Spatial proteomics of human diabetic kidney disease, from health to class III.

AIMS/HYPOTHESIS: Diabetic kidney disease (DKD) is the leading cause of chronic and end-stage kidney disease in the USA and worldwide. Animal models have taught us much about DKD mechanisms, but translation of this knowledge into treatments for human disease has been slowed by the lag in our molecular understanding of human DKD. METHODS: Using our Spatial TissuE Proteomics (STEP) pipeline (comprising curated human kidney tissues, multiplexed immunofluorescence and powerful analysis tools), we imaged and analysed the expression of 21 proteins in 23 tissue sections from individuals with diabetes and healthy kidneys (n=5), compared to those with DKDIIA, IIA-B and IIB (n=2 each) and DKDIII (n=1). RESULTS: These analyses revealed the existence of 11 cellular clusters (kidney compartments/cell types): podocytes, glomerular endothelial cells, proximal tubules, distal nephron, peritubular capillaries, blood vessels (endothelial cells and vascular smooth muscle cells), macrophages, myeloid cells, other CD45+ inflammatory cells, basement membrane and the interstitium. DKD progression was associated with co-localised increases in inflammatory cells and collagen IV deposition, with concomitant loss of native proteins of each nephron segment. Cell-type frequency and neighbourhood analyses highlighted a significant increase in inflammatory cells and their adjacency to tubular and αSMA+ (α-smooth muscle actin-positive) cells in DKD. Finally, DKD progression showed marked regional variability within single tissue sections, as well as inter-individual variability within each DKD class. CONCLUSIONS/INTERPRETATION: Using the STEP pipeline, we found alterations in protein expression, cellular phenotypic composition and microenvironment structure with DKD progression, demonstrating the power of this pipeline to reveal the pathophysiology of human DKD.

Dynamic Changes in ELF Score Predict Hepatocellular Carcinoma in Chronic Hepatitis B Patients Receiving Antiviral Treatment.

Enhanced liver fibrosis (ELF) score is a noninvasive assessment for liver fibrosis. We aimed to evaluate the performance of changes in ELF score 3 years apart in combination with liver stiffness measurement (LSM)-hepatocellular carcinoma (HCC) score to predict HCC in chronic hepatitis B (CHB) patients. This is a prospective cohort study. Patients who underwent transient elastography (TE) examinations and at intermediate or high risk of HCC defined by LSM-HCC score were invited to repeat the examination about 3 years later. Their serum samples at these two time points were retrieved to assess the ELF score changes. The primary endpoint was HCC. There were 445 CHB patients (males: 73.9%; mean age: 51.6 ± 10.3 years) who received two TE examinations and ELF scores. Among them, 252 (56.6%) and 193 (43.4%) patients were at intermediate and high HCC risk at first assessment defined by LSM-HCC score, respectively. Kaplan-Meier analysis showed that the changes in ELF score could stratify the HCC risk in both intermediate- and high-risk patients defined by LSM-HCC score (p < 0.001 for intermediate-risk group; p = 0.011 for high-risk group). Patients remained having mild or moderate fibrosis at both assessments had the lowest risk of HCC (4.0%), followed by patients with fibrosis regressed (11.3%; p = 0.014) during a mean follow-up of 163 months. Patients remained having or progressed to severe fibrosis were at highest risk of HCC (>20%). Consistent findings were demonstrated in patients at both intermediate and high risk of HCC defined by LSM-HCC score. Dynamic changes in ELF score provided additional value to LSM-HCC score for stratifying HCC risk in CHB patients.

Single-virus assay reveals membrane determinants and mechanistic features of Sendai virus binding.

