The Fine-Tuning Approach for Training Monitoring

PURPOSE

Monitoring is a fundamental part of the training process to guarantee that the programmed training loads are executed by athletes and result in the intended adaptations and enhanced performance. A number of monitoring tools have emerged during the last century in sport. These tools capture different facets (eg, psychophysiological, physical, biomechanical) of acute training bouts and chronic adaptations while presenting specific advantages and limitations. Therefore, there is a need to identify what tools are more efficient in each sport context for better monitoring of training process.

METHODS AND RESULTS

We present and discuss the fine-tuning approach for training monitoring, which consists of identifying and combining the best monitoring tools with experts' knowledge in different sport settings, designed to improve (1) the control of actual training loads and (2) understanding of athletes' training adaptations. Instead of using single-tool approaches or merely subjective decision making, the identification of the best combination of monitoring tools to assist experts' decisions in each specific context (ie, triangulation) is necessary to better understand the link between acute and chronic adaptations and their impact on health and performance. Future studies should elaborate on the identification of the best combination of monitoring tools for each specific sport setting.

CONCLUSION

The fine-tuning monitoring approach requires the simultaneous use of several valid and practical tools, instead of a single tool, to improve the effectiveness of monitoring practices when added to experts' knowledge.

Comparison of anaerobic speed reserve and maximal aerobic speed methods to prescribe short format high-intensity interval training

The purpose of the study was to compare the degree of intersubject variability in the cardiorespiratory, metabolic, and perceptual responses to high-intensity interval training (HIIT) prescribed based on the relative anaerobic speed reserve (ASR) or maximal aerobic speed (MAS) and to identify the optimal % ASR for execution of such HIIT. Seventeen male physical education students (age: 23.6 ± 1.1 years, height: 180.2 ± 5.9, body mass: 78.3 ± 8.1 kg; % body fat: 14.3 ± 2.7%) volunteered to execute three randomly scheduled 10-min HIIT exercises at 110% vVO2max , Δ15% ASR, or Δ25% ASR. Analysis of variance for repeated measures and the least significant difference post-hoc test were used to compare the physiological responses and the mean of individual residuals between the training sessions. The coefficients of variation (CV) of time spent ≥90% of maximal oxygen uptake (VO2max ) and maximal heart rate (HRmax ), peak VO2 , mean VO2 , peak HR, mean HR, blood lactate [La], and rating of perceived exertion (RPE) were 48.7%, 35.9%, 9.3%, 7%, 3.5%, 4.8%, 32%, and 16.9% during 110% vVO2max , 47.2%, 31%, 7.5%, 6.7%, 3.9%, 4.6%, 24.2%, and 14.6% during Δ15% ASR, and 48.1%, 31.5%, 7.6%, 8.4%, 3.6%, 4.1%, 20.2%, and 3.4% during Δ25% ASR session, respectively. Only the residuals in RPE were significantly (p < 0.001) higher in 110% vVO2max and Δ15% ASR in comparison to Δ25% ASR. Time spent ≥90% HRmax /VO2max was maximized during Δ15% ASR session, albeit this was not significantly different from other sessions. The ASR-based method leads to reduced CVs of physiological and perceptual responses during 10-min HIIT; however, only reductions in [La] and RPE may be considered practically meaningful. Practitioners can use vVO2max for prescription of 10-min HIIT session comprised of 15-s work and passive recovery intervals.

Accuracy of the 20-m shuttle run test for individualizing exercise intensity of high-intensity interval training

The aim of the study was to investigate the accuracy of the 20 m shuttle run test (20mSRT) for the prescription of high-intensity interval training (HIIT) and to examine the appropriate intensity, prescribed by the 20mSRT end-test speed, for the execution of HIIT. Twenty physical education students (age: 22.4 ± 0.8 years, body height: 175.7 ± 8.9 cm, body weight: 73.8 ± 13.4 kg) participated in the study. On two separate occasions the participants were first tested with a maximal incremental exercise test and the 20mSRT. On another two occasions they were required to perform a 10-minute HIIT session comprised of 15-s runs interspersed with 15-s passive recovery. The intensities of the HIIT sessions were either 100% (T100%) or 110% (T110%) of the end-test speed reached in the 20mSRT. Mean oxygen uptake (VO2) (84.4 ± 5.5% vs 77.8 ± 6.9% of VO2max), mean heart rate (HR) (93 ± 2.8% vs 87.6 ± 4.6% of HRmax), blood lactate concentration (12.6 ± 2.1 vs 5.4 ± 2.6 mmol/l), and ratings of perceived exertion (9.5 ± 0.5 vs 6.7 ± 1) were all significantly (p&lt;.01) higher during T110% vs T100%. The percentage of the total exercise time spent ≥ 90% VO2max (37.6 ± 25.3 vs 18.6 ± 18.0%, p&lt;.05) and ≥ 90% HRmax (73.9 ± 17.7% vs 37.5 ± 33.3, p&lt;.001) were also significantly higher during T110%. The mean VO2 and HR coefficient of variation during T110% were 6.5 and 3%, respectively. The cardiorespiratory, metabolic, and perceptual responses to T110% were reflective of the responses typical for HIIT, while T100% induced insufficient physiological stress to enable optimal cardiorespiratory adaptation. Therefore, the intensity of 110% 20mSRT is preferable for inducing the appropriate acute physiological responses and the 20mSRT can be used to accurately prescribe HIIT.

An Examination and Critique of Subjective Methods to Determine Exercise Intensity: The Talk Test, Feeling Scale, and Rating of Perceived Exertion

Prescribing exercise intensity is crucial in achieving an adequate training stimulus. While numerous objective methods exist and are used in practical settings for exercise intensity prescription, they all require anchor measurements that are derived from a maximal or submaximal graded exercise test or a series of submaximal or supramaximal exercise bouts. Conversely, self-reported subjective methods such as the Talk Test (TT), Feeling Scale (FS) affect rating, and rating of perceived exertion (RPE) do not require exercise testing prior to commencement of the exercise training and therefore appear as more practical tools for exercise intensity prescription. This review is intended to provide basic information on reliability and construct validity of the TT, FS, and RPE measurements to delineate intensity domains. The TT and RPE appear to be valid measures of both the ventilatory threshold and the respiratory compensation threshold. Although not specifically examined, the FS showed tendency to demarcate ventilatory threshold, but its validity to demarcate the respiratory compensation threshold is limited. Equivocal stage of the TT, RPE of 10-11, and FS ratings between fairly good (+ 1) and good (+ 3) are reflective of the ventilatory threshold, while negative stage of the TT, RPE of 13-15, and FS ratings around neutral (0) are reflective of the respiratory compensation threshold. The TT and RPE can effectively be used to elicit homeostatic disturbances consistent with the moderate, heavy, and severe intensity domains, while physiological responses to constant FS ratings show extensive variability around ventilatory threshold to be considered effective in demarcating transition between moderate and heavy intensity domains.

Training practices of Filipino athletes during the early covid-19 lockdown

The imposition of COVID-19 lockdown restricted the daily activities of many people, including athletes. This study investigated the training practices of athletes in the Philippines during the first COVID-19 lockdown. A total of 442 athletes answered an online survey (May-July 2020), with questions pertaining to training practices, such as training frequency and duration. Data were analyzed according to: athlete classification (world-class, international, national, state, or recreational), sport category (individual or team), and sex (male or female). During lockdown, significant reductions in training frequency (except recreational, i.e., lower pre-lockdown training) and duration were observed for all athlete classifications. Similarly, training frequency and duration decreased significantly irrespective of sport category and sex. World class athletes appeared to be less affected by lockdown (types of exercise and specific training) as compared to lower-classification athletes. Athletes grouped in accordance with sex and sport category demonstrated little to no difference in training practices during the COVID-19 lockdown. The findings of the current study highlight the challenges experienced by athletes during lockdown, which may aid policy makers in the development of guidelines related to lockdown or lockdown-like situations and establish appropriate support for affected athletes.

