Squamous Cell Carcinoma of the Lung With Microsatellite Instability in a Patient With Lynch Syndrome: A Case Report

Lynch syndrome is the most common autosomal dominant inherited cancer predisposing syndrome, due to mutations in DNA mismatch repair genes. The key feature of cancers in Lynch syndrome is microsatellite instability and a high risk of developing mainly colorectal and uterine cancers. However, cancers with microsatellite instability outside this spectrum, for example, lung cancer, are extremely rare. Here, we report a case of squamous cell carcinoma of the lung with microsatellite instability in a patient with Lynch syndrome.

Association and performance of polygenic risk scores for breast cancer among French women presenting or not a familial predisposition to the disease

BACKGROUND

Three partially overlapping breast cancer polygenic risk scores (PRS) comprising 77, 179 and 313 SNPs have been proposed for European-ancestry women by the Breast Cancer Association Consortium (BCAC) for improving risk prediction in the general population. However, the effect of these SNPs may vary from one country to another and within a country because of other factors.

OBJECTIVE

To assess their associated risk and predictive performance in French women from (1) the CECILE population-based case-control study, (2) BRCA1 or BRCA2 (BRCA1/2) pathogenic variant (PV) carriers from the GEMO study, and (3) familial breast cancer cases with no BRCA1/2 PV and unrelated controls from the GENESIS study.

RESULTS

All three PRS were associated with breast cancer in all studies, with odds ratios per standard deviation varying from 1.7 to 2.0 in CECILE and GENESIS, and hazard ratios varying from 1.1 to 1.4 in GEMO. The predictive performance of PRS₃₁₃ in CECILE was similar to that reported in BCAC but lower than that in GENESIS (area under the receiver operating characteristic curve (AUC) = 0.67 and 0.75, respectively). PRS were less performant in BRCA2 and BRCA1 PV carriers (AUC = 0.58 and 0.54 respectively).

CONCLUSION

Our results are in line with previous validation studies in the general population and in BRCA1/2 PV carriers. Additionally, we showed that PRS may be of clinical utility for women with a strong family history of breast cancer and no BRCA1/2 PV, and for those carrying a predicted PV in a moderate-risk gene like ATM, CHEK2 or PALB2.

Diagnostic chest X-rays and breast cancer risk among women with a hereditary predisposition to breast cancer unexplained by a BRCA1 or BRCA2 mutation

Background

Diagnostic ionizing radiation is a risk factor for breast cancer (BC). BC risk increases with increased dose to the chest and decreases with increased age at exposure, with possible effect modification related to familial or genetic predisposition. While chest X-rays increase the BC risk of BRCA1/2 mutation carriers compared to non-carriers, little is known for women with a hereditary predisposition to BC but who tested negative for a BRCA1 or BRCA2 (BRCA1/2) mutation.

Methods

We evaluated the effect of chest X-rays from diagnostic medical procedures in a dataset composed of 1552 BC cases identified through French family cancer clinics and 1363 unrelated controls. Participants reported their history of X-ray exposures in a detailed questionnaire and were tested for 113 DNA repair genes. Logistic regression and multinomial logistic regression models were used to assess the association with BC.

Results

Chest X-ray exposure doubled BC risk. A 3% increased BC risk per additional exposure was observed. Being 20 years old or younger at first exposure or being exposed before first full-term pregnancy did not seem to modify this risk. Birth after 1960 or carrying a rare likely deleterious coding variant in a DNA repair gene other than BRCA1/2 modified the effect of chest X-ray exposure.

Conclusion

Ever/never chest X-ray exposure increases BC risk 2-fold regardless of age at first exposure and, by up to 5-fold when carrying 3 or more rare variants in a DNA repair gene.

Further studies are needed to evaluate other DNA repair genes or variants to identify those which could modify radiation sensitivity. Identification of subpopulations that are more or less susceptible to ionizing radiation is important and potentially clinically relevant.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01456-1.

Mutational analysis of apoptotic genes in familial aggregation of hematological malignancies

INTRODUCTION

Apoptosis deregulation have been associated to tumorigenesis process and was highlighted as a prominent hallmark of cancer. Several mutations have been reported in several forms of Blood cancer. However, it has never been investigated in familial aggregations of hematological malignancies.

METHODS

In this study, we performed a mutational analysis by sequencing the entire coding regions in four key apoptotic genes FAS, FASLG, CASP8 and CASP10 in 92 independent families belonging to French and Tunisian populations and diagnosed with several forms of familial hematological malignancies.

RESULTS

We report 15 genetic variations among which 7 were previously reported in several form of cancers and have a potential effect on gene expression. Particularly, the CASP8 variants p.Asp302His and p.Lys337Lys were detected in 15% and 10% of our group of patients respectively and were previously reported in association to breast cancer and to breast cancer susceptibility.

DISCUSSION

In this study, we do not report the underlining deleterious mutations in familial hematological malignancies, but we describe some variants with potential risk of developing blood cancer. To gain further insights on the association between apoptosis pathway deregulation and familial hematological malignancies, more apoptotic genes should be investigated.

Gene- and pathway-level analyses of iCOGS variants highlight novel signaling pathways underlying familial breast cancer susceptibility

Single‐nucleotide polymorphisms (SNPs) in over 180 loci have been associated with breast cancer (BC) through genome‐wide association studies involving mostly unselected population‐based case‐control series. Some of them modify BC risk of women carrying a BRCA1 or BRCA2 (BRCA1/2) mutation and may also explain BC risk variability in BC‐prone families with no BRCA1/2 mutation. Here, we assessed the contribution of SNPs of the iCOGS array in GENESIS consisting of BC cases with no BRCA1/2 mutation and a sister with BC, and population controls. Genotyping data were available for 1281 index cases, 731 sisters with BC, 457 unaffected sisters and 1272 controls. In addition to the standard SNP‐level analysis using index cases and controls, we performed pedigree‐based association tests to capture transmission information in the sibships. We also performed gene‐ and pathway‐level analyses to maximize the power to detect associations with lower‐frequency SNPs or those with modest effect sizes. While SNP‐level analyses identified 18 loci, gene‐level analyses identified 112 genes. Furthermore, 31 Kyoto Encyclopedia of Genes and Genomes and 7 Atlas of Cancer Signaling Network pathways were highlighted (false discovery rate of 5%). Using results from the “index case‐control” analysis, we built pathway‐derived polygenic risk scores (PRS) and assessed their performance in the population‐based CECILE study and in a data set composed of GENESIS‐affected sisters and CECILE controls. Although these PRS had poor predictive value in the general population, they performed better than a PRS built using our SNP‐level findings, and we found that the joint effect of family history and PRS needs to be considered in risk prediction models.

What's new?

Genetic studies have identified more than 180 single‐nucleotide polymorphisms (SNPs) associated with breast cancer susceptibility, but these studies are reaching their limits. Here, the authors evaluated SNPs in the iCOGS genotyping array using a multilevel approach, including single variant, gene, and pathway analyses. They measured the contribution of the SNPs to breast cancer in patients who have a sister with breast cancer but do not carry a BRCA1/2 mutation. They showed that a pathway‐derived polygenic risk score performed poorly in the general population, and that the best predictive model must include family history.