Sendai virus (SeV, formally murine respirovirus) is a membrane-enveloped, negative-sense RNA virus in the Paramyxoviridae family and is closely related to human parainfluenza viruses. SeV has long been utilized as a model paramyxovirus and has recently gained attention as a viral vector candidate for both laboratory and clinical applications. To infect host cells, SeV must first bind to sialic acid glycolipid or glycoprotein receptors on the host cell surface via its hemagglutinin-neuraminidase (HN) protein. Receptor binding induces a conformational change in HN, which allosterically triggers the viral fusion (F) protein to catalyze membrane fusion. While it is known that SeV binds to α2,3-linked sialic acid receptors, and there has been some study into the chemical requirements of those receptors, key mechanistic features of SeV binding remain unknown, in part because traditional approaches often convolve binding and fusion. Here, we develop and employ a fluorescence microscopy-based assay to observe SeV binding to supported lipid bilayers (SLBs) at the single-particle level, which easily disentangles binding from fusion. Using this assay, we investigate mechanistic questions of SeV binding. We identify chemical structural features of ganglioside receptors that influence viral binding and demonstrate that binding is cooperative with respect to receptor density. We measure the characteristic decay time of unbinding and provide evidence supporting a "rolling" mechanism of viral mobility following receptor binding. We also study the dependence of binding on target cholesterol concentration. Interestingly, we find that although SeV binding shows striking parallels in cooperative binding with a prior report of Influenza A virus, it does not demonstrate a similar sensitivity to cholesterol concentration and receptor nanocluster formation.

Tenofovir alafenamide is associated with improved alanine aminotransferase and renal safety compared to tenofovir disoproxil fumarate.

Tenofovir alafenamide (TAF) is a novel prodrug of tenofovir for the treatment of chronic hepatitis B (CHB) infection. We aimed to evaluate the impact of switching to TAF on alanine aminotransferase (ALT) normalization and renal safety. We also described the indications of switching to TAF. Consecutive adult CHB patients switched from tenofovir disoproxil fumarate (TDF) dominant therapy to TAF for more than 12 months were identified retrospectively. A subgroup of patients newly switched to TAF was prospectively invited to perform transient elastography examination and dual-energy X-ray absorptiometry. The time of switching to TAF was defined as baseline. Among 393 patients in the retrospective cohort, the median ALT at month 12 was significantly lower (21.0 [16.0-29.9] U/L vs. 25.0 [19.0-34.0] U/L; p < 0.001) and ALT normalization rate was higher (89.9% vs. 83.7%; p = 0.037) than those at baseline. Estimated glomerular filtration rate decreased from 12 months before baseline and then increased from baseline to month 12 significantly (69.7 ± 22.0 ml/min/1.73 m2 vs. 68.5 ± 21.5 ml/min/1.73 m2 vs. 69.2 ± 21.5 ml/min/1.73 m2 , p = 0.002 (-12 m vs. baseline), p = 0.004 (baseline vs. 12 m)). In the prospective cohort, 103 patients switched to TAF because of age > 60 years (63.1%), bone diseases (54.4%), and renal alteration (42.7%). TAF is associated with ALT improvement and better renal safety than TDF dominant therapy in CHB patients. Most CHB patients switched to TAF because of advanced age, followed by bone disease and renal alteration.

Antihypertensive treatments and risks of lung Cancer: a large population-based cohort study in Hong Kong.

BACKGROUND: There is a growing concern that the use of anti-hypertensives may be associated with an increased risk of cancer, but it remains uncertain for the association between anti-hypertensives and lung cancer risk, as well as their interaction with aspirin in chemoprotective effects. METHODS: The goal of this study is to assess the association between anti-hypertensives use and the risk of lung cancer, as well as the chemopreventive impacts from the combination usage of aspirin and anti-hypertensives. A retrospective cohort study was conducted based on all the public hospital electronic medical records in Hong Kong. Patients with prescription records of anti-hypertensives (ACEi/ARB, CCB, ß-blocker,α-blocker) and/or aspirin were included as the exposure groups. Using the Cox proportional hazards model with inverse probability weighting, we estimated hazard ratios (HRs) with 95% confidence intervals (CIs) for lung cancer risk from anti-hypertensives usage or combination usage of aspirin with anti-hypertensives. The likelihood ratio test and interaction model were adopted for exploring the interaction effects with aspirin. RESULTS: A total of 6592 and 84,116 lung cancer cases were identified from the groups of anti-hypertensives users and anti-hypertensives users with aspirin, respectively. The group of non-aspirin patients who received anti-hypertensives showed a significantly lower risk of lung cancer (HR: 0.63, 95% CI: 0.60-0.66), compared to those without anti-hypertensives. When aspirin and α-blocker were used simultaneously, it could lower the risk of lung cancer significantly (HR: 0.53, 95% CI: 0.34-0.84). Moreover, the lower risk of lung cancer persisted with a longer follow-up period of anti-hypertensives usage. Combination usage with aspirin in the users of ACEi/ARB, CCB, and α-blocker showed significant interaction effects. However, the smoking effect could not be eliminated in this analysis. DISCUSSION: Anti-hypertensive treatment was associated with a lower risk of lung cancer, which is associated with the anti-hypertensives exposure period. The potential interaction on the chemopreventive influence from combination usage of α-blocker and aspirin might exist. More corroborations on these findings are needed to focus on the different settings in future studies.

