SURGICAL DRAINAGE METHODS DURING PARS PLANA VITRECTOMY FOR RHEGMATOGENOUS RETINAL DETACHMENT: A Systematic Review and Meta-Analysis.

PURPOSE: To assess efficacy and safety outcomes of subretinal fluid drainage methods during pars plana vitrectomy for rhegmatogenous retinal detachment. METHODS: A systematic search strategy was conducted for studies published between January 2000 and October 2022. Included studies reported on either the safety or efficacy of two or more drainage methods during pars plana vitrectomy for patients with rhegmatogenous retinal detachment. RESULTS: Two randomized and five observational studies consisting of 1,524 eyes were included. Best-corrected visual acuity at the last study observation and primary reattachment rates were similar across groups. A significantly lower risk of epiretinal membrane formation was associated with draining subretinal fluid through preexisting retinal breaks (risk ratio = 0.70, 95% confidence interval = [0.60, 0.83], P = <0.01, I 2 = 0%) or with perfluorocarbon liquid (risk ratios = 0.70, 95% confidence interval = [0.59, 0.83], P = <0.01, I 2 = 0%) compared with posterior retinotomy. The risk of an abnormal foveal contour was significantly greater in perfluorocarbon liquid-treated eyes relative to posterior retinotomy (risk ratios = 1.56, 95% confidence interval = [1.13, 2.17], P = <0.01, I 2 = 0%). CONCLUSION: No significant differences were observed in the final best-corrected visual acuity at the last study observation and primary reattachment rates across different drainage methods. There remains limited information on the topic, so future research is warranted.

Two-year outcomes of different subretinal fluid drainage techniques during vitrectomy for fovea-off rhegmatogenous retinal detachments: ELLIPSOID-2 Study.

BACKGROUND: The purpose of the study is to compare visual acuity, complications and outer retinal integrity following subretinal fluid (SRF) drainage from the peripheral retinal breaks (PRBs) versus posterior retinotomy (PR) versus perfluorocarbon liquid (PFCL) for macula-off rhegmatogenous retinal detachments (RRDs) at 2 years post-surgery. METHODS: Retrospective analysis of 300 consecutive patients with primary RRD undergoing 23-gauge pars plana vitrectomy with SRF drainage through (1) PRB (n=100), (2) PR (n=100) or (3) with PFCL (n=100). Primary outcomes were visual acuity (best-corrected visual acuity (BCVA)) and complications (cystoid macular oedema (CMO) and epiretinal membrane (ERM)). Secondary outcomes were discontinuity of the external limiting membrane (ELM), ellipsoid zone (EZ) and interdigitation zone (IDZ) at 2 years post-surgery. RESULTS: Mean (±SD) logMAR BCVA at 24 months was better in the PRB compared with PR and PFCL, with PFCL having the worst BCVA (PRB 0.5±0.6; PR 0.7±0.5; PFCL 0.9±0.7, p=0.001). CMO was higher with PFCL (PRB 29.7%; PR 30.2%; PFCL 45.9%, p=0.0015) and ERM formation was higher in PR (PRB 62.6%; PR 93.0%; PFCL 68.9%, p=0.002). There were no differences in ELM or EZ discontinuity. However, IDZ discontinuity was higher in PFCL (PRB 34%; PR 27%; PFCL 46%, p=0.002) at 2 years. CONCLUSIONS: Visual acuity was worse and discontinuity of the IDZ and CMO was greater in eyes with PFCL-assisted drainage compared with PRB or PR. Drainage technique may impact long-term visual acuity and photoreceptor integrity.

Toxoplasmosis chorioretinitis mimicking cytomegalovirus retinitis in an immunocompromised pediatric patient following bone marrow transplantation.

Objective: To review a case of toxoplasmosis chorioretinitis mimicking cytomegalovirus retinitis in an immunocompromised patient following bone marrow transplantation. Methods: Retrospective chart review of a 14-year-old female who had a history of leukemia and allogeneic bone marrow transplants prior to her ocular symptoms. Results: Anterior chamber fluid analysis was positive for Toxoplasma gondii. The patient responded well when cytomegalovirus retinitis treatment was switched to intravitreal clindamycin with systemic sulfadiazine and prednisone. Conclusions: This case demonstrates the challenges of diagnosing and treating retinal infections in immunocompromised patients as they may present with atypical findings that mimic other pathologies and may have contraindications against standard treatment.