Muscle Damage During a Soccer World Cup Preparatory and Competition Period

PURPOSE

To report creatine kinase ([CK]) responses during a soccer World Cup preparatory and first-leg period and to determine the influence of aerobic fitness on postmatch [CK] responses.

METHODS

Eleven national-team players were analyzed in this study. A lactate threshold test was performed during the first 3 d, whereas fingertip blood was drawn most mornings (21 out of 30 d) for [CK] measurements. One-way repeated-measures analysis of variance was used for determining the effect of time on [CK] measurements, whereas Pearson correlation coefficient was used for assessing associations between the changes in [CK] and velocities associated with blood lactate concentrations of 2 (v2) and 4 mmol·L-1 (v4).

RESULTS

Peak [CK] concentrations were consistently reached on the first day after the match with values of 474 (261), 520 (419), and 460 (126) U·L-1 but with no significant differences between them. [CK] concentrations returned to prematch values (331 [201] U·L-1) on the second day after the match. The change in [CK] concentration between prematch and postmatch day was largely correlated (r = .614, P = .044) with v2.

CONCLUSIONS

Top-level soccer players display low levels of muscle damage during official tournaments, and they recover before the next match. Postmatch muscle damage is greater in players with higher aerobic endurance because this fitness quality enables them to execute high-intensity activities known to be a major contributor to muscle damage.

Beating Yourself: How Do Runners Improve Their Own Records?

BACKGROUND

Pacing studies suggest the distribution of effort for optimizing performance. Cross-sectional studies of 1-mile world records (WRs) suggest that WR progression includes a smaller coefficient of variation of velocity.

PURPOSE

This study evaluates whether intraindividual pacing used by elite runners to break their own WR (1 mile, 5 km, and 10 km) is related to the evolution of pacing strategy. We provide supportive data from analysis in subelite runners.

METHODS

Men's WR performances (with 400-m or 1-km splits) in 1 mile, 5 km, and 10 km were retrieved from the IAAF database (from 1924 to present). Data were analyzed relative to pacing pattern when a runner improved their own WR. Similar analyses are presented for 10-km performance in subelite runners before and after intensified training.

RESULTS

WR performance was improved in 1 mile (mean [SD]: 3:59.4 [11.2] to 3:57.2 [8.6]), 5 km (13:27 [0:33] to 13:21 [0:33]), and 10 km (28:35 [1:27] to 28:21 [1:21]). The average coefficient of variation did not change in the 1 mile (3.4% [1.8%] to 3.6% [1.6%]), 5 km (2.4% [0.9%] to 2.2% [0.8%]), or 10 km (1.4% [0.1%] to 1.5% [0.6%]) with improved WR. When velocity was normalized to the percentage mean velocity for each race, the pacing pattern was almost identical. Very similar patterns were observed in subelite runners in the 10 km. When time improved from 49:20 (5:30) to 45:56 (4:58), normalized velocity was similar, terminal RPE increased (8.4 [1.6] to 9.1 [0.8]), coefficient of variation was unchanged (4.4% [1.1%] to 4.8% [2.1%]), and VO2max increased (49.8 [7.4] to 55.3 [8.8] mL·min-1·kg-1).

CONCLUSION

The results suggest that when runners break their own best performances, they employ the same pacing pattern, which is different from when WRs are improved in cross-sectional data.

Alterations in redox homeostasis following repeated sprint training

This study examined the effects of a 6-week repeated sprint training on redox-based homeostasis and their association with muscle damage. Fifteen male physical education students (aged 20.0±1.0 years; body weight 77.7±6.0 kg; height 181.0±4.4 cm; %body fat 8.7±3.0 %), familiar with intermittent activities, volunteered to participate in the study. Experimental training program consisted of 2-3 sets of 6-10 straight-line or shuttle 20-m repeated sprints with departures every 25 seconds and a 2-minute inter-set passive recovery. The training intervention lasted six weeks during which 18 training sessions were performed. The levels were measured of the following: 15-F2t-isoprostanes in plasma and 24-hour urine; superoxide dismutase, glutathione peroxidase and glutathione reductase in erythrocytes; uric acid and creatine kinase in serum after the first and the penultimate training session. The level of muscle damage following the repeated sprint exercise was not significantly altered (402 to 496 U/L; p=.151) and had no significant associations with the changes in markers depicting redox-homeostasis. A significant increase in plasma 15-F2t-isoprostanes (0.32 to 0.56 ng/mL; p=.026), and a subsequent decrease in glutathione reductase (7.7 to 3.4 U/g Hb; p&lt;.001) were observed. Urinary 15-F2t-isoprostane levels were 25% greater at post-training, although this increase did not reach statistical significance. These results indicate that repeated sprint training stimulates the equilibrium in redox homeostasis developing antioxidant protection to the constantly increasing training load.

Intense Physical Exercise Induces an Anti-inflammatory Change in IgG N-Glycosylation Profile

Exercise is known to improve many aspects of human health, including modulation of the immune system and inflammatory status. It is generally understood that exercise reduces inflammation, but there are missing links in terms of understanding the mechanisms as well as the differences between exercise modalities. N-glycosylation of immunoglobulin G (IgG) and total plasma proteins was previously shown to reflect changes in inflammatory pathways, which could provide valuable information to further clarify exercise effects. In order to further expand the understanding of the relationship between physical activity and inflammation, we examined the effect of intense exercise, in the form of repeated sprint training (RST), on IgG and total plasma proteins N-glycosylation in combination with traditionally used inflammation markers: C-reactive protein (CRP), interleukin 6 (IL-6), and leukocyte count. Twenty-nine male physical education students were separated into treatment (RST, N = 15) and control (N = 14) groups. The RST group completed a 6-week exercise protocol while the control group was instructed to refrain from organized physical activity for the duration of the study. Three blood samples were taken at different time points: prior to start of the training program, the final week of the exercise intervention (EXC), and at the end of the 4-week recovery period (REC). Following the end of the recovery period IgG N-glycosylation profiles showed anti-inflammatory changes in RST group compared to the control group, which manifested as a decrease in agalactosylated (p = 0.0473) and an increase in digalactosylated (p = 0.0473), and monosialylated (p = 0.0339) N-glycans. Plasma protein N-glycans didn’t change significantly, while traditional inflammatory markers also didn’t show significant change in inflammatory status. Observed results demonstrate the potential of intense physical exercise to reduce levels of systemic basal inflammation as well as the potential for IgG N-glycosylation to serve as a sensitive longitudinal systemic inflammation marker.

Why the macula?

The regional susceptibility of the retina to diseases has been well known by clinicians for many years. It is surprising that the implications of these observations have not spawned major research efforts to characterise the structural and functional attributes of the outer retina in different regions of a foveate retina. Without such an effort, the understanding of the disease mechanisms in retinal dystrophies will remain limited and may hamper therapeutic efforts. That outer retinal disease is responsible for over 50% of blind registration in the western world underlines the importance of these considerations.