Five year letrozole versus placebo in BRCA1/2 germline mutations carriers: Final results of LIBER, a double-blind randomized phase III breast cancer prevention trial

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Background: Women with germline BRCA1/2 (gBRCA1/2) mutations have a 70% lifetime risk of breast cancer (BC). Medical prevention by aromatase inhibitors is effective in high-risk patients (pts), including those with familial risk. However, hormone prevention has not been specifically addressed in women (wn) carrying gBRCA1/2 mutations. Methods: LIBER is a randomized, double-blind, placebo-controlled phase III trial evaluating 5-year treatment with letrozole 2.5 mg/day (L) versus placebo (P) on decreasing BC incidence in post-menopausal women with gBRCA1/2 mutations ( NCT00673335 ). Eligible wn were aged 40-70 and could have had unilateral BC > 5 years ago. Randomization was stratified on mutation ( BRCA1/BRCA2), bilateral oophorectomy and history of prior BC. Primary endpoint was 5-year invasive BC-free survival (BC-FS) in wn with or without previous BC. Main secondary endpoints were safety and quality of life (menopause rating scale, SF36). 270 pts were required to observe 37 events to show a gain in 5-year invasive BC-FS from 80% to 92% (HR=0.35) with 1-sided α=0.05 and 90% power. Results: 170 wn were randomized from 02/2008 to 02/2013; 86 and 84 were assigned to the P and L arm. Median age was 55 years (range 40-70). Pt characteristics were well balanced; 59% and 41% carried gBRCA1 and gBRCA2 mutations. In P and L arms, 47% and 43% had prior BC, 43% and 42% stopped treatment prematurely, 37 and 23 serious adverse events occurred, and during active treatment, 8 and 10 wn had grade 3/4 toxicity. Median follow-up was 72.7 months. Five-year BC-FS did not significantly differ between the P and L arms (92% vs 91%, HR 0.83; 95%CI: 0.3-2.3, p=0.73) in the overall population, nor in the subgroups of wn with and without previous BC (74% vs 91%; HR 0.43; 95% CI: 0.1-1.3; 90% vs 86%; HR 1.29; 95% CI 0.4-3.9), gBRCA1 versus gBRCA2 or hormone receptor-positive BC. Letrozole had no effect on quality of life. The two groups did not significantly differ in bone density, which decreased over time in the overall population. Conclusions: In this prospective preventive trial, BC-FS was not significantly decreased by letrozole versus placebo in women with BRCA1/2 mutations. However, the study was underpowered (170 of 270 pts expected). Despite no differences in safety and quality of life, drop-out rate was high in both P and L arms. Clinical trial information: NCT00673335.

Enhancer Domains in Gastrointestinal Stromal Tumor Regulate KIT Expression and Are Targetable by BET Bromodomain Inhibition

Gastrointestinal stromal tumor (GIST) is a mesenchymal neoplasm characterized by activating mutations in the related receptor tyrosine kinases KIT and PDGFRA. GIST relies on expression of these unamplified receptor tyrosine kinase (RTK) genes through a large enhancer domain, resulting in high expression levels of the oncogene required for tumor growth. Although kinase inhibition is an effective therapy for many patients with GIST, disease progression from kinase-resistant mutations is common and no other effective classes of systemic therapy exist. In this study, we identify regulatory regions of the KIT enhancer essential for KIT gene expression and GIST cell viability. Given the dependence of GIST upon enhancer-driven expression of RTKs, we hypothesized that the enhancer domains could be therapeutically targeted by a BET bromodomain inhibitor (BBI). Treatment of GIST cells with BBIs led to cell-cycle arrest, apoptosis, and cell death, with unique sensitivity in GIST cells arising from attenuation of the KIT enhancer domain and reduced KIT gene expression. BBI treatment in KIT-dependent GIST cells produced genome-wide changes in the H3K27ac enhancer landscape and gene expression program, which was also seen with direct KIT inhibition using a tyrosine kinase inhibitor (TKI). Combination treatment with BBI and TKI led to superior cytotoxic effects in vitro and in vivo, with BBI preventing tumor growth in TKI-resistant xenografts. Resistance to select BBI in GIST was attributable to drug efflux pumps. These results define a therapeutic vulnerability and clinical strategy for targeting oncogenic kinase dependency in GIST. SIGNIFICANCE: Expression and activity of mutant KIT is essential for driving the majority of GIST neoplasms, which can be therapeutically targeted using BET bromodomain inhibitors.

Familial breast cancer and DNA repair genes: Insights into known and novel susceptibility genes from the GENESIS study, and implications for multigene panel testing

Pathogenic variants in BRCA1 and BRCA2 only explain the underlying genetic cause of about 10% of hereditary breast and ovarian cancer families. Because of cost‐effectiveness, multigene panel testing is often performed even if the clinical utility of testing most of the genes remains questionable. The purpose of our study was to assess the contribution of rare, deleterious‐predicted variants in DNA repair genes in familial breast cancer (BC) in a well‐characterized and homogeneous population. We analyzed 113 DNA repair genes selected from either an exome sequencing or a candidate gene approach in the GENESIS study, which includes familial BC cases with no BRCA1 or BRCA2 mutation and having a sister with BC (N = 1,207), and general population controls (N = 1,199). Sequencing data were filtered for rare loss‐of‐function variants (LoF) and likely deleterious missense variants (MV). We confirmed associations between LoF and MV in PALB2, ATM and CHEK2 and BC occurrence. We also identified for the first time associations between FANCI, MAST1, POLH and RTEL1 and BC susceptibility. Unlike other associated genes, carriers of an ATM LoF had a significantly higher risk of developing BC than carriers of an ATM MV (OR_LoF = 17.4 vs. OR_MV = 1.6; p_Het = 0.002). Hence, our approach allowed us to specify BC relative risks associated with deleterious‐predicted variants in PALB2, ATM and CHEK2 and to add MAST1, POLH, RTEL1 and FANCI to the list of DNA repair genes possibly involved in BC susceptibility. We also highlight that different types of variants within the same gene can lead to different risk estimates.

What's new?

Pathogenic variants in BRCA1 and BRCA2 only explain the genetic cause of about 10% of hereditary breast and ovarian cancer families, and the clinical usefulness of testing other genes following the recent introduction of cost‐effective multigene panel sequencing in diagnostics laboratories remains questionable. This large case‐control study describes genetic variation in 113 DNA repair genes and specifies breast cancer relative risks associated with rare deleterious‐predicted variants in PALB2, ATM, and CHEK2. Importantly, different types of variants within the same gene can lead to different risk estimates. The results may help improve risk prediction models and define gene‐specific consensus management guidelines.

ARLTS1, potential candidate gene in familial aggregation of hematological malignancies

INTRODUCTION

Genetic predisposition to familial hematological malignancies was previously described through several epidemiological analyses, but the genetic basis remains unclear. The tumor-suppressor ARLTS1 gene was previously described in sporadic hematological malignancies and familial cancer context.

METHODS

In this study, we sequence the ARLTS1 gene in 100 patients belonging to 88 independent Tunisian and French families.

RESULTS

After gene sequencing, we report 8 genetic variations, most of which were previously reported in several cancer forms. The most common variants were W149X and C148R and were previously associated to B-cell chronic lymphocytic leukemia and to high-risk of familial breast cancer.

CONCLUSIONS

These results emphasize the fact that ARLTS1 gene mutations can be considered as a potential predisposing factor in familial hematological malignancies and other several cancer forms.

