The association between influenza vaccination uptake and influenza and pneumonia-associated deaths in the United States

BACKGROUND

The influenza mortality burden has remained substantial in the United States (US) despite relatively high levels of influenza vaccine uptake. This has led to questions regarding the effectiveness of the program against this outcome, particularly in the elderly. The aim of this evaluation was to develop and explore a new approach to estimating the population-level effect of influenza vaccination uptake on pneumonia and influenza (P&I) associated deaths.

METHODS

Using publicly available data we examined the association between state-level influenza vaccination and all-age P&I associated deaths in the US from the 2013-2014 influenza season to the 2018-2019 season. In the main model, we evaluated influenza vaccine uptake in all those age 6 months and older. We used a mixed-effects regression analysis with generalised least squares estimation to account for within state correlation in P&I mortality.

RESULTS

From 2013-2014 through 2018-2019, the total number of all-age P&I related deaths during the influenza seasons was 480,111. The mean overall cumulative influenza vaccine uptake (age 6 months and older) across the states and years considered was 46.7%, with higher uptake (64.8%) observed in those aged ≥ 65 years. We found that overall influenza vaccine uptake (6 months and older) had a statistically significant protective association with the P&I death rate. This translated to a 0.33 (95% CI: 0.20, 0.47) per 100,000 population reduction in P&I deaths in the influenza season per 1% increase in overall influenza vaccine uptake.

DISCUSSION

These results using a population-level statistical approach provide additional support for the overall effectiveness of the US influenza vaccination program. This reassurance is critical given the importance of ensuring confidence in this life saving program. Future research is needed to expand on our approach using more refined data.

Supply-side readiness to deliver HIV testing and treatment services in Indonesia: Going the last mile to eliminate mother-to-child transmission of HIV

INTRODUCTION

Despite national efforts to integrate Prevention of Mother-to-Child Transmission (PMTCT) of HIV services into antenatal care in Indonesia, the rate of mother-to-child transmission of HIV remains the highest in the world. A range of barriers to uptake and long-term engagement in care have been identified, but far less is known about health system preparedness to deliver PMTCT of HIV services. This study explored supply-side barriers to the delivery of PMTCT services in Indonesia and whether these factors are associated with the uptake of antenatal HIV testing.

MATERIALS AND METHODS

An ecological analysis was undertaken, linking data from the World Bank Quality Service and Delivery Survey (2016) with routine data from Indonesia's HIV and AIDS case surveillance system and district health profile reports (2016). Supply-side readiness scores-generated from a readiness index that measures overall structural capacity and is often used as proxy for quality of care-were adapted from the WHO Service Availability and Readiness Assessment and presented by sector and geographic area. Univariate and multivariate regression analysis was used to explore factors associated with the uptake of antenatal HIV testing in public facilities.

RESULTS

In general, public facilities scored more highly in most inputs compared to private facilities. Facilities located in urban areas also scored more highly in the majority of inputs compared to ones in rural areas. Readiness scores were lowest for PMTCT services compared to Antenatal Care and HIV Care and Support services, especially for the availability of medicines such as zidovudine and nevirapine. The national composite readiness score for PMTCT was only 0.13 (based on a maximum score of 1) with a composite score of 0.21 for public facilities and 0.06 for private facilities. The multivariate analysis shows that the proportion of pregnant women tested for HIV was more likely to be greater than or equal to 10% in facilities with a higher readiness score and a higher number of trained counsellors available, and less likely in facilities located outside of Java-Bali and in facilities supporting a higher number of village midwives.

DISCUSSION

Despite targeted efforts by the Indonesian government and multinational agencies, significant gaps exist in the delivery of PMTCT that compromise the standard of care delivered in Indonesia. Future strategies should focus on improving the availability of tests and treatment, especially in the private sector and in rural areas.

Virological failure and treatment switch after ART initiation among people living with HIV with and without routine viral load monitoring in Asia

Introduction

Viral load (VL) testing is still challenging to monitor treatment responses of antiretroviral therapy (ART) for HIV treatment programme in Asia. We assessed the association between routine VL testing and virological failure (VF) and determine factors associated with switching to second‐line regimen.

Methods

Among 21 sites from the TREAT Asia HIV Observational Database (TAHOD), people living with HIV (PLHIV) aged ≥18 years initiating ART from 2003 to 2021 were included. We calculated the average number of VL tests per patient per year between the date of ART initiation and the most recent visit. If the median average number of VL tests was ≥ 0.80 per patient per year, the site was classified as a routine VL site. A site with a median < 0.80 was classified into the non‐routine VL sites. VF was defined as VL ≥1000 copies/ml during first‐line therapy. Factors associated with VF were analysed using generalized estimating equations with Poisson distribution.

Results

Of 6277 PLHIV starting ART after 2003, 3030 (48%) were from 11 routine VL testing sites and 3247 (52%) were from 10 non‐routine VL testing sites. The median follow‐up was 9 years (IQR 5–13). The median age was 35 (30–42) years; 68% were male and 5729 (91%) started non‐nucleoside reverse‐transcriptase inhibitor‐based regimen. The median pre‐ART CD4 count in PLHIV from routine VL sites was lower compared to non‐routine VL sites (144 vs. 156 cells/mm³, p <0.001). Overall, 1021 subsequent VF at a rate of 2.15 (95% CI 2.02–2.29) per 100 person‐years (PY). VF was more frequent at non‐routine VL sites (adjusted incidence rate ratio 2.85 [95% CI 2.27–3.59]) compared to routine VL sites. Other factors associated with an increased rate of VF were age <50 years and CD4 count <350 cells/mm³. A total of 817 (13%) patients switched to second‐line regimen at a rate of 1.44 (95% CI 1.35–1.54) per 100 PY. PLHIV at routine VL monitoring sites were at higher risk of switching than those at non‐routine VL sites (adjusted sub‐hazard ratio 1.78 95% CI [1.17–2.71]).

Conclusions

PLHIV from non‐routine VL sites had a higher incidence of persistent VF and a low switching regimen rate, reflecting possible under‐utilized VL testing.

Relationship between symptoms, barriers to care and healthcare utilisation among children under five in rural Mali

Objectives

To identify social and structural barriers to timely utilisation of qualified providers among children under five years in a high‐mortality setting, rural Mali and to analyse how utilisation varies by symptom manifestation.

Methods

Using baseline household survey data from a cluster‐randomised trial, we assessed symptom patterns and healthcare trajectories of 5117 children whose mothers reported fever, diarrhoea, bloody stools, cough and/or fast breathing in the preceding two weeks. We examine associations between socio‐demographic factors, symptoms and utilisation outcomes in mixed‐effect logistic regressions.

Results

Almost half of recently ill children reported multiple symptoms (46.2%). Over half (55.9%) received any treatment, while less than one‐quarter (21.7%) received care from a doctor, nurse, midwife, trained community health worker or pharmacist within 24 h of symptom onset. Distance to primary health facility, household wealth and maternal education were consistently associated with better utilisation outcomes. While children with potentially more severe symptoms such as fever and cough with fast breathing or diarrhoea with bloody stools were more likely to receive any care, they were no more likely than children with fever to receive timely care with a qualified provider.

Conclusions

Even distances as short as 2–5 km significantly reduced children’s likelihood of utilising healthcare relative to those within 2 km of a facility. While children with symptoms indicative of pneumonia and malaria were more likely to receive any care, suggesting mothers and caregivers recognised potentially severe illness, multiple barriers to care contributed to delays and low utilisation of qualified providers, illustrating the need for improved consideration of barriers.

β1D integrin splice variant stabilizes integrin dynamics and reduces integrin signaling by limiting paxillin recruitment

Heterodimeric integrin receptors control cell adhesion, migration and extracellular matrix assembly. While the α integrin subunit determines extracellular ligand specificity, the β integrin chain binds to an acidic residue of the ligand, and cytoplasmic adapter protein families such as talins, kindlins and paxillin, to form mechanosensing cell matrix adhesions. Alternative splicing of the β1 integrin cytoplasmic tail creates ubiquitously expressed β1A, and the heart and skeletal muscle-specific β1D form. To study the physiological difference between these forms, we developed fluorescent β1 integrins and analyzed their dynamics, localization, and cytoplasmic adapter recruitment and effects on cell proliferation. On fibronectin, GFP-tagged β1A integrin showed dynamic exchange in peripheral focal adhesions, and long, central fibrillar adhesions. In contrast, GFP-β1D integrins exchanged slowly, forming immobile and short central adhesions. While adhesion recruitment of GFP-β1A integrin was sensitive to C-terminal tail mutagenesis, GFP-β1D integrin was recruited independently of the distal NPXY motif. In addition, a P786A mutation in the proximal, talin-binding NPXY⁷⁸³ motif switched β1D to a highly dynamic integrin. In contrast, the inverse A786P mutation in β1A integrin interfered with paxillin recruitment and proliferation. Thus, differential β1 integrin splicing controls integrin-dependent adhesion signaling, to adapt to the specific physiological needs of differentiated muscle cells.

