STAC3 as a poor prognostic biomarker in renal clear cell carcinoma: relationship with immune infiltration.

Calcium ions (Ca2+) are crucial in tumorigenesis and progression, with their elevated levels indicating a negative prognosis in Kidney Renal Clear Cell Carcinoma (KIRC). The influence of genes regulating calcium ions on the survival outcomes of KIRC patients and their interaction with the tumor's immune microenvironment is yet to be fully understood. This study analyzed gene expression data from KIRC tumor and adjacent non-tumor tissues using the TCGA-KIRC dataset to pinpoint genes that are differentially expressed in KIRC. Intersection of these genes with those regulating calcium ions highlighted specific calcium ion-regulating genes that exhibit differential expression in KIRC. Subsequently, prognostic risk models were developed using univariate Cox and LASSO-Cox regression analyses to verify their diagnostic precision. Additionally, the study investigated the correlation between tumor immunity and KIRC patient outcomes, assessing the contribution of STAC3 genes to tumor immunity. Further exploration entailed SSGASE, single-cell analysis, pseudotime analysis and both in vivo and in vitro experiments to evaluate STAC3's role in tumor immunity and progression. Notably, STAC3 was significantly overexpressed in tumor specimens and positively correlated with the degree of malignancy of KIRC, affecting patients' prognosis. Elevated STAC3 expression correlated with enhanced immune infiltration in KIRC tumors. Furthermore, silencing STAC3 curtailed KIRC cell proliferation, migration, invasion, and stemness properties. Experimental models in mice confirmed that STAC3 knockdown led to a reduction in tumor growth. Elevated STAC3 expression is intricately linked with immune infiltration in KIRC tumors, as well as with the aggressive biological behaviors of tumor cells, including their proliferation, migration, and invasion. Targeting STAC3 presents a promising strategy to augment the efficacy of current therapeutic approaches and to better the survival outcomes of patients with KIRC.

Examining the impact of Native American myopathy on the quality of life and healthcare accessibility of patients and caregivers.

Native American myopathy (NAM, also known as STAC3 disorder) (OMIM 255995) is an ultra-rare genetic disease impacting multiple body systems. The quality of life and caregiver burden associated with this condition remain poorly characterized. In this study, the Pediatric Quality of Life Inventory and a survey comprised of de novo questions concerning genetic testing, counseling, and caregiver burden were employed to investigate the health-related quality of life (HRQoL) in patients and caregivers with NAM. Study findings uncovered a concerning trend: patients with NAM experienced a notable decline in HRQoL, with reasons that warrant further investigation. Particularly striking was the downturn observed during the transition from adolescence to adulthood-across Physical, Social, and Emotional Functioning domains. Taken together, this study has elucidated novel insights into the impact of NAM, and areas of concern to improve HRQoL have subsequently been highlighted.

Age-related similarities and differences in cognitive and neural processing revealed by task-related microstate analysis.

We explored neural processing differences associated with aging across four cognitive functions. In addition to ERP analysis, we included task-related microstate analyses, which identified stable states of neural activity across the scalp over time, to explore whole-head neural activation differences. Younger and older adults (YA, OA) completed face perception (N170), word-pair judgment (N400), visual oddball (P3), and flanker (ERN) tasks. Age-related effects differed across tasks. Despite age-related delayed latencies, N170 ERP and microstate analyses indicated no age-related differences in amplitudes or microstates. However, age-related condition differences were found for P3 and N00 amplitudes and scalp topographies: smaller condition differences were found for in OAs as well as broader centroparietal scalp distributions. Age group comparisons for the ERN revealed similar focal frontocentral activation loci, but differential activation patterns. Our findings of differential age effects across tasks are most consistent with the STAC-r framework which proposes that age-related effects differ depending on the resources available and the kinds of processing and cognitive load required of various tasks.

Severe trauma associated cardiac failure.

Although significant efforts have been made to enhance trauma care, the mortality rate for traumatic cardiac arrest (TCA) remains exceedingly high. Therefore, our institution has implemented special measures to optimize the treatment of major trauma patients. These measures include a prehospital Medical Intervention Car (MIC) and a 'code red' protocol in the trauma resuscitation room for patients with TCA or shock. These measures enable the early treatment of reversible causes of TCA and have resulted in a significant number of patients achieving adequate ROSC. However, a significant proportion of these patients still die due to circulatory failure shortly after. Our observations from patients who underwent clamshell thoracotomy or received echocardiographic evaluation in conjunction with current scientific findings led us to conclude that dysfunction of the heart itself may be the cause. Therefore, we propose discussing severe trauma-associated cardiac failure (STAC) as a new entity to facilitate scientific research and the development of specific treatment strategies, with the aim of improving the outcome of severe trauma.

