The effect of estrogen on ovine anterior cruciate ligament fibroblasts: cell proliferation and collagen synthesis

A New Culture Model for Enhancing Estrogen Responsiveness in HR+ Breast Cancer Cells through Medium Replacement: Presumed Involvement of Autocrine Factors in Estrogen Resistance

Hormone receptor-positive breast cancer (HR+ BC) cells depend on estrogen and its receptor, ER. Due to this dependence, endocrine therapy (ET) such as aromatase inhibitor (AI) treatment is now possible. However, ET resistance (ET-R) occurs frequently and is a priority in HR+ BC research. The effects of estrogen have typically been determined under a special culture condition, i.e., phenol red-free media supplemented with dextran-coated charcoal-stripped fetal bovine serum (CS-FBS). However, CS-FBS has some limitations, such as not being fully defined or ordinary. Therefore, we attempted to find new experimental conditions and related mechanisms to improve cellular estrogen responsiveness based on the standard culture medium supplemented with normal FBS and phenol red. The hypothesis of pleiotropic estrogen effects led to the discovery that T47D cells respond well to estrogen under low cell density and medium replacement. These conditions made ET less effective there. The fact that several BC cell culture supernatants reversed these findings implies that housekeeping autocrine factors regulate estrogen and ET responsiveness. Results reproduced in T47D subclone and MCF-7 cells highlight that these phenomena are general among HR+ BC cells. Our findings offer not only new insights into ET-R but also a new experimental model for future ET-R studies.

Mechano Growth Factor Accelerates ACL Repair and Improves Cell Mobility of Mechanically Injured Human ACL Fibroblasts by Targeting Rac1-PAK1/2 and RhoA-ROCK1 Pathways

Exceeded mechanical stress leads to a sublethal injury to anterior cruciate ligament (ACL) fibroblasts, and it will hinder cell mobility and ACL regeneration, and even induce osteoarthritis. The mechano growth factor (MGF) could be responsible for mechanical stress and weakening its negative effects on cell physiological behaviors. In this study, effects of MGF on cell mobility and relevant molecules expression in injured ACL fibroblasts were detected. After an injurious mechanical stretch, the analysis carried out, at 0 and 24 h, respectively, showed that the cell area, roundness, migration, and adhesion of ACL fibroblasts were reduced. MGF (10, 100 ng/mL) treatment could improve cell area, roundness and promote cell migration and adhesion capacity compared with the injured group without MGF. Further study indicated that cell mobility-relevant molecules (PAK1/2, Cdc42, Rac1, RhoA, and ROCK1) expression in ACL fibroblasts was down-regulated at 0 or 24 h after injurious stretch (except Rac1 and RhoA at 0 h). Similarly, MGF improved cell mobility-relevant molecule expression, especially the ROCK1 expression level in ACL fibroblasts at 0 or 24 h after injurious stretch. Protein expression of ROCK1 in injured ACL fibroblasts was also reduced and could be recovered by MGF treatment. In a rabbit partial ACL transection (ACLT) model, ACL exhibited poor regenerative capacity in collagen and extracellular matrix (ECM) synthesis after partial ACLT for 2 or 4 weeks, and MGF remarkably accelerated ACL regeneration and restored its mechanical loading capacity after partial ACLT for four weeks. Our findings suggest that MGF weakens the effects of pathological stress on cell mobility of ACL fibroblasts and accelerates ACL repair, and might be applied as a future treatment approach to ACL rupture in the clinic.

Supraspinatus Tendons Have Different Mechanical Properties Across Sex

Sex differences in the mechanical properties of different musculoskeletal tissues and their impact on tendon function and disease are becoming increasingly recognized. Tendon mechanical properties are influenced by the presence or absence of sex hormones and these effects appear to be tendon- or ligament-specific. The objective of this study was to determine how sex and hormone differences in rats affect supraspinatus tendon and muscle properties. We hypothesized that male supraspinatus tendons would have increased cross-sectional area but no differences in tendon material properties or muscle composition when compared to supraspinatus tendons from female or ovariectomized (OVX) female rats. Uninjured supraspinatus tendons and muscles from male, female, and OVX female rats were collected and mechanical and histological properties were determined. Our analysis demonstrated decreased dynamic modulus and increased hysteresis and cross-sectional area in male tendons. We found that male tendons exhibited decreased dynamic modulus (during low strain frequency sweep and high strain fatigue loading), increased hysteresis, and increased cross-sectional area compared to female and OVX female tendons. Despite robust mechanical differences, tendon cell density and shape, and muscle composition remained unchanged between groups. Interestingly, these differences were unique compared to previously reported sex differences in rat Achilles tendons, which further supports the concept that the effect of sex on tendon varies anatomically. These differences may partially provide a mechanistic explanation for the increased rate of acute supraspinatus tendon ruptures seen in young males.