GENESIS: a French national resource to study the missing heritability of breast cancer

Background

Less than 20 % of familial breast cancer patients who undergo genetic testing for BRCA1 and BRCA2 carry a pathogenic mutation in one of these two genes. The GENESIS (GENE SISter) study was designed to identify new breast cancer susceptibility genes in women attending cancer genetics clinics and with no BRCA1/2 mutation.

Methods

The study involved the French national network of family cancer clinics. It was based on enrichment in genetic factors of the recruited population through case selection relying on familial criteria, but also on the consideration of environmental factors and endophenotypes like mammary density or tumor characteristics to assess potential genetic heterogeneity. One of the initial aims of GENESIS was to recruit affected sibpairs. Siblings were eligible when index cases and at least one affected sister were diagnosed with infiltrating mammary or ductal adenocarcinoma, with no BRCA1/2 mutation. In addition, unrelated controls and unaffected sisters were recruited. The enrolment of patients, their relatives and their controls, the collection of the clinical, epidemiological, familial and biological data were centralized by a coordinating center.

Results

Inclusion of participants started in February 2007 and ended in December 2013. A total of 1721 index cases, 826 affected sisters, 599 unaffected sisters and 1419 controls were included. 98 % of participants completed the epidemiological questionnaire, 97 % provided a blood sample, and 76 % were able to provide mammograms. Index cases were on average 59 years old at inclusion, were born in 1950, and were 49.7 years of age at breast cancer diagnosis. The mean age at diagnosis of affected sisters was slightly higher (51.4 years). The representativeness of the control group was verified.

Conclusions

The size of the study, the availability of biological specimens and the clinical data collection together with the detailed and complete epidemiological questionnaire make this a unique national resource for investigation of the missing heritability of breast cancer, by taking into account environmental and life style factors and stratifying data on endophenotypes to decrease genetic heterogeneity.

An original phylogenetic approach identified mitochondrial haplogroup T1a1 as inversely associated with breast cancer risk in BRCA2 mutation carriers

INTRODUCTION

Individuals carrying pathogenic mutations in the BRCA1 and BRCA2 genes have a high lifetime risk of breast cancer. BRCA1 and BRCA2 are involved in DNA double-strand break repair, DNA alterations that can be caused by exposure to reactive oxygen species, a main source of which are mitochondria. Mitochondrial genome variations affect electron transport chain efficiency and reactive oxygen species production. Individuals with different mitochondrial haplogroups differ in their metabolism and sensitivity to oxidative stress. Variability in mitochondrial genetic background can alter reactive oxygen species production, leading to cancer risk. In the present study, we tested the hypothesis that mitochondrial haplogroups modify breast cancer risk in BRCA1/2 mutation carriers.

METHODS

We genotyped 22,214 (11,421 affected, 10,793 unaffected) mutation carriers belonging to the Consortium of Investigators of Modifiers of BRCA1/2 for 129 mitochondrial polymorphisms using the iCOGS array. Haplogroup inference and association detection were performed using a phylogenetic approach. ALTree was applied to explore the reference mitochondrial evolutionary tree and detect subclades enriched in affected or unaffected individuals.

RESULTS

We discovered that subclade T1a1 was depleted in affected BRCA2 mutation carriers compared with the rest of clade T (hazard ratio (HR) = 0.55; 95% confidence interval (CI), 0.34 to 0.88; P = 0.01). Compared with the most frequent haplogroup in the general population (that is, H and T clades), the T1a1 haplogroup has a HR of 0.62 (95% CI, 0.40 to 0.95; P = 0.03). We also identified three potential susceptibility loci, including G13708A/rs28359178, which has demonstrated an inverse association with familial breast cancer risk.

CONCLUSIONS

This study illustrates how original approaches such as the phylogeny-based method we used can empower classical molecular epidemiological studies aimed at identifying association or risk modification effects.

A nonsynonymous polymorphism in IRS1 modifies risk of developing breast and ovarian cancers in BRCA1 and ovarian cancer in BRCA2 mutation carriers

BACKGROUND

We previously reported significant associations between genetic variants in insulin receptor substrate 1 (IRS1) and breast cancer risk in women carrying BRCA1 mutations. The objectives of this study were to investigate whether the IRS1 variants modified ovarian cancer risk and were associated with breast cancer risk in a larger cohort of BRCA1 and BRCA2 mutation carriers.

METHODS

IRS1 rs1801123, rs1330645, and rs1801278 were genotyped in samples from 36 centers in the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA). Data were analyzed by a retrospective cohort approach modeling the associations with breast and ovarian cancer risks simultaneously. Analyses were stratified by BRCA1 and BRCA2 status and mutation class in BRCA1 carriers.

RESULTS

Rs1801278 (Gly972Arg) was associated with ovarian cancer risk for both BRCA1 (HR, 1.43; 95% confidence interval (CI), 1.06-1.92; P = 0.019) and BRCA2 mutation carriers (HR, 2.21; 95% CI, 1.39-3.52, P = 0.0008). For BRCA1 mutation carriers, the breast cancer risk was higher in carriers with class II mutations than class I mutations (class II HR, 1.86; 95% CI, 1.28-2.70; class I HR, 0.86; 95%CI, 0.69-1.09; P(difference), 0.0006). Rs13306465 was associated with ovarian cancer risk in BRCA1 class II mutation carriers (HR, 2.42; P = 0.03).

CONCLUSION

The IRS1 Gly972Arg single-nucleotide polymorphism, which affects insulin-like growth factor and insulin signaling, modifies ovarian cancer risk in BRCA1 and BRCA2 mutation carriers and breast cancer risk in BRCA1 class II mutation carriers.

IMPACT

These findings may prove useful for risk prediction for breast and ovarian cancers in BRCA1 and BRCA2 mutation carriers.

Common genetic variation at BARD1 is not associated with breast cancer risk in BRCA1 or BRCA2 mutation carriers

BACKGROUND

Inherited BRCA1 and BRCA2 (BRCA1/2) mutations confer elevated breast cancer risk. Knowledge of factors that can improve breast cancer risk assessment in BRCA1/2 mutation carriers may improve personalized cancer prevention strategies.

METHODS

A cohort of 5,546 BRCA1 and 2,865 BRCA2 mutation carriers was used to evaluate risk of breast cancer associated with BARD1 Cys557Ser. In a second nonindependent cohort of 1,537 of BRCA1 and 839 BRCA2 mutation carriers, BARD1 haplotypes were also evaluated.

RESULTS

The BARD1 Cys557Ser variant was not significantly associated with risk of breast cancer from single SNP analysis, with a pooled effect estimate of 0.90 (95% CI: 0.71-1.15) in BRCA1 carriers and 0.87 (95% CI: 0.59-1.29) in BRCA2 carriers. Further analysis of haplotypes at BARD1 also revealed no evidence that additional common genetic variation not captured by Cys557Ser was associated with breast cancer risk.

CONCLUSION

Evidence to date does not support a role for BARD1 variation, including the Cy557Ser variant, as a modifier of risk in BRCA1/2 mutation carriers.

IMPACT

Interactors of BRCA1/2 have been implicated as modifiers of BRCA1/2-associated cancer risk. Our finding that BARD1 does not contribute to this risk modification may focus research on other genes that do modify BRCA1/2-associated cancer risk.