Evaluation of Subretinal fluid Drainage Techniques During Pars Plana Vitrectomy for Primary Rhegmatogenous Retinal Detachment-ELLIPSOID Study.

PURPOSE: To compare visual acuity and photoreceptor integrity following pars plana vitrectomy with drainage from the peripheral retinal break(s) (PRB), posterior retinotomy (PR), or perfluorocarbon liquid (PFCL) for macula-off rhegmatogenous retinal detachment. DESIGN: Retrospective consecutive interventional comparative clinical study. METHODS: 300 consecutive patients (300 eyes) with primary macula-off rhegmatogenous retinal detachment underwent 23-gauge pars plana vitrectomy with subretinal fluid drainage through PRB (n = 100), PR (n = 100), or with PFCL (n = 100). Visual acuity and spectral-domain optical coherence tomography were performed preoperatively and at 3, 6, and 12 months postoperatively. Primary outcomes were visual acuity and discontinuity of the external limiting membrane, ellipsoid zone, interdigitation zone, and retinal pigment epithelium at 1 year. RESULTS: Baseline characteristics were similar. Single-operation reattachment rates were as follows: PRB 86%, PR 85%, and PFCL 83% (P = .9). Mean (±SD) logMAR visual acuity at 1 year was greater with PRB and PR compared with PFCL (PRB 0.6 ± 0.5, PR 0.7 ± 0.6, PFCL 0.9 ± 0.6, P = .002). There was an association between drainage technique and discontinuity of the external limiting membrane (PRB 26%, PR 24%, PFCL 44%, P = .001), ellipsoid zone (PRB 29%, PR 31%, PFCL 49%, P < .001), and interdigitation zone (PRB 43%, PR 39%, PFCL 56%, P = .004). There was an association between drainage technique and risk of cystoid macular edema (PRB 28%, PR 39%, PFCL 46%, P = .003) and epiretinal membrane (PRB 64%, PR 90%, PFCL 61%, P < .001). CONCLUSIONS: PFCL-assisted drainage is associated with worse visual acuity and greater risk of outer retinal band discontinuity and cystoid macular edema compared with PRB or PR. PR had a greater risk of epiretinal membrane compared with PRB and PFCL. PRB had the best outcomes overall. Drainage technique may impact long-term anatomic and functional outcomes.

Brain-derived neurotrophic factor is associated with human muscle satellite cell differentiation in response to muscle-damaging exercise.

Muscle satellite cell (SC) regulation is a complex process involving many key signalling molecules. Recently, the neurotrophin brain-derived neurotropic factor (BDNF) has implicated in SC regulation in animals. To date, little is known regarding the role of BDNF in human SC function in vivo. Twenty-nine males (age, 21 ± 0.5 years) participated in the study. Muscle biopsies from the thigh were obtained prior to a bout of 300 maximal eccentric contractions (Pre), and at 6 h, 24 h, 72 h, and 96 h postexercise. BDNF was not detected in any quiescent (Pax7+/MyoD-) SCs across the time-course. BDNF colocalized to 39% ± 5% of proliferating (Pax7+/MyoD+) cells at Pre, which increased to 84% ± 3% by 96 h (P < 0.05). BDNF was only detected in 13% ± 5% of differentiating (Pax7-/MyoD+) cells at Pre, which increased to 67% ± 4% by 96 h (P < 0.05). The number of myogenin+ cells increased 95% from Pre (1.6 ± 0.2 cells/100 myofibres (MF)) at 24 h (3.1 ± 0.3 cells/100 MF) and remained elevated until 96 h (cells/100 MF), P < 0.05. The proportion of BDNF+/myogenin+ cells was 26% ± 0.3% at Pre, peaking at 24 h (49% ± 3%, P < 0.05) and remained elevated at 96 h (P < 0.05). These data are the first to demonstrate an association between SC proliferation and differentiation and BDNF expression in humans in vivo, with BDNF colocalization to SCs increasing during the later stages of proliferation and early differentiation. Novelty BDNF is associated with SC response to muscle injury. BDNF was not detected in nonactivated (quiescent) SCs. BDNF is associated with late proliferation and early differentiation of SCs in vivo in humans.