Effect of Estrogen on Musculoskeletal Performance and Injury Risk

Estrogen has a dramatic effect on musculoskeletal function. Beyond the known relationship between estrogen and bone, it directly affects the structure and function of other musculoskeletal tissues such as muscle, tendon, and ligament. In these other musculoskeletal tissues, estrogen improves muscle mass and strength, and increases the collagen content of connective tissues. However, unlike bone and muscle where estrogen improves function, in tendons and ligaments estrogen decreases stiffness, and this directly affects performance and injury rates. High estrogen levels can decrease power and performance and make women more prone for catastrophic ligament injury. The goal of the current work is to review the research that forms the basis of our understanding how estrogen affects muscle, tendon, and ligament and how hormonal manipulation can be used to optimize performance and promote female participation in an active lifestyle at any age.

Presynaptic inhibition decreases when estrogen level rises

The objective was to determine estrogen's influence on control of a skeletal muscle through measurements of motorneuron excitability (H:M ratio) and presynaptic inhibition (PI). Estrogen serum concentrations were measured at menses and ovulation of female subjects and compared to male controls. Data were analyzed from 12 women and 13 men reporting no history of knee ligament injury. Women reported regular menstrual cycles and no hormone-based contraceptive use for the previous year. Women were tested at menses (Time1) and ovulation (Time2). Men were tested twice, approximately 14 days apart. Analysis indicated no difference in the H:M ratio between the sexes at either time point. A significant difference for the sexes was detected in the magnitude of estrogen change (∆EST) between observations. At Time1, the male and female estrogen concentrations were not different; however, they were different at Time2, primarily due to the large rise observed in the women. A significant difference between the sexes was also seen in the magnitude of change for PI (∆PI) between observations. As with EST, the levels of PI between the sexes at Time1 were not different; however, a difference existed at Time 2. Estrogen interacts with GABA at several nervous system locations affecting inhibition of synaptic transmission. This is the first study to investigate changes in PI of a skeletal muscle between times of low and high estrogen. Improving the understanding of estrogen's influence on skeletal muscles may provide answers to why noncontact anterior cruciate ligament injuries of the knee occur more frequently in women.

Estrogen inhibits lysyl oxidase and decreases mechanical function in engineered ligaments

Women are more likely to suffer an anterior cruciate ligament (ACL) rupture than men, and the incidence of ACL rupture in women rises with increasing estrogen levels. We used an engineered ligament model to determine how an acute rise in estrogen decreases the mechanical properties of ligaments. Using fibroblasts isolated from human ACLs from male or female donors, we engineered ligaments and determined that ligaments made from female ACL cells had more collagen and were equal in strength to those made from male ACL cells. We then treated engineered ligaments for 14 days with low (5 pg/ml), medium (50 pg/ml), or high (500 pg/ml) estrogen, corresponding to the range of in vivo serum estrogen concentrations and found that collagen within the grafts increased without a commensurate increase in mechanical strength. Mimicking the menstrual cycle, with 12 days of low estrogen followed by 2 days of physiologically high estrogen, resulted in a decrease in engineered ligament mechanical function with no change in the amount of collagen in the graft. The decrease in mechanical stiffness corresponded with a 61.7 and 76.9% decrease in the activity of collagen cross-linker lysyl oxidase with 24 and 48 h of high estrogen, respectively. Similarly, grafts treated with the lysyl oxidase inhibitor β-aminoproprionitrile (BAPN) for 24 h showed a significant decrease in ligament mechanical strength [control (CON) = 1.58 ± 0.06 N; BAPN = 1.06 ± 0.13 N] and stiffness (CON = 7.7 ± 0.46 MPa; BAPN = 6.1 ± 0.71 MPa) without changing overall collagen levels (CON = 396 ± 11.5 μg; BAPN = 382 ± 11.6 μg). Together, these data suggest that the rise in estrogen during the follicular phase decreases lysyl oxidase activity in our engineered ligament model and if this occurs in vivo may decrease the stiffness of ligaments and contribute to the elevated rate of ACL rupture in women.