Common breast cancer susceptibility alleles and the risk of breast cancer for BRCA1 and BRCA2 mutation carriers: implications for risk prediction

The known breast cancer susceptibility polymorphisms in FGFR2, TNRC9/TOX3, MAP3K1, LSP1, and 2q35 confer increased risks of breast cancer for BRCA1 or BRCA2 mutation carriers. We evaluated the associations of 3 additional single nucleotide polymorphisms (SNPs), rs4973768 in SLC4A7/NEK10, rs6504950 in STXBP4/COX11, and rs10941679 at 5p12, and reanalyzed the previous associations using additional carriers in a sample of 12,525 BRCA1 and 7,409 BRCA2 carriers. Additionally, we investigated potential interactions between SNPs and assessed the implications for risk prediction. The minor alleles of rs4973768 and rs10941679 were associated with increased breast cancer risk for BRCA2 carriers (per-allele HR = 1.10, 95% CI: 1.03-1.18, P = 0.006 and HR = 1.09, 95% CI: 1.01-1.19, P = 0.03, respectively). Neither SNP was associated with breast cancer risk for BRCA1 carriers, and rs6504950 was not associated with breast cancer for either BRCA1 or BRCA2 carriers. Of the 9 polymorphisms investigated, 7 were associated with breast cancer for BRCA2 carriers (FGFR2, TOX3, MAP3K1, LSP1, 2q35, SLC4A7, 5p12, P = 7 × 10(-11) - 0.03), but only TOX3 and 2q35 were associated with the risk for BRCA1 carriers (P = 0.0049, 0.03, respectively). All risk-associated polymorphisms appear to interact multiplicatively on breast cancer risk for mutation carriers. Based on the joint genotype distribution of the 7 risk-associated SNPs in BRCA2 mutation carriers, the 5% of BRCA2 carriers at highest risk (i.e., between 95th and 100th percentiles) were predicted to have a probability between 80% and 96% of developing breast cancer by age 80, compared with 42% to 50% for the 5% of carriers at lowest risk. Our findings indicated that these risk differences might be sufficient to influence the clinical management of mutation carriers.

Breast radiotherapy in the lateral decubitus position: A technique to prevent lung and heart irradiation

PURPOSE

To present an original technique for breast radiotherapy, with the aim of limiting lung and heart irradiation, satisfying quality assurance criteria.

METHODS AND MATERIAL

An original radiotherapy technique for breast irradiation has been developed at the Institute Curie in January 1996. It consists of isocentric breast irradiation in the lateral decubitus position (isocentric lateral decubitus [ILD]). This technique is indicated for voluminous or pendulous breasts needing breast irradiation only. Thin carbon fiber supports and special patient positioning devices have been developed especially for this technique. In vivo measurements were performed to check the dose distribution before the routine use of the technique.

RESULTS

ILD has been successfully implemented in routine practice, and 500 patients have been already treated. Breast radiotherapy is performed using a dose of 50 Gy at ICRU point in 25 fractions. ILD shows good homogeneity of the dose in breast treatment volume, treatment fields are perpendicular to the skin ensuring its protection, and extremely low dose is delivered to the underlying lung and heart.

CONCLUSION

In cases of voluminous breasts or patients with a history of lung and heart disease, our technique provides several advantages over the conventional technique with opposing tangential fields. This technique improves the dose homogeneity according to the ICRU recommendations.

Selective excitotoxic degeneration of adult pig retinal ganglion cells in vitro

PURPOSE

Excitotoxicity is proposed to play a prominent role in retinal ganglion cell (RGC) death ensuing from diseases such as glaucoma and ischemia, but cell culture studies have used tissue from newborn rodents, yielding conflicting data that implicate either N-methyl D-aspartate (NMDA) or non-NMDA glutamate (Glu) receptor-mediated pathways. Excitotoxic RGC death was examined in vitro in this study, using adult pigs, a large-animal model for human retina.

METHODS

Adult pig retina (and for comparative purposes young and adult rat retina) were dissociated and maintained in monolayer culture. Medium was supplemented with Glu or pharmacologic agonists or antagonists, and surviving RGCs and other retinal neurons were quantified using specific immunolabeling methods. Electrophysiological responses to externally applied Glu of RGCs in culture were recorded using whole-cell patch-clamp techniques.

RESULTS

Application of Glu led to selective, dose-dependent losses in large RGCs (maximal 37% decrease at 1 mM; median effective dose [ED50], approximately 80 microM) and neurite damage in surviving RGCs. Application of Glu agonists and Glu receptor subclass antagonists showed that large RGC death was mediated through both NMDA and non-NMDA receptor pathways. Small RGCs, amacrine cells, and all other retinal neurons were resistant to Glu-induced death. By comparison, rat retinal cultures displayed heightened RGC vulnerability to Glu, mediated exclusively by non-NMDA receptor-mediated pathways. Amacrine cells were unaffected by NMDA but were very sensitive to kainate application (>90% loss). Other retinal neurons were unaffected by any treatment.

CONCLUSIONS

The molecular pathways underlying excitotoxic RGC death in vitro (non-NMDA or NMDA-preferring Glu receptors) vary among species and developmental stages. The selective elimination of adult pig large RGCs by NMDA receptor-mediated pathways more closely resembles human and animal glaucoma in vivo than other published culture models, providing a simplified experimental system for investigating the pharmacologic and toxicologic bases of glaucoma-like neuronal death.

Familial invasive breast cancers: worse outcome related to BRCA1 mutations

PURPOSE

Although all studies confirm that BRCA1 tumors are highly proliferative and poorly differentiated, their outcomes remain controversial. We propose to examine, through a cohort study, the pathologic characteristics, overall survival, local recurrence, and metastasis-free intervals of 40 patients with BRCA1 breast cancer.

PATIENTS AND METHODS

A cohort of 183 patients with invasive breast cancer, treated at the Institut Curie and presenting with a familial history of breast and/or ovarian cancer, were tested for BRCA1 germ-line mutation. Tumor characteristics and clinical events were extracted from our prospectively registered database.

RESULTS

Forty BRCA1 mutations were found among the 183 patients (22%). Median follow-up was 58 months. BRCA1 tumors were larger in size (P =.03), had a higher rate of grade 3 histoprognostic factors (P =.002), and had a higher frequency of negative estrogen (P =.003) and progesterone receptors (P =.002) compared with non-BRCA1 tumors. Overall survival was poorer for carriers than for noncarriers (5-year rate, 80% v 91%, P =.002). Because a long time interval between cancer diagnosis and genetic counseling artificially increases survival time due to unrecorded deaths, the analysis was limited to the 110 patients whose diagnosis-to-counseling interval was less than 36 months (19 BRCA1 patients and 91 non-BRCA1 patients). The differences between the BRCA1 and non-BRCA1 groups regarding overall survival and metastasis-free interval were dramatically increased (49% v 85% and 18% v 84%, respectively). Multivariate analysis showed that BRCA1 mutation was an independent prognostic factor.

CONCLUSION

Our results strongly support that among patients with familial breast cancer, those who have a BRCA1 mutation have a worse outcome than those who do not.