Consistent expression pattern of myogenic regulatory factors in whole muscle and isolated human muscle satellite cells after eccentric contractions in humans.

Skeletal muscle satellite cells (SC) play an important role in muscle repair following injury. The regulation of SC activity is governed by myogenic regulatory factors (MRF), including MyoD, Myf5, myogenin, and MRF4. The mRNA expression of these MRF in humans following muscle damage has been predominately measured in whole muscle homogenates. Whether the temporal expression of MRF in a whole muscle homogenate reflects SC-specific expression of MRF remains largely unknown. Sixteen young men (23.1 ± 1.0 yr) performed 300 unilateral eccentric contractions (180°/s) of the knee extensors. Percutaneous muscle biopsies from the vastus lateralis were taken before (Pre) and 48 h postexercise. Fluorescence-activated cell sorting analysis was utilized to purify NCAM+ muscle SC from the whole muscle homogenate. Forty-eight hours post-eccentric exercise, MyoD, Myf5, and myogenin mRNA expression were increased in the whole muscle homogenate (~1.4-, ~4.0-, ~1.7-fold, respectively, P < 0.05) and in isolated SC (~19.3-, ~17.5-, ~58.9-fold, respectively, P < 0.05). MRF4 mRNA expression was not increased 48 h postexercise in the whole muscle homogenate (P > 0.05) or in isolated SC (P > 0.05). In conclusion, our results suggest that the directional changes in mRNA expression of the MRF in a whole muscle homogenate in response to acute eccentric exercise reflects that observed in isolated muscle SC.NEW & NOTEWORTHY The myogenic program is controlled via transcription factors referred to as myogenic regulatory factors (MRF). Previous studies have derived MRF expression from whole muscle homogenates, but little work has examined whether the mRNA expression of these transcripts reflects the pattern of expression in the actual population of satellite cells (SC). We report that MRF expression from an enriched SC population reflects the directional pattern of expression from skeletal muscle biopsy samples following eccentric contractions.

Combined branch retinal artery and branch retinal vein occlusion from a globe penetrating nail gun injury.

Background: Nail gun injuries represent a significant proportion of work-related ocular trauma. Here we report a rare case of a combined branch retinal arterial occlusion (BRAO) and branch retinal venous occlusion (BRVO) from a nail gun injury in a patient who was wearing eye protection. Case description: A 23-year-old male presented with a left globe penetrating injury from a pneumatic nail gun. The nail ricochet bypassed the patient's protective eyewear, penetrating the left globe causing multiple retinal tears and a combined BRAO and BRVO in the inferior temporal vascular arcade. The patient underwent prompt surgical repair obtaining an excellent anatomic outcome. However, the visual outcome was 20/200 OS at one and two years post injury primarily due to extensive ischemic damage of the retina. Conclusion: This case is the first to describe a combined BRAO and BRVO from a globe penetrating injury. What makes this case even rarer is that the patient was wearing eye protection at the time of the injury. Despite appropriate emergency management, rapid referral for ophthalmologist assessment, and timely surgical management of this patient, the visual outcome was poor. The vascular injury ultimately compromised a significant segment of the retina, including the macula.

Adherence to World Glaucoma Association Guidelines for Surgical Trials in the Era of Microinvasive Glaucoma Surgeries.