Is the use of oral contraceptives associated with operatively treated anterior cruciate ligament injury? A case-control study from the Danish Knee Ligament Reconstruction Registry

BACKGROUND

The incidence of anterior cruciate ligament (ACL) injuries is 2 to 9 times higher in women than in men. In addition, in vitro studies have demonstrated that ACL is an estrogen target tissue, and some studies have therefore suggested a protective association between oral contraceptives (OC) and the likelihood of sustaining ACL injury.

HYPOTHESIS

There is a protective association between OC use and the likelihood of operatively treated ACL injury.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

The study population included 4497 women with an operatively treated ACL injury registered in the Danish Knee Ligament Reconstruction Registry for the 2005 to 2011 period and 8858 age-matched controls with no ACL injury. The study evaluated exposure to OC use at the time of ACL injury (index date) and in the 5 previous years ("ever user") or no OC use ("never user"). Ever users were further classified as either new users (patients who redeemed their first prescription within the first year before the index date), long-term users (redeemed additional prescriptions 1 to 5 years before the index date), or recent users (redeemed their most recent prescription >1 year before the index date). Finally, a dose-response analysis of OC use was performed. Conditional logistic regression was used to calculate the relative risk (RR) with a 95% CI of sustaining an operatively treated ACL injury according to OC use.

RESULTS

The adjusted RR associating OC with ACL injury was 0.82 (95% CI, 0.75-0.90) between ever users and never users. Furthermore, there was a decreased RR of sustaining ACL injury of 0.80 (95% CI, 0.74-0.91) in long-term users and 0.81 (95% CI, 0.72-0.89) in recent users. Using OC for more than 4 years did not seem to alter the likelihood of sustaining an operatively treated ACL injury.

CONCLUSION

This population-based pharmacoepidemiological study including 13,355 women indicates that a protective association exists between OC use and the likelihood of sustaining an operatively treated ACL injury. Although this study does indicate a protective association of OC use, OC should not be used as a prophylactic measure before additional clinical studies have further clarified the biological and causal association between OC use and the likelihood of sustaining operatively treated ACL injury.

Prevalence of and risk factors for asymptomatic rotator cuff tears in postmenopausal women

OBJECTIVE

Rotator cuff tendon tears increase with age, but no study has specifically addressed prevalence changes in women from premenopause to postmenopause. The aims of this study were to evaluate the prevalence of rotator cuff asymptomatic tears in postmenopausal women and to study their relationship with anthropometric and metabolic measures.

METHODS

Premenopausal and postmenopausal women who were free from shoulder pain/functional impairment were enrolled. Body mass index (BMI), fasting glucose, triglycerides, total cholesterol, and high-density lipoprotein (HDL) cholesterol were evaluated. Both shoulders were examined by ultrasound imaging. For the purposes of this study, only full-thickness tears (classified as small, large, or massive) were taken into account.

RESULTS

The prevalence of full-thickness tears (mainly localized in the supraspinatus tendon of the dominant side) was significantly higher in the postmenopausal group (8.9% vs 3.1%), with small, medium, and large tears in 60%, 20%, and 20% of cases, respectively. In women with tears, intragroup comparison showed significantly higher values for BMI and fasting glucose, and lower levels of HDL cholesterol; no difference was found for triglycerides and total cholesterol in premenopausal and postmenopausal women, respectively. On multiple logistic regression analysis, the probability of detecting a tear in both groups was positively related to high values of BMI and lower levels of HDL cholesterol.

CONCLUSIONS

The prevalence of asymptomatic full-thickness tears is increased in the postmenopausal period, and there is an association between tears and metabolic disorders. Because asymptomatic tears have a great potential to evolve into symptomatic painful shoulder, a precocious discovery of this pathology may allow the planning of preventive and therapeutic measures.

Medial tibiofemoral-joint stiffness in males and females across the lifespan

CONTEXT

Analyzing ligament stiffness between males and females at 3 maturational stages across the lifespan may provide insight into whether changes in ligament behavior with aging may contribute to joint laxity.

OBJECTIVE

To compare the stiffness of the medial structures of the tibiofemoral joint and the medial collateral ligament to determine if there are differences at 3 distinct ages and between the sexes.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 108 healthy and physically active volunteers with no previous knee surgery, no acute knee injury, and no use of exogenous hormones in the past 6 months participated. They were divided into 6 groups based on sex and age (8-10, 18-40, 50-75 years).