GABAC receptors are localized with microtubule-associated protein 1B in mammalian cone photoreceptors

Protein MAP1B was recently reported to link GABA(C) receptors to the cytoskeleton at neuronal synapses. This interaction was demonstrated in the mammalian retina, where GABA(C) receptors were thought to be exclusively expressed in bipolar cells. Our previous studies on cultured photoreceptors suggested however the presence of GABA(C) receptors in cones. To further investigate GABA(C) receptor expression in cones, we measured GABA responses in mammalian photoreceptors in situ, and we examined the distribution of the receptor and that of protein MAP1B in the mammalian outer retina. Photoreceptors were recorded from flat-mounted retinas of retinal degeneration mice at an age when the retina becomes cone-dominated after rod cell death. GABA(A) and GABA(C)-gated currents were produced only in cones but not rods. Recording freshly dissociated retinal cells from wild-type C57 mice confirmed the presence of GABA(A) and GABA(C) receptors in cones. Immunohistochemical labeling of mouse and rat retinal sections localized GABA(C) receptors to cone terminals that were identified by peanut agglutinin lectin staining. As expected from previous studies on bipolar cells, the punctate immunostaining was not restricted to cone terminals in the outer plexiform layer. MAP1B immunolabeling was obtained in rat and pig retinas and was similarly found in cone terminals identified by the peanut agglutinin lectin staining. These results provide physiological and histological evidence that cones receive a GABA feedback in the mammalian retina and are consistent with the notion that protein MAP1B links GABA(C) receptors to the cytoskeleton at postsynaptic sites.

Selective transplantation of rods delays cone loss in a retinitis pigmentosa model

BACKGROUND

Rod-cone retinal degenerations (retinitis pigmentosa) are typified by initial rod loss followed by secondary cone death. Rod death, predominantly caused by gene mutations expressed specifically in these cells, induces scotopic vision loss. Cone death, the overriding cause of blindness, has no current explanation. Disease progression and preliminary data suggest that cone survival depends on rods.

OBJECTIVE

To establish whether rod transplantation into mutant rodless retinas could halt cone loss.

METHODS

We transplanted pure sheets of rods isolated from normal-sighted mice into the subretinal space of recipient retinal degeneration mice lacking rods but possessing approximately 30% residual cones. Control animals were unoperated on or grafted with inner retinal cells from young normal donors, entire retinas from aged retinal degeneration mice, or gelatin. Two weeks after surgery, we quantified by an unbiased method the numbers of host retinal cones after immunolabeling with specific markers.

RESULTS

Only mice receiving rod-rich transplants demonstrated statistically significant greater cone numbers, with rescue of 40% of host cones normally destined to die during this period.

CONCLUSION

Cone survival depends specifically on rods.

CLINICAL RELEVANCE

Such findings indicate that transplantation of rods could limit loss of cones, thus preserving useful vision in human retinitis pigmentosa. Arch Ophthalmol. 2000;118:807-811

Glial cell line-derived neurotrophic factor induces histologic and functional protection of rod photoreceptors in the rd/rd mouse

PURPOSE

To evaluate the neuroprotective potential of glial cell line-derived neurotrophic factor (GDNF) in the retinal degeneration (rd/rd) mouse model of human retinitis pigmentosa.

METHODS

Subretinal injections of GDNF were made into rd/rd mice at 13 and 17 days of age and electroretinograms (ERGs) recorded at 22 days. Control mice received saline vehicle injections or underwent no procedure. At 23 days of age, retinas from treated and control mice were fixed and processed for wholemount immunohistochemistry using an anti-rod opsin antibody, and rod numbers were estimated using an unbiased stereological systematic random approach. Subsequent to counting, immunolabeled retinas were re-embedded and sectioned in a transverse plane and the numbers of rods recalculated.

RESULTS

Although ERGs could not be recorded from sham-operation or nonsurgical rd/rd mice at 22 days of age, detectable responses (both a- and b-waves) were observed in 4 of 10 GDNF-treated mice. Stereological assessment of immunolabeled rods at 23 days showed that control rd/rd retinas contained 41,880+/-3,890 (mean +/- SEM; n = 6), phosphate-buffered saline (PBS)-injected retinas contained 61,165+/-4,932 (n = 10; P < 0.001 versus control retinas) and GDNF-injected retinas contained 89,232+/-8,033 (n = 10; P < 0.001 versus control retinas, P < 0.002 versus PBS). This increase in rod numbers after GDNF treatment was confirmed by cell counts obtained from frozen sections.

CONCLUSIONS

GDNF exerts both histologic and functional neuroprotective effects on rod photoreceptors in the rd/rd mouse. Thus rescue was demonstrated in an animal model of inherited retinal degeneration in which the gene defect was located within the rods themselves, similar to most forms of human retinitis pigmentosa. GDNF represents a candidate neurotrophic factor for palliating some forms of hereditary human blindness.

Retinitis pigmentosa: rod photoreceptor rescue by a calcium-channel blocker in the rd mouse

Retinitis pigmentosa is an inherited degenerative disease of photoreceptors leading to blindness. A well-characterized model for this disease is provided by the retinal degeneration mouse, in which the gene for the rod cGMP phosphodiesterase is mutated, as in some affected human families. We report that D-cis-diltiazem, a calcium-channel blocker that also acts at light-sensitive cGMP-gated channels, rescued photoreceptors and preserved visual function in the retinal degeneration mouse. The long record of diltiazem prescription in cardiology should facilitate the design of clinical trials for some forms of retinitis pigmentosa.

Differential distribution of dystrophins in rat retina

PURPOSE

Duchenne muscular dystrophy is frequently associated with a reduced amplitude of b-wave under scotopic conditions in the electroretinogram. This suggests that the dystrophin gene-encoded proteins play a role in retinal neurotransmission. The abnormal neurotransmission has been attributed to altered expressions of C-terminal products of the dystrophin gene in the outer plexiform layer, where photoreceptor cells form synapses with secondary neurons. The present study was undertaken to determine the cellular distribution of each member of the dystrophin superfamily in rat retina.

METHODS

Examined in the study were the developmental pattern of dystrophins in rat retinae that exhibit inherited progressive photoreceptor degeneration; dystrophins messengers expression in the outer and the inner retina of normal rats, prepared by mechanical fractionation through the outer plexiform layer; and immunolocalization of dystrophin proteins and utrophin in normal and degenerated adult rat retinae, with several antibodies prepared against specific regions of the dystrophin superfamily.

RESULTS

The results showed that Dp260 is exclusively localized in photoreceptor cells; Dp140 seems to be present in perivascular astrocytes; the exon 78 spliced isoform of Dp71 and the unspliced form are located in Müller glial cells and in perivascular astrocytes, respectively. Müller glial cells also contain utrophin.

CONCLUSIONS

Although the role of these membrane cytoskeletal proteins remains to be elucidated in retina, the results support the hypothesis that b-wave reduction may be caused by molecular anomalies of C-terminal products of the dystrophin gene expressed in both neuron and glial cells.

