The role of megalin (LRP-2/Gp330) during development

The human gestational sac as a choriovitelline placenta during early pregnancy; the secondary yolk sac and organoid models

The yolk sac is phylogenetically the oldest of the extra-embryonic membranes and plays important roles in nutrient transfer during early pregnancy in many species. In the human this function is considered largely vestigial, in part because the secondary yolk sac never makes contact with the inner surface of the chorionic sac. Instead, it is separated from the chorion by the fluid-filled extra-embryonic coelom and attached to the developing embryo by a relatively long vitelline duct. The coelomic fluid is, however, rich in nutrients and key co-factors, including folic acid and anti-oxidants, derived from maternal plasma and the endometrial glands. Bulk sequencing has recently revealed the presence of transcripts encoding numerous transporter proteins for these ligands. Mounting evidence suggests the human secondary yolk sac plays a pivotal role in the transfer of histotrophic nutrition during the critical phase of organogenesis but also of chemicals such as medical drugs and cotinine. We therefore propose that the early placental villi, coelomic cavity and yolk sac combine to function physiologically as a choriovitelline placenta during the first weeks of pregnancy. We have derived organoids from the mouse yolk sac as proof-of-principle of a model system that could be used to answer many questions concerning the functional capacity of the human yolk sac as a maternal-fetal exchange interface during the first trimester of pregnancy.

A pilot study of transcriptomic preimplantation genetic testing (PGT-T): towards a new step in embryo selection?

STUDY QUESTION

Is it possible to predict an euploid chromosomal constitution and identify a transcriptomic profile compatible with extended embryonic development from RNA sequencing (RNA-Seq) data?

SUMMARY ANSWER

It has been possible to obtain a karyotype comparable to preimplantation genetic testing for aneuploidy (PGT-A), in addition to a transcriptomic signature of embryos which might be suggestive of improved implantation capacity.

WHAT IS KNOWN ALREADY

Conventional assessment of embryo competence, based on morphology and morphokinetic, lacks knowledge of molecular aspects and faces controversy in predicting ploidy status. Understanding the embryonic transcriptome is crucial, as gene expression influences development and implantation. PGT has improved pregnancy rates, but problems persist when high-quality euploid embryos do not reach term. In fact, only around 50-60% implant, of which 10% result in miscarriage. Comprehensive approaches, including RNA-Seq, offer the potential to discover molecular markers of reproductive competence, and could theoretically be combined with extended-embryo culture platforms up to Day 14 that can be utilized as a proxy to study embryo development at post-implantation stages.

STUDY DESIGN, SIZE, DURATION

This prospective pilot cohort study was conducted from March 2023 to August 2023. A total of 30 vitrified human blastocysts with previous PGT-A diagnosis on Day 5 (D5) or Day 6 (D6) of development were analysed: n = 15 euploid and n = 15 aneuploid. Finally, 21 embryo samples were included in the study; the rest (n = 9) were excluded due to poor quality pre-sequencing data (n = 7) or highly discordant data (n = 2).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Following warming and re-expansion, embryos underwent a second trophectoderm (TE) biopsy. The embryos were then cultured until day 11 to assess their development. Biopsy analysis by RNA-Seq, studied the differential expressed genes (DEG) to compare embryos which did not or did attach to the plate: unattached embryos (n = 12) versus attached embryos (n = 9). Thus, we also obtained a specific transcriptomic signature of embryos with a "theoretical" capacity for sustained implantation, based on plate attachment on day 11.