The Cardioprotective Role of Flaxseed in the Prevention of Doxorubicin- and Trastuzumab-Mediated Cardiotoxicity in C57BL/6 Mice.

BACKGROUND: Although the combination of doxorubicin (DOX) and trastuzumab (TRZ) reduces the progression and recurrence of breast cancer, these anticancer drugs are associated with significant cardiotoxic side effects. OBJECTIVE: We investigated whether prophylactic administration of flaxseed (FLX) and its bioactive components, α-linolenic acid (ALA) and secoisolariciresinol diglucoside (SDG), would be cardioprotective against DOX + TRZ-mediated cardiotoxicity in a chronic in vivo female murine model. METHODS: Wild-type C57BL/6 female mice (10-12 wk old) received daily prophylactic treatment with one of the following diets: 1) regular control (RC) semi-purified diet; 2) 10% FLX diet; 3) 4.4% ALA diet; or 4) 0.44% SDG diet for a total of 6 wks. Within each arm, mice received 3 weekly injections of 0.9% saline or a combination of DOX [8 mg/(kg.wk)] and TRZ [3 mg/(kg.wk)] starting at the end of week 3. The main outcome was to evaluate the effects of FLX, ALA, and SDG on cardiovascular remodeling and markers of apoptosis, inflammation, and mitochondrial dysfunction. Significance between measurements was determined using a 4 (diet) × 2 (chemotherapy) × 2 (time) mixed factorial design with repeated measures. RESULTS: In the RC + DOX + TRZ-treated mice at week 6 of the study, the left ventricular ejection fraction (LVEF) decreased by 50% compared with the baseline LVEF (P < 0.05). However, the prophylactic administration of the FLX, ALA, or SDG diet was partially cardioprotective, with mice in these treatment groups showing an ∼68% increase in LVEF compared with the RC + DOX + TRZ-treated group at week 6 (P < 0.05). Although markers of inflammation (nuclear transcription factor κB), apoptosis [poly (ADP-ribose) polymerase-1 and the ratio of BCL2-associated X protein to B-cell lymphoma-extra large], and mitochondrial dysfunction (BCL2-interacting protein 3) were significantly elevated by approximately 2-fold following treatment with RC + DOX + TRZ compared with treatment with RC + saline at week 6, prophylactic administration of FLX, ALA, or SDG partially downregulated these signaling pathways. CONCLUSION: In a chronic in vivo female C57BL/6 mouse model of DOX + TRZ-mediated cardiotoxicity, FLX, ALA, and SDG were partially cardioprotective.

Warfarin control in Hong Kong clinical practice: a single-centre observational study.

INTRODUCTION: Time in therapeutic range (TTR) assesses the safety and effectiveness of warfarin therapy using the international normalised ratio. This study investigated the TTR in Hong Kong patients using both European and Japanese therapeutic ranges and patients' economic and clinical outcomes. Predictors of poor warfarin control and patient knowledge concerning warfarin therapy were assessed. METHODS: A 5-month observational study with retrospective and prospective components was conducted in the Prince of Wales Hospital. The study examined electronic patient records of patients who received warfarin for at least 1 year during the period from January 2010 to August 2015. Patient knowledge was assessed via phone interview using the Oral Anticoagulation Knowledge (OAK) test. RESULTS: In total, 259 patients were included; 174 completed the OAK test. The calculated mean TTR was 40.2±17.1% (European therapeutic range), compared with 49.1±16.1% (Japanese therapeutic range) [P<0.001]. Mean TTR was higher in patients with atrial fibrillation than in patients with prosthetic heart valve (P<0.001). The abilities of TTR to predict clinical and economic outcomes were comparable between European and Japanese therapeutic ranges. Patients with ideal TTR had fewer clinical complications and lower healthcare costs. Patients with younger age exhibited worse TTR, as did those with concurrent use of furosemide, famotidine, or simvastatin. Mean OAK test score was 54.1%. Only 24 (13.8%) patients achieved a satisfactory overall score of ≥75% in the test. CONCLUSION: Warfarin use in Hong Kong patients was poorly controlled, regardless of indication. Patient knowledge concerning warfarin use was suboptimal; thus, additional patient education is warranted regarding warfarin.

