyotrophic lateral sclerosis (ALS) mouse model throughout disease progression with whole-body plethysmography and electromyography via an implanted telemetry device.

Accessory respiratory muscles help to maintain ventilation when diaphragm function is impaired. The following protocol describes a method for repeated ...

In Vivo Electrophysiological Measurement of Compound Muscle Action Potential from the Forelimbs in Mouse Models of Motor Neuron Degeneration

Assessing the functionality of the nerve axon provides detailed information on the progression of neuromuscular disorders. Electrophysiological recordings provide a sensitive approach to measure nerve conduction in humans and rodent models. To broaden the technical possibilities for electromyography in mice, the measurement of compound muscle action potentials (CMAPs) from the brachial plexus nerve in the forelimb using needle electrodes is described here. CMAP recordings after stimulating the sciatic nerve in hindlimbs have been previously described. The newly introduced method here allows for the evaluation of the nerve conductivity at an additional site, and thus provides a more profound overview of the neuromuscular functionality. The technique provides information on both the relative number of functional axons and the myelination level. Thereby, this method can be applied to assess both axonal diseases as well as demyelinating conditions. This minimally invasive method does not require extraction of the nerve and therefore it is suitable for repeated measurements for longitudinal follow-up in the same animal. Similar recordings are performed in clinical setups to emphasize the translational relevance of the method.

In Vivo Electrophysiological Measurement of Compound Muscle Action Potential from the Forelimbs in Mouse Models of Motor Neuron Degeneration

The measurement of nerve conduction is a useful tool to assess mouse models of neurodegeneration but it is frequently only applied to stimulate the sciatic nerve in hindlimbs. Here, we describe a technique to measure compound muscle action potential (CMAP) in vivo in the mouse forelimb muscles innervated by the brachial plexus.

Assessing the functionality of the nerve axon provides detailed information on the progression of neuromuscular disorders. Electrophysiological recordings ...

Neuroscience

Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies

Critical to the evaluation of potential therapeutics for muscular disease are sensitive and reproducible physiological assessments of muscle function. Because many pre-clinical trials rely on mouse models for these diseases, isolated muscle function has become one of the standards for Go/NoGo decisions in moving drug candidates forward into patients. We will demonstrate the preparation of the extensor digitorum longus (EDL) and diaphragm muscles for functional testing, which are the predominant muscles utilized for these studies. The EDL muscle geometry is ideal for isolated muscle preparations, with two easily accessible tendons, and a small size that can be supported by superfusion in a bath. The diaphragm exhibits profound progressive pathology in dystrophic animals, and can serve as a platform for evaluating many potential therapies countering fibrosis, and promoting myofiber stability. Protocols for routine testing, including isometric and eccentric contractions, will be shown. Isometric force provides assessment of strength, and eccentric contractions help to evaluate sarcolemma stability, which is disrupted in many types of muscular dystrophies. Comparisons of the expected results between muscles from wildtype and dystrophic muscles will also be provided. These measures can complement morphological and biochemical measurements of tissue homeostasis, as well as whole animal assessments of muscle function.

Muscle function measurements contribute to the evaluation of potential therapeutics for muscle pathology, as well as to the determination of mechanisms underlying physiology of this tissue. We will demonstrate the preparation of the extensor digitorum longus and diaphragm muscles for functional testing. Protocols for isometric and eccentric contractions will be shown, as well as differences in results between dystrophic muscles, representing a pathological state, and wildtype muscles.

Critical to the evaluation of potential  therapeutics for muscular disease are sensitive and reproducible physiological  assessments of muscle function. ...

Biology

Non-invasive Assessment of Dorsiflexor Muscle Function in Mice

Assessment of skeletal muscle contractile function is an important measurement for both clinical and research purposes. Numerous conditions can negatively affect skeletal muscle. This can result in a loss of muscle mass (atrophy) and/or loss of muscle quality (reduced force per unit of muscle mass), both of which are prevalent in chronic disease, muscle-specific disease, immobilization, and aging (sarcopenia). Skeletal muscle function in animals can be evaluated by a range of different tests. All tests have limitations related to the physiological testing environment, and the selection of a specific test often depends on the nature of the experiments. Here, we describe an in vivo, non-invasive technique involving a helpful and easy assessment of force frequency-curve (FFC) in mice that can be performed on the same animal over time. This permits monitoring of disease progression and/or efficacy&#160;of a potential therapeutic treatment.

Measurement of rodent skeletal muscle contractile function is a useful tool that can be used to track disease progression as well as efficacy of therapeutic intervention. We describe here the non-invasive, in vivo assessment of the dorsiflexor muscles that can be repeated over time in the same mouse.

Assessment of skeletal muscle contractile function is an important measurement for both clinical and research purposes. Numerous conditions can negatively ...

A Preclinical Model of Sepsis-Induced Myopathy with Disuse in Mice

Summary

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Electrophysiological Motor Unit Number Estimation (MUNE) Measuring Compound Muscle Action Potential (CMAP) in Mouse Hindlimb Muscles

A Murine Model of Muscle Training by Neuromuscular Electrical Stimulation

Use of Animal Model of Sepsis to Evaluate Novel Herbal Therapies

Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice

A Controlled Mouse Model for Neonatal Polymicrobial Sepsis

Repeated Measurement of Respiratory Muscle Activity and Ventilation in Mouse Models of Neuromuscular Disease

In Vivo Electrophysiological Measurement of Compound Muscle Action Potential from the Forelimbs in Mouse Models of Motor Neuron Degeneration

Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies

Non-invasive Assessment of Dorsiflexor Muscle Function in Mice