MAIN RESULTS AND THE ROLE OF CHANCE

The digital karyotype obtained by RNA-Seq showed good concordance with the earlier PGT-A data, with a sensitivity of 0.81, a specificity of 0.83, a Cohen's Kappa of 0.66, and an area under the ROC of 0.9. At the gene level, 76 statistically significant DEGs were found in the comparison unattached versus attached embryos (Padj < 0.05; FC > 1). To address the functional implications of these differences, significantly deregulated pathways according to GO and KEGG categories were identified. The mural trophectoderm (TE) of the unattached blastocysts showed 63 significantly deregulated terms, displaying upregulation in autophagy, apoptosis, protein kinase and ubiquitin-like protein ligase activity, and downregulation of ribosome, spliceosome, kinetochore, segregation, and chromosome condensation processes. The overall transcriptomic signature specific to embryos still attached to the plate on day 11 (with a theoretically higher implantation capacity) consists of 501 genes, including: EMP2, AURKB, FOLR1, NOTCH3, LRP2, FZD5, MDH1, APOD, GPX8, COLEC12, HSPA1A, CMTM7, BEX3, which are related to implantation and embryonic development (raw P-value < 0.05; shrunk LFC > 1.1). These findings indicate that it might be possible to identify euploid embryos with a greater capacity for implantation and development, after excluding those embryos that present chromosomal alterations.

LIMITATIONS, REASONS FOR CAUTION

This study included a small sample size, remarkable variability between samples, and low success rate of RNA amplification. Also, structural chromosomal abnormalities were not included, and it was not possible to diagnose mosaic embryos. TE biopsy does not assure the chromosomal status of the whole embryo. The maximum day for in vitro development was Day 11, and attachment to the plate on this day does not provide a clear indication of implantation capacity and viability, which was not tested in this study.

WIDER IMPLICATIONS OF THE FINDINGS

The short-term goals following on from this pilot study is to expand the sample size with embryos of more complex abnormalities, and to perform a prospective in vitro preclinical validation. In a more distant future and with optimal results, this technique could have clinical application, thus increasing clinical outcomes by assessing both chromosomal content and transcriptomic profiling.

STUDY FUNDING/COMPETING INTEREST(S)

The Institut Valencià de Competitivitat Empresarial (IVACE) (IMIDCA/2022/39) and Generalitat Valenciana (CIACIF/2021/11) supported the present study. A.C. is an employee of JUNO Genetics. He has received honoraria for an IBSA lecture and a Merck lecture. He is also a minor shareholder of IVIRMA Global. The other authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Renal Proximal Tubule Cell-Specific Megalin Deletion Does Not Affect Atherosclerosis But Induces Tubulointerstitial Nephritis in Mice Fed a Western Diet

BACKGROUND

Pharmacological inhibition of megalin (also known as LRP2 [low-density lipoprotein receptor-related protein-2]) attenuates atherosclerosis in hypercholesterolemic mice. Since megalin is abundant in renal proximal tubule cells (PTCs), the purpose of this study was to determine whether PTC-specific deletion of megalin reduces hypercholesterolemia-induced atherosclerosis in mice.

METHODS

Female Lrp2 f/f mice were bred with male Ndrg1-Cre ERT2 +/0 mice to develop PTC-LRP2 +/+ and PTC-LRP2 -/- littermates. To study atherosclerosis, all mice were bred to an LDL (low-density lipoprotein) receptor -/- background and fed a Western diet to induce atherosclerosis.

RESULTS

PTC-specific megalin deletion did not attenuate atherosclerosis in LDL receptor -/- mice in either sex. Serendipitously, we discovered that PTC-specific megalin deletion led to interstitial infiltration of CD68+ cells and tubular atrophy. The pathology was only evident in male PTC-LRP2 -/- mice fed a Western diet but not in mice fed a normal laboratory diet. Renal pathologies were also observed in male PTC-LRP2 -/- mice in an LDL receptor +/+ background fed the same Western diet, demonstrating that the renal pathologies were dependent on diet and not on hypercholesterolemia. In contrast, female PTC-LRP2 -/- mice had no apparent renal pathologies. In vivo multiphoton microscopy demonstrated that PTC-specific megalin deletion dramatically diminished ALB (albumin) accumulation in PTCs within 10 days of Western diet feeding. RNA-sequencing analyses demonstrated the upregulation of inflammation-related pathways in the kidney.

CONCLUSIONS

PTC-specific megalin deletion does not affect atherosclerosis but leads to tubulointerstitial nephritis in mice fed a Western diet, with severe pathologies in male mice.