The effect of cigarette smoking history on muscular and cardiorespiratory endurance

The purpose of this study was to investigate the effect of cigarette smoking history on physical fitness in younger adults. Small, insignificant differences in BMI between non-smokers and smokers were shown regardless of cigarette smoking history duration. Although the differences in muscular endurance increased in the samples with progressing cigarette smoking history duration, a highly significant difference in aerobic endurance was observed between the group of non-smokers and smokers with a history of smoking up to 5 years and persisted at the same level in smokers with a history of smoking for longer than 10 years.

Effects of a training program for special operations battalion on soldiers' fitness characteristics

The aim of this study was to investigate the effects of special operations battalion (SOB) training program on soldiers' fitness parameters. The research was conducted on a sample of 25 members (mean ± SD: age 27.93 ± 5.12 years, height 178.64 ± 6.91 cm, body mass 81.42 ± 9.18 kg) of the Croatian Armed Forces for SOB, divided into control and experimental groups. Total duration of the SOB basic training was 62 days. The sample of variables consists of 12 tests for the assessment of fitness characteristics, 2 tests for functional capacity, and 18 morphological measures. Morphological parameters were measured according to the instructions of the International Biological Program. Fitness characteristics were measured with the following tests: 1-kg medicine ball throw from a seated position, standing broad jump (SBJ), relative sergeant test, 20-m sprint, the maximum thrust from the bench, push-ups in 2 minutes (PU(2minutes)), sit-ups in 2 minutes (SU(2minutes)), pull-ups (PU), thrust from the bench with 70% of body weight (BP(70%)), crawling and jumping, agility test 93639 with turn (A9-3-6-3-9), and sit and reach. Functional abilities were evaluated with 2 tests: 3,200 m running (SK3200) and 300 yards running (MBI3Y). There was a statistically significant difference in a set of fitness characteristics variables analyzed between the 2 groups in initial and final measurements in the multivariate level. Analyzing the results of t-test, differences of variables, it was evident that the difference after the SOB program occurred in 7 variables in the experimental group: SBJ, PU2minutes, SU2minutes, PU, BP70%, MBI3Y, and SK3200. Basic training for SOB during 8 weeks has produced significant burnout of the body for the participants who have completed their training. This led to a reduction in fitness performance manifested through the tested variables.

Impact of body composition on performance in fitness tests among personnel of the Croatian navy

The purpose of this study was to determine the impact of body weight on fitness tests among the personnel of the Croatian navy. Forty two naval personnel (age 27 +/- 4.1 years; body mass 86.2 +/- 4.9 kg; height 184.6 +/- 7.4 cm; body fat percentage 17.3 +/- 5.2) participated in this study. In order to evaluate the fitness of the naval servicemen, we applied a testing procedure that included measurements of 7 fitness tests and 15 body anthropometric tests. A negative correlation was found between the body fat percentage and all the analyzed sprint tests and three anaerobic power tests (r), SP5 (r = -0.42), SP10 (r = -0.51), SP20 (r = -0.53), SJ (r = -0.45), CM (r = -0.57), SLJ (r = -0.67). Also a negative correlation was found between the body fat percentage and VO2(max) (r = -0.44). A positive correlation was found between the sprint test and the power performance test and thigh and calf girth. Spiriting ability is influenced by the strength of a person. This is one of the reasons why we found a positive correlation between the sprint test (SP5, SP10 and SP20) and thigh and calf girth. In this study we found a negative correlation between body fat percentages and all the sprint tests and three anaerobic power tests and VO2(max). The ectomorph somatotypes have positive correlations with all variables. The mesomorph somatotypes have the greatest positive correlations with all variables. The endomorph somatotypes have negative correlations with all variables. According to the body composition of Croatian naval servicemen we can conclude that they need a sufficient level of strength and endurance for everyday tasks. The effectiveness of a weight-management program is determined by the success of the participants in losing the necessary amount of weight and being able to maintain that weight loss. This requires long-term tracking of these individuals in a naval environment.

How reliable are the equations for predicting maximal heart rate values in military personnel?

OBJECTIVES

The purpose of this study was to evaluate the validity and reliability of equations for predicting maximal values of heart rate (HR) in military personnel.

METHODS

Five hundred and nine members of the Croatian Armed Forces (age 29.1 +/- 5.5 years; height 180.1 +/- 6.6 cm; body mass 83.4 +/- 11.3 kg; maximal oxygen uptake [VO2(max)] 49.7 +/- 6.9 mL O2/kg/min) were tested. The graded exercise test with gas exchange measurements was used to determine VO2(max) and maximum HR (HR(max)). The analysis of variance was used to determine the differences between the equations to calculate HR(max).

RESULTS

The analysis of variance yielded statistically significant differences between seven HR equations (p < 0.05). The values from Stevens Creek's (HR(max) = 205 - [age/2]) and Fox and Haskell's (HR(max) = 220 - age) equations had the highest correlation with the HRmax obtained by the graded exercise test.

CONCLUSION

The authors recommend using the HR(max) values from the Stevens Creek and the Fox and Haskell equations for the purpose of training, testing, and daily exercise routine in military personnel.

Immunolocalization of electrogenic sodium-bicarbonate cotransporters pNBC1 and kNBC1 in the rat eye

The human NBC1 gene encodes two electrogenic sodium-bicarbonate cotransport proteins, pNBC1 and kNBC1, which are candidate proteins for mediating electrogenic sodium-bicarbonate cotransport in ocular cells. Mutations in the coding region of the human NBC1 gene in exons common to both pNBC1 and kNBC1 result in a syndrome with a severe ocular and renal phenotype (blindness, band keratopathy, glaucoma, cataracts, and proximal renal tubular acidosis). In the present study, we determined the pattern of electrogenic sodium-bicarbonate cotransporter protein expression in rat eye. For this purpose, pNBC1- and kNBC1-specific antibodies were generated and used to detect these NBC1 protein variants by immunoblotting and immunocytochemistry. pNBC1 is expressed in cornea, conjunctiva, lens, ciliary body, and retina, whereas the expression of kNBC1 is restricted to the conjunctiva. These results provide the first evidence for extrarenal kNBC1 protein expression. The data in this study will serve as a basis for understanding the molecular mechanisms responsible for abnormalities in ocular electrogenic sodium-bicarbonate cotransport in patients with mutations in the NBC1 gene.

Deficiency of rds/peripherin causes photoreceptor death in mouse models of digenic and dominant retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of inherited blinding diseases caused by mutations in multiple genes including RDS. RDS encodes rds/peripherin (rds), a 36-kDa glycoprotein in the rims of rod and cone outer-segment (OS) discs. Rom1 is related to rds with similar membrane topology and the identical distribution in OS. In contrast to RDS, no mutations in ROM1 alone have been associated with retinal disease. However, an unusual digenic form of RP has been described. Affected individuals in several families were doubly heterozygous for a mutation in RDS causing a leucine 185 to proline substitution in rds (L185P) and a null mutation in ROM1. Neither mutation alone caused clinical abnormalities. Here, we generated transgenic/knockout mice that duplicate the amino acid substitutions and predicted levels of rds and rom1 in patients with RDS-mediated digenic and dominant RP. Photoreceptor degeneration in the mouse model of digenic RP was faster than in the wild-type and monogenic controls by histological, electroretinographic, and biochemical analysis. We observed a positive correlation between the rate of photoreceptor loss and the extent of OS disorganization in mice of several genotypes. Photoreceptor degeneration in RDS-mediated RP appears to be caused by a simple deficiency of rds and rom1. The critical threshold for the combined abundance of rds and rom1 is approximately 60% of wild type. Below this value, the extent of OS disorganization results in clinically significant photoreceptor degeneration.