PURPOSE: To determine how well microinvasive glaucoma surgical (MIGS) trials conform to the World Glaucoma Association (WGA) guidelines. Lack of well-designed MIGS studies hinders meaningful evaluation of these technologies. DESIGN: Cross-sectional literature survey. METHODS: Using a predefined search strategy, the following databases were searched for comparative trials involving MIGS in the English peer-reviewed literature from January 1, 2000, through June 21, 2018: Medline, EMBASE, BIOSIS, Cochrane, and Web of Science. From the WGA guidelines, 53 outcomes were selected for evaluation: methodology (n = 31), definition of success (n = 7), ethics (n = 10), postoperative complications (n = 1), economic evaluation (n = 1), and statistical reporting (n = 3). Each article was assessed by 2 reviewers; differences were resolved by consensus. RESULTS: Twenty-five eligible publications were identified: 10 randomized controlled trials (RCTs) and 15 nonrandomized comparative trials (non-RCTs). The mean follow-up was 19.9±11.6 months (range, 6-48 months). The mean number of outcomes adhering to the WGA guidelines of the 53 evaluated was 24.2±6.1 (45.6% compliance): 28.0±6.2 (52.8%) and 21.6±4.7 (40.8%) for RCTs and non-RCTs, respectively (P = 0.01). Mean percent compliance for each subsection were: methodology, 48.8%; definition of success, 21.1%; ethics, 55.6%; postoperative complications, 88%; economic evaluation, 0%; and statistical reporting, 37.3%. In 16 studies (64%), at least 1 author reported an association with the industry. Thirty-two percent of studies reported an author being a shareholder. Twenty-four percent of studies had an industry employee author. The primary intraocular pressure (IOP) end point was defined as both an upper limit and percentage reduction in only 4 studies (16%; 1 RCT, 3 non-RCTs). An IOP-based survival curve was provided in 7 studies (28%; none of the RCTs). Two studies (8%) included an IOP scatterplot. Twelve studies (48%) reported 95% confidence intervals. Only 4 studies (16%) used the mean of 3 diurnal IOP readings as the baseline IOP. CONCLUSIONS: Published comparative MIGS trials show low adherence (45.6%) to the WGA guidelines. Development of standardized methodology and outcomes could enhance interpretation and transparency of study results and facilitate comparisons between trials. Authors and journals should be encouraged to follow the WGA guidelines.

Acute intraocular pressure responses to high-intensity interval-training protocols in men and women.

We aimed (1) to test the acute impact of two high-intensity interval-training (HIIT) protocols differing in the level of effort on intraocular pressure (IOP) responses, and (2) to elucidate whether the IOP responses differ between men and women. Twenty-four physically active collegiate (12 men and 12 women) performed three protocols: low-fatigue HIIT (eight 30-m sprints with 60-s of rest), high-fatigue HIIT (eight 30-m sprints with 30-s of rest), and control (walking). IOP was taken at baseline, after sprints and recovery by rebound tonometry. Our data revealed an acute IOP reduction during both HIIT protocols compared to the control condition (effect size [ES]:0.81-1.65). The differences between both HIIT protocols were generally negligible (ES<0.30), however, the reduction of IOP was moderately higher for the low-fatigue HIIT protocol after the 7th (ES: 0.67) and 8th (ES: 0.74) sprints. Women showed a more prominent lowering effect on IOP during the control condition (ES: 0.42-1.02), and during the two first sprints of both HIIT protocols (ES: 0.54-1.03). These findings highlight that a time-efficient HIIT protocol may acutely reduce IOP levels, while low-fatigue HIIT protocol could be recommended since it induced a higher reduction on IOP than the high-fatigue HIIT protocol.

Blunted satellite cell response is associated with dysregulated IGF-1 expression after exercise with age.