MAIN OUTCOME MEASURE(S)

Ligament stiffness of the tibiofemoral joint was measured with an arthrometer in 0° and 20° of tibiofemoral-joint flexion. The slope values of the force-strain line that represents stiffness of the medial tibiofemoral joint at 0° and the medial collateral ligament at 20° of flexion were obtained.

RESULTS

When height and mass were controlled, we found a main effect (P < .001) for age group: the 8- to 10-year olds were less stiff than both the 18- to 40- and the 50- to 75-year-old groups. No effects of sex or tibiofemoral-joint position on stiffness measures were noted when height and mass were included as covariates.

CONCLUSIONS

Prepubescent medial tibiofemoral-joint stiffness was less than postpubescent knee stiffness. Medial tibiofemoral-joint stiffness was related to height and mass after puberty in men and women.

Impact of oral contraceptive use and menstrual phases on patellar tendon morphology, biochemical composition, and biomechanical properties in female athletes

Sex differences exist with regards to ligament and tendon injuries. Lower collagen synthesis has been observed in exercising women vs. men, and in users of oral contraceptives (OC) vs. nonusers, but it is unknown if OC will influence tendon biomechanics of women undergoing regular training. Thirty female athletes (handball players, 18-30 yr) were recruited: 15 long-term users of OC (7.0 ± 0.6 yr) and 15 nonusers (>5 yr). Synchronized values of patellar tendon elongation (obtained by ultrasonography) and tendon force were sampled during ramped isometric knee extensor maximum voluntary contraction to estimate mechanical tendon properties. Furthermore, tendon cross-sectional area and length were measured from MRI images, and tendon biopsies were obtained for analysis of tendon fibril characteristics and collagen cross-linking. Overall, no difference in tendon biomechanical properties, tendon fibril characteristics, or collagen cross-linking was observed between the OC users and nonusers, or between the different phases of the menstrual cycle. In athletes, tendon cross-sectional area in the preferred jumping leg tended to be larger than that in the contralateral leg (P = 0.09), and a greater absolute (P = 0.01) and normalized tendon stiffness (P = 0.02), as well as a lower strain (P = 0.04), were observed in the jumping leg compared with the contralateral leg. The results indicate that long-term OC use or menstrual phases does not influence structure or mechanical properties of the patellar tendon in female team handball athletes.

Changes in serum collagen markers, IGF-I, and knee joint laxity across the menstrual cycle

Variations in serum markers of collagen production (CICP) and degradation (ICTP), insulin-like growth factor I (IGF-I) and anterior knee laxity (AKL) were measured in 20 women [10 with spontaneous cycles (eumenorrheic), 10 using oral contraceptives] over 5 consecutive days at menses (M1-M5, 1st pill week), the initial estrogen rise near ovulation (O1-O5, 2nd pill week), the initial progesterone rise of the early luteal phase (EL1-EL5, 3rd pill week) and post-progesterone peak of the late luteal phase (LL1-LL5, 4th pill week). ICTP was higher in oral contraceptive women (5.3 ± 1.7 vs. 3.7 ± 1.3 µg/L; p = 0.030), primarily during days near ovulation and the early luteal phase when concentrations decreased in eumenorrheic women (p = 0.04). IGF-I concentrations increased during menses then decreased and remained lower during the early and late luteal phase in oral contraceptive women, resulting in lower concentrations compared to eumenorrheic women at EL2 and LL1 (p = 0.03). CICP decreased in early and late luteal days (p <0.01), and there was a trend toward lower concentrations in eumenorrheic versus oral contraceptive women (85.7 ± 35.7 ng/ml vs. 123.2 ± 49.8 ng/ml; p = 0.07). Lower CICP and greater IGF-I concentrations predicted greater AKL across the 20 cycle days in both groups (R(2)  = 0.310 and 0.400). Sex hormone concentration changes across the menstrual cycle are of sufficient magnitude to influence collagen metabolism, and may indirectly influence knee structure and function.