Ability of retinal Müller glial cells to protect neurons against excitotoxicity in vitro depends upon maturation and neuron-glial interactions

Glutamate is the most abundant excitatory amino acid in the central nervous system. It has also been described as a potent toxin when present in high concentrations because excessive stimulation of its receptors leads to neuronal death. Glial influence on neuronal survival has already been shown in the central nervous system, but the mechanisms underlying glial neuroprotection are only partly known. When cells isolated from newborn rat retina were maintained in culture as enriched neuronal populations, 80% of the cells were destroyed by application of excitotoxic concentrations of glutamate. Massive neuronal death was also observed in newborn retinal cultures containing large numbers of glia, or when neurons were seeded onto feeder layers of purified cells prepared from immature (postnatal 8 day) rat retina. When newborn retinal neurons were seeded onto feeder layers of purified glial cells prepared from adult retinas, application of excitotoxic amino acids no longer led to neuronal death. Furthermore, neuronal death was not observed in mixed neuron/glial cultures prepared from adult retina. However, in all cases (newborn and adult) application of kainate led to amacrine cell-specific death. Activity of glutamine synthetase, a key glial enzyme involved in glutamate detoxification, was assayed in these cultures in the presence or absence of exogenous glutamate. Whereas pure glial cultures alone (from young or adult retina) showed low activity that was not stimulated by glutamate addition, mixed or co-cultured neurons and adult glia exhibited up to threefold higher levels of activity following glutamate treatment. These data indicate that two conditions must be satisfied to observe glial neuroprotection: maturation of glutamine synthetase expression, and neuron-glial signalling through glutamate-elicited responses.

Neurotrophic growth factors stimulate glycosaminoglycan synthesis in identified retinal cell populations in vitro

Glycosaminoglycans (GAG) are known to participate in central nervous system processes such as development, cell migration, and neurite outgrowth, but little is known with respect to their regulation through soluble neurotrophic factors. In the present study, we have addressed this issue using cell culture models of three distinct cell populations derived from young rat retinas, namely, purified M uller glia, pigmented epithelium, and neurons respectively. Cultures were maintained in chemically defined media in the presence or absence of either basic fibroblast or epidermal growth factor. In control glial and epithelial cultures, hyaluronic acid dominated the soluble GAG pool, with lesser contributions from dermatan sulfate, chondroitin sulfate, and heparan sulfate (in decreasing order). Retinal neuronal GAG were almost exclusively chondroitin sulfate (approximately 90%). Treatment of glial and epithelial cultures with either factor led to dose-dependent increases in especially hyaluronic acid synthesis (a maximum 6-fold increase relative to control levels), with smaller but consistent changes in chondroitin sulfate. Similar treatment of retinal neurons did not lead to any changes in GAG synthesis. These data indicate that glia and pigment epithelia are the principal sources of GAG components in retina at least in vitro, and that endogenous neurotrophic growth factors can greatly modify GAG synthesis in these two retinal cell populations. Such data suggest that a delicate balance may exist between growth factor availability and glycoconjugate metabolism in vivo, participating in normal or pathological states of the retina.

Adult human retinal neurons in culture: Physiology of horizontal cells

PURPOSE

Adult postmortem human retinal neurons in long-term monolayer cultures were recorded to characterize the voltage- and transmitter-gated currents in putative human horizontal cells (HCs).

METHODS

Enzymatically and mechanically dissociated human retinal cells were seeded on polylysine and laminin- coated coverslips. Cells were identified by immunocytochemistry with cell type-specific antibodies and recorded with the patch-clamp technique.

RESULTS

Immunostaining and responses to voltage steps confirmed the survival of various retinal cell types. Horizontal cells were identified by their specific glutamate-modulated anomalous rectifier K+ current conductance. This identification was further confirmed by subsequent immunolabeling of dye-labeled recorded cells with an anti-parvalbumin antibody that selectively stained HCs in frozen human retinal sections. Horizontal cells generated voltage-gated currents classically observed in HCs from fish to mammals: a transient outward K+ current, a sustained outward K+ current, and an L-type (Ca2+ current. Na+ currents were observed in only a few HCs. As in other species, glutamate, gamma-aminobutyric acid (GABA), and glycine generated responses mediated by the activation of kainate/(RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), GABA(A), and glycine receptors, respectively.

CONCLUSIONS

Various human retinal cell populations survive in vitro as indicated by immunolabeling with specific cell markers and by the diversity of responses to voltage steps. Human HCs exhibited extensive physiological similarities to HCs from other vertebrate species and a maintained expression of parvalbumin. These results constitute a comprehensive analysis of voltage- and transmitter-gated currents in a primate retinal neuron and validate the use of long-term monolayer culture of adult human neurons as a novel in vitro model for the study of human vision.

Survival of purified rat photoreceptors in vitro is stimulated directly by fibroblast growth factor-2

Basic fibroblast growth factor (FGF-2) influences the differentiation and survival of retinal photoreceptors in vivo and in vitro, but it is not known whether it acts directly on photoreceptor FGF receptors or indirectly through activation of surrounding cells. To clarify the effects of FGF-2 on photoreceptor survival, we developed a purified photoreceptor culture system. The outer nuclear layers of postnatal day 5-15 rat retinas were isolated by vibratome sectioning, and the photoreceptor fractions obtained were enzymatically dissociated. Photoreceptors were maintained in monolayer culture for 1 week in a chemically defined medium. Immunocytochemical labeling showed that >99.5% of cells were photoreceptors, and glial contamination represented approximately 0. 2%. Photoreceptors from postnatal day 5-9 retinas survived for at least 24 hr in vitro, whereas cells from postnatal day 10-15 retinas died rapidly. Subsequent studies performed with postnatal day 5 photoreceptors showed that their survival was increased in a dose-dependent manner after the addition of FGF-2. In control cultures, 36% of originally seeded photoreceptors were alive after 5 d in vitro, and in the presence of 20 ng/ml FGF-2 this number was doubled to 62%. This increase was not caused by proliferation of photoreceptor precursors. Denaturing or blocking FGF-2 prevented enhancement of survival. Conversely, only 25.5% of photoreceptors survived in the presence of epidermal growth factor (EGF). FGF- and EGF-receptor mRNA and proteins were detected in purified photoreceptors in vitro, and addition of FGF-2 or EGF led to tyrosine phosphorylation of photoreceptor proteins. These data support a direct mechanism of action for FGF-2 stimulation of photoreceptor survival.

GABAA and GABAC receptors in adult porcine cones: evidence from a photoreceptor-glia co-culture model

1. Edge contrast enhancement is an integrated visual function based on the complex centre-surround organization of the cone photoreceptor light response. While centre responses result from direct light activation, surround responses are thought to result from lateral inhibition mediated by horizontal cells. This feedback signal has been attributed to GABAA receptors which have been found in lower vertebrate cones. 2. In order to study the GABA response of adult mammalian photoreceptors, we designed a culture system consisting of isolated photoreceptors seeded on a layer of retinal glial cells. Mature rods and cones required the presence of Muller glial cells to survive and develop neurites; they degenerated in the absence of glial cells. 3. Cone photoreceptors generated large GABA responses whereas rod photoreceptors did not respond to GABA applications. 4. Cone GABA responses consisted of two distinct components, one suppressed by the GABAA receptor blockers bicuculline and SR95531, and the second by the GABAC receptor antagonists TPMPA and imidazole-4-acetic acid (I4AA). Pentobarbital greatly increased the GABAA receptor component whereas it did not affect, or even reduced, the GABAC receptor component. During long GABA applications, GABAA receptor currents desensitized by 78%, contrasting with the sustained GABAC response. 5. Expression of GABAC receptors in cone photoreceptors was confirmed by anti-rho-subunit immunolabelling of porcine retinal sections. 6. These results indicate that both GABAA and GABAC receptors may participate in the feedback synapse from horizontal cells to cone photoreceptors in the mammalian retina.