Knockdown of ADAM8 inhibits the proliferation, migration, invasion, and tumorigenesis of renal clear cell carcinoma cells to enhance the immunotherapy efficacy.

The current study performed bioinformatics and in vitro and in vivo experiments to explore the effects of ADAM8 on the malignant behaviors and immunotherapeutic efficacy of renal clear cell carcinoma (ccRCC) Cells. The modular genes most associated with immune cells were screened. Then, prognostic risk models were constructed by univariate COX analysis, LASSO regression analysis and multivariate COX analysis, and their diagnostic value was determined. The correlation between tumor mutation load (TMB) scores and the prognosis of ccRCC patients was clarified. Finally, six key genes (ABI3, ADAM8, APOL3, MX2, CCDC69, and STAC3) were analyzed for immunotherapy efficacy. Human and mouse ccRCC cell lines and human proximal tubular epithelial cell lines were used for in vitro cell experiments. The effect of ADAM8 overexpression or knockdown on tumor formation and survival in ccRCC cells was examined by constructing subcutaneous transplanted tumor model. Totally, 636 Black module genes were screened as being most associated with immune cell infiltration. Six genes were subsequently confirmed for the construction of prognostic risk models, of which ABI3, APOL3 and CCDC69 were low-risk factors, while ADAM8, MX2 and STAC3 were high-risk factors. The constructed risk model based on the identified six genes could accurately predict the prognosis of ccRCC patients. Besides, TMB was significantly associated with the prognosis of ccRCC patients. Furthermore, ABI3, ADAM8, APOL3, MX2, CCDC69 and STAC3 might play important roles in treatment concerning CTLA4 inhibitors or PD-1 inhibitors or combined inhibitors. Finally, we confirmed that ADAM8 could promote the proliferation, migration and invasion of ccRCC cells through in vitro experiments, and further found that in in vivo experiments, ADAM8 knockdown could inhibit tumor formation in ccRCC cells, improve the therapeutic effect of anti-PD1, and prolong the survival of mice. Our study highlighted the alleviative role of silencing ADAM8 in ccRCC patients.

Bailey-Bloch Congenital Myopathy in Brazilian Patients: A Very Rare Myopathy with Malignant Hyperthermia Susceptibility.

BACKGROUND: Congenital myopathy-13 (CMYP13), also known as Bailey-Bloch congenital myopathy and Native American myopathy (NAM), is a condition caused by biallelic missense pathogenic variants in STAC3, which encodes an important protein necessary for the excitation-relaxation coupling machinery in the muscle. Patients with biallelic pathogenic variants in STAC3 often present with congenital weakness and arthrogryposis, cleft palate, ptosis, myopathic facies, short stature, kyphoscoliosis, and susceptibility to malignant hyperthermia provoked by anesthesia. We present two unrelated cases of Bailey-Bloch congenital myopathy descendants of non-consanguineous parents, which were investigated for delayed psychomotor development and generalized weakness. To the best of our knowledge, these are the first descriptions of CMYP13 in Brazil. In both patients, we found the previously described pathogenic missense variant p.Trp284Ser in homozygosity. CONCLUSION: We seek to highlight the need for screening for CMYP13 in patients expressing the typical phenotype of the disease even in the absence of Lumbee Native American ancestry, and to raise awareness to possible complications like malignant hyperthermia in Bailey-Bloch congenital myopathy.

STAC1 is required for glioblastoma cell invasion and survival.

Glioblastoma Multiforme (GBM) is a highly malignant brain tumor with poor prognosis. Understanding the molecular mechanisms driving GBM tumorigenesis is crucial for developing effective therapeutic strategies. This study investigates the role of STAC1, a gene belonging to the SH3 and cysteine-rich domain family, in glioblastoma cell invasion and survival. Computational analyses of patient samples reveal that STAC1 expression is elevated in GBM tissues, and higher STAC1 expression is associated with lower overall survival rates. Consistently, we find that overexpression of STAC1 in glioblastoma cells enhances invasion, while knockdown of STAC1 reduces invasion and the expression of genes associated with epithelial-to-mesenchymal transition (EMT). STAC1 depletion also induces apoptosis in glioblastoma cells. Furthermore, we show that STAC1 regulates AKT and calcium channel signaling in glioblastoma cells. Collectively, our study provides valuable insights into the pathogenic roles of STAC1 in GBM and highlights its potential as a promising target for the treatment of high-grade glioblastoma.