Prediction Model of Pre-treatment HIV RNA Levels in Naïve Thai HIV-infected Patients: Application for Resource-limited Settings

A prediction model for pretreatment HIV RNA level ≤100,000 copies/ml would provide a useful tool for selection of abacavir (ABC) or rilpivirine (RPV) in the first-line regimen in a resource-limited setting. Factors associated with pre-treatment HIV RNA ≤100,000 copies/ml were determined from a cohort of 1,223 patients divided into a derivation (n = 873) and the remaining in a validation group. Their median [interquartile range (IQR)] age was 36.3 (30.5-42.9) years, CD4 count 122 (39-216) cells/mm3 and pre-treatment HIV RNA level 100,000 (32,449-229,777) copies/ml. Factors associated with pretreatment HIV RNA ≤100,000 copies/ml were non-anemia [odds ratio (OR)= 2.05; 95% confidence interval (CI): 1.28-3.27, p= 0.003], CD4 count ≥200 cells/mm3 (OR= 3.00; 95% CI: 2.08-4.33, p<0.001) and non-heterosexual HIV exposure (OR= 1.61; 95% CI: 1.07-2.43, p= 0.021). The area under a receiver operating characteristic curve was 0.66 (95% CI: 0.62-0.69), but specificity was 97.3%. The prediction model identified a set of readily available clinical data but lacked the requisite predictive performance to fulfill its purpose.

Changes in renal function with long-term exposure to antiretroviral therapy in HIV-infected adults in Asia

PURPOSE

Renal disease is common among people living with human immunodeficiency virus (HIV). However, there is limited information on the incidence and risk factors associated with renal dysfunction among this population in Asia.

METHODS

We used data from the TREAT Asia HIV Observational Database. Patients were included if they started antiretroviral therapy during or after 2003, had a serum creatinine measurement at antiretroviral therapy initiation (baseline), and had at least 2 follow-up creatinine measurements taken ≥3 months apart. Patients with a baseline estimated glomerular filtration rate (eGFR) ≤60 mL/min/1.73 m2 were excluded. Chronic kidney disease was defined as 2 consecutive eGFR values ≤60 mL/min/1.73 m2 taken ≥3 months apart. Generalized estimating equations were used to identify factors associated with eGFR change. Competing risk regression adjusted for study site, age and sex, and cumulative incidence plots were used to evaluate factors associated with chronic kidney disease (CKD).

RESULTS

Of 2547 patients eligible for this analysis, tenofovir was being used by 703 (27.6%) at baseline. Tenofovir use, high baseline eGFR, advanced HIV disease stage, and low nadir CD4 were associated with a decrease in eGFR during follow-up. Chronic kidney disease occurred at a rate of 3.4 per 1000 patient/years. Factors associated with CKD were tenofovir use, old age, low baseline eGFR, low nadir CD4, and protease inhibitor use.

CONCLUSIONS

There is an urgent need to enhance renal monitoring and management capacity among at-risk groups in Asia and improve access to less nephrotoxic antiretrovirals.

The treatment outcomes of antiretroviral substitutions in routine clinical settings in Asia; data from the TREAT Asia HIV Observational Database (TAHOD)

Introduction

Although substitutions of antiretroviral regimen are generally safe, most data on substitutions are based on results from clinical trials. The objective of this study was to evaluate the treatment outcomes of substituting antiretroviral regimen in virologically suppressed HIV‐infected patients in non‐clinical trial settings in Asian countries.

Methods

The study population consisted of HIV‐infected patients enrolled in the TREAT Asia HIV Observational Database (TAHOD). Individuals were included in this analysis if they started combination antiretroviral treatment (cART) after 2002, were being treated at a centre that documented a median rate of viral load monitoring ≥0.8 tests/patient/year among TAHOD enrolees, and experienced a minor or major treatment substitution while on virally suppressive cART. The primary endpoint to evaluate outcomes was clinical or virological failure (VF), followed by an ART class change. Clinical failure was defined as death or an AIDS diagnosis. VF was defined as confirmed viral load measurements ≥400 copies/mL followed by an ART class change within six months. Minor regimen substitutions were defined as within‐class changes and major regimen substitutions were defined as changes to a drug class. The patterns of substitutions and rate of clinical or VF after substitutions were analyzed.

Results

Of 3994 adults who started ART after 2002, 3119 (78.1%) had at least one period of virological suppression. Among these, 1170 (37.5%) underwent a minor regimen substitution, and 296 (9.5%) underwent a major regimen substitution during suppression. The rates of clinical or VF were 1.48/100 person years (95% CI 1.14 to 1.91) in the minor substitution group, 2.85/100 person years (95% CI 1.88 to 4.33) in the major substitution group and 2.53/100 person years (95% CI 2.20 to 2.92) among patients that did not undergo a treatment substitution.

Conclusions

The rate of clinical or VF was low in both major and minor substitution groups, showing that regimen substitution is generally effective in non‐clinical trial settings in Asian countries.

Effect of Macrolide Prophylactic Therapy on AIDS-Defining Conditions and HIV-Related Mortality

Background

Mycobacterium avium–intracelllulare complex (MAC) prophylaxis is recommended for patients with CD4 counts of &lt; 50 cells/mm3. With the significant decrease in incidence of disseminated MAC infection and the effective immune recovery due to the availability of combination antiretroviral therapy (ART), the benefits of giving MAC prophylaxis were investigated. This study examined the impact of macrolide prophylaxis on AIDS-defining conditions and HIV-associated mortality in a cohort of HIV-infected patients on ART.

Methods

TREAT Asia HIV Observational Database (TAHOD) patients aged ≥18 years with a CD4 count &lt; 50 cells/mm3 at ART initiation were included. The effect of macrolide prohylaxis on HIV-associated mortality or an AIDS event (as a combined outcome) and HIV-associated mortality alone were evaluated using competing risk regression. Sensitivity analysis was conducted to assess whether results were consistent in patients with a CD4 &lt; 100 cells/mm3 at ART initiation.

Results

Of 1,345 eligible patients (78% male with median age at ART initiation of 34.8 years), 10.6% received macrolide prophylaxis. The rates of the combined outcome and HIV-associated mortality per 100 patient years were 7.35 [95% confidence interval (CI): 6.04–8.95] and 3.14 (95% CI: 2.35–4.19), respectively. After adjusting for possible confounders, macrolide use was associated with a significantly decreased risk of HIV-associated mortality (HR 0.10, 95% CI: 0.01–0.80, P = 0.031) but not the combined outcome (HR 0.86, 95% CI: 0.32–2.229, P = 0.764). Sensitivity analyses showed that, among patients with a CD4 &lt; 100 cells/ mm3 at ART initiation, these results were consistent.

Conclusion

Macrolide prophylaxis is associated with significantly improved survival among Asian HIV-infected patients with very low CD4 cell counts. The benefits of giving macrolide prophylaxis remain despite the availability of effective ART.

Disclosures

All authors: No reported disclosures.

The Safety of Substitution of Antiretroviral Regimen in Non-Clinical Trial Settings in Asian Countries

Background

Although substitutions of antiretroviral regimen are generally safe, most data on substitutions are based on results from clinical trials. The objective of this study was to evaluate the safety of substituting antiretroviral regimen in virologically suppressed HIV-infected patients in non-clinical trial settings in Asian countries.

Methods

HIV-infected patients enrolled in the TREAT Asia HIV Observational Database (TAHOD) were included in this analysis if they started combination antiretroviral therapy (cART) after 2002, were being treated at a center that documented a median rate of viral load (VL) monitoring ≥ 1 tests/patient/year, and experienced a minor or major treatment substitution while on virally suppressive cART (VL &lt; 200 copies/mL). Minor regimen substitutions were defined as within-class changes and major regimen substitutions were defined as changes to a drug class. Virologic failure was defined as having had two viral load measurements &gt; 400 copies/mL. The patterns of substitutions and rate of virologic failure after substitutions were analyzed.

Results

Of 3,994 adults who started ART after 2002, 3,119 (78.1%) had at least one period of virological suppression. Among these, 1,170 (37.5%) underwent a minor regimen substitution, and 296 (9.5%) underwent a major regimen substitution during suppression. The rates of virological failure were 1.48/100person years (95% CI 1.14–1.91) in the minor substitution group and 2.85/100person years (95% CI 1.88–4.33) in the major substitution group, and 2.53/100person years (95% CI 2.20–2.92) among patients that did not undergo a treatment substitution.

Conclusion

The rate of virological failure was relatively low in both major and minor substitution groups, showing that regimen substitution is generally safe in non-clinical trial settings in Asian countries.

Disclosures

All authors: No reported disclosures.