The soy isoflavone genistein inhibits the reduction in Achilles tendon collagen content induced by ovariectomy in rats

The objective of this study was to evaluate the effects of genistein and moderate intensity exercise on Achilles tendon collagen and cross-linking in intact and ovariectomized (OVX) female Sprague-Dawley rats. Rats were separated into eight groups (n = 9/group): intact or OVX, treadmill exercised or sedentary, genistein-treated (300 mg/kg/day) or vehicle. After 6 weeks, tendons were assayed for the collagen-specific amino acid hydroxyproline and hydroxylyslpyridinoline (HP). Collagen content was not influenced by exercise (P = 0.40) but was lower (P < 0.001) in OVX-vehicle rats compared with intact vehicle rats (OVX: 894 ± 35 μg collagen/mg dry weight; intact: 1185 ± 72 μg collagen/mg dry weight). In contrast, collagen content in OVX rats treated with genistein was greater (P = 0.010, 1198 ± 121 μg collagen/mg dry weight) when compared with untreated rats and was not different from intact rats (P = 0.89). HP content was lower in OVX genistein-treated rats when compared with intact genistein-treated rats, but only within the sedentary animals (P = 0.05, intact-treated: 232 ± 39 mmol/mol collagen; OVX-treated: 144 ± 21 mmol/mol collagen). Our findings suggest that ovariectomy leads to a reduction in tendon collagen, which is prevented by genistein. HP content, however, may not have increased in proportion to the addition of collagen. Genistein may be useful for improving tendon collagen content in conditions of estrogen deficiency.

Gender and eccentric training in Achilles mid-portion tendinopathy

The role of gender in Achilles tendinopathy is yet to be determined. We hypothesized that female patients respond the same as males to 12 weeks of painful eccentric training. A total number of 75 consecutive mid-portion patients with Achilles tendinopathy (25 females, 38 males) were enrolled in a cohort study with 63 being analyzed after 12 weeks according to their gender for tendon and paratendon microcirculatory mapping. Outcome was determined by pain on visual analogue scale, VISA-A score, Foot Ankle Outcome Score (FAOS), tendon and paratendon capillary blood flow, oxygen saturation, and postcapillary venous filling pressures. Eccentric training resulted in a morning resting pain reduction by 44% in males (P = 0.001) and by 27% in females (P = 0.08). VISA-A score improved in males by 27% from 63 +/- 12 to 86 +/- 13 (P = 0.036) and by 20% in females from 60 +/- 14 to 75 +/- 11 (P = 0.043, P < 0.05 for gender difference). Among females, only one out of five FAOS items was increased (sport 72 +/- 21 to 82 +/- 15, P = 0.045), while in males, four out of five items were increased (symptoms, pain, all-day-life, and sport, all P < 0.01). The microcirculatory gender-specific response to eccentric training revealed a greater postcapillary venous filling pressure reduction among symptomatic females and inconclusive capillary blood flow changes. No change in tendon oxygenation was noted in both genders. Symptomatic females suffering Achilles tendinopathy do not benefit as much as symptomatic males from 12 weeks of eccentric training. The pain reduction is significantly lower among symptomatic females in contrast to males, and the improvement in the FAOS and VISA-A scores is significantly lower among females in contrast to males. Additional treatment options warrant scrutiny to symptomatic females suffering Achilles tendinopathy beyond eccentric training.

Biomechanical and histological comparison of the influence of oestrogen deficient state on tendon healing potential in rats

Thirty-six female Sprague-Dawley rats were divided into two groups: oophrectomised (oestrogen deficient) rats and sham operated (oestrogen maintained) rats. Rats were sacrificed at six, ten, and 14 weeks. The rats were randomly chosen to have biomechanical evaluation on one side and histological evaluation on the other. Biomechanical testing was performed on an Instron machine to measure peak load. Histological sections were evaluated for cell proliferation, collagen-fibre organisation, fibroblast density, angiogenesis, inflammatory cells, chondroid and osseous metaplasia. Compared with the sham operated group, the oophrectomised group showed a lesser average maximum stress (42.9 N/m(2) versus 33.7 N/m(2)) at six weeks, which was significant (p < .05). Succeeding weeks showed no significant biomechanical differences between the two groups. The sham operated group showed greater inflammatory response, which was statistically significant (p < 0.05), and also revealed greater cell proliferation and density. The results of this study revealed that endogenous oestrogen may improve healing of the Achilles tendon in rats.