CaV1.1 Calcium Channel Signaling Complexes in Excitation-Contraction Coupling: Insights from Channelopathies.

In skeletal muscle, excitation-contraction (EC) coupling relies on the mechanical coupling between two ion channels: the L-type voltage-gated calcium channel (CaV1.1), located in the sarcolemma and functioning as the voltage sensor of EC coupling, and the ryanodine receptor 1 (RyR1), located on the sarcoplasmic reticulum serving as the calcium release channel. To this day, the molecular mechanism by which these two ion channels are linked remains elusive. However, recently, skeletal muscle EC coupling could be reconstituted in heterologous cells, revealing that only four proteins are essential for this process: CaV1.1, RyR1, and the cytosolic proteins CaVß1a and STAC3. Due to the crucial role of these proteins in skeletal muscle EC coupling, any mutation that affects any one of these proteins can have devastating consequences, resulting in congenital myopathies and other pathologies.Here, we summarize the current knowledge concerning these four essential proteins and discuss the pathophysiology of the CaV1.1, RyR1, and STAC3-related skeletal muscle diseases with an emphasis on the molecular mechanisms. Being part of the same signalosome, mutations in different proteins often result in congenital myopathies with similar symptoms or even in the same disease.

Feasibility of a Bullying Bystander Intervention (STAC) Parent Module for Rural Schools.

The purpose of this study was to assess the feasibility of parent training designed as a companion module to a bullying bystander intervention (STAC) for middle school students in rural communities. Parents (N = 23) invited from three rural middle schools viewed a parent training and completed measures to assess limited efficacy through immediate program outcomes (e.g., knowledge, confidence, self-efficacy, attitudes, behavioral intentions) and program feasibility, as well as participated in focus groups to provide feedback about program acceptability, demand, practicality, and online delivery adaptation. Parents reported increases in knowledge and confidence in supporting their adolescents to intervene in bullying situations, confidence and comfort in managing bullying, bullying self-efficacy, communication self-efficacy, responsibility to actively engage in bullying prevention, and anti-bullying attitudes from pre-training to post-training. Parents also reported behavioral intentions to use strategies they learned to support their adolescents to intervene in bullying situations. Further, parents' responses suggested high levels of program acceptability, as well as interest in an interactive, self-paced online parent training. Themes from focus groups (n = 12) revealed a need for bullying prevention training for both students and parents in rural communities and found the training to be useful, easy to understand, and relevant and appropriate for their community. Parents identified barriers including cost, time, program flexibility, and the importance of parent buy-in. Parents also provided feedback specific to an online training, including a preference for a smartphone application and design elements to increase engagement. Implications for program development for rural communities are discussed.

Posttraining Outcomes, Acceptability, and Technology-Based Delivery of the STAC Bystander Bullying Intervention Teacher Module: Mixed Methods Study.

BACKGROUND: Bullying is a significant problem for youth associated with wide-ranging negative consequences. Providing students who witness bullying with intervention strategies to act as defenders can reduce bullying and negative associated outcomes for both targets and bystanders. Educating teachers about bullying and training them to support students to intervene as defenders may increase the efficacy of bystander programs as teachers' attitudes and responses to bullying relate to bystander behavior. This is particularly important in middle school, when bullying peaks and rates of reporting bullying to teachers begin to decline. Reducing implementation barriers, including limited time and resources, must also be considered, particularly for schools in low-income and rural areas. Technology-based programs can increase access and scalability but require participant buy-in for adoption. OBJECTIVE: We used a mixed methods design to inform the development of the STAC teacher module, a companion training to a brief bullying bystander intervention. STAC stands for the four bystander intervention strategies: Stealing the Show, Turning it Over, Accompanying Others, and Coaching Compassion. Objectives included examining the effectiveness of the STAC teacher module and informing the translation of the training into a technology-based format that can be used as a companion to the technology-based STAC. METHODS: A sample of 17 teachers recruited from 1 middle school in a rural, low-income community completed pre- and posttraining surveys assessing immediate outcomes (ie, knowledge, confidence, comfort, and self-efficacy), intention to use program strategies, and program acceptability and relevance, followed by a qualitative focus group obtaining feedback regarding program appropriateness, feasibility, content, perception of need, and desire for web-based training. Descriptive statistics, 2-tailed independent-sample t tests, and thematic analyses were used to analyze the data. RESULTS: Assessment of pre- and posttraining surveys indicated that teachers reported an increase in knowledge and confidence to support defenders, confidence and comfort in managing bullying, and bullying self-efficacy. Furthermore, most participants reported that they were likely or very likely to use STAC strategies to support students who intervene in bullying. Quantitative and qualitative data revealed that participants found the training easy to use, useful, relevant, and appropriate. Qualitative data provided feedback on ways of improving the program, including revising role-plays and guidance on understanding student behavior. Participants shared positive perceptions regarding program feasibility and need for bullying-specific prevention, the most significant barriers being cost and parent buy-in, suggesting the importance of including parents in the prevention process. Finally, participants shared the strengths of a web-based program, including ease of implementation and time efficiency, while indicating the importance of participant engagement and administration buy-in. CONCLUSIONS: This study demonstrates the effectiveness of the STAC teacher module in increasing knowledge and bullying self-efficacy and provides support for developing the module, including key information regarding considerations for web-based translation.