A Prediction Model of Pretreatment HIV RNA Levels in Naïve Thai HIV-infected Patients: An Application for Resource-limited Settings

Background

The use of abacavir (ABC) and rilpivirine (RPV) in the first-line regimen for naïve HIV-infected patients with pretreatment HIV RNA >100,000 copies/mL is not recommended due to a high rate of treatment failure. If a model could accurately predict pretreatment HIV RNA levels, it would be a useful tool for the selection ABC or RPV in the first-line regimen.

Methods

Thai HIV-infected adults enrolled in the TREAT Asia HIV Observational Database (TAHOD) and additional patients of Ramathibodi Hospital were eligible if they had an HIV RNA result at the time of antiretroviral therapy initiation. Factors associated with pretreatment HIV RNA <100,000 copies/mL were determined by logistic regression. Based on the results of the final model, a prediction model was created.

Results

A total of 1,223 patients were included in the analysis. Among those in the derivation data set, median [interquartile range (IQR)] age was 36.3 (30.5–42.9) years, median (IQR) CD4 count was 122 (39–216) cells/mm³, and pretreatment HIV RNA was 100,000 (32,449–229,777) copies/mL. Factors associated with pretreatment HIV RNA <100,000 copies/mL were anemia [odds ratio (OR) 2.05 vs. no anemia; 95% confidence interval (CI) 1.28–3.27], CD4 count >200 cells/mm³ (OR 3.00 vs. CD4 count <200 cells/mm³; 95% CI 2.08–4.33), and non-heterosexual HIV exposure (OR 1.61 vs. heterosexual HIV exposure; 95% CI 1.07–2.43). No AIDS-defining illness (11.5), no anemia (18.5), age <35 years (11), CD4 count >200 cells/mm³ (27), duration of HIV infection >1 year (9), and weight >50 years (11) were included in the clinical prediction tool scores. A score ≥45 yielded a sensitivity of 45.3%, specificity of 76.7%, positive predictive value of 68.1%, and negative predictive value of 56.1% among patients in the derivation. The area under the receiver-operator characteristic curve was 0.655 (95% CI 0.614- 0.696) and 0.600 (95% CI 0.533–0.667) in the derivation and validation patients, respectively.

Conclusion

Our final prediction model had poor sensitivity and specificity for predicting HIV RNA <100,000 copies/mL. Further study on a larger population with a greater diversity of data variables available is necessary to improve the model. Pretreatment HIV RNA remains necessary before ABC or RPV initiation for naïve Thai HIV-infected patients.

Disclosures

All authors: No reported disclosures.

Smoking and projected cardiovascular risk in an HIV-positive Asian regional cohort

OBJECTIVES

The aim of the study was to assess the prevalence and characteristics associated with current smoking in an Asian HIV-positive cohort, to calculate the predictive risks of cardiovascular disease (CVD), coronary heart disease (CHD) and myocardial infarction (MI), and to identify the impact that simulated interventions may have.

METHODS

Logistic regression analysis was used to distinguish associated current smoking characteristics. Five-year predictive risks of CVD, CHD and MI and the impact of simulated interventions were calculated utilizing the Data Collection on Adverse Effects of Anti-HIV Drugs Study (D:A:D) algorithm.

RESULTS

Smoking status data were collected from 4274 participants and 1496 of these had sufficient data for simulated intervention calculations. Current smoking prevalence in these two groups was similar (23.2% vs. 19.9%, respectively). Characteristics associated with current smoking included age > 50 years compared with 30-39 years [odds ratio (OR) 0.65; 95% confidence interval (CI) 0.51-0.83], HIV exposure through injecting drug use compared with heterosexual exposure (OR 3.03; 95% CI 2.25-4.07), and receiving antiretroviral therapy (ART) at study sites in Singapore, South Korea, Malaysia, Japan and Vietnam in comparison to Thailand (all OR > 2). Women were less likely to smoke than men (OR 0.11; 95% CI 0.08-0.14). In simulated interventions, smoking cessation demonstrated the greatest impact in reducing CVD and CHD risk and closely approximated the impact of switching from abacavir to an alternate antiretroviral in the reduction of 5-year MI risk.

CONCLUSIONS

Multiple interventions could reduce CVD, CHD and MI risk in Asian HIV-positive patients, with smoking cessation potentially being the most influential.

Factors associated with pre-treatment HIV RNA: application for the use of abacavir and rilpivirine as the first-line regimen for HIV-infected patients in resource-limited settings

Background

Abacavir and rilpivirine are alternative antiretroviral drugs for treatment-naïve HIV-infected patients. However, both drugs are only recommended for the patients who have pre-treatment HIV RNA <100,000 copies/mL. In resource-limited settings, pre-treatment HIV RNA is not routinely performed and not widely available. The aims of this study are to determine factors associated with pre-treatment HIV RNA <100,000 copies/mL and to construct a model to predict this outcome.

Methods

HIV-infected adults enrolled in the TREAT Asia HIV Observational Database were eligible if they had an HIV RNA measurement documented at the time of ART initiation. The dataset was randomly split into a derivation data set (75% of patients) and a validation data set (25%). Factors associated with pre-treatment HIV RNA <100,000 copies/mL were evaluated by logistic regression adjusted for study site. A prediction model and prediction scores were created.

Results

A total of 2592 patients were enrolled for the analysis. Median [interquartile range (IQR)] age was 35.8 (29.9–42.5) years; CD4 count was 147 (50–248) cells/mm³; and pre-treatment HIV RNA was 100,000 (34,045–301,075) copies/mL. Factors associated with pre-treatment HIV RNA <100,000 copies/mL were age <30 years [OR 1.40 vs. 41–50 years; 95% confidence interval (CI) 1.10–1.80, p = 0.01], body mass index >30 kg/m² (OR 2.4 vs. <18.5 kg/m²; 95% CI 1.1–5.1, p = 0.02), anemia (OR 1.70; 95% CI 1.40–2.10, p < 0.01), CD4 count >350 cells/mm³ (OR 3.9 vs. <100 cells/mm³; 95% CI 2.0–4.1, p < 0.01), total lymphocyte count >2000 cells/mm³ (OR 1.7 vs. <1000 cells/mm³; 95% CI 1.3–2.3, p < 0.01), and no prior AIDS-defining illness (OR 1.8; 95% CI 1.5–2.3, p < 0.01). Receiver-operator characteristic (ROC) analysis yielded area under the curve of 0.70 (95% CI 0.67–0.72) among derivation patients and 0.69 (95% CI 0.65–0.74) among validation patients. A cut off score >25 yielded the sensitivity of 46.7%, specificity of 79.1%, positive predictive value of 67.7%, and negative predictive value of 61.2% for prediction of pre-treatment HIV RNA <100,000 copies/mL among derivation patients.

Conclusion

A model prediction for pre-treatment HIV RNA <100,000 copies/mL produced an area under the ROC curve of 0.70. A larger sample size for prediction model development as well as for model validation is warranted.

Chronic hepatitis C infection and liver disease in HIV-coinfected patients in Asia

Data on markers of hepatitis C virus (HCV) disease in HIV-HCV-coinfected patients in resource-limited settings are scarce. We assessed HCV RNA, HCV genotype (GT), IL28B GT and liver fibrosis (FibroScan® ) in 480 HIV-infected patients with positive HCV antibody in four HIV treatment centres in South-East Asia. We enrolled 165 (34.4%) patients in Jakarta, 158 (32.9%) in Bangkok, 110 (22.9%) in Hanoi and 47 (9.8%) in Kuala Lumpur. Overall, 426 (88.8%) were male, the median (IQR) age was 38.1 (34.7-42.5) years, 365 (76.0%) reported HCV exposure through injecting drug use, and 453 (94.4%) were on combination antiretroviral therapy. The median (IQR) CD4 count was 446 (325-614) cells/mm3 and 208 (94.1%) of 221 patients tested had HIV-1 RNA <400 copies/mL. A total of 412 (85.8%) had detectable HCV RNA, at a median (IQR) of 6.2 (5.4-6.6) log10 IU/mL. Among 380 patients with HCV GT, 223 (58.7%) had GT1, 97 (25.5%) had GT3, 43 (11.3%) had GT6, eight (2.1%) had GT4, two (0.5%) had GT2, and seven (1.8%) had indeterminate GT. Of 222 patients with IL28B testing, 189 (85.1%) had rs12979860 CC genotype, and 199 (89.6%) had rs8099917 TT genotype. Of 380 patients with FibroScan® , 143 (37.6%) had no/mild liver fibrosis (F0-F1), 83 (21.8%) had moderate fibrosis (F2), 74 (19.5%) had severe fibrosis (F3), and 79 (20.8%) had cirrhosis (F4). One patient (0.3%) had FibroScan® failure. In conclusion, a high proportion of HIV-HCV-coinfected patients had chronic HCV infection. HCV GT1 was predominant, and 62% of patients had liver disease warranting prompt treatment (≥F2).