Low docosahexaenoic acid levels in rod outer segment membranes of mice with rds/peripherin and P216L peripherin mutations

PURPOSE

Humans with retinitis pigmentosa and dogs with progressive rod-cone degeneration (prcd) have lower than normal blood levels of long-chain polyunsaturated fatty acids, including docosahexaenoic acid (DHA), the major fatty acid found in retinal rod outer segments (ROS). In addition, prcd-affected dogs have lower levels of DHA in their ROS than control animals. The present study was designed to determine whether mice that are heterozygous for the rds mutation and transgenic mice heterozygous for a specific rds/peripherin mutation (P216L) have lower DHA levels in their ROS and other tissues than do control mice.

METHODS

Wild-type (rds(+/+)) mice, mice with the rds(-/-) (null) and rds(+/-) mutations, and mice with the P216L rds/peripherin mutation on the rds(+/-) background were maintained in the vivarium under identical husbandry conditions, and tissues were removed from each group for analysis at approximately 2 months of age. Fatty acid compositions of total lipids from plasma, red blood cells, liver, and ROS were determined by gas-liquid chromatography. ROS purity from each group was determined by SDS-PAGE with silver staining. The morphologic status of retinas representing each genotype was analyzed by light and electron microscopy.

RESULTS

There was no difference between rds(+/-), P216L on rds(+/-), and rds(+/+) (control) animals in the fatty acid composition of plasma, expressed as relative mole percent or as nanomoles fatty acid per milliliter of plasma. Small but statistically significant differences were found in 18:0 and C-22 polyunsaturated fatty acids of red blood cells. In the liver, the control animals had higher levels of 20:4n-6. In contrast, the ROS of control animals had levels of DHA that were 1.4 times that of ROS from either rds(+/-) or P216L on rds(+/-) mice of the same age. The reduction in DHA was not accompanied by an increase in 22:5n-6, which always occurs in neural tissues of animals deprived of n-3 fatty acids. SDS-PAGE of the three ROS membrane preparations showed that they were of identical purity.

CONCLUSIONS

Mice heterozygous for the spontaneous rds/peripherin mutation or mice carrying the P216L mutation on this heterozygous background have a statistically significant reduction of DHA in their ROS membranes. The authors propose that reduction in DHA is an adaptive response to metabolic stress caused by the mutation.

Glutathione transport in human retinal pigment epithelial (HRPE) cells: apical localization of sodium-dependent gsh transport

The study was undertaken to identify and localize GSH transport in non-transformed cultured human retinal pigmented epithelial cells (HRPE). In confluent monolayers exhibiting high transepithelial resistance (TER 700-1000 Omega cm(-2)), apical and basolateral GSH uptake were determined after introducing(35)S-GSH (+ 1 m M GSH) to the apical side or basal side in NaCl (Na+ -containing) or choline chloride (Na+ -free) buffers. Cells in growth medium or in incubation buffers were pretreated with acivicin to inhibit gamma-glutamyltranspeptidase (GGT). GSH efflux was measured after labelling the intracellular GSH pool by incubation overnight with 35 S-cysteine and quantitating the release of labelled GSH into the medium. Uptake of GSH was found at both the apical and basolateral membranes of HRPE cells. Inhibition of gamma-glutamyltranspeptidase (GGT) with acivicin did not alter mean GSH uptake (nmol per million cells per 30 min) significantly at the apical (1.63 +/- 0.32 vs 1.45 +/- 0.30; with and without acivicin respectively) or the basolateral (1.17 +/- 0.21 vs 1.44 +/- 0.38) membranes. Transport was verified to be in the form of intact GSH by HPLC. Uptake was unaffected by the removal of Na+ at the basolateral membrane while apical uptake exhibited partial but significant (approximately 40%) Na+ -dependency. Net GSH efflux (nmol per million cells per min) to the apical side of HRPE cells was higher than to the basolateral side in the presence of sodium. Transepithelial flux in the basolateral to apical direction was approximately 17-fold higher than the apical to basolateral direction resulting in a net flux of GSH to the apical side. In conclusion, HRPE cells exhibit GSH transport by Na+ -dependent and Na+ -independent mechanisms. The Na+ -dependent GSH transporter is localized to the apical membrane of HRPE cells.

Reduced levels of retinyl esters and vitamin A in human renal cancers

Clinical and preclinical studies suggest that retinoids can inhibit the growth of a small percentage of human renal cancers (RCs), although the majority of RCs both in vitro and in vivo are retinoid resistant. Our recent studies indicate that the metabolism of retinol to retinyl esters is greatly reduced in human carcinoma cell lines of the oral cavity, skin, and breast as compared with their normal epithelial counterparts, suggesting that human carcinoma cells are retinoid deficient relative to normal epithelial cells. We considered whether retinoid resistance in RCs was related to an abnormality in retinoid metabolism. The metabolism of [3H]retinol and of [3H]retinoic acid (RA) was examined in RC cell lines and normal human kidney (NK) epithelial cells cultured in media, in RA, or in RA plus IFN-alpha. The expression of LRAT (lecithin:retinol acyltransferase) was assessed by Northern and Western analysis. Retinol and retinyl ester levels were determined in tissue samples of normal human kidney and renal cell carcinoma. NK cells esterified all of the 50 nM [3H]retinol in which they were cultured. In contrast, six of the seven RC cell lines metabolized only trace amounts of [3H]retinol to [3H]retinyl esters. Consistent with this relative lack of [3H]retinol esterification by the tumor cells, the tumor cells exhibited LRAT transcripts of aberrantly low sizes relative to those in normal epithelial cells. Moreover, the NK cells expressed abundant levels of LRAT protein by Western analysis, whereas the RC cells did not express LRAT protein. When samples of human kidney tumor tissue were compared with samples of normal kidney tissue from patients who had undergone surgery for primary RC, the normal kidney tissues contained much higher levels of retinol and retinyl esters (approximately 0.5-2 microg/gram wet weight) than the tumor tissues in all seven patients examined. Culture of the RC lines in IFN-alpha plus all-trans-RA, a combination therapy used clinically, resulted in higher intracellular levels of [3H]retinol and [3H]retinyl esters. The metabolism of [3H]RA was also examined in these RC lines versus NK cells. Although the NK epithelial cells metabolized [3H]RA, the majority of the RC lines metabolized [3H]RA at a much slower rate. Most of the RC lines metabolized only 10-30% of the 50 nM [3H]RA over 6 h of culture. These data indicate that RCs both in vitro and in vivo are retinol and retinyl ester deficient relative to the normal human kidney, and they suggest that the aberrant differentiation of the neoplastic renal cells results in part from a defect in retinoid metabolism.

A cell culture medium that supports the differentiation of human retinal pigment epithelium into functionally polarized monolayers

PURPOSE

The retinal pigment epithelium (RPE) in vivo is known to have polarized membrane domains that are essential for its normal function. Unless the proper cell culture conditions are used, these polarized features are often lost. In the past, the use of Chee's Essential Medium (CEM) in our RPE cultures has produced functional polarity of the cell monolayers. Unfortunately, except by custom formulation, which is costly, this product is no longer commercially available. We therefore sought to develop a replacement culture medium that would support morphological and functional polarity of RPE membrane domains when the cells are removed from the in vivo milieu.