Dissociation of SH3 and cysteine-rich domain 3 and junctophilin 1 from dihydropyridine receptor in dystrophin-deficient muscles.

The disruption of excitation-contraction (EC) coupling and subsequent reduction in Ca2+ release from the sarcoplasmic reticulum (SR) have been shown to account for muscle weakness seen in patients with Duchenne muscular dystrophy (DMD). Here, we examined the mechanisms underlying EC uncoupling in skeletal muscles from mdx52 and DMD-null/NSG mice, animal models for DMD, focusing on the SH3 and cysteine-rich domain 3 (STAC3) and junctophilin 1 (JP1), which link the dihydropyridine receptor (DHPR) in the transverse tubule and the ryanodine receptor 1 in the SR. The isometric plantarflexion torque normalized to muscle weight of whole plantar flexor muscles was depressed in mdx52 and DMD-null/NSG mice compared with their control mice. This was accompanied by increased autolysis of calpain-1, decreased levels of STAC3 and JP1 content, and dissociation of STAC3 and JP1 from DHPR-α1s in gastrocnemius muscles. Moreover, in vitro mechanistic experiments demonstrated that STAC3 and JP1 underwent Ca2+-dependent proteolysis that was less pronounced in dystrophin-deficient muscles where calpastatin, the endogenous calpain inhibitor, was upregulated. Eccentric contractions further enhanced autolysis of calpain-1 and proteolysis of STAC3 and JP1 that were associated with severe torque depression in gastrocnemius muscles from DMD-null/NSG mice. These data suggest that Ca2+-dependent proteolysis of STAC3 and JP1 may be an essential factor causing muscle weakness due to EC coupling failure in dystrophin-deficient muscles.NEW & NOTEWORTHY The mechanisms underlying the disruption of excitation-contraction (EC) coupling in dystrophin-deficient muscles are not well understood. Here, using animal models for Duchenne muscular dystrophies (DMD), we show a Ca2+-dependent protease (calpain-1)-mediated proteolysis of SH3 and cysteine-rich domain 3 (STAC3) and junctophilin 1 (JP1), essential EC coupling proteins, in dystrophin-deficient muscle, and highlighting the dissociation of STAC3 and JP1 from dihydropyridine receptor as a causative factor in EC uncoupling of dystrophic muscles.

STAC3 related congenital myopathy: A case series of seven Comorian patients.

The Bailey-Bloch congenital myopathy, also known as Native American myopathy (NAM), is an autosomal recessive congenital myopathy first reported in the Lumbee tribe people settled in North Carolina (USA), and characterized by congenital weakness and arthrogryposis, cleft palate, ptosis, short stature, kyphoscoliosis, talipes deformities, and susceptibility to malignant hyperthermia (MH) triggered by anesthesia. NAM is linked to STAC3 gene coding for a component of excitation-contraction coupling in skeletal muscles. A homozygous missense variant (c.851G > C; p.Trp284Ser) in STAC3 segregated with NAM in the Lumbee families. Non-Native American patients with STAC3 related congenital myopathy, and with other various variants of STAC3 have been reported. Here, we present seven patients from the Comoros Islands (located in the Mozambique Channel) diagnosed with STAC3 related congenital myopathy and having the recurrent variant identified in the Lumbee people. The series is the second largest series of patients having STAC3 related congenital myopathy with a shared ethnicity after le Lumbee series. Local history and geography may explain the overrepresentation of NAM in the Comorian Archipelago with a founder effect. Further researches would be necessary for the understanding of the onset of the NAM in Comorian population as search of the "classical" STAC3 variant in East African population, and haplotypes comparison between Comorian and Lumbee patients.