The Reliability, Validity and Responsiveness of Two Disease Scores (BPDAI and ABSIS) for Bullous Pemphigoid: Which One to Use?

A significant obstacle in guiding evidence-based management of bullous pemphigoid (BP) is the lack of a standardised, validated scoring system for the condition. The aim of this study is to evaluate the suitability of the Bullous Pemphigoid Disease Area Index (BPDAI) and the Autoimmune Bullous Skin disorder Intensity Score (ABSIS) as outcome measures for BP in clinical trials. Thirty-two BP patients were repeatedly assessed over four years using Physician Global Assessment (PGA), anti-BP180 ELISA titres, BPDAI, ABSIS, BPDAI-Pruritus, Autoimmune Bullous Disease Quality of Life (ABQOL) and Treatment of Autoimmune Bullous Disease Quality of Life (TABQOL) questionnaires. The reliability, validity, responsiveness, and minimal clinically important differences (MCIDs) were calculated. For inter-rater reliability, the intraclass correlation coefficients (95% CI) were: BPDAI 0.957 (0.901-0.982) and ABSIS 0.881 (0.736-0.949). Compared to ABSIS, BPDAI was better correlated with PGA(r = 0.875, p < 0.001), BPDAI-Pruritus (r=0.632, p = 0.004), ABQOL (r = 0.521, p = 0.011) and TABQOL (r=0.538, p = 0.008). MCIDs for BPDAI were 4-points for assessing clinical improvement and 3-points for deterioration. ABSIS demonstrated less responsiveness with MCIDs at 8.6-points for improvement and 4-points for deterioration. These results indicate that BPDAI demonstrated excellent reliability, validity and responsiveness, while ABSIS had moderate to good reliability, validity and responsiveness.

Incidence of syphilis seroconversion among HIV-infected persons in Asia: results from the TREAT Asia HIV Observational Database

INTRODUCTION

Outbreaks of syphilis have been described among HIV-infected men who have sex with men (MSM) in Western communities, whereas reports in Asian countries are limited. We aimed to characterize the incidence and temporal trends of syphilis among HIV-infected MSM compared with HIV-infected non-MSM in Asian countries.

METHODS

Patients enrolled in the TREAT Asia HIV Observational Database cohort and with a negative non-treponemal test since enrolment were analyzed. Incidence of syphilis seroconversion, defined as a positive non-treponemal test after previously testing negative, was evaluated among patients at sites performing non-treponemal tests at least annually. Factors associated with syphilis seroconversion were investigated at sites doing non-treponemal testing in all new patients and subsequently testing routinely or when patients were suspected of having syphilis.

RESULTS

We included 1010 patients from five sites that performed non-treponemal tests in all new patients; those included had negative non-treponemal test results during enrolment and subsequent follow-ups. Among them, 657 patients were from three sites conducting regular non-treponemal testing. The incidence of syphilis seroconversion was 5.38/100 person-years (PY). Incidence was higher in MSM than non-MSM (7.64/100 PY vs. 2.44/100 PY, p<0.001). Among MSM, the incidence rate ratio (IRR) for every additional year from 2009 was 1.19 (p=0.051). MSM status (IRR 3.48, 95% confidence interval (CI) 1.88-6.47), past syphilis diagnosis (IRR 5.15, 95% CI 3.69-7.17) and younger age (IRR 0.84 for every additional 10 years, 95% CI 0.706-0.997) were significantly associated with syphilis seroconversion.

CONCLUSIONS

We observed a higher incidence of syphilis seroconversion among HIV-infected MSM and a trend to increasing annual incidence. Regular screening for syphilis and targeted interventions to limit transmission are needed in this population.

HIV-infected children in the Asia-Pacific region with baseline severe anemia: antiretroviral therapy and outcomes

BACKGROUND

Severe anemia is common among children infected with human immunodeficiency virus (HIV). The choice of antiretroviral (ART) regimen needs careful consideration. No information is available regarding the initial ART regimens used in the Asia-Pacific region and the rate of switch of ART regimens in HIV-infected children with severe anemia.

OBJECTIVES

To study the initial ART regimens and the rate of switch of ART regimens used during the first 36 months in HIV-infected children with severe anemia and to evaluate their clinical and laboratory outcomes.

METHODS

We analyzed regional cohort data of 130 Asian children aged <18 years with baseline severe anemia (hemoglobin <7.5 g/dl) who started antiretroviral therapy (ART) between January 2003 and September 2013.

RESULTS

At ART initiation, median age was 3.5 years old (interquartile range (IQR) 1.7 to 6.3) and median hemoglobin was 6.7 g/dL (IQR 5.9-7.1, range 3.0-7.4). Initial ART regimens included stavudine (85.4%), zidovudine (13.8%), and abacavir (0.8%). In 81 children with available hemoglobin data after 6 months of ART, 90% recovered from severe anemia with a median hemoglobin of 10.7 g/dL (IQR 9.6-11.7, range 4.4-13.5). Those starting AZT-based ART had a mortality rate of 10.8 (95% confidence interval (CI) 4.8-23.9) per 100 patient-years compared to 2.7 (95% CI 1.6-4.6) per 100 patient-years among those who started d4T-based ART.

CONCLUSIONS

With the phase-out of stavudine, age-appropriate non-zidovudine options are needed for younger Asian children with severe anemia.

Niche anchorage and signaling through membrane-bound Kit-ligand/c-kit receptor are kinase independent and imatinib insensitive

Kit ligand (KitL) and its tyrosine kinase receptor c-kit are critical for germ cells, melanocytes, mastocytes, and hematopoietic stem cells. Alternative splicing of KitL generates membrane-bound KitL (mb-KitL) or soluble KitL, providing survival or cell migration, respectively. Here we analyzed whether c-kit can function both as an adhesion and signaling receptor to mb-KitL presented by the environmental niche. At contacts between fibroblasts and MC/9 mast cells, mb-KitL, and c-kit formed ligand/receptor clusters that formed stable complexes, which resisted dissociation by c-kit blocking mAbs and provided cell anchorage under physiological shear stresses. Clusters recruited tyrosine-phosphorylated proteins and induced spatially restricted F-actin polymerization. Mutational analysis of c-kit demonstrated kinase-independent mb-KitL/c-kit clustering, anchorage, F-actin polymerization, and Tyr567-dependent cluster phosphorylation. Kinase inhibition of c-kit by imatinib reduced cluster coalescence, but allowed cluster phosphorylation and F-actin polymerization, which required PI3K recruitment and a newly identified juxtamembrane residue. Synergies between integrin and c-kit-mediated spreading and adhesion of MC/9 cells were studied in vitro on immobilized-KitL/fibronectin surfaces. While c-kit blocking antibodies prevented spreading, imatinib blocked spreading induced by soluble- but not immobilized KitL. Thus, "mechanical" activation of c-kit provides signaling, niche-anchorage, and synergies with integrin-mediated adhesion, which is independent of kinase function and resistant to c-kit kinase inhibitors.-

Trends of CD4 cell count levels at the initiation of antiretroviral therapy over time and factors associated with late initiation of antiretroviral therapy among Asian HIV-positive patients

INTRODUCTION

Although antiretroviral therapy (ART) has been rapidly scaled up in Asia, most HIV-positive patients in the region still present with late-stage HIV disease. We aimed to determine trends of pre-ART CD4 levels over time in Asian HIV-positive patients and to determine factors associated with late ART initiation.

METHODS

Data from two regional cohort observational databases were analyzed for trends in median CD4 cell counts at ART initiation and the proportion of late ART initiation (CD4 cell counts <200 cells/mm(3) or prior AIDS diagnosis). Predictors for late ART initiation and mortality were determined.

RESULTS

A total of 2737 HIV-positive ART-naïve patients from 22 sites in 13 Asian countries and territories were eligible. The overall median (IQR) CD4 cell count at ART initiation was 150 (46-241) cells/mm(3). Median CD4 cell counts at ART initiation increased over time, from a low point of 115 cells/mm(3) in 2008 to a peak of 302 cells/mm(3) after 2011 (p for trend 0.002). The proportion of patients with late ART initiation significantly decreased over time from 79.1% before 2007 to 36.3% after 2011 (p for trend <0.001). Factors associated with late ART initiation were year of ART initiation (e.g. 2010 vs. before 2007; OR 0.40, 95% CI 0.27-0.59; p<0.001), sex (male vs. female; OR 1.51, 95% CI 1.18-1.93; p=0.001) and HIV exposure risk (heterosexual vs. homosexual; OR 1.66, 95% CI 1.24-2.23; p=0.001 and intravenous drug use vs. homosexual; OR 3.03, 95% CI 1.77-5.21; p<0.001). Factors associated with mortality after ART initiation were late ART initiation (HR 2.13, 95% CI 1.19-3.79; p=0.010), sex (male vs. female; HR 2.12, 95% CI 1.31-3.43; p=0.002), age (≥51 vs. ≤30 years; HR 3.91, 95% CI 2.18-7.04; p<0.001) and hepatitis C serostatus (positive vs. negative; HR 2.48, 95% CI 1.-4.36; p=0.035).