Simultaneous dual-color fluorescence lifetime imaging with novel red-shifted fluorescent proteins.

We describe a red-shifted fluorescence resonance energy transfer (FRET) pair optimized for dual-color fluorescence lifetime imaging (FLIM). This pair utilizes a newly developed FRET donor, monomeric cyan-excitable red fluorescent protein (mCyRFP1), which has a large Stokes shift and a monoexponential fluorescence lifetime decay. When used together with EGFP-based biosensors, the new pair enables simultaneous imaging of the activities of two signaling molecules in single dendritic spines undergoing structural plasticity.

Fluorescent indicators for simultaneous reporting of all four cell cycle phases.

A robust method for simultaneous visualization of all four cell cycle phases in living cells is highly desirable. We developed an intensiometric reporter of the transition from S to G2 phase and engineered a far-red fluorescent protein, mMaroon1, to visualize chromatin condensation in mitosis. We combined these new reporters with the previously described Fucci system to create Fucci4, a set of four orthogonal fluorescent indicators that together resolve all cell cycle phases.

Reversibly Bound Kinesin-1 Motor Proteins Propelling Microtubules Demonstrate Dynamic Recruitment of Active Building Blocks.

Biological materials and systems often dynamically self-assemble and disassemble, forming temporary structures as needed and allowing for dynamic responses to stimuli and changing environmental conditions. However, this dynamic interplay of localized component recruitment and release has been difficult to achieve in artificial molecular-scale systems, which are usually designed to have long-lasting, stable bonds. Here, we report the experimental realization of a molecular-scale system that dynamically assembles and disassembles its building blocks while retaining functionality. In our system, filaments (microtubules) recruit biomolecular motors (kinesins) to a surface engineered to allow for the reversible binding of the kinesin-1 motors. These recruited motors work to propel the cytoskeletal filaments along the surface. After the microtubules leave the motors behind, the trail of motors disassembles, releasing the motors back into solution. Engineering such dynamic systems may allow us to create materials that mimic the way in which biological systems achieve self-healing and adaptation.

Non-invasive intravital imaging of cellular differentiation with a bright red-excitable fluorescent protein.

A method for non-invasive visualization of genetically labeled cells in animal disease models with micrometer-level resolution would greatly facilitate development of cell-based therapies. Imaging of fluorescent proteins (FPs) using red excitation light in the 'optical window' above 600 nm is one potential method for visualizing implanted cells. However, previous efforts to engineer FPs with peak excitation beyond 600 nm have resulted in undesirable reductions in brightness. Here we report three new red-excitable monomeric FPs obtained by structure-guided mutagenesis of mNeptune. Two of these, mNeptune2 and mNeptune2.5, demonstrate improved maturation and brighter fluorescence than mNeptune, whereas the third, mCardinal, has a red-shifted excitation spectrum without reduction in brightness. We show that mCardinal can be used to non-invasively and longitudinally visualize the differentiation of myoblasts into myocytes in living mice with high anatomical detail.

Improving FRET dynamic range with bright green and red fluorescent proteins.

A variety of genetically encoded reporters use changes in fluorescence (or Förster) resonance energy transfer (FRET) to report on biochemical processes in living cells. The standard genetically encoded FRET pair consists of CFPs and YFPs, but many CFP-YFP reporters suffer from low FRET dynamic range, phototoxicity from the CFP excitation light and complex photokinetic events such as reversible photobleaching and photoconversion. We engineered two fluorescent proteins, Clover and mRuby2, which are the brightest green and red fluorescent proteins to date and have the highest Förster radius of any ratiometric FRET pair yet described. Replacement of CFP and YFP with these two proteins in reporters of kinase activity, small GTPase activity and transmembrane voltage significantly improves photostability, FRET dynamic range and emission ratio changes. These improvements enhance detection of transient biochemical events such as neuronal action-potential firing and RhoA activation in growth cones.

Exchange protein activated by cAMP 1 (Epac1)-deficient mice develop ß-cell dysfunction and metabolic syndrome.