Effect of estrogen on tendon collagen synthesis, tendon structural characteristics, and biomechanical properties in postmenopausal women

The knowledge about the effect of estradiol on tendon connective tissue is limited. Therefore, we studied the influence of estradiol on tendon synthesis, structure, and biomechanical properties in postmenopausal women. Nonusers (control, n = 10) or habitual users of oral estradiol replacement therapy (ERT, n = 10) were studied at rest and in response to one-legged resistance exercise. Synthesis of tendon collagen was determined by stable isotope incorporation [fractional synthesis rate (FSR)] and microdialysis technique (NH2-terminal propeptide of type I collagen synthesis). Tendon area and fibril characteristics were determined by MRI and transmission electron microscopy, whereas tendon biomechanical properties were measured during isometric maximal voluntary contraction by ultrasound recording. Tendon FSR was markedly higher in ERT users ( P < 0.001), whereas no group difference was seen in tendon NH2-terminal propeptide of type I collagen synthesis ( P = 0.32). In ERT users, positive correlations between serum estradiol (s-estradiol) and tendon synthesis were observed, whereas change in tendon synthesis from rest to exercise was negatively correlated to s-estradiol. Tendon area, fibril density, fibril volume fraction, and fibril mean area did not differ between groups. However, the percentage of medium-sized fibrils was higher in ERT users ( P < 0.05), whereas the percentage of large fibrils tended to be greater in control ( P = 0.10). A lower Young's modulus (GPa/%) was found in ERT users ( P < 0.05). In conclusion, estradiol administration was associated with higher tendon FSR and a higher relative number of smaller fibrils. Whereas this indicates stimulated collagen turnover in the resting state, collagen responses to exercise were negatively associated with s-estradiol. These results indicate a pivotal role for estradiol in maintaining homeostasis of female connective tissue.

The interrelationships among sex hormone concentrations, motoneuron excitability, and anterior tibial displacement in women and men

CONTEXT

Sex hormone fluctuations have been implicated as a contributing factor to the high rates of noncontact injury to the anterior cruciate ligament in females.

OBJECTIVE

To determine the strength of the relationships among variables of sex hormone concentrations, motoneuron excitability, and anterior tibial displacement (ATD) in women and men and to determine if these relationships differ between the sexes.

DESIGN

Cohort study.

SETTING

Sports medicine laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty-eight regularly menstruating women (age = 22.4 +/- 3.4 years) and 15 men (age = 22.3 +/- 3.7 years) participated in the study.

INTERVENTION(S)

Fluctuations in sex hormones were determined for the participants. Female participants were tested every other day of their menstrual cycles, whereas male participants were tested every fourth day during the 28-day period.

MAIN OUTCOME MEASURE(S)

We measured Hoffmann reflexes (maximum Hoffmann reflex [H(max)] to maximum M-wave [M(max)] ratio in the soleus), ATD under a 134-N load, and saliva concentrations of estrogen and progesterone. The independent variable was sex. Pearson product moment correlation coefficients were calculated for each participant by pairing measurements made on the same day. Two-tailed independent-samples t tests were used to determine the difference between the male and female correlations for each variable.

RESULTS

Over the course of the study, the relationships between H(max)ratioM(max) and estrogen, H(max)ratioM(max) and progesterone, ATD and estrogen, and ATD and progesterone were not different between the sexes. However, the relationship between ATD and progesterone was different between the sexes (P = .036).

CONCLUSIONS

The observed correlations did not support our hypothesis that the relationships between sex hormone levels and reflex activity or between sex hormone levels and ATD would be different for women compared with men. If sex hormone concentrations significantly contribute to anterior cruciate ligament ruptures because of changes in laxity or in motoneuron excitability, their mechanism of action is likely multifactorial and complex.

Effect of administration of oral contraceptives in vivo on collagen synthesis in tendon and muscle connective tissue in young women

Women are at greater risk than men for certain kinds of diseases and injuries, which may at least partly be caused by sex hormonal differences. We aimed to test the influence of estradiol in vivo on collagen synthesis in tendon, bone, and muscle. Two groups of young, healthy women similar in age, body composition, and exercise-training status were included. The two groups were either habitual users of oral contraceptives exposed to a high concentration of synthetic estradiol and progestogens (OC, n = 11), or non-OC-users tested in the follicular phase of the menstrual cycle characterized by low concentrations of estradiol and progesterone (control, n = 12). Subjects performed 1 h of one-legged kicking exercise. The next day collagen fractional synthesis rates (FSR) in tendon and muscle connective tissue were measured after a flooding dose of [(13)C]proline followed by biopsies from the patellar tendon and vastus lateralis in both legs. Simultaneously, microdialysis catheters were inserted in vastus lateralis and in front of the patellar tendon for measurement of insulin-like growth factor I (IGF-I) and its binding proteins. Serum NH(2)-terminal propeptide of type I collagen (PINP) and urine COOH-terminal telopeptides of type-I collagen (CTX-I) were measured as markers for bone synthesis and breakdown, respectively. Tendon FSR and PINP were lower in OC compared with control. An increase in muscle collagen FSR postexercise was only observed in control (P < 0.05). Furthermore, the results indicate a lower bioavailability of IGF-I in OC. In conclusion, synthetic female sex hormones administered as OC had an inhibiting effect on collagen synthesis in tendon, bone, and muscle connective tissue, which may be related to a lower bioavailability of IGF-I.