CONCLUSIONS

Median CD4 cell count at ART initiation among Asian patients significantly increases over time but the proportion of patients with late ART initiation is still significant. ART initiation at higher CD4 cell counts remains a challenge. Strategic interventions to increase earlier diagnosis of HIV infection and prompt more rapid linkage to ART must be implemented.

The glycophorin A transmembrane sequence within integrin αvβ3 creates a non-signaling integrin with low basal affinity that is strongly adhesive under force

Integrin heterodimeric cell adhesion and signaling receptors bind ligands of the extracellular matrix and relay signals bidirectionally across cell membranes. Thereby, integrins adopt multiple conformational and functional states that control ligand binding affinity and linkage to cytosolic/cytoskeletal proteins. Here, we designed an integrin chimera encompassing the strongly dimerizing transmembrane domain (TMD) of glycophorin A (GpA) in the context of the otherwise unaltered integrin αvβ3. We hypothesized that this chimera should have a low basal affinity to soluble ligand but should be force-activatable. By cellular expression of this chimera, we found a decreased integrin affinity to a soluble peptide ligand and inhibited intracellular signaling. However, under external forces applied by an atomic force microscope or by a spinning disc device causing shear forces, the mutant caused stronger cell adhesion than the wild-type integrin. Our results demonstrate that the signaling- and migration-incapable integrin αvβ3-TMD mutant TMD-GpA shows the characteristics of a primed integrin state, which is of low basal affinity in the absence of forces, but may form strong bonds in the presence of forces. Thus, TMD-GpA may mimic a force-activatable signaling intermediate.

Using force to visualize conformational activation of integrins

The development of biophysical approaches to analyze integrin–ligand binding allows us to visualize in real time the conformational changes that shift the bond affinity between low- and high-affinity states. In this issue, Chen et al. (2012. J. Cell Biol.http://dx.doi.org/jcb.201201091) use these approaches to validate some aspects of the classical integrin regulation model; however, their data suggest that much of the regulation occurs after ligand binding rather than in preparation for ligand binding to occur.

Mechanical control of integrin-mediated adhesion and signaling

Integrin-mediated adhesion is controlled by the number of bonds between cell surface integrins and substrate-bound ligands. Integrin-ligand affinity is modulated by chemical allostery, mechanical allostery and integrin clustering. This review analyzes how each of these factors changes through the phases of cell attachment, adhesion strengthening, and clustering. The analysis predicts a dominant role of mechanical factors in both adhesive regulation and integrin signaling for adherent cells. New approaches and experimental analyses will be required to substantiate this hypothesis.

Fibronectin extra domain-A promotes hepatic stellate cell motility but not differentiation into myofibroblasts

BACKGROUND & AIMS

Myofibroblasts are the primary cell type involved in physiologic wound healing and its pathologic counterpart, fibrosis. Cellular fibronectin that contains the alternatively spliced extra domain A (EIIIA) is up-regulated during these processes and is believed to promote myofibroblast differentiation. We sought to determine the requirement for EIIIA in fibrosis and differentiation of myofibroblasts in rodent livers.

METHODS

We used a mechanically tunable hydrogel cell culture system to study differentiation of primary hepatic stellate cells and portal fibroblasts from rats into myofibroblasts. Liver fibrosis was induced in mice by bile duct ligation or administration of thioacetamide.

RESULTS

EIIIA was not required for differentiation of rat hepatic stellate cells or portal fibroblasts into fibrogenic myofibroblasts. Instead, hepatic stellate cells cultured on EIIIA-containing cellular fibronectin formed increased numbers of lamellipodia; their random motility and chemotaxis also increased. These increases required the receptor for EIIIA, the integrin α(9)β(1). In contrast, the motility of portal fibroblasts did not increase on EIIIA, and these cells expressed little α(9)β(1). Male EIIIA(-/-) mice were modestly protected from thioacetamide-induced fibrosis, which requires motile hepatic stellate cells, but not from bile duct ligation-induced fibrosis, in which portal fibroblasts are more important. Notably, myofibroblasts developed during induction of fibrosis with either thioacetamide or bile duct ligation in EIIIA(-/-) mice.

CONCLUSIONS

EIIIA is dispensable for differentiation of hepatic stellate cells and portal fibroblasts to myofibroblasts, both in culture and in mouse models of fibrosis. Our findings, however, indicate a role for EIIIA in promoting stellate cell motility and parenchymal liver fibrosis.

Integrin adhesion and force coupling are independently regulated by localized PtdIns(4,5)2 synthesis

The 90-kDa isoform of the lipid kinase PIP kinase Type I γ (PIPKIγ) localizes to focal adhesions (FAs), where it provides a local source of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)). Although PtdIns(4,5)P(2) regulates the function of several FA-associated molecules, the role of the FA-specific pool of PtdIns(4,5)P(2) is not known. We report that the genetic ablation of PIPKIγ specifically from FAs results in defective integrin-mediated adhesion and force coupling. Adhesion defects in cells deficient in FAPtdIns(4,5)P(2) synthesis are corrected within minutes while integrin-actin force coupling remains defective over a longer period. Talin and vinculin, but not kindlin, are less efficiently recruited to new adhesions in these cells. These data demonstrate that the specific depletion of PtdIns(4,5)P(2) from FAs temporally separates integrin-ligand binding from integrin-actin force coupling by regulating talin and vinculin recruitment. Furthermore, it suggests that force coupling relies heavily on locally generated PtdIns(4,5)P(2) rather than bulk membrane PtdIns(4,5)P(2).

Integrin and glycocalyx mediated contributions to cell adhesion identified by single cell force spectroscopy

The measurement of cell adhesion using single cell force spectroscopy methods was compared with earlier methods for measuring cell adhesion. This comparison provided a means and rationale for separating components of the measurement retract curve that were due to interactions between the substrate and the glycocalyx, and interactions that were due to cell surface integrins binding to a substrate-bound ligand. The glycocalyx adhesion was characterized by multiple jumps with dispersed jump sizes that extended from 5 to 30 µm from the origin. The integrin mediated adhesion was represented by the F(max) (maximum detachment force), was generally within the first 5 µm and commonly detached with a single rupture cascade. The integrin peak (F(max)) increases with time and the rate of increase shows large cell to cell variability with a peak ∼ 50 nN s(-1) and an average rate of increase of 75 pN s(-1). This is a measure of the rate of increase in the number of adhesive integrin-ligand bonds/cell as a function of contact time.

Integrin clustering is driven by mechanical resistance from the glycocalyx and the substrate

Integrins have emerged as key sensory molecules that translate chemical and physical cues from the extracellular matrix (ECM) into biochemical signals that regulate cell behavior. Integrins function by clustering into adhesion plaques, but the molecular mechanisms that drive integrin clustering in response to interaction with the ECM remain unclear. To explore how deformations in the cell-ECM interface influence integrin clustering, we developed a spatial-temporal simulation that integrates the micro-mechanics of the cell, glycocalyx, and ECM with a simple chemical model of integrin activation and ligand interaction. Due to mechanical coupling, we find that integrin-ligand interactions are highly cooperative, and this cooperativity is sufficient to drive integrin clustering even in the absence of cytoskeletal crosslinking or homotypic integrin-integrin interactions. The glycocalyx largely mediates this cooperativity and hence may be a key regulator of integrin function. Remarkably, integrin clustering in the model is naturally responsive to the chemical and physical properties of the ECM, including ligand density, matrix rigidity, and the chemical affinity of ligand for receptor. Consistent with experimental observations, we find that integrin clustering is robust on rigid substrates with high ligand density, but is impaired on substrates that are highly compliant or have low ligand density. We thus demonstrate how integrins themselves could function as sensory molecules that begin sensing matrix properties even before large multi-molecular adhesion complexes are assembled.

Critical cell decisions, including whether to live, proliferate, or assemble into tissue structures, are directed by cues from the extracellular matrix, the external protein scaffold that surrounds cells. Integrin receptors on the cell surface bind to the extracellular matrix and cluster into complexes that translate matrix cues into the set of instructions a cell follows. Using a newly developed model of the cell-matrix interface, in this work we detail a simple yet efficient mechanism by which integrins could “sense” important matrix properties, including chemical composition and mechanical stiffness, and cluster appropriately. This mechanism relies on mechanical resistance to integrin-matrix interaction provided by the glycocalyx, the slimy sugar and protein coating on the cell, as well as the stiffness of the matrix and the cell itself. In general, the resistance alters integrin-ligand reaction rates, such that integrin clustering is favored for many physiologically relevant conditions. Interestingly, the mechanical properties of the cell and ECM are altered in many prevalent diseases, such as cancer, and our work suggests how these mechanical perturbations might adversely influence integrin function.