RpuS/R Is a Novel Two-Component Signal Transduction System That Regulates the Expression of the Pyruvate Symporter MctP in Sinorhizobium fredii NGR234.

The SLC5/STAC histidine kinases comprise a recently identified family of sensor proteins in two-component signal transduction systems (TCSTS), in which the signaling domain is fused to an SLC5 solute symporter domain through a STAC domain. Only two members of this family have been characterized experimentally, the CrbS/R system that regulates acetate utilization in Vibrio and Pseudomonas, and the CbrA/B system that regulates the utilization of histidine in Pseudomonas and glucose in Azotobacter. In an attempt to expand the characterized members of this family beyond the Gammaproteobacteria, we identified two putative TCSTS in the Alphaproteobacterium Sinorhizobium fredii NGR234 whose sensor histidine kinases belong to the SLC5/STAC family. Using reverse genetics, we were able to identify the first TCSTS as a CrbS/R homolog that is also needed for growth on acetate, while the second TCSTS, RpuS/R, is a novel system required for optimal growth on pyruvate. Using RNAseq and transcriptional fusions, we determined that in S. fredii the RpuS/R system upregulates the expression of an operon coding for the pyruvate symporter MctP when pyruvate is the sole carbon source. In addition, we identified a conserved DNA sequence motif in the putative promoter region of the mctP operon that is essential for the RpuR-mediated transcriptional activation of genes under pyruvate-utilizing conditions. Finally, we show that S. fredii mutants lacking these TCSTS are affected in nodulation, producing fewer nodules than the parent strain and at a slower rate.

Molecular interactions of STAC proteins with skeletal muscle dihydropyridine receptor and excitation-contraction coupling.

Excitation-contraction coupling (ECC) is the physiological process in which an electrical signal originating from the central nervous system is converted into muscle contraction. In skeletal muscle tissue, the key step in the molecular mechanism of ECC initiated by the muscle action potential is the cooperation between two Ca2+ channels, dihydropyridine receptor (DHPR; voltage-dependent L-type calcium channel) and ryanodine receptor 1 (RyR1). These two channels were originally postulated to communicate with each other via direct mechanical interactions; however, the molecular details of this cooperation have remained ambiguous. Recently, it has been proposed that one or more supporting proteins are in fact required for communication of DHPR with RyR1 during the ECC process. One such protein that is increasingly believed to play a role in this interaction is the SH3 and cysteine-rich domain-containing protein 3 (STAC3), which has been proposed to bind a cytosolic portion of the DHPR α1S subunit known as the II-III loop. In this work, we present direct evidence for an interaction between a small peptide sequence of the II-III loop and several residues within the SH3 domains of STAC3 as well as the neuronal isoform STAC2. Differences in this interaction between STAC3 and STAC2 suggest that STAC3 possesses distinct biophysical features that are potentially important for its physiological interactions with the II-III loop. Therefore, this work demonstrates an isoform-specific interaction between STAC3 and the II-III loop of DHPR and provides novel insights into a putative molecular mechanism behind this association in the skeletal muscle ECC process.

The First Russian Patient with Native American Myopathy.

Congenital myopathy associated with pathogenic variants in the STAC3 gene has long been considered native American myopathy (NAM). In 2017, the first case of a non-Amerindian patient with this myopathy was described. Here, we report the first Russian patient with NAM. The patient is a 17-year-old female with compound-heterozygous single nucleotide variants in the STAC3 gene: c.862A>T, p.(Lys288Ter) and c.93del, p.(Lys32ArgfsTer78). She has a milder phenotype than the earlier described patients. To our knowledge, this is the first case of a patient who had both nonsense and frameshift variants. It is assumed that the frameshift variant with premature stop codon lead to nonsense-mediated RNA decay. However, there are two additional coding isoforms of the STAC3 gene, which are not affected by this frameshift variant. We can speculate that these isoforms may partially carry out the function, and possibly explain the milder phenotype of our patient.

Usability of a Technology-Based Bystander Bullying Intervention for Middle School Students in Rural, Low-Income Communities: Mixed Methods Study.