Superior Achilles tendon microcirculation in tendinopathy among symptomatic female versus male patients

BACKGROUND

Higher estrogen levels in women seem to play a role regarding an increased ligament and tendon injury rate among women. However, gender differences of tendon microcirculation have not yet been reported.

HYPOTHESIS

Female patients suffering Achilles tendinopathy have worse tendon and paratendon microcirculation than symptomatic male patients.

STUDY DESIGN

Cross-sectional study; Level of evidence, 2.

METHODS

A total of 139 Achilles tendinopathy patients (58 women, 81 men) were analyzed according to their gender for tendon and paratendon microcirculation by mapping at 12 positions (4 tendons, 8 paratendons) in each limb. Tendon and paratendon capillary blood flow, oxygen saturation, and postcapillary venous filling pressures were measured at 2-mm and 8-mm tissue depths.

RESULTS

Symptomatic women had similarly elevated tendon capillary blood flow as men at 4 Achilles tendon positions. However, distal medial (83 +/- 40 vs 105 +/- 74, P < .05) and lateral (98 +/- 49 vs 121 +/- 74) paratendon capillary blood flow were significantly lower among men. Symptomatic female patients had superior tendon and paratendon oxygen saturation at 11 of 12 positions (P < .05) as well as reduced postcapillary venous filling pressures at the proximal midportion tendon (55 +/- 17 vs 63 +/- 20, P < .05) and paratendon (69 +/- 19 vs 77 +/- 26) location. Pain level was not different between female (5.3 +/- 2.2) and male patients (5.4 +/- 2, P = .864). Female patients had significantly higher Foot and Ankle Outcome Sports Scores (71 +/- 22 vs 64 +/- 23 in the men, P = .041), while 4 out of 5 other Foot and Ankle Outcome Score items were not different.

CONCLUSION

Symptomatic female patients have similarly elevated tendon capillary blood flow compared with symptomatic male patients suffering Achilles tendinopathy, but superior tendon and paratendon oxygen saturations and reduced postcapillary venous filling pressures indicate better tendon and paratendon Achilles tendon microcirculation in women.

ACL Tears in Female Athletes

With the growing number of female athletes, an increase is occurring in the number of sports-related injuries, which can cause physical, psychological, academic, and financial suffering. Female athletes are reported to be two to eight times more likely to sustain an anterior cruciate ligament (ACL) injury than male athletes. Further research on risk factors and preventative strategies for the female ACL is needed, because the cause of the disparity in injury rates remains equivocal and controversial. Individualized treatment for the injured knee is necessary and can include either conservative treatment or reconstructive surgery.

Quantitation of estrogen receptors and relaxin binding in human anterior cruciate ligament fibroblasts

The significantly higher incidence of anterior cruciate ligament (ACL) injuries in collegiate women compared with men may result from relative ligament laxity. Differences in estrogen and relaxin activity, similar to that seen in pregnancy, may account for this. We quantified estrogen receptors by flow cytometry and relaxin receptors by radioligand binding assay in human ACL cells and compared the presence of these receptors in males and females. ACL stumps were harvested from seven males and eight females with acute ACL injuries. The tissue was placed in M199 cell culture medium. Outgrowth cultures were obtained, and passage 2 cells were used for all studies. Estrogen receptor determination was performed using flow cytometry. Relaxin binding was performed in ACL cells derived from five female and male patients using I(125)-labeled relaxin. Estrogen receptors were identified by flow cytometry in 4 to 10% of ACL cells. Mean fluorescence of cells expressing estrogen receptors was approximately twice that of controls, with no significant differences between males and females. Relaxin studies showed low-level binding of I(125)-relaxin-labeled ACL cells. Relaxin binding was present in four out of five female ACL cells versus one out of five male ACL cells.