Normal retina releases a diffusible factor stimulating cone survival in the retinal degeneration mouse

The role of cellular interactions in the mechanism of secondary cone photoreceptor degeneration in inherited retinal degenerations in which the mutation specifically affects rod photoreceptors was studied. We developed an organ culture model of whole retinas from 5-week-old mice carrying the retinal degeneration mutation, which at this age contain few remaining rods and numerous surviving cones cocultured with primary cultures of mixed cells from postnatal day 8 normal-sighted mice (C57BL/6) retinas or retinal explants from normal (C57BL/6) or dystrophic (C3H/He) 5-week-old mice. After 7 days, the numbers of residual cone photoreceptors were quantified after specific peanut lectin or anti-arrestin antibody labeling by using an unbiased stereological approach. Examination of organ cultured retinas revealed significantly greater numbers of surviving cones (15-20%) if cultured in the presence of retinas containing normal rods as compared with controls or cocultures with rod-deprived retinas. These data indicate the existence of a diffusible trophic factor released from retinas containing rod cells and acting on retinas in which only cones are present. Because cones are responsible for high acuity and color vision, such data could have important implications not only for eventual therapeutic approaches to human retinal degenerations but also to define interactions between retinal photoreceptor types.

Gangliosides and neurotrophic growth factors in the retina. Molecular interactions and applications as neuroprotective agents

Polypeptide growth factors and gangliosides can both be considered as trophic agents involved in almost all stages of neural cell development, differentiation, survival, and pathology. In most cases their physiological roles are still not clear due to the considerable complexity in their regulation. Several growth factors [e.g., basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF)] and one species of ganglioside (GM1) have been shown to exert interactions with each other and also to exhibit neuroprotective effects against retinal ischemia in vivo and cerebral excitotoxicity in vitro. Different experimental models are used to investigate their relevance to ischemic and excitotoxic conditions in the retina, and it is shown that (1) both bFGF and EGF show very effective neuroprotection for rat retinal neurones exposed to toxic levels of glutamate or its nonphysiological agonist kainate in vitro; (2) GM1 (10(-5M) used under the same conditions does not afford protection; (3) retinal glial cells also suffer morphological perturbations following glutamate or kainate treatment, but this effect is dependent on neuron-glial interactions, indicating the existence of intermediate neuron-derived messenger molecules; (4) these glial changes can be corrected by posttreatment with either bFGF or EGF in vitro; (5) using an in vivo animal model involving anterior chamber pressure-induced ischemia in adult rats, it is shown that either pretreatment by intraperitoneal injection of GM1, or posttreatment by intraocular injection of the same ganglioside, reduces significantly histological damage to inner nuclear regions; and (6) in cultured retinal Müller glial cells the existence of molecular and metabolic interactions between both types of trophic factors is demonstrated. Hence both these groups of trophic molecules show interesting features for retinal ischemic treatment.

Excitotoxic damage of retinal glial cells depends upon normal neuron-glial interactions

Glutamate, the principal retinal neurotransmitter, can also act as a toxin when present in excessive concentrations as may occur in pathologies such as retinal ischemia or more generally in cerebral neuronal degenerative disease. As glial cells play pivotal roles in transfer of blood-borne molecules and in glutamate clearance, we investigated the effects of the excitatory amino acids glutamic and kainic acid on different in vitro preparations of retinal Müller glial cells. Glial viability or morphology were not influenced by excitatory amino acid exposure in either pure glial cultures or in monolayer cultures of mixed neonatal neurons and glia, whereas kainic acid specifically lysed amacrine cells in mixed or pure neuronal cultures. When retinal fragments were pre-incubated in excitatory amino acids prior to dissociation and seeding into culture, under these conditions Müller glial cells exhibited a dramatic loss of their normal epithelioid form to a retracted morphology. However, glial cell viability was not compromised, and rapid restoration of epithelioid in vitro glial morphology could be achieved by addition of exogenous epidermal and basic fibroblast growth factor to the culture medium. This study demonstrates that glial cells are structurally perturbed by excitotoxic conditions and that such effects are dependent on normal glial-neuronal interactions.

Growth factors and gangliosides as neuroprotective agents in excitotoxicity and ischemia

1. At least two different groups of molecules can be considered neurotrophic factors because they exert a variety of effects upon neural cells. The first consists of the numerous families of polypeptide growth factors known to take part in almost all stages of neural cell growth and functioning, including development, differentiation, survival and pathology. The second group also is characterized by extensive complexity of multiple forms, and consists of the sialic acid-containing glycosphingolipids or gangliosides. These molecules also take part in the transfer of information from the extracellular milieu to the cell interior, and, similarly to growth factors, are participants in such aspects as development, differentiation and functioning. 2. In this short overview, we consider the existing data on the neuroprotective effects of growth factors [e.g., basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and brain-derived neurotrophic factor] and one species of ganglioside (GM1) against retinal ischemia in vivo and cerebral excitotoxicity in vitro. 3. We used three different experimental models to investigate their relevance to ischemic and excitotoxic conditions in the retina and have shown that: (a) both bFGF and EGF show highly effective neuroprotection for rat retinal neurons exposed to toxic levels of glutamate or its nonphysiological agonist kainate in vitro (b) retinal glial cells suffer morphological perturbations after glutamate or kainate treatment, and this effect depends on neuron-glial interactions; (c) these glial changes can also be corrected by posttreatment with either bFGF or EGF in vitro; (d) with the use of an in vivo animal model involving anterior chamber pressure-induced ischemia in adult rats, either pretreatment by intraperitoneal injection of GM1 or posttreatment by intraocular injection of the same ganglioside significantly reduces histological damage to inner nuclear regions. 4. Hence both groups of trophic molecules show interesting features for retinal ischemic treatment.

Changes in ganglioside composition of photoreceptors during postnatal maturation of the rat retina

To examine at which stage the unusual ganglioside composition observed in adult retinal photoreceptor cells was established, and to see whether ganglioside changes could be correlated to distinct maturational events, quantitative and qualitative variations in gangliosides within pure sheets of photoreceptors during postnatal differentiation and aging of retina were studied. Retinas were separated into their component layers, (particularly photoreceptor layers uncontaminated by other neuronal types) by exploiting a technique of mechanical separation by vibratome. We extracted lipids from the cell membranes and analyzed the ganglioside composition by high performance thin layer chromatography. The data show that from the earliest recordable postnatal age (6 days) until late in life (18 months), photoreceptors contain low quantities of lipid-bound N-acetyl neuraminic acid and a simplified ganglioside profile compared to inner retinal neurons. Specific ganglioside changes occur within photoreceptor cells during postnatal maturation and aging, with downregulation of a-pathway GM1 and overlapping upregulation of b-pathway GD1b taking place during the period corresponding to outer segment formation, correlating with the onset of retinal function.

Photoreceptor transplants increase host cone survival in the retinal degeneration (rd) mouse

Retinal transplants offer a potentially interesting approach to treating human retinal degenerations, but so far little quantitative data are available on possible beneficial effects. We isolated photoreceptor layers from normal-sighted mice and grafted them into the subretinal space of retinal degeneration (rd) mice lacking rod photoreceptors. At 2 weeks after surgery, the numbers of residual host cone photoreceptors outside the graft zone were quantified following specific labelling. Examination of operated retinas revealed highly significantly greater numbers of surviving cones (mean of 38% more at 2 weeks) within the central field compared to sham-operated paired control retinas (p < 0.01). These are the first quantified data indicating a trophic effect of transplanted photoreceptors upon host cone cells. As cone cells are responsible for high acuity and colour vision, such data could have important implications not only for eventual therapeutic approaches to human retinal degenerations but also to understanding underlying interactions between retinal photoreceptors.