Previously, exchange protein directly activated by cAMP 2 (Epac2) and PKA were known to play a role in glucose-stimulated insulin secretion (GSIS) by pancreatic ß cells. The present study shows that Epac1 mRNA is also expressed by ß cells. Therefore, we generated mice and embryonic stem (ES) cells with deletion of the Epac1 gene to define its role in ß-cell biology and metabolism. The homozygous Epac1-knockout (Epac1(-/-)) mice developed impaired glucose tolerance and GSIS with deranged islet cytoarchitecture, which was confirmed by isolated islets from adult Epac1(-/-) mice. Moreover, Epac1(-/-) mice developed more severe hyperglycemia with increased ß-cell apoptosis and insulitis after multiple low-dose streptozotocin (MLDS; 40 mg/kg) treatment than Epac1(+/+) mice. Interestingly, Epac1(-/-) mice also showed metabolic defects, including increased respiratory exchange ratio (RER) and plasma triglyceride (TG), and more severe diet-induced obesity with insulin resistance, which may contributed to ß-cell dysfunction. However, islets differentiated from Epac1(-/-) ES cells showed insulin secretion defect, reduced Glut2 and PDX-1 expression, and abolished GLP-1-stimulated PCNA induction, suggesting a role of Epac1 in ß-cell function. The current study provides in vitro and in vivo evidence that Epac1 has an important role in GSIS of ß cells and phenotype resembling metabolic syndrome.

Nanoscale transport enables active self-assembly of millimeter-scale wires.

Active self-assembly processes exploit an energy source to accelerate the movement of building blocks and intermediate structures and modify their interactions. A model system is the assembly of biotinylated microtubules partially coated with streptavidin into linear bundles as they glide on a surface coated with kinesin motor proteins. By tuning the assembly conditions, microtubule bundles with near millimeter length are created, demonstrating that active self-assembly is beneficial if components are too large for diffusive self-assembly but too small for robotic assembly.

3D Imaging for Cleared Tissues and Thicker Samples on Confocal and Light-Sheet Microscopes.

Advances in fluorescence microscopy, specifically the development of confocal and light-sheet microscopes, have enabled researchers to harness tissue clearing techniques to image-stained intact tissue samples in 3D. Using these techniques, tissue structure and biomarker distributions in 3D structures are preserved, thus allowing researchers to gain a wealth of spatial information about their tissue of interest. However, the execution of imaging these larger tissue samples can be challenging. Broadly speaking, tissue clearing techniques unify the refractive indices inside tissue samples, thus enabling deep tissue imaging on a confocal or light-sheet microscope. Here, we provide an overview to tissue clearing and 3D immunohistochemistry staining in general and discuss some difficulties that researchers may encounter when using these techniques. We then focus on imaging CLARITY-processed samples with both confocal and light-sheet microscopes and optimizing the acquisition parameters, before noting potential issues that may come up in imaging.

Advocating for language equity: a community-public health partnership.

In the United States, 21.5% of individuals aged 5 or older speak a language other than English at home and 8.2% have Limited English Proficiency (LEP). LEP individuals experience healthcare disparities, including lower access to healthcare services, poorer health outcomes, and higher levels of uninsurance. The COVID-19 pandemic highlighted and exacerbated these health disparities and unmet healthcare needs. In Alameda County (CA), where 46% of foreign-born residents speak a language other than English at home, community-based organizations have been crucial in providing translated materials and one-on-one support to ensure LEP residents receive critical COVID-19 updates and services. Refugee and Immigrant Collaborative for Empowerment (RICE) is a multilingual coalition of seven Alameda County community-based organizations led by the Korean Community Center of the East Bay (KCCEB). During the COVID-19 pandemic, RICE expanded its public health role to fill service and information gaps, advocate on behalf of LEP groups, and build a linguistically and culturally responsive public health safety network. This community case study describes a three-part advocacy-focused intervention that RICE undertook from September 2021 to October 2022. It included (1) a community needs survey, (2) a landscape assessment of the Alameda County Health Department's (ACPHD) communication materials and online platforms, and (3) relationship building with the ACPHD. The community survey revealed differences across LEP subgroups and highlighted the importance of gathering data disaggregated by language preference. The landscape assessment allowed RICE to understand the ACPHD's decision-making process and develop data-informed advocacy requests on behalf of LEP communities. Effective communication and coordination between RICE and the ACPHD shortened the feedback loop between public health authorities and LEP communities and laid the groundwork for the RICE organizations to be part of the ACPHD's future decision making. Data disaggregation, language equity-based advocacy, and cross-sector collaboration were critical ingredients in RICE's intervention. RICE's partnership and relationship of mutual accountability with the ACPHD may provide a useful model for other community-based organizations and public health departments seeking to form similar partnerships.