METHODS

To test the performance of this CEM replacement medium in comparison with three other culture media, we grew fetal human RPE to confluence on Millipore Millicell culture wells. We then used Na,K ATPase as a membrane domain marker by displaying it with polyclonal antibodies. This marker was chosen because it is not always properly polarized in culture. Immunofluorescence was imaged by laser confocal microscopy of whole mounted intact monolayers on their Millicell supports. We also used transepithelial resistance (TER) as a measurement of functional polarity as well as bestrophin protein expression as an index of cell differentiation. The expression of Na,K ATPase and bestrophin was confirmed by Western blot analysis of whole RPE cell extracts.

RESULTS

Immunofluorescence labeling of cultured RPE Na,K ATPase was observed exclusively on the apical membrane when the CEM replacement or DMEM with high glucose was used. However Na,K ATPase was not completely polarized in DMEM/F12 medium and the cells did not express detectable Na,K ATPase in DMEM with low glucose. Western blots showed that Na,K ATPase was expressed at similar levels in CEM replacement, DMEM with high glucose and DMEM/F12 as indicated by the intensity of an approximately 100 kDa band representing the a subunit. The CEM replacement gave superior TERs as well, ranging from about 2 to 5.6 fold higher than the other media. Bestrophin protein was readily detectable by Western blot in CEM replacement medium whereas it was barely detectable in DMEM/F12 and undetectable in DMEM with high and low glucose.

CONCLUSIONS

We have provided immunocytochemical evidence that the CEM replacement medium supports the appropriate membrane domain expression of Na,K ATPase when the cells are grown on Millicell chambers. Excellent TERs and robust expression of bestrophin are also observed. This combination of features was not observed when other, standard culture media were used. The results suggest that, under these conditions, cultured human RPE develops a highly differentiated and functional polarity appropriate for the in vitro modeling of RPE in vivo function.

Two histidine residues are essential for catalysis by lecithin retinol acyl transferase

Lecithin retinol acyl transferase (LRAT) is a novel membrane bound enzyme that catalyzes the formation of retinyl esters from vitamin A and lecithin. The enzyme is both essential for vision and for the general mobilization of vitamin A. The sequence of LRAT defines it as a novel enzyme unrelated to any other protein of known function. LRAT possesses a catalytically essential active site cysteine residue. The enzyme also contains six histidine residues. It is shown here that two of these residues (H57 and H163) are essential for catalysis. A mechanistic hypothesis is presented to account for these observations.

Glycosaminoglycan synthesis and secretion by the retinal pigment epithelium: polarized delivery of hyaluronan from the apical surface

Hyaluronan and chondroitin sulfate glycosaminoglycan secretion from retinal pigment epithelial cells was established in confluent cultures with high transepithelial resistance. Cell cultures were maintained on Millicell-PCF culture plates, which allow separation of culture medium exposed to apical and basal epithelial surfaces. Following various times in culture, apical and basal culture media were sampled at three day intervals and the glycosaminoglycan content was quantified. Samples were digested with proteinase K to free the glycosaminoglycans from their core proteins, the glycosaminoglycans were ethanol precipitated, and subjected to hyaluronidase SD and chondroitinase ABC digestion to release hyaluronan and chondroitin sulfate disaccharides. Disaccharides were fluorotagged with 2-aminoacridone, separated on polyacrylamide gels and the molar fluorescence in each disaccharide band quantitated. Hyaluronan in the apical medium was significantly higher than in the basal medium (5-12 times) at all recovery intervals (P&lt;0.0001). In contrast, the distribution of unsulfated chondroitin, 4-sulfated chondroitin and 6-sulfated chondroitin disaccharides in apical and basal media was non-polar. Confocal microscopy of cultures probed with a hyaluronan-specific fluorotag established that the HA evident in these cultures is restricted to the apical border of the RPE cultures. Collectively, these data indicate that hyaluronan synthesized by the retinal pigment epithelium is secreted preferentially from the apical surface, suggesting that this tissue is an important source of hyaluronan present in the interphotoreceptor matrix.

Genomic organization and mutation analysis of the gene encoding lecithin retinol acyltransferase in human retinal pigment epithelium

PURPOSE

To determine the structure of the human lecithin retinol acyltransferase (LRAT) gene, map its chromosomal localization, and screen for mutations in humans with various hereditary retinal degenerations.

METHODS

Using DNA probes specific for LRAT, a bacterial artificial chromosome (BAC) clone containing the LRAT gene was isolated, subcloned into DNA fragments and relevant subclones characterized by sequencing. Exon-intron junctions were determined by comparison with the cDNA sequence previously published. Southern blot analysis was performed on human genomic DNA samples digested with several restriction enzymes. Fluorescence in situ hybridization (FISH) analysis of normal metaphase chromosomes derived from phytohemagglutinin (PHA) stimulated peripheral blood lymphocytes and radiation hybrid mapping were used for localization of the LRAT gene. Single-strand conformation polymorphism analysis (SSCP) was used to screen for potential mutations in patients with age-related macular degeneration, Leber congenital amaurosis, retinitis pigmentosa, and cone-rod dystrophy.

RESULTS

The human LRAT gene is organized into three exons of 219, 541, and 2058 bp and two introns of 103 and 4117 bp. Southern blot analysis of digested genomic DNA revealed a single band, suggesting a single copy of the LRAT gene. The human LRAT gene was localized to chromosome 4q31.2, a locus having no previous association with human eye disease. Additionally, the bovine LRAT homologue sequence was deduced and a general LRAT protein topology is suggested. No polymorphisms that segregated with retinal disease phenotypes were identified in 374 unrelated probands.

CONCLUSIONS

The organization of the LRAT gene, based on cDNA clones derived from the retinal pigment epithelium (RPE) has been determined. Its structure is less complex than other acyltransferases such as lecithin cholesterol acyltransferase (LCAT) and acyl CoA acyltransferase (ACAT). The absence of polymorphisms in the probands examined suggests a very low mutation level in the LRAT gene from the diseases analyzed.

Tetracycline-inducible system for photoreceptor-specific gene expression

PURPOSE

To develop a system for inducible photoreceptor-specific gene expression in transgenic mice. The tetracycline regulatory system was chosen because it possesses the useful property of direct control of gene expression through use of an exogenous agent, doxycycline, a tetracycline derivative.

METHODS

Transgenic mice were generated that carried the reverse tetracycline-controlled transactivator under the control of the photoreceptor-specific promoters for rhodopsin and interphotoreceptor retinoid-binding protein. These animals were crossed with transgenic mice carrying the lacZ reporter gene under control of the tetracycline operator cassette, creating doubly transgenic mice. Doxycycline was administered to induce expression of the reporter gene. Reporter assays were then performed to evaluate lacZ expression.

RESULTS

Doxycycline administration led to photoreceptor-specific expression of the lacZ reporter gene in the doubly transgenic mice. X-gal staining was restricted to photoreceptor inner segments and synaptic termini. Induction could be achieved by addition of the drug to the animals' drinking water or by intravitreal injection. Induction was noted within 24 hours of doxcycline administration. Because of variability among animals, there was an approximate correlation, but not a clean dose-response curve relating drug dose to level of reporter expression.

CONCLUSIONS

A transgenic system for inducible photoreceptor-specific gene expression has been developed. This system is currently being exploited to study the effects of regulated expression of genes of biological interest.