A novel mode of cell detachment from fibrillar fibronectin matrix under shear

Cells within tissues are surrounded by fibrillar extracellular matrix (ECM) that supports cell adhesion via integrin receptors. The strength of cell interactions with fibrillar matrix and the effects of force on these interactions have not been quantified. To this end, we used a spinning disc device to apply radially increasing shear to human HT1080 fibrosarcoma cells attached to a cell-derived fibrillar fibronectin (FN) matrix. The shear required to detach 50% of HT1080 cells was eight times greater on a FN-coated, rigid glass substrate than on fibrillar FN matrix. Covalent crosslinking of the FN matrix increased its stiffness tenfold and produced a modest increase in shear detachment force for these cells. On FN-coated surfaces, cells detach by releasing interactions between alpha5beta1 integrin and FN. By contrast, cell detachment from fibrillar matrix occurred through a novel mechanism of fibril breakage, which left holes in the matrix visible by fluorescence microscopy. These results show that cells require less force to detach from fibrillar matrix than from FN adsorbed on glass and that detachment occurs through breaking fibrils instead of by release of integrin-matrix bonds. Thus, ECM fibril breakage is another molecular feature to consider when understanding cell and tissue homeostasis.

Mechanically activated integrin switch controls alpha5beta1 function

The cytoskeleton, integrin-mediated adhesion, and substrate stiffness control a common set of cell functions required for development and homeostasis that are often deranged in cancer. The connection between these mechanical elements and chemical signaling processes is not known. Here, we show that alpha(5)beta(1) integrin switches between relaxed and tensioned states in response to myosin II-generated cytoskeletal force. Force combines with extracellular matrix stiffness to generate tension that triggers the integrin switch. This switch directly controls the alpha(5)beta(1)-fibronectin bond strength through engaging the synergy site in fibronectin and is required to generate signals through phosphorylation of focal adhesion kinase. In the context of tissues, this integrin switch connects cytoskeleton and extracellular matrix mechanics to adhesion-dependent motility and signaling pathways.

Rab-coupling protein coordinates recycling of alpha5beta1 integrin and EGFR1 to promote cell migration in 3D microenvironments

Here we show that blocking the adhesive function of αvβ3 integrin with soluble RGD ligands, such as osteopontin or cilengitide, promoted association of Rab-coupling protein (RCP) with α5β1 integrin and drove RCP-dependent recycling of α5β1 to the plasma membrane and its mobilization to dynamic ruffling protrusions at the cell front. These RCP-driven changes in α5β1 trafficking led to acquisition of rapid/random movement on two-dimensional substrates and to a marked increase in fibronectin-dependent migration of tumor cells into three-dimensional matrices. Recycling of α5β1 integrin did not affect its regulation or ability to form adhesive bonds with substrate fibronectin. Instead, α5β1 controlled the association of EGFR1 with RCP to promote the coordinate recycling of these two receptors. This modified signaling downstream of EGFR1 to increase its autophosphorylation and activation of the proinvasive kinase PKB/Akt. We conclude that RCP provides a scaffold that promotes the physical association and coordinate trafficking of α5β1 and EGFR1 and that this drives migration of tumor cells into three-dimensional matrices.

alpha6beta4 integrin activates Rac-dependent p21-activated kinase 1 to drive NF-kappaB-dependent resistance to apoptosis in 3D mammary acini

Malignant transformation and multidrug resistance are linked to resistance to apoptosis, yet the molecular mechanisms that mediate tumor survival remain poorly understood. Because the stroma can influence tumor behavior by regulating the tissue phenotype, we explored the role of extracellular matrix signaling and tissue organization in epithelial survival. We report that elevated (alpha6)beta4 integrin-dependent Rac-Pak1 signaling supports resistance to apoptosis in mammary acini by permitting stress-dependent activation of the p65 subunit of NF-kappaB through Pak1. We found that inhibiting Pak1 through expression of N17Rac or PID compromises NF-kappaB activation and renders mammary acini sensitive to death, but that resistance to apoptosis could be restored to these structures by overexpressing wild-type NF-kappaB p65. We also observed that acini expressing elevated levels of Pak1 can activate p65 and survive death treatments, even in the absence of activated Rac, yet will die if activation of NF-kappaB is simultaneously inhibited through expression of IkappaBalphaM. Thus, mammary tissues can resist apoptotic stimuli by activating NF-kappaB through alpha6beta4 integrin-dependent Rac-Pak1 signaling. Our data emphasize the importance of the extracellular matrix stroma in tissue survival and suggest that alpha6beta4 integrin-dependent Rac stimulation of Pak1 could be an important mechanism mediating apoptosis-resistance in some breast tumors.

Adhesion of MC3T3-E1 cells to RGD peptides of different flanking residues: detachment strength and correlation with long-term cellular function

We synthesized a series of RGD peptides and immobilized them to an amine-functional self-assembled monolayer using a modified maleimide-based conjugate technique that minimizes nonspecific interactions. Using a spinning disc apparatus, a trend in the detachment strength (tau(50)) of RGD peptides of different flanking residues was found: RGDSPK > RGDSVVYGLR approximately RGDS > RGES. Using blocking monoclonal antibodies, cellular adhesion to the peptides was shown to be primarily alpha(v)-integrin-mediated. In contrast, the tau(50) value of the cells on fibronectin (Fn)-coated substrates of similar surface density was 6-7 times higher and involved both alpha(5)beta(1) and alpha(v)beta(3) integrins. Cellular spreading was enhanced on RGD peptides after 1 h when compared to RGE and unmodified substrates. However, no significant differences were observed between the different RGD peptides. Long-term function of MC3T3-E1 cells was also evaluated by measuring alkaline phosphatase (ALP) activity and mineral deposition. Among the four peptides, RGDSPK exhibited the highest level of ALP activity after 11 days and mineralization after 15 days and reached comparable levels as Fn substrates after 15 and 24 days, respectively. These findings collectively illustrate both the advantages and limitations of enhancing cellular adhesion and function by the design of RGD peptides.

Quantitative measurements of integrin-mediated adhesion to extracellular matrix

Integrin-mediated adhesion is based on the binding of integrins to immobilized ligands either in the extracellular matrix or on the surface of adjacent cells. The strength of adhesion is determined primarily by the number of adhesive bonds that form. Integrins have also been described as signaling receptors. Like adhesion, signals from integrins receptors can depend on the number of integrins that are bound to substrate attached ligands. The common methods for measuring cell adhesion are only capable of measuring initial interactions because the multivalent nature of adhesive bonds when the cell is considered as a unit, these assays reach plateau levels. To measure adhesive integrin-ligand bonds, a spinning disc device is described in which the mean cell detachment force is proportional to the number of adhesive bonds. Particularly as the field has moved from identification of integrins and their ligands into the analysis of adhesion and its relationship to cell signaling, it is important to shift to assays that relate the extracellular binding to the intracellular signals. Specific plans, methods, and analytic strategies are provided to apply this technology to current problems in integrin biology. At present, this is the only published approach that will provide good measures of the number of adhesive bonds that can be generally applied.

Effect of biomaterial surface properties on fibronectin-alpha5beta1 integrin interaction and cellular attachment

The ability of fibronectin (Fn) to mediate cell adhesion through binding to alpha(5)beta(1) integrins is dependent on the conditions of its adsorption to the surface. Using a model system of alkylsilane SAMs with different functional groups (X=OH, COOH, NH(2) and CH(3)) and an erythroleukemia cell line expressing a single integrin (alpha(5)beta(1)), the effect of surface properties on the cellular adhesion with adsorbed Fn layers was investigated. (125)I-labeled Fn, a modified biochemical cross-linking/extraction technique and a spinning disc apparatus were combined to quantify the Fn adsorption, integrin binding and adhesion strength, respectively. This methodology allows for a binding equilibrium analysis that more closely reflects cellular adhesion found in stable tissue constructs in vivo. Differences in detachment strength and integrin binding were explained in terms of changes in the adhesion constant (psi, related to affinity) and binding efficiency of the adsorbed Fn for the alpha(5)beta(1) integrins (CH(3) approximately NH(2)<COOH approximately OH) and the resulting average bond strength. Fn interacted more strongly with alpha(5)beta(1) integrins when adsorbed on COOH vs. OH surfaces suggesting that negative charge may be a critical component of inducing efficient cellular adhesion. As evident by the low psi values, Fn adsorbed on NH(2) and CH(3) surfaces interacted inefficiently with alpha(5)beta(1) integrins and also possessed significant non-specific components to adhesion. Lastly, comparison of cellular adhesion to Fn adsorbed onto smooth and rough surfaces showed that nano-scale roughness altered cellular adhesion by increasing the surface density of adsorbed Fn.