PURPOSE: Insulin-like growth factor-1 (IGF-1) regulates protein synthesis and cell cycle kinetics. Given that aging is associated with anabolic resistance, we sought to determine if the attenuated exercise-induced satellite cell (SC) expression in older muscle is associated with a blunted IGF-1 response. METHODS: SC expression (Pax7+ cells) and protein (Western blot) and mRNA (RT-PCR) expression of IGF-1 splice variants and ubiquitous (IGFBP4) and muscle-specific (IGFBP3 and -5) IGF-1 binding proteins were measured in skeletal muscle of young (Y: 22 ± 2, n = 7) and older (O: 70 ± 2, n = 7) adults up to 48 h after an acute bout of resistance exercise. RESULTS: SC expression was greater in Y compared to O (age; P < 0.01) and increased (interaction; P < 0.05) by 24 h after exercise in Y only. IGF-1Ea and IGF-1Eb mRNA tended to be greater in O (age; P < 0.06-0.09). IGF-1Eb mRNA increased at 48 h (time; P < 0.05), whereas IGF-1Ec mRNA increased (interaction; P < 0.05) at 24 and 48 h in O only. IGF binding protein (IGFBP)4 mRNA was greater (age; P < 0.01) in O with the increase at 24 h and 48 h (time; P < 0.01) primarily driven by changes in O (interaction; P < 0.01). Despite IGFBP3 mRNA being greater in O (age; P < 0.01) and increasing at 48 h (time; P < 0.01), there was no effect of age or exercise on IGFBP3 protein expression. In contrast, IGFBP5 mRNA was greater (age; P < 0.01) despite IGFBP5 protein expression being lower (age; P < 0.01) in O compared to Y. CONCLUSIONS: The greater muscle-specific expression of IGF-1 family members with a blunted post-exercise SC expression may be a compensatory attempt to rescue age-related anabolic resistance.

Skeletal Muscle Regeneration, Repair and Remodelling in Aging: The Importance of Muscle Stem Cells and Vascularization.

Sarcopenia is the age-related loss of skeletal muscle mass and strength. Ultimately, sarcopenia results in the loss of independence, which imposes a large financial burden on healthcare systems worldwide. A critical facet of sarcopenia is the diminished ability for aged muscle to regenerate, repair and remodel. Over the years, research has focused on elucidating underlying mechanisms of sarcopenia and the impaired ability of muscle to respond to stimuli with aging. Muscle-specific stem cells, termed satellite cells (SC), play an important role in maintaining muscle health throughout the lifespan. It is well established that SC are essential in skeletal muscle regeneration, and it has been hypothesized that a reduction and/or dysregulation of the SC pool, may contribute to accelerated loss of skeletal muscle mass that is observed with advancing age. The preservation of skeletal muscle tissue and its ability to respond to stimuli may be impacted by reduced SC content and impaired function observed with aging. Aging is also associated with a reduction in capillarization of skeletal muscle. We have recently demonstrated that the distance between type II fibre-associated SC and capillaries is greater in older compared to younger adults. The greater distance between SC and capillaries in older adults may contribute to the dysregulation in SC activation ultimately impairing muscle's ability to remodel and, in extreme circumstances, regenerate. This viewpoint will highlight the importance of optimal SC activation in addition to skeletal muscle capillarization to maximize the regenerative potential of skeletal muscle in older adults.

Discrepancies in physician-patient agreement in reporting ocular history.

OBJECTIVE: The purpose of this study was to investigate the extent of agreement between physicians and patients in reporting ocular history and to determine whether there are any predictive factors for physician-patient consensus. DESIGN: Retrospective chart review. PARTICIPANTS: Between June and September 2014, adult patients undergoing cataract surgery were recruited for the study. METHODS: Before surgery, patient demographics and self-reported ocular history were extracted from a prospectively collected database. Medical charts were retrospectively examined to retrieve physician-reported ocular history. RESULTS: One hundred and thirty-eight patients participated. Mean cohort logMAR visual acuity was 0.46 ± 0.34 (Snellen equivalent of approximately 20/60) and mean age was 74.1 ± 8.3 years. For glaucoma, Cohen's kappa revealed a moderate-to-good concordance between physicians and patients (κ = 0.604), whereas a poor-to-fair level of agreement existed in reporting maculopathy, such as age-related macular degeneration and macular holes (κ = 0.254). The logistic regression model revealed that preoperative visual acuity (p = 0.223), sex (p = 0.736), age (p = 0.910), and education (p = 0.738) were not significant predictors of physician-patient agreement. CONCLUSIONS: The accuracy of patient-reported ocular history varies by pathology. Self-reported glaucoma history is consistent between patients and physicians; however, patients under-report the diagnosis of maculopathy. Age, sex, and level of education do not appear to influence patient-reported accuracy of ocular comorbidities.