Esterification of all-trans-retinol in normal human epithelial cell strains and carcinoma lines from oral cavity, skin and breast: reduced expression of lecithin:retinol acyltransferase in carcinoma lines

When exogenous [(3)H]retinol (vitamin A) was added to culture medium, normal human epithelial cells from the oral cavity, skin, lung and breast took up and esterified essentially all of the [(3)H]retinol within a few hours. As shown by [(3)H]retinol pulse-chase experiments, normal epithelial cells then slowly hydrolyzed the [(3)H]retinyl esters to [(3)H]retinol, some of which was then oxidized to [(3)H]retinoic acid (RA) over a period of several days. In contrast, cultured normal human fibroblasts and human umbilical vein endothelial cells (HUVEC) did not esterify significant amounts of [(3)H]retinol; this lack of [(3)H]retinol esterification was correlated with a lack of expression of lecithin:retinol acyltransferase (LRAT) transcripts in normal fibroblast and HUVEC strains. These results indicate that normal, differentiated cell types differ in their ability to esterify retinol. Human carcinoma cells (neoplastically transformed epithelial cells) of the oral cavity, skin and breast did not esterify much [(3)H]retinol and showed greatly reduced LRAT expression. Transcripts of the neutral, bile salt-independent retinyl ester hydrolase and the bile salt-dependent retinyl ester hydrolase were undetectable in all of the normal cell types, including the epithelial cells. These experiments suggest that retinoid-deficiency in the tumor cells could develop because of the lack of retinyl esters, a storage form of retinol.

Analysis and quantitation of mRNAs encoding the alpha- and beta-subunits of rod photoreceptor cGMP phosphodiesterase in neonatal retinal degeneration (rd) mouse retinas

The retinal degeneration(rd) mouse is a commonly-studied animal model of the family of human-inherited retinal blindness known as retinitis pigmentosa, and is a likely model in which therapies for these conditions will continue to be developed and tested. Mutation of the beta-subunit of the rod photoreceptor cell-specific cyclic GMP phosphodiesterase is known to cause photoreceptor apoptosis in these mice. However, the molecular phenotype of this mutation in terms of quantitative levels of the phosphodiesterase alpha- and beta-subunit messenger RNAs remains unknown. In this study, the expression of the alpha- and beta-phosphodiesterase subunits is compared in C57BL/6J +/+, rd /+, and rd / rd mouse retinas. Using the techniques of quantitative reverse transcription polymerase chain reaction and quantitative in situ hybridization, the expression of the subunit mRNAs was measured in retinas of postnatal mice 0-14 days of age. Additionally, full length coding sequences were amplified for both subunits, and the beta-phosphodiesterase subunit mRNA was further evaluated for evidence of alternative splicing. Lastly, a relative decrease in expression of the mutant beta-phosphodiesterase allele in rd /+ mice was observed.

Osteonectin/SPARC secreted by RPE and localized to the outer plexiform layer of the monkey retina

PURPOSE

Osteonectin/SPARC is a secreted protein that has been implicated in ocular disease. Deletion of osteonectin/SPARC causes age-onset cataract in mice and the cataractous human lens has increased expression of osteonectin/SPARC. In this study, the expression and localization of osteonectin/SPARC in the monkey retina were determined as was secretion by cultured human retinal pigment epithelial (RPE) cells.

METHODS

Adult Rhesus monkey eyes (Macaca mulatta) were dissected, and 5-mm macula and peripheral retina punches were obtained. Supernatants were collected from cultured human RPE cells. Subcellular fractionation of whole monkey retina was also performed. Osteonectin/SPARC expression and/or secretion was monitored by Northern and Western blot analyses, and localization was determined by immunocytochemistry.

RESULTS

Outside of the retina osteonectin/SPARC mRNA is broadly expressed in many human tissues. Northern blot analysis shows that in the retina osteonectin/SPARC is expressed almost exclusively by the macular RPE/choroid. Western blot analysis revealed osteonectin/SPARC in both the macula and the peripheral neural retina but only in trace amounts in the RPE/choroid. In subcellular fractions of the whole retina, osteonectin/SPARC was detected, mainly in the soluble fraction but also in the membrane and nuclear fractions. Immunohistochemical analysis localized osteonectin/SPARC specifically to the outer plexiform layer. Western blot analysis of conditioned medium from human RPE cells cultured on porous substrates indicated that osteonectin/SPARC is secreted in large amounts from both the apical and basal sides of the RPE.

CONCLUSIONS

Collectively these data provide evidence that osteonectin/SPARC is synthesized in the macular RPE, secreted, and subsequently transported to the outer plexiform layer. The expression pattern of osteonectin/SPARC in the subcellular retinal fractions is consistent with a soluble protein that is transported and internalized.

A brief review of retinitis pigmentosa and the identified retinitis pigmentosa genes

The family of inherited ocular diseases that is collectively known as retinitis pigmentosa is a major cause of progressive retinal disease worldwide. As such, this family of diseases has been the object of much scientific scrutiny, both clinical and basic. The recent application of molecular genetic analyses has heralded the rapid elucidation of the underlying gene defects in many cases. In this article, the fundamental clinical and electroretinographic characteristics of retinitis pigmentosa will be recalled. Additionally, the current understanding of the genetic causes of retinitis pigmentosa will be reviewed, and the identified causative genes will be classified into groups related by function.

Lecithin retinol acyltransferase contains cysteine residues essential for catalysis

Lecithin retinol acyltransferase (LRAT) is an essential enzyme in vitamin A metabolism and mobilization. The membrane-bound enzyme catalyzes the transfer of an acyl group from the sn-1 position of lecithin to vitamin A to generate retinyl esters. The sequence of LRAT is novel and hence does not suggest a mechanistic class to which the enzyme belongs. However, the activity of the enzyme is exceedingly sensitive to affinity labeling and group-specific reagents directed toward thiol groups. LRAT from human retinal pigment epithelium has cysteine residues at positions 161, 168, 182, and 208. Site-specific mutagenic studies show that C182 and C208 can be converted to alanines with little affect on activity. The activities of the C161A and C168A mutants are virtually nil. Moreover, while C168S is substantially active, C161S possesses only a few percent of the activity of wild-type (WT) LRAT. Also, pH-rate profiles show that C168S has virtually the same profile as WT LRAT, while C161S shows an aberrant profile quite unlike that of WT LRAT. Therefore, LRAT is a thiol acyltransferase and C161 may be the essential nucleophilic residue critical for catalysis.

Is the Duchenne muscular dystrophy gene also an X-linked retinitis pigmentosa locus?

Deletion mutations and linkage mapping have localized an X-linked retinitis pigmentosa locus to Xp21, and a disease gene (RPGR) has been characterized. However, mutations have not been identified in most families expected to segregate the disease at this locus. Here, a retina-specific mRNA transcript from the Duchenne muscular dystrophy gene is identified. Based on these data, it is hypothesized that the Duchenne muscular dystrophy gene may represent a second Xp21 site at which retinitis pigmentosa mutations occur.

Molecular and biochemical characterization of lecithin retinol acyltransferase

The enzyme responsible for conversion of all-trans-retinol into retinyl esters, the lecithin retinol acyltransferase (LRAT) has been characterized at the molecular level. The cDNA coding for this protein was cloned and its amino acid sequence deduced. LRAT is composed of a polypeptide of 230 amino acid residues with a calculated mass of 25.3 kDa. Tissue distribution analysis by Northern blot showed expression of a 5.0-kilobase transcript in the human retinal pigment epithelium as well as in other tissues that are known for their high LRAT activity and vitamin A processing. Affinity labeling experiments using specific compounds with high affinity for LRAT and monospecific polyclonal antibodies raised in rabbits against two peptide sequences for LRAT confirmed the molecular mass of LRAT as a 25-kDa protein. High performance liquid chromatography analysis of the reaction product formed by HEK-293 cells transfected with LRAT cDNA confirmed the ability of the transfected cells to convert [3H]all-trans-retinol into authentic [3H]all-trans-retinyl palmitate as chemically determined.