Activities of enzymes involved in the metabolism of platelet-activating factor in neural cell cultures during proliferation and differentiation

Platelet-Activating Factor (PAF) is a potent lipid mediator involved in physiological and pathological events in the nervous tissue where it can be synthesized by two distinct pathways. The last reaction of the de novo pathway utilizes CDPcholine and alkylacetylglycerol and is catalyzed by a specific phosphocholinetransferase (PAF-PCT) whereas the remodelling pathway ends with the reaction catalyzed by lyso-PAF acetyltransferase (lyso-PAF AcT) utilizing lyso-PAF, a product of phospholipase A2 activity, and acetyl-CoA. The levels of PAF in the nervous tissue are also regulated by PAF acetylhydrolase that inactivates this mediator. We have studied the activities of these enzymes during cell proliferation and differentiation in two experimental models: 1) neuronal and glial primary cell cultures from chick embryo and 2) LA-N-1 neuroblastoma cells induced to differentiate by retinoic acid (RA). In undifferentiated neuronal cells from 8-days chick embryos the activity of PAF-PCT was much higher than that of lyso-PAF AcT but it decreased during the period of cellular proliferation up to the arrest of mitosis (day 1-3). During this period no significant changes of lyso-PAF AcT activity was observed. Both enzyme activities increased during the period of neuronal maturation and the formation of cellular contacts and synaptic-like junctions. The activity of PAF acetylhydrolase was unchanged during the development of the neuronal cultures. PAF-PCT activity did not change during the development of chick embryo glial cultures but lyso-PAF AcT activity increased up to the 12th day. RA treatment of LA-N-1 cell culture in proliferation decreased PAF-PCT activity and had no significant effect on lyso-PAF AcT and PAF acetylhydrolase indicating that the synthesis of PAF by the enzyme catalyzing the last step of the de novo pathway is inhibited when the LA-N-1 cells are induced to differentiate. These data suggest that: 1) in chick embryo primary cultures, both pathways are potentially able to contribute to PAF synthesis during development of neuronal cells particularly when they form synaptic-like junctions whereas, during development of glial cells, only the remodelling pathway might be particularly active on synthesizing PAF; 2) in LA-N-1 neuroblastoma cells PAF-synthesizing enzymes coexist and, when cells start to differentiate the contribution of the de novo pathway to PAF biosynthesis might be reduced.

Peptide growth factors but not ganglioside protect against excitotoxicity in rat retinal neurons in vitro

Glutamate is the major excitatory neurotransmitter in the retina, but excessive stimulation of its receptors leads to widespread neuronal stress and death. Both growth factors and gangliosides display important influences on responses to neuronal injury and degeneration. In this study, we have investigated the potential protective effects of two well characterized growth factors, epidermal and basic fibroblast growth factor (EGF and bFGF respectively), and the monosialoganglioside GM1, on cultured rat retinal neurons submitted to toxic levels of excitatory amino acids. Application of 1 mM glutamic acid reduced global neuronal viability by 80% when compared to control untreated cultures, whereas treatment with the glutamic acid agonist kainic acid (1 mM) led to specific, large decreases (75% reduction) in amacrine cell numbers. 24 h pretreatment with either EGF or bFGF (500 pM each) prevented the majority of excitatory amino acid-induced neuronal death, whereas similar treatment with 10(-5) M GM1 did not block neuronal degeneration. These findings demonstrate that EGF and bFGF act as neuroprotective agents against retinal excitotoxicity in vitro, whereas ganglioside GM1 is not effective in this particular paradigm.

Dystrophins in developing retina: Dp260 expression correlates with synaptic maturation

Dystrophin, the protein altered in Duchenne muscular dystrophy (DMD), is necessary for normal retinal function and exists in several isoforms. We examined the expression of dystrophin and utrophin proteins and transcripts in the rat retina at different developmental stages using Western blots and semi-quantitative RT-PCR. Our results revealed the presence of utrophin (DRP1), G-utrophin and/or DRP2 and four dystrophin isoforms (Dp427, Dp260, Dp140, Dp71) in the normal adult rat retina. Only Dp260 showed a marked progressive increase with age at both protein and mRNA levels. This variation is consistent with the establishment of synaptic functions in the developing retina and suggests a key role for this apo-dystrophin in synaptogenesis.

Successive isolation and separation of the major lipid fractions including gangliosides from single biological samples

Currently available techniques concerning extraction and characterization of the different lipids from biological specimens are designed for particular families and do not address consecutive isolation of lipid constituents in their globality. We describe here a simple, nondestructive chromatographic procedure that allows efficient elution and further analysis of the major lipid classes (neutral lipids, phospholipids, nonsialylated sphingolipids, and gangliosides) in their natural states from the same starting material. The procedure describes the use of solvent mixtures adapted to silicic acid column chromatography and permits 90-97% recovery of each of the above lipid groups. We have particularly concentrated on optimizing the efficient recovery of the diverse minor forms of gangliosides, free of other contaminants, from relatively small amounts of neural tissue. As model systems we have used in vivo and in vitro preparations of mammalian retina for which only fragmentary data are available on lipid composition. We show that relative to brain, retina contains, for example, twofold more sphingomyelin and sixfold more GD3 ganglioside. In turn, cultured retinal glial cells contain twofold higher levels of globoside and eightfold higher amounts of GM3 ganglioside with respect to intact retina. Compared to previously published techniques, we obtain improved total ganglioside recovery, with enrichment of poly-sialogangliosides. The technique presented here should be widely applicable to analyze global lipid composition of diverse biological samples.

Intravitreal injection of ganglioside GM1 after ischemia reduces retinal damage in rats

BACKGROUND AND PURPOSE

Gangliosides are normal components of cell membranes and contribute to structural rigidity and membrane function. They have been shown to protect against various insults in the brain. We have shown previously that GM1 administered intraperitoneally before the induction of retinal ischemia provides a protective effect. This study evaluates the protective effect of GM1 administered intravitreally after ischemia on retinal lesions.

METHODS

We induced retinal ischemia unilaterally in Long-Evans rats by increasing intraocular pressure to 160 mm Hg for 60 minutes. GM1 (20 microL x 10(-5) mol/L) or saline (20 microL) was injected into the vitreous 15 minutes after ischemia, and the postischemic survival time was either 8 or 15 days. The degree of retinal damage was assessed by histopathological study.

RESULTS

Retinal ischemia led to reductions in thickness and cell number, principally in the inner retinal layers (39% to 80%) and to a lesser extent in the outer retinal layers (26% to 45%). Postischemic treatment with intravitreally injected GM1 conferred significant protection against retinal ischemic damage after both 8 and 15 days of survival time. After 8 days of reperfusion, the ischemia-induced loss in overall retinal thickness was reduced by 15% and those of the inner nuclear and plexiform layers by 44% and 17%, respectively. Ischemic-induced ganglion cell and inner nuclear cell density losses were reduced by 37% and 27%, respectively. After 15 days of reperfusion, approximately the same statistically significant differences could be observed in comparison with the 15-day saline-injected group.

CONCLUSIONS

GM1 protects the rat retina from pressure-induced ischemic injury when given intravitreally after the insult. The protection provided by GM1 after initiation of retinal damage could be of therapeutic interest.