Satellite cells in human skeletal muscle plasticity.

Skeletal muscle satellite cells are considered to play a crucial role in muscle fiber maintenance, repair and remodeling. Our knowledge of the role of satellite cells in muscle fiber adaptation has traditionally relied on in vitro cell and in vivo animal models. Over the past decade, a genuine effort has been made to translate these results to humans under physiological conditions. Findings from in vivo human studies suggest that satellite cells play a key role in skeletal muscle fiber repair/remodeling in response to exercise. Mounting evidence indicates that aging has a profound impact on the regulation of satellite cells in human skeletal muscle. Yet, the precise role of satellite cells in the development of muscle fiber atrophy with age remains unresolved. This review seeks to integrate recent results from in vivo human studies on satellite cell function in muscle fiber repair/remodeling in the wider context of satellite cell biology whose literature is largely based on animal and cell models.

Satellite cell activity, without expansion, after nonhypertrophic stimuli.

The purpose of the present studies was to determine the effect of various nonhypertrophic exercise stimuli on satellite cell (SC) pool activity in human skeletal muscle. Previously untrained men and women (men: 29 ± 9 yr and women: 29 ± 2 yr, n = 7 each) completed 6 wk of very low-volume high-intensity sprint interval training. In a separate study, recreationally active men (n = 16) and women (n = 3) completed 6 wk of either traditional moderate-intensity continuous exercise (n = 9, 21 ± 4 yr) or low-volume sprint interval training (n = 10, 21 ± 2 yr). Muscle biopsies were obtained from the vastus lateralis before and after training. The fiber type-specific SC response to training was determined, as was the activity of the SC pool using immunofluorescent microscopy of muscle cross sections. Training did not induce hypertrophy, as assessed by muscle cross-sectional area, nor did the SC pool expand in any group. However, there was an increase in the number of active SCs after each intervention. Specifically, the number of activated (Pax7(+)/MyoD(+), P ≤ 0.05) and differentiating (Pax7(-)/MyoD(+), P ≤ 0.05) SCs increased after each training intervention. Here, we report evidence of activated and cycling SCs that may or may not contribute to exercise-induced adaptations while the SC pool remains constant after three nonhypertrophic exercise training protocols.

Reduced satellite cell number in situ in muscular contractures from children with cerebral palsy.

Satellite cells (SC) are quiescent adult muscle stem cells critical for postnatal development. Children with cerebral palsy have impaired muscular growth and develop contractures. While flow cytometry previously demonstrated a reduced SC population, extracellular matrix abnormalities may influence the cell isolation methods used, systematically isolating fewer cells from CP muscle and creating a biased result. Consequently, the purpose of this study was to use immunohistochemistry on serial muscle sections to quantify SC in situ. Serial cross-sections from human gracilis muscle biopsies (n = 11) were labeled with fluorescent antibodies for Pax7 (SC transcriptional marker), laminin (basal lamina), and 4',6-diamidino-2-phenylindole (nuclei). Fluorescence microscopy under high magnification was used to identify SC based on labeling and location. Mean SC/100 myofibers was reduced by ∼70% (p < 0.001) in children with CP (2.89 ± 0.39) compared to TD children (8.77 ± 0.79). Furthermore, SC distribution across fields was different (p < 0.05) with increased percentage of SC in fields being solitary cells (p < 0.01) in children with CP. Quantification of SC number in situ, without any other tissue manipulation confirms children with spastic CP have a reduced number. This stem cell loss may, in part, explain impaired muscle growth and apparent decreased responsiveness of CP muscle to exercise.

Effects of age and unaccustomed resistance exercise on mitochondrial transcript and protein abundance in skeletal muscle of men.