Polarity of 11-cis retinal release from cultured retinal pigment epithelium

PURPOSE

Fetal bovine retinal pigment epithelium (RPE) was grown on porous supports to investigate the polarity of 11-cis retinal (RAL) release from these cells and the influence that the interphotoreceptor retinoid-binding protein (IRBP) has on this process.

METHODS

[3H]all-trans retinol (ROL) was delivered to the basal surface of the cultured RPE by serum retinol-binding protein (RBP). Apo IRBP was added to either the apical or basal medium, or was absent from the incubation entirely.

RESULTS

The greatest level of [3H]11-cis RAL was detected in the apical medium but only when apo IRBP was present there. When apo IRBP was present only in the basal medium, or was absent from the incubation entirely, low levels of [3H]11-cis RAL were released apically and basally.

CONCLUSIONS

If 11-cis RAL release were constitutive, one would expect to find elevated levels of this retinoid in the apical and basal media in the absence of apo IRBP. Instead, the enhancement of [3H]11-cis RAL release into the apical, but not the basal, medium in the presence of apo IRBP suggests that [3H]11-cis RAL release is polarized and dependent on the presence of apo IRBP. It is postulated, therefore, that a mechanism such as an IRBP membrane receptor in the apical plasma membrane may be responsible for this polarity.

A report card on diversity: lessons for business from higher education

Institutions of higher learning in the United States have long played a disproportionate role in supplying leadership talent to the world's business and professional organizations. For 30 years, the most selective schools have been working to increase diversity in their student bodies. New research by the former presidents of Princeton and Harvard suggests that the experiences and initiatives of these academic institutions can provide business leaders with insight into how to create diverse organizations that succeed. The first insight has to do with clarity of mission. It is not enough to pursue diversity because it is "the right thing to do." In an insert, Raymond Gilmartin, the CEO of Merck, echoes that view, discussing the relationship between diversity and Merck's competitiveness. The second insight concerns recruiting. The authors challenge what they call "the myth of pure merit," the notion that recruiting is a precise science based only on grades and test scores. Instead, they argue, merit is about assembling a team by deciding which applicants, considered individually and collectively, will contribute most to achieving the company's goals. The third insight concerns how organizations help employees perform to their potential. Of the factors contributing to high graduation rates at the most selective schools, higher expectations and the efforts of mentors stand out as most important. Finally, the fourth insight is about how to achieve accountability in a corporate setting. Boards must ask: Are our recruiting policies working? and How are recruited employees doing?

Transgenic analysis of rds/peripherin N-glycosylation: effect on dimerization, interaction with rom1, and rescue of the rds null phenotype

Rds/peripherin is an integral membrane glycoprotein that is present in the rims of photoreceptor outer segment disks. In mammals, it is thought to stabilize the disk rim through heterophilic interactions with the related nonglycosylated protein roml. Glycosylation of rds/peripherin at asparagine 229 is widely conserved in vertebrates. In this study, we investigated the role of rds/peripherin N-glycosylation. We generated transgenic mice that expressed only S231A-substituted rds/peripherin in their retinas. This protein was not glycosylated but formed covalent dimers with itself and with glycosylated rds/peripherin. Nonglycosylated rds/peripherin also interacted noncovalently with rom1 homodimers to form a heterooligomeric complex. The glycosylated rds/peripherin..rom1 complex bound to concanavalin A-Sepharose, suggesting that the glycan is not directly involved in the interaction between these proteins. In double transgenic mice expressing normal and S231A-substituted rds/peripherin, the mRNA-to-protein ratios were similar for both transgenes, indicating no effect of N-glycosylation on rds/peripherin stability. Finally, expression of nonglycosylated rds/peripherin in transgenic mice rescued the phenotype of outer segment nondevelopment in retinal degeneration slow (rds-/-) null mutants. These observations indicate that N-glycosylation of rds/peripherin is not required for its normal processing, stability, or in vivo function.

Rpe65 is necessary for production of 11-cis-vitamin A in the retinal visual cycle

Mutation of RPE65 can cause severe blindness from birth or early childhood, and RPE65 protein is associated with retinal pigment epithelium (RPE) vitamin A metabolism. Here, we show that Rpe65-deficient mice exhibit changes in retinal physiology and biochemistry. Outer segment discs of rod photoreceptors in Rpe65-/- mice are disorganized compared with those of Rpe65+/+ and Rpe65+/- mice. Rod function, as measured by electroretinography, is abolished in Rpe65-/- mice, although cone function remains. Rpe65-/- mice lack rhodopsin, but not opsin apoprotein. Furthermore, all-trans-retinyl esters over-accumulate in the RPE of Rpe65-/- mice, whereas 11-cis-retinyl esters are absent. Disruption of the RPE-based metabolism of all-trans-retinyl esters to 11-cis-retinal thus appears to underlie the Rpe65-/- phenotype, although cone pigment regeneration may be dependent on a separate pathway.

Non-cell-autonomous photoreceptor degeneration in rds mutant mice mosaic for expression of a rescue transgene

The inherited retinal dystrophies represent a large and heterogenous group of hereditary neurodegenerations, for many of which, the molecular defect has been defined. However, the mechanism of cell death has not been determined for any form of retinal degeneration. The retinal degeneration slow (rds-/-) mutation of mice is associated with nondevelopment of photoreceptor outer segments and gradual death of photoreceptor cell bodies, attributed to the absence of the outer segment protein rds/peripherin. Here, we examined the effects of a transgene encoding normal rds/peripherin that had integrated into the X-chromosome in male and female rds-/- mutant retinas. In 2-month-old transgenic males and homozygous-transgenic females on rds-/-, we observed virtually complete rescue of both the outer segment nondevelopment and photoreceptor degeneration. In contrast, hemizygous-transgenic rds-/- female littermates showed patchy distributions of the transgene mRNA, by in situ hybridization analysis, and of photoreceptor cells that contain outer segments. This pattern is consistent with random inactivation of the X-chromosome and mosaic expression of the transgene. Surprisingly, we observed significant photoreceptor cell loss in both transgene-expressing and nonexpressing patches in hemizygous female retinas. These observations were supported by nuclease protection analysis, which showed notably lower than predicted levels of transgene mRNA in retinas from hemizygous females compared with male and homozygous female littermates. This phenotype suggests an important component of non-cell-autonomous photoreceptor death in rds-/- mutant mice. These results have significance to both the etiology and potential treatment of human inherited retinal degenerations.

Transplantation of retinal pigment epithelial cells and immune response in the subretinal space

PURPOSE

To evaluate the fate of retinal pigment epithelial cell (RPE) allografts in the subretinal space.

METHODS

Transplantation was performed in Royal College of Surgeons (RCS) rats. Two rat strains, BD IX and LEJ, which have incompatible major histocompatibility complex (MHC) haplotypes, were selected as healthy RPE donors. Transplantation was performed when recipients were 19 to 21 days old. Host systemic immunity was enhanced by challenge with donor spleen cells 2 weeks after RPE transplantation. Control subjects were administered injections of saline or host spleen cells. The animals were killed at 3 or 5 months of age. The extent of photoreceptor rescue was determined by counting the maximum layers of surviving photoreceptor nuclei in histologic sections. Reverse transcription-polymerase chain reaction analysis of the grafts was performed with host- and donor-specific primers.