The Western and Chinese exercise training for blood pressure reduction among hypertensive patients: An overview of systematic reviews.

Hypertension remains the world's leading cause of premature death. Interventions such as exercise, diet modification, and pharmacological therapy remain the mainstay of hypertension treatment. Numerous systematic reviews and meta-analyses demonstrated the effectiveness of western exercises, such as aerobic exercise and resistance exercise, in reducing blood pressure in hypertensive patients. There is recently emerging evidence of blood pressure reduction with Chinese exercises, such as Tai Chi, Baduanjin, and Qigong. The current overview of systematic reviews aims to evaluate the quality and descriptively summarize the evidence for the effectiveness of western and Chinese exercises for hypertension management. Thirty-nine systematic reviews were included in this overview, with 15 of those being on Chinese exercise. Evidence suggests that exercise training, regardless of Western or Chinese exercise, generally reduced both systolic and diastolic blood pressure. High-intensity intermittent training did not further reduce blood pressure when compared to moderate-intensity continuous training. Conflicting results on the effectiveness of blood pressure reduction when comparing Chinese and Western exercise training were observed. This suggests the comparable effectiveness of Chinese exercise training, in particularly Tai Chi, to general or aerobic exercise training in terms of blood pressure reduction. The Chinese exercise modality and intensity may be more suitable for the middle-aged and elderly population.

Nuclear factor of activated T cells 5 deficiency increases the severity of neuronal cell death in ischemic injury.

Nuclear factor of activated T cells 5 (NFAT5) has been implicated in regulating several genes that are thought to be neuroprotective in ischemic injury. Because of the embryonic lethality of NFAT5 knockout (NFAT5(-/-)) mice, the heterozygous (NFAT5(+/-)) mice were used to study the in vivo role of NFAT5 in hypoxia/ischemia (H/I) condition. The NFAT5(+/-) mice exhibited more severe neurological deficits, larger infarct area and edema formation associated with increased aquaporin 4 expressions in the brain. Under in vitro H/I condition, increased apoptotic cell death was found in NFAT5(-/-) neurons. Moreover, SMIT, a downstream to NFAT5, was upregulated in NFAT5(+/+) neurons, while the SMIT level could not be upregulated in NFAT5(-/-) neurons under H/I condition. The elevation of reactive oxygen species generation in NFAT5(-/-) neurons under H/I condition further confirmed that NFAT5(-/-) neurons were more susceptible to oxidative stress. The present study demonstrated that activation of NFAT5 and its downstream SMIT induction is important in protecting neurons from ischemia-induced oxidative stress.

Modeling negative cooperativity in streptavidin adsorption onto biotinylated microtubules.

The nanoscale architecture of binding sites can result in complex binding kinetics. Here, the adsorption of streptavidin and neutravidin to biotinylated microtubules is found to exhibit negative cooperativity due to electrostatic interactions and steric hindrance. This behavior is modeled by a newly developed kinetic analogue of the Fowler-Guggenheim adsorption model. The complex adsorption kinetics of streptavidin to biotinylated structures needs to be considered when these intermolecular bonds are employed in self-assembly and nanobiotechnology.

Neuromuscular electrical stimulation for skeletal muscle function.

Lack of neural innervation due to neurological damage renders muscle unable to produce force. Use of electrical stimulation is a medium in which investigators have tried to find a way to restore movement and the ability to perform activities of daily living. Different methods of applying electrical current to modify neuromuscular activity are electrical stimulation (ES), neuromuscular electrical stimulation (NMES), transcutaneous electrical nerve stimulation (TENS), and functional electrical stimulation (FES). This review covers the aspects of electrical stimulation used for rehabilitation and functional purposes. Discussed are the various parameters of electrical stimulation, including frequency, pulse width/duration, duty cycle, intensity/amplitude, ramp time, pulse pattern, program duration, program frequency, and muscle group activated, and how they affect fatigue in the stimulated muscle.