Mitochondrial dysfunction may contribute to age-associated muscle atrophy. Previous data has shown that resistance exercise (RE) increases mitochondrial gene expression and enzyme activity in older adults; however, the acute response to RE has not been well characterized. To characterize the acute mitochondrial response to unaccustomed RE, healthy young (21 ± 3 yr) and older (70 ± 4 yr) men performed a unilateral RE bout for the knee extensors. Muscle biopsies were taken at rest and 3, 24, and 48 h following leg press and knee extension exercise. The expression of the mitochondrial transcriptional regulator proliferator-activated receptor γ coactivator 1-α (PGC-1α) mRNA was increased at 3 h postexercise; however, all other mitochondrial variables decreased over the postexercise period, irrespective of age. ND1, ND4, and citrate synthase (CS) mRNA were all lower at 48 h postexercise, along with specific protein subunits of complex II, III, IV, and ATP synthase. Mitochondrial DNA (mtDNA) copy number decreased by 48 h postexercise, and mtDNA deletions were higher in the older adults and remained unaffected by acute exercise. Elevated mitophagy could not explain the reduction in mitochondrial proteins and DNA, because there was no increase in ubiquitinated voltage-dependent anion channel (VDAC) or its association with PTEN-induced putative kinase 1 (Pink1) or Parkin, and elevated p62 content indicated an impairment or reduction in autophagocytic flux. In conclusion, age did not influence the response of specific mitochondrial transcripts, proteins, and DNA to a bout of RE.

The acute satellite cell response and skeletal muscle hypertrophy following resistance training.

The extent of skeletal muscle hypertrophy in response to resistance training is highly variable in humans. The main objective of this study was to explain the nature of this variability. More specifically, we focused on the myogenic stem cell population, the satellite cell (SC) as a potential mediator of hypertrophy. Twenty-three males (aged 18-35 yrs) participated in 16 wk of progressive, whole body resistance training, resulting in changes of 7.9±1.6% (range of -1.9-24.7%) and 21.0±4.0% (range of -7.0 to 51.7%) in quadriceps volume and myofibre cross-sectional area (CSA), respectively. The SC response to a single bout of resistance exercise (80% 1RM), analyzed via immunofluorescent staining resulted in an expansion of type II fibre associated SC 72 h following exercise (pre: 11.3±0.9; 72 h: 14.8±1.4 SC/type II fibre; p<0.05). Training resulted in an expansion of the SC pool associated with type I (pre: 10.7±1.1; post: 12.1±1.2 SC/type I fibre; p<0.05) and type II fibres (pre: 11.3±0.9; post: 13.0±1.2 SC/type II fibre; p<0.05). Analysis of individual SC responses revealed a correlation between the relative change in type I associated SC 24 to 72 hours following an acute bout of resistance exercise and the percentage increase in quadriceps lean tissue mass assessed by MRI (r2 = 0.566, p = 0.012) and the relative change in type II associated SC following 16 weeks of resistance training and the percentage increase in quadriceps lean tissue mass assessed by MRI (r2 = 0.493, p = 0.027). Our results suggest that the SC response to resistance exercise is related to the extent of muscular hypertrophy induced by training.

The skeletal muscle satellite cell response to a single bout of resistance-type exercise is delayed with aging in men.

Skeletal muscle satellite cells (SCs) have been shown to be instrumental in the muscle adaptive response to exercise. The present study determines age-related differences in SC content and activation status following a single bout of exercise. Ten young (22 ± 1 years) and 10 elderly (73 ± 1 years) men performed a single bout of resistance-type exercise. Muscle biopsies were collected before and 12, 24, 48, and 72 h after exercise. SC content and activation status were assessed in type I and type II muscle fibers by immunohistochemistry. Myostatin and MyoD protein and messenger RNA (mRNA) expression were determined by Western blotting and rtPCR, respectively. In response to exercise, it took 48 h (young) and 72 h (elderly) for type II muscle fiber SC content to exceed baseline values (P < 0.01). The number of myostatin + SC in type I and II muscle fibers was significantly reduced after 12, 24, and 48 h of post-exercise recovery in both groups (P < 0.01), with a greater reduction observed at 24 and 48 h in the young compared with that in the elderly men (P < 0.01). In conclusion, the increase in type II muscle fiber SC content during post-exercise recovery is delayed with aging and is accompanied by a blunted SC activation response.