Anterior cruciate ligament biology and its relationship to injury forces

Anterior cruciate ligament injury is determined by two variables: the ultimate failure load of the ligament and the mechanical load applied to the ligament. All factors that contribute to anterior cruciate ligament injury must do so by affecting one or both of these two basic variables. Some factors, such as sex hormones and tissue remodeling, have a multifaceted effect on the failure load of the anterior cruciate ligament and the magnitude of the load applied to it. The model also illustrates the potentially profound effects that sex hormones and tissue remodeling likely have on female susceptibility to anterior cruciate ligament injuries.

Understanding and preventing noncontact anterior cruciate ligament injuries: a review of the Hunt Valley II meeting, January 2005

The incidence of noncontact anterior cruciate ligament injuries in young to middle-aged athletes remains high. Despite early diagnosis and appropriate operative and nonoperative treatments, posttraumatic degenerative arthritis may develop. In a meeting in Atlanta, Georgia (January 2005), sponsored by the American Orthopaedic Society for Sports Medicine, a group of physicians, physical therapists, athletic trainers, biomechanists, epidemiologists, and other scientists interested in this area of research met to review current knowledge on risk factors associated with noncontact anterior cruciate ligament injuries, anterior cruciate ligament injury biomechanics, and existing anterior cruciate ligament prevention programs. This article reports on the presentations, discussions, and recommendations of this group.

Knee ligament mechanical properties are not influenced by estrogen or its receptors

Women are at greater risk of tearing their knee anterior cruciate ligament (ACL) than men participating in similar athletic activities. There is currently no conclusive explanation for this disparity; however, as ACL injuries in women have been linked with estrogen fluctuations during the menstrual cycle, one hypothesis is that estrogen has a direct detrimental effect on knee ligament mechanical properties. This study investigated the influence of estrogen and its receptors (ER alpha and ER beta) on knee ligament mechanical properties. This was achieved by testing the viscoelastic and tensile mechanical properties of knee medial collateral ligaments (MCL) and ACLs from: 1) male Sprague-Dawley rats treated with either estrogen (17alpha-ethynylestradiol; 0.03 mg/kg) or an ER alpha-specific agonist (propyl pyrazole triol; 2 mg/kg), and 2) female mice with a null mutation of the gene encoding for ER beta. Estrogen treatment had no significant effects on the viscoelastic or tensile mechanical properties of the rat MCL or ACL. Similarly, pharmacological stimulation of ER alpha using a selective agonist in rats and genetic modulation of ER beta by null mutation of its gene in mice did not influence MCL or ACL properties. These data indicate that estrogen does not have a major direct effect on ligament mechanical properties. Energies for the prevention of the disproportionately high rate of knee ligament injuries in women may be better spent focusing on more established and modifiable risk factors, such as abnormalities in neuromuscular control about the knee.

Anterior cruciate ligament injuries in female athletes: Part 1, mechanisms and risk factors

The mechanism underlying gender disparity in anterior cruciate ligament injury risk is likely multifactorial in nature. Several theories have been proposed to explain the mechanisms underlying the gender difference in anterior cruciate ligament injury rates. These theories include the intrinsic variables of anatomical, hormonal, neuromuscular, and biomechanical differences between genders and extrinsic variables. Identification of both extrinsic and intrinsic risk factors associated with the anterior cruciate ligament injury mechanism may provide direction for targeted prophylactic treatment to high-risk individuals.

Transcriptional coregulator SNW/SKIP: the concealed tie of dissimilar pathways

Eukaryotic gene expression requires that all the steps of messenger RNA production are regulated in concert to integrate the diverse inputs cells receive. We discuss the functioning of SNW/SKIP, an essential spliceosomal component and transcriptional coregulator, which may provide regulatory coupling of transcription initiation and splicing. SNW/SKIP potentiates the activity of important transcription factors, such as vitamin D receptor, CBF1 (RBP-Jkappa), Smad2/3, and MyoD. It synergizes with Ski in overcoming pRb-mediated cell cycle arrest, and it is targeted by the viral transactivators EBNA2 and E7. SNW/SKIP may aid in conformational transition of the gene expression machine through its avidity to nuclear matrix fractions or by recruiting foldases such as the prolyl isomerase PPIL1. The extensive list of SNW/SKIP partners, its unique primary structure, conserved from yeast to humans, and its essential character suggest a distinct function of general importance.