RESULTS

Despite the absence of acute immune rejection, chronic rejection occurred and was evidenced by an increased loss of photoreceptor cells in immunologically challenged RCS rats. Grafts with disparity at MHC class I and class II lost their ability to rescue photoreceptor cells more readily than did grafts with disparity at MHC class II alone. Furthermore, the donor RPE cells that were normally MHC class II-negative expressed MHC class II mRNA in the subretinal space after transplantation.

CONCLUSIONS

Systemic immunity appeared to exert a slow but significant influence in the subretinal space. Therefore, in planning future trials involving human subjects, the immunologically privileged status of the subretinal space should be regarded as imperfect.

Bovine epidermal fatty acid-binding protein: determination of ligand specificity and cellular localization in retina and testis

The fatty acid-binding protein (FABP) family consists of small, cytosolic proteins believed to be involved in the uptake, transport, and solubilization of their hydrophobic ligands. Members of this family have highly conserved sequences and tertiary structures. Using an antibody against testis lipid-binding protein, a member of the FABP family, a protein was identified from bovine retina and testis that coeluted with exogenously added docosahexaenoic acid during purification. Amino acid sequencing and subsequent isolation of its cDNA revealed it to be nearly identical to a bovine protein expressed in the differentiating lens and to be the likely bovine homologue of the human epidermal fatty acid-binding protein (E-FABP). From quantitative Western blot analysis, it was estimated that bovine E-FABP comprised 0.9%, 0.1%, and 2.4% of retina, testis, and lens cytosolic proteins, respectively. Binding studies using the fluorescent probe ADIFAB indicated that this protein bound fatty acids of differing levels of saturation with relatively high affinities. Kd values ranged from 27 to 97 nM. In addition, the protein was immunolocalized to the Müller cells in the retina as well as to Sertoli cells in the testis. The location of bovine E-FABP in cells known to be supportive to other cell types in their tissues and the ability of E-FABP to bind a variety of fatty acids with similar affinities indicate that it may be involved in the uptake and transport of fatty acids essential for the nourishment of the surrounding cell types.

Structural and functional characterization of recombinant human cellular retinaldehyde-binding protein

Cellular retinaldehyde-binding protein (CRALBP) is abundant in the retinal pigment epithelium (RPE) and Müller cells of the retina where it is thought to function in retinoid metabolism and visual pigment regeneration. The protein carries 11-cis-retinal and/or 11-cis-retinol as endogenous ligands in the RPE and retina and mutations in human CRALBP that destroy retinoid binding functionality have been linked to autosomal recessive retinitis pigmentosa. CRALBP is also present in brain without endogenous retinoids, suggesting other ligands and physiological roles exist for the protein. Human recombinant cellular retinaldehyde-binding protein (rCRALBP) has been over expressed as non-fusion and fusion proteins in Escherichia coli from pET3a and pET19b vectors, respectively. The recombinant proteins typically constitute 15-20% of the soluble bacterial lysate protein and after purification, yield about 3-8 mg per liter of bacterial culture. Liquid chromatography electrospray mass spectrometry, amino acid analysis, and Edman degradation were used to demonstrate that rCRALBP exhibits the correct primary structure and mass. Circular dichroism, retinoid HPLC, UV-visible absorption spectroscopy, and solution state 19F-NMR were used to characterize the secondary structure and retinoid binding properties of rCRALBP. Human rCRALBP appears virtually identical to bovine retinal CRALBP in terms of secondary structure, thermal stability, and stereoselective retinoid-binding properties. Ligand-dependent conformational changes appear to influence a newly detected difference in the bathochromic shift exhibited by bovine and human CRALBP when complexed with 9-cis-retinal. These recombinant preparations provide valid models for human CRALBP structure-function studies.

Generation and analysis of transgenic mice expressing P216L-substituted rds/peripherin in rod photoreceptors

PURPOSE

In this study, the authors present the biochemical, morphologic, and physiological analyses of a transgenic mouse model for retinal degeneration slow (RDS)-mediated retinitis pigmentosa caused by a proline 216 to leucine (P216L) amino acid substitution in rds/peripherin.

METHODS

The authors assembled a mutant rds transgene that encodes rds/peripherin with a P216L substitution. Transgenic mice were generated on wild-type (+/+), heterozygous (rds-/+), and homozygous (rds-/rds-) null genetic backgrounds. These mice were analyzed biochemically, by light and electron microscopy, and by electroretinography.

RESULTS

In P216L-transgenic mice on a +/- background, the authors observed expression-level-dependent photoreceptor degeneration and outer-segment shortening. Expression of the P216L transgene on an rds-/+ background resulted in more severe photoreceptor degeneration and outer-segment dysplasia than seen in nontransgenic rds-/+ mutants. Severely dysplastic outer segments were detectable in P216L transgenics on an rds-/rds-null background. The reduction in b-wave amplitudes by electroretinography were well correlated with the degree of photoreceptor degeneration, but not outer-segment dysplasia in these different rds mutants.

CONCLUSIONS

The phenotype in P216L-transgenic mice on an rds-/+ genetic background probably is caused by a combination of two genetic mechanisms: a direct dominant effect of the P216L substituted protein, and a reduction in the level of normal rds/peripherin. The expression pattern of the normal and mutant genes in these animals is similar to that predicted for humans with RDS-mediated autosomal-dominant retinitis pigmentosa. These mice may thus be considered an animal model for this disease.

Expression and synthesis of the Na,K-ATPase beta 2 subunit in human retinal pigment epithelium

Na,K-ATPase in the retinal pigment epithelium (RPE) is apically localized, whereas in most other tissues this pump is found predominantly in the basolateral membrane domain. As part of our investigations into the molecular aspects of this pump in the RPE, we have cloned the cDNA and characterized the expression of the gene encoding the beta 2 subunit isoform of Na,K-ATPase in human, rat and bovine RPE and in the bovine choroid plexus. We have also detected the beta 2 isoform polypeptide in the human RPE (hRPE). Comparison of complete coding sequences derived from cloned cDNAs revealed that all beta 2 sequences from RPE, and the choroid plexus, differed uniformly at positions: P51/L, M121/I, and L148/R from the published sequences for human retina and liver. However, analysis of 10 RT-PCR clones derived from 5 fetal and 2 adult human retinas sequenced in our laboratory, revealed that only the P51/L residue was different with the hRPE beta 2 subunit sequence. Northern blot analysis indicated a 3.4-kb RNA transcript for the beta 2 subunit, a 4.5-kb RNA for the alpha 1 subunit and a doublet of 2.3 and 2.6 kb for the beta 1 subunit, respectively. alpha 1 (100 kDa), beta 1 (45 kDa) and beta 2 (65 kDa) isoforms were detected in hRPE extracts by immunoblotting. No alpha 2 and alpha 3 RNA transcripts were found in the hRPE. Quantification of beta 2 mRNA by RT-PCR revealed 2.7 x 10(5) molecules per ng of poly A+ RNA. This is similar to the beta 1 isoform levels reported previously from our laboratory. These data demonstrate the coexistence of significant amounts of alpha 1, beta 1 and beta 2 Na,K-ATPase subunits in the RPE. It is therefore reasonable to suggest that both alpha 1 beta 1 and alpha 1 beta 2 heterodimers are present in these cells.