BACKGROUND: Students who are targets of bullying and who witness bullying are at high risk for negative mental health outcomes. Bystander training is essential to reduce bullying and the negative associated consequences for targets and bystanders. Resources necessary for program delivery, however, pose significant barriers for schools, particularly those in rural, low-income communities. Technology-based programs can reduce health disparities for students in these communities through cost-effective, easy-to-disseminate programming. OBJECTIVE: The aim of this study is to conduct usability testing of a bystander bullying web app prototype, STAC-T (technology-based STAC, which stands for the 4 bystander strategies Stealing the Show, Turning it Over, Accompanying Others, and Coaching Compassion) as an initial step in the development of a full-scale STAC-T intervention. Objectives include assessing usability and acceptability of the STAC-T prototype, understanding school needs and barriers to program implementation, and assessing differences in usability between school personnel and students. METHODS: A sample of 16 participants, including school personnel and students recruited from 3 middle schools in rural, low-income communities, completed usability testing followed by a qualitative interview. Descriptive statistics, 2-tailed independent sample t tests, and consensual qualitative research were used to assess usability and program satisfaction and to extract themes related to acceptability, feasibility, needs, barriers, and feedback for intervention development. RESULTS: Usability testing indicated that the app was easy to use, acceptable, and feasible. Both school personnel (mean rating 89.6, SD 5.1) and students (mean rating 91.8, SD 7.0) rated the app well above the standard cutoff score for above-average usability (ie, 68), and both school personnel (mean rating 5.83, SD 0.41) and students (mean rating 6.10, SD 0.57) gave the app high user-friendliness ratings (0-7 scale, with 7 as high user-friendliness). The overall ratings also suggested that school personnel and students were satisfied with the program. Of the 6 school personnel who said they would recommend the program, 1 (17%), 4 (66%), and 1 (17%) rated the program as 3, 4, and 5 stars, respectively; 80% (8/10) of students said they would recommend the program; and 60% (6/10) and 40% (4/10) rated the program as 4 stars and 5 stars, respectively. Qualitative data revealed that school personnel and students found the STAC-T app to be useful, user-friendly, and relevant, while providing feedback related to the importance of digital learning activities that engage the user. Data from school personnel also indicated positive perceptions regarding program feasibility and probability of program adoption, with the most significant barrier being cost, suggesting the importance of considering the financial resources available to schools in rural, low-income communities when setting the price point for the full-scale STAC-T intervention. CONCLUSIONS: This study provides support for the full-scale development of the STAC-T app and provides key information for revision to enhance used engagement. TRIAL REGISTRATION: ClinicalTrials.gov NCT04681495; https://clinicaltrials.gov/ct2/show/NCT04681495.

Preconditioning contractions prevent prolonged force depression and Ca2+-dependent proteolysis of STAC3 after damaging eccentric contractions.

Preconditioning contractions (PCs) have been shown to markedly improve recovery from eccentric contractions (ECCs)-induced force depression. We here examined the mechanism behind the effects of PCs with focusing on the SH3 and cysteine-rich domain 3 (STAC3) that is essential for coupling membrane depolarization to Ca2+ release from the sarcoplasmic reticulum. Rat medial gastrocnemius (MG) muscles were excised immediately (REC0), 1 day (REC1), and 4 days (REC4) after exposure to 100 repeated damaging ECCs in vivo. PCs with 10 repeated nondamaging ECCs were applied 2 days before the damaging ECCs. Damaging ECCs induced in vivo isometric torque depression at 50 and 100 Hz stimulation frequencies, which was accompanied by a significant decrease in the amount of full-length STAC3, an activation of calpain 1, and an increased number of Evans Blue dye-positive fibers in MG muscles at REC1 and REC4. Interestingly, PCs attenuated all these deleterious alterations induced by damaging ECCs. Moreover, mechanistic experiments performed on normal muscle samples exposed to various concentration of Ca2+ showed a Ca2+-dependent proteolysis of STAC3, which was prevented by calpain inhibitor MDL-28170. In conclusion, PCs may improve recovery from force depression after damaging ECCs, in part by inhibiting the loss of STAC3 due to the increased permeability of cell membrane and subsequent activation of calpain 1.NEW & NOTEWORTHY The SH3 and cysteine-rich domain 3 (STAC3) is a skeletal muscle-specific protein that couples membrane depolarization to sarcoplasmic reticulum Ca2+ release. No studies, however, examined the role of STAC3 in protective effects of preconditioning contractions (PCs) against damaging eccentric contractions (ECCs). Here, we demonstrate that PCs may improve recovery from damaging ECCs-induced force depression, in part by an inhibition of Ca2+-dependent proteolysis of STAC3 due to increased membrane permeability and subsequent calpain 1 activation.