Renal Proximal Tubule Cell-specific Megalin Deletion Does Not Affect Atherosclerosis But Induces Tubulointerstitial Nephritis in Mice Fed Western Diet

Background

Pharmacological inhibition of megalin (also known as low-density lipoprotein receptor-related protein 2: LRP2) attenuates atherosclerosis in hypercholesterolemic mice. Since megalin is abundant in renal proximal tubule cells (PTCs), the purpose of this study was to determine whether PTC-specific deletion of megalin reduces hypercholesterolemia-induced atherosclerosis in mice.

Methods

Female Lrp2 f/f mice were bred with male Ndrg1-Cre ERT2 +/0 mice to develop PTC-LRP2 +/+ and -/- littermates. To study atherosclerosis, all mice were bred to an LDL receptor -/- background and fed a Western diet to induce atherosclerosis.

Results

PTC-specific megalin deletion did not attenuate atherosclerosis in LDL receptor -/- mice in either sex. Serendipitously, we discovered that PTC-specific megalin deletion led to interstitial infiltration of CD68+ cells and tubular atrophy. The pathology was only evident in male PTC-LRP2 -/- mice fed the Western diet, but not in mice fed a normal laboratory diet. Renal pathologies were also observed in male PTC-LRP2 -/- mice in an LDL receptor +/+ background fed the same Western diet, demonstrating that the renal pathologies were dependent on diet and not hypercholesterolemia. In contrast, female PTC-LRP2 -/- mice had no apparent renal pathologies. In vivo multiphoton microscopy demonstrated that PTC-specific megalin deletion dramatically diminished albumin accumulation in PTCs within 10 days of Western diet feeding. RNA sequencing analyses demonstrated the upregulation of inflammation-related pathways in kidney.

Conclusions

PTC-specific megalin deletion does not affect atherosclerosis, but leads to tubulointerstitial nephritis in mice fed Western diet, with severe pathologies in male mice.

Aprotinin (II): Inhalational Administration for the Treatment of COVID-19 and Other Viral Conditions

Aprotinin is a broad-spectrum inhibitor of human proteases that has been approved for the treatment of bleeding in single coronary artery bypass surgery because of its potent antifibrinolytic actions. Following the outbreak of the COVID-19 pandemic, there was an urgent need to find new antiviral drugs. Aprotinin is a good candidate for therapeutic repositioning as a broad-spectrum antiviral drug and for treating the symptomatic processes that characterise viral respiratory diseases, including COVID-19. This is due to its strong pharmacological ability to inhibit a plethora of host proteases used by respiratory viruses in their infective mechanisms. The proteases allow the cleavage and conformational change of proteins that make up their viral capsid, and thus enable them to anchor themselves by recognition of their target in the epithelial cell. In addition, the activation of these proteases initiates the inflammatory process that triggers the infection. The attraction of the drug is not only its pharmacodynamic characteristics but also the possibility of administration by the inhalation route, avoiding unwanted systemic effects. This, together with the low cost of treatment (≈2 Euro/dose), makes it a good candidate to reach countries with lower economic means. In this article, we will discuss the pharmacodynamic, pharmacokinetic, and toxicological characteristics of aprotinin administered by the inhalation route; analyse the main advances in our knowledge of this medication; and the future directions that should be taken in research in order to reposition this medication in therapeutics.

Maternal Diet High in Linoleic Acid Alters Renal Branching Morphogenesis and mTOR/AKT Signalling Genes in Rat Fetal Kidneys