Tensional homeostasis and the malignant phenotype

Tumors are stiffer than normal tissue, and tumors have altered integrins. Because integrins are mechanotransducers that regulate cell fate, we asked whether tissue stiffness could promote malignant behavior by modulating integrins. We found that tumors are rigid because they have a stiff stroma and elevated Rho-dependent cytoskeletal tension that drives focal adhesions, disrupts adherens junctions, perturbs tissue polarity, enhances growth, and hinders lumen formation. Matrix stiffness perturbs epithelial morphogenesis by clustering integrins to enhance ERK activation and increase ROCK-generated contractility and focal adhesions. Contractile, EGF-transformed epithelia with elevated ERK and Rho activity could be phenotypically reverted to tissues lacking focal adhesions if Rho-generated contractility or ERK activity was decreased. Thus, ERK and Rho constitute part of an integrated mechanoregulatory circuit linking matrix stiffness to cytoskeletal tension through integrins to regulate tissue phenotype.

Insulin-like growth factor I controls adhesion strength mediated by alpha5beta1 integrins in motile carcinoma cells

One of the intriguing questions regarding cell motility concerns the mechanism that makes stationary cells move. Here, we provide the first physical evidence that the onset of breast cancer cell motility in response to insulin-like growth factor I (IGF-I) correlates with lowering of adhesion strength from 2.52 +/- 0.20 to 1.52 +/- 0.13 microdynes/microm2 in cells attached to fibronectin via alpha5beta1 integrin. The adhesion strength depends on the dose of IGF-I and time of IGF-I treatment. Weakening of cell-matrix adhesion is blocked significantly (p < 0.01) by the catalytically inactive IGF-I receptor (IGF-IR) and the phosphoinositide 3-kinase (PI-3 kinase) inhibitor LY-294002, but it is unaffected by mitogen-activated protein kinase kinase inhibitor UO-126 and Src kinase inhibitor PP2. Sustained blockade of Rho-associated kinase (ROCK) with Y-27632 down-regulates adhesion strength in stationary, but not in IGF-I-treated, cells. Jasplakinolide, a drug that prevents actin filament disassembly, counteracts the effect of IGF-I on integrin-mediated cell adhesion. In the absence of growth factor signaling, ROCK supports a strong adhesion via alpha5beta1 integrin, whereas activation of the IGF-IR kinase reduces cell-matrix adhesion through a PI-3K-dependent, but ROCK-independent, mechanism. We propose that disassembly of the actin filaments via PI-3 kinase pathway contributes to weakening of adhesion strength and induction of cell movement. Understanding how cell adhesion and migration are coordinated has an important application in cancer research, developmental biology, and tissue bioengineering.

Receptor−Ligand Binding in the Cell−Substrate Contact Zone: A Quantitative Analysis Using CX3CR1 and CXCR1 Chemokine Receptors†

Receptor-ligand binding analyses have generally used soluble components to measure thermodynamic binding constants. In their biological context, adhesion receptors bind to an immobile ligand and the binding reaction is confined to the cell-substrate contact zone. We have developed a new procedure based on the spinning disk technology to measure the number of receptor-ligand bonds in the contact zone. Application of this methodology to the CX3CR1-fractalkine and the CXCR1-IL-8 receptor-ligand systems demonstrated that the level of binding to an immobilized ligand is reduced by several orders of magnitude in comparison to solution binding. A comparison of the solution binding and contact zone binding constants shows that the effect of ligand immobilization was similar for each system. In contrast, although the CXCR1-IL-8 bond had the higher affinity, the average bond strength was only 10% of that for the CX3CR1 bond. Because fractalkine can be expressed as a cell surface-bound protein, CX3CR1 has been proposed to function as an adhesion receptor. The higher bond strength suggests that the bond architecture has also evolved to serve an adhesion function.

A novel mode for integrin-mediated signaling: tethering is required for phosphorylation of FAK Y397

The common model for integrin mediated signaling is based on integrin clustering and the potential for that clustering to recruit signaling molecules including FAK and src. The clustering model for transmembrane signaling originated with the analysis of the EGF receptor signaling and remains the predominant model. The roles for substrate-bound ligand and ligand occupancy in integrin-mediated signaling are less clear. A kinetic model was established using HT1080 cells in which there was a linear relationship between the strength of adhesion, the proportion of alpha5beta1 integrin that could be chemically cross-linked, and the number of receptor-ligand bonds. This graded signal produced a similarly graded response measured by the level of specific phosphorylation of FAK Y397. FAK Y397 phosphorylation could also be induced by antibody bound to the substrate. In contrast, clustering of alpha5beta1 on suspended cells with either antibody to beta1 or by clustering of soluble ligand bound to alpha5beta1 induced the phosphorylation of FAK Y861 but not Y397. There were no differences in signaling when activating antibodies were compared with blocking antibodies, presence or absence of ligand. Only tethering of alpha5beta1 to the substrate was required for induction of FAK Y397 phosphorylation.

Localization of BCR-ABL to F-actin regulates cell adhesion but does not attenuate CML development

We have previously found that P210BCR-ABL increases the adhesion of hematopoietic cell lines to fibronectin by a mechanism that is independent of tyrosine kinase activity. To investigate the pathway(s) by which P210BCR-ABL influences cell adhesion, we used a quantitative cell adhesion device that can discern small changes in cell adhesion to assay P210BCR-ABL with mutations in several critical domains. We expressed P210BCR-ABL mutants in 32D myeloblast cells and found that binding to fibronectin is mediated primarily by the alpha5beta1 integrin. We performed a structure/function analysis to map domains important for cell adhesion. Increased adhesion was mediated by 3 domains: (1) the N-terminal coiled-coil domain that facilitates oligomerization and F-actin localization; (2) bcr sequences between aa 163 to 210; and (3) F-actin localization through the C-terminal actin-binding domain of c-abl. We compared our adhesion results with the ability of these mutants to cause a chronic myelogenous leukemia (CML)-like disease in a murine bone marrow transplantation assay and found that adhesion to fibronectin did not correlate with the ability of these mutants to cause CML. Together, our results suggest that F-actin localization may play a pivotal role in modulating adhesion but that it is dispensable for the development of CML.

Functional role of alpha-actinin, PI 3-kinase and MEK1/2 in insulin-like growth factor I receptor kinase regulated motility of human breast carcinoma cells

Within epithelial tissue, cells are held together by specialized lateral junctions. At particular stages of development and in pathological processes such as metastasis, cells break down the intercellular junctions, separate from the epithelial sheet and migrate individually. Despite the importance of these processes, little is understood about the regulatory mechanisms of active cell separation. In view of the effects of insulin-like growth factor I (IGF-I) on mammary gland development and cancer, we developed a model using MCF-7 human breast cancer cells in which the process of cell separation can be induced by IGF-I. The separation was enhanced in MCF-7 cells overexpressing the IGF-IR and blocked in the cells expressing a dead-kinase mutant of this receptor. Activation of the IGF-IR resulted in a rapid formation of motile actin microspikes at the regions of cell-cell contacts, disorganization of mature adherens junctions and the onset of cell migration. In cell separation, the signaling between the IGF-IR kinase and actin required phosphatidylinositol 3 (PI 3)-kinase-generated phospholipids but not MAP kinases and was mediated by alpha-actinin. The activity of MEK1/2 kinases was needed for consecutive cell migration. This work also defined a new function for alpha-actinin. Upon IGF-IR activation, green fluorescence protein (GFP)-labeled alpha-actinin concentrated at the base of actin microspikes. Deletion of the N-terminal actin-binding domain of alpha-actinin prevented this redistribution, indicating that this domain is necessary. Detection of the C-terminal tail of alpha-actinin reduced the number of microspikes, showing that alpha-actinin has a role in the development of microspikes and is not passively reorganized with filamentous actin. We suggest that the signaling pathway from the IGF-IR kinase through the PI-3 kinase to alpha-actinin participates in the rapid organization of actin into microspikes at the cell-cell junctions and leads to active cell separation, whereas signaling through ERK1/2 MAP kinases controls cell migration following cell separation.

Distinct activation states of alpha5beta1 integrin show differential binding to RGD and synergy domains of fibronectin

alpha5beta1 integrin can occupy several distinct conformational states which support different strengths of binding to fibronectin [García, A. J., et al. (1998) J. Biol. Chem. 273, 34710-34715]. Using a model system in which specific activating monoclonal antibodies were used to achieve uniform activated states, the binding of alpha5beta1 to full-length wild-type fibronectin and mutants of fibronectin in the defined RGD and PHSRN synergy sites was analyzed using a novel method that measures the strength of the coupling between integrin and its ligand. Neither TS2/16- nor AG89-activated alpha5beta1 showed significant mechanical coupling to RGD-deleted fibronectin. However, peptide competition assays demonstrated a 6-fold difference in the binding affinities of these two states for RGD. The mutant synergy site reduced the AG89 (low)-activated state to background levels, but the TS2/16-activated state still retained approximately 30% of the wild-type activity. Thus, these two active binding states of alpha5beta1 interact differently with both the RGD and synergy domains. The failure of the AG89-activated state to show mechanical coupling to either the RGD or synergy domain mutants was unexpected and implies that the RGD domain itself does not contribute significant mechanical strength to the alpha5beta1-fibronectin interaction. The lack of RGD alone to support alpha5beta1 coupling was further confirmed using a synthetic polymer presenting multiple copies of the RGD loop. These results suggest a model in which the RGD domain serves to activate and align the alpha5beta1-fibronectin interface, and the synergy site provides the mechanical strength to the bond.

BCR-ABL-induced adhesion defects are tyrosine kinase-independent

The t(9;22) chromosomal translocation results in expression of P210(BCR-ABL), a fusion protein necessary for the development of chronic myelogenous leukemia (CML). The constitutive activation of the P210(BCR-ABL) tyrosine kinase results in phosphorylation of multiple signaling pathways leading to the transformed phenotype. Additionally, extracellular interactions between P210(BCR-ABL)-expressing progenitor cells and bone marrow stroma may provide external signals that facilitate CML development. In contrast to the intracellular signaling pathways involved in CML, little is known about how P210(BCR-ABL) expression modifies cell-cell and cell-substratum interactions. To investigate the role of P210(BCR-ABL) in modulating cellular adhesion, we used a highly sensitive and quantitative cell detachment apparatus that measures the strength of association between a population of cells and an adhesive matrix. Our findings show that P210(BCR-ABL) expression increased adhesion nearly 2-fold between the myeloblastic cell line, 32D, and fibronectin compared to a control vector. We then investigated whether abnormal adhesion due to P210(BCR-ABL) expression was caused by its tyrosine kinase activity. A quantitative analysis of cell-fibronectin adhesion found that neither expression of a kinase-inactive P210(BCR-ABL) mutant in 32D cells or attenuation of kinase activity by STI571 (imatinib mesylate) in 32D cells transduced with wild-type P210(BCR-ABL) could correct the nearly 2-fold increase in cell-fibronectin adhesion. Similarly, STI571 treatment of Meg-01 cells, a P210(BCR-ABL)-expressing cell line derived from a patient in blast crisis, failed to inhibit adhesion to fibronectin. Together, our results indicate that changes in adhesion induced by P210(BCR-ABL) are independent of its tyrosine kinase activity.

Induction of fascin spikes in breast cancer cells by activation of the insulin-like growth factor-I receptor

Insulin-like growth factor-I receptor (IGF-IR) signaling contributes to the formation of mammary carcinomas and has chiefly been studied with regard to the proliferative and anti-apoptotic effects of IGF-IR signaling. However, IGF-IR activation also affects the actin cytoskeleton and alterations in cell migratory behavior are of known importance for the malignant conversion and metastasis of epithelial cells. The actin-binding protein fascin is found in cell projections and spikes that are involved in the locomotion of mesenchymal cells. Fascin expression is typically low in normal epithelial cells, but is markedly upregulated in several types of carcinomas. Here, we also demonstrate increased fascin expression in breast carcinoma cell lines and adopt MCF-7 human mammary carcinoma cells that over-express wild-type or kinase-inactivated forms of the IGF-IR as a model system to test the hypothesis that IGF-IR activation induces fascin projections. We show that the time-dependent dissociation of cell colonies that occurs upon receptor activation by IGF-I involves the formation of dynamic, fascin-containing lateral cell projections that co-localize with ruffling membranes in association with protrusive activity and cell migratory phenotype. The molecular mechanism of these effects is completely dependent on IGF-IR tyrosine kinase activity and is mediated by a phosphatidylinositol (PI) 3-kinase-dependent process. In demonstrating transduction of fascin spike assembly by activation of a peptide growth factor receptor, these novel data reveal a wide role for fascin spikes in cell motility and provide new insight into the complex effects of IGF-IR signaling on actin cytoskeletal organization.

Phosphorylation of beta3 integrin controls ligand binding strength

The cytoplasmic domain of beta(3) integrin contains tyrosines at positions 747 and 759 in domains that have been implicated in regulation of alpha(v)beta(3) function and that serve as potential substrates for Src family kinases. The phosphorylation level of beta(3) integrin was modulated using a temperature-sensitive v-Src kinase. Increased beta(3) phosphorylation abolished alpha(v)beta(3)- but not alpha(5)beta(1)-mediated adhesion to fibronectin. alpha(v)beta(3)-Mediated cell adhesion was restored by the expression of beta(3) containing Y747F or Y759F mutations but not by wild type beta(3) integrin. Thus, phosphorylation of the cytoplasmic domain of beta(3) is a negative regulator of alpha(v)beta(3)-fibronectin binding strength.

Activation of alpha(v)beta3-vitronectin binding is a multistage process in which increases in bond strength are dependent on Y747 and Y759 in the cytoplasmic domain of beta3

Integrin receptors serve as mechanical links between the cell and its structural environment. Using alpha(v)beta3 integrin expressed in K562 cells as a model system, the process by which the mechanical connection between alpha(v)beta3 and vitronectin develops was analyzed by measuring the resistance of these bonds to mechanical separation. Three distinct stages of activation, as defined by increases in the alpha(v)beta3-vitronectin binding strength, were defined by mutational, biochemical, and biomechanical analyses. Activation to the low binding strength stage 1 occurs through interaction with the vitronectin ligand and leads to the phosphorylation of Y747 in the beta3 subunit. Stage 2 is characterized by a 4-fold increase in binding strength and is dependent on stage1 and the phosphorylation of Y747. Stage 3 is characterized by a further 2.5-fold increase in binding strength and is dependent on stage 2 events and the availability of Y759 for interaction with cellular proteins. The Y747F mutant blocked the transition from stage 1 to stage 2, and the Y759F blocked the transition from stage 2 to stage 3. The data suggest a model for tension-induced activation of alpha(v)beta3 integrin.

Distinct ligand-binding modes for integrin alpha(v)beta(3)-mediated adhesion to fibronectin versus vitronectin

Cell surface integrins can adopt distinct conformations in response to ligand binding and intracellular signals. Several integrins including alpha(v)beta(3) can bind to multiple ligands. The binding of alpha(v)beta(3) to fibronectin and vitronectin was used as a model to determine whether the same or distinct forms of the receptor were utilized in strong binding to the two different ligands. A spinning-disc device was used to measure the relative strength of the alpha(v)beta(3)-ligand bonds. The initial binding reaction for both ligands occurred in the absence of metabolic energy and resulted in a strong adhesion to fibronectin but a weak adhesion to vitronectin. Increases in the strength of the alpha(v)beta(3)-vitronectin bond required phosphorylation of the beta(3) cytoplasmic domain, intracellular signals, and the binding of cytoskeletal proteins to cytoplasmic domains of beta(3) controlled by Tyr-747 and Tyr-759. In contrast, alpha(v)beta(3)-mediated adhesion to fibronectin was unaffected by phorbol 12-myristate 13-acetate, mutations of Tyr-747 and Tyr-759 to phenylalanine, or availability of metabolic energy. This suggests that strong adhesion to fibronectin used the initial binding conformation, whereas strong binding to vitronectin required signaling-induced changes in the conformation of alpha(v)beta(3).

Insertional mutagenesis as a route to identifying genes involved in self renewal of haemopoietic stem cells

The genes controlling self renewal in the haemopoietic system are still unknown. Using retroviral insertional mutagenesis we have established multipotent haemopoietic stem cell lines (FDCP-mix) that possess an increased self renewal capacity in vitro. To identify genes involved in the regulation of self renewal, proviral integration sites were cloned from FDCP-mix cells and used as probes to screen independently isolated FDCP-mix cell lines for a common proviral insertion site. So far, two common integration sites have been identified, A25 and M4. A25 is rearranged in 50% of the FDCP-mix cell lines and M4 in 10%. Genes located at or near these sites are likely candidates for the control of self renewal of haemopoietic stem cells.

Integrin-fibronectin interactions at the cell-material interface: initial integrin binding and signaling

Integrin receptors mediate cell adhesion to extracellular matrices and provide signals that direct proliferation and differentiation. Integrin binding involves receptor-ligand interactions at the cell-substrate interface and assembly and reorganization of structural and signaling elements at the cytoplasmic face. Using a cross-linking/extraction/reversal method to quantify bound integrins, we demonstrate that the density of alpha5beta1 integrin-fibronectin bonds increases linearly with ligand density, as predicted by simple receptor-ligand equilibrium. This linear relationship is consistent with linear increases in cell adhesion strength with receptor and ligand surface densities. Furthermore, we show that phosphorylation of FAK, a tyrosine kinase involved in early integrin-mediated signaling, increases linearly with the number of integrin-Fn bonds. These linear relationships suggest the absence of cooperative effects in the initial stages of mechanical coupling and adhesion-mediated signaling.