Linoleic acid (LA), an n-6 polyunsaturated fatty acid (PUFA), is obtained from the maternal diet during pregnancy, and is essential for normal fetal growth and development. A maternal high-LA (HLA) diet alters maternal and offspring fatty acids, maternal leptin and male/female ratio at embryonic (E) day 20 (E20). We investigated the effects of an HLA diet on embryonic offspring renal branching morphogenesis, leptin signalling, megalin signalling and angiogenesis gene expression. Female Wistar Kyoto rats were fed low-LA (LLA; 1.44% energy from LA) or high-LA (HLA; 6.21% energy from LA) diets during pregnancy and gestation/lactation. Offspring were sacrificed and mRNA from kidneys was analysed by real-time PCR. Maternal HLA decreased the targets involved in branching morphogenesis Ret and Gdnf in offspring, independent of sex. Furthermore, downstream targets of megalin, namely mTOR, Akt3 and Prkab2, were reduced in offspring from mothers consuming an HLA diet, independent of sex. There was a trend of an increase in the branching morphogenesis target Gfra1 in females (p = 0.0517). These findings suggest that an HLA diet during pregnancy may lead to altered renal function in offspring. Future research should investigate the effects an HLA diet has on offspring kidney function in adolescence and adulthood.

Comparing the effects of developmental exposure to alpha lipoic acid (ALA) and perfluorooctanesulfonic acid (PFOS) in zebrafish (Danio rerio)

Alpha lipoic acid (ALA) is a dietary supplement that has been used to treat a wide range of diseases, including obesity and diabetes, and have lipid-lowering effects, making it a potential candidate for mitigating dyslipidemia resulting from exposures to the per- and polyfluoroalkyl substance (PFAS) family member perfluorooctanesulfonic acid (PFOS). ALA can be considered a non-fluorinated structural analog to PFOS due to their similar 8-carbon chain and amphipathic structure, but, unlike PFOS, is rapidly metabolized. PFOS has been shown to reduce pancreatic islet area and induce β-cell lipotoxicity, indicating that changes in β-cell lipid microenvironment is a mechanism contributing to hypomorphic islets. Due to structural similarities, we hypothesized that ALA may compete with PFOS for binding to proteins and distribution throughout the body to mitigate the effects of PFOS exposure. However, ALA alone reduced islet area and fish length, with several morphological endpoints indicating additive toxicity in the co-exposures. Individually, ALA and PFOS increased fatty acid uptake from the yolk. ALA alone increased liver lipid accumulation, altered fatty acid profiling and modulated PPARɣ pathway signaling. Together, this work demonstrates that ALA and PFOS have similar effects on lipid uptake and metabolism during embryonic development in zebrafish.

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

Behavioral Phenotype, Electroclinical Features, and Treatment Options in Twins with Lrp2 Candidate Variants (Donnay-Barrow/Foar Syndrome)

The LRP2 gene encodes megalin (LRP-2/GP330), a large single-spanning transmembrane glycoprotein that serves as a multiligand endocytotic receptor and mediates the reabsorption of albumin in the proximal renal tubule. LRP2 is implicated in an autosomal recessive disorder characterized by dimorphisms, ocular anomalies, sensorineural deafness, proteinuria, epilepsy, and intellectual disability: a clinical condition called Donnai-Barrow syndrome (DBS) or facio-oculo-acoustico-renal (FOAR) syndrome. Pathogenic variants in LRP2 have been reported in fewer than 60 patients, but a detailed description of seizures, electroencephalographic patterns, imaging findings, behavioral phenotype, and long-term follow-up is still needed. We provide a clinical report of two mono-chorionic twins with LRP2-related disease manifesting developmental delay, autistic features, seizures, proteinuria, and sleep disorders. By sequencing clinical exome, LRP2 candidate rare variants, c.6815G > A, p. (Arg2272His), inherited from the mother and c.12725A > G, p. (Asp4242Gly), inherited from the father, were identified. During follow-up, at the age of 7, the main clinical features of the patients included insomnia, autistic features, severe psychomotor delay, and absent speech. The patients were under treatment with risperidone, antiseizure medications (ASMs), and supplementation of alpha-lactalbumin for self-injury and sleep disturbance. Our study confirmed the wide spectrum of behavioral and neurological and psychiatric features of this rare condition, suggesting new treatment options.

Effects of taurine on metal cations, transthyretin and LRP-1 in a rat model of Alzheimer's disease

BACKGROUND

Researches on diagnosis and treatment of Alzheimer's disease, the most common type of dementia, are still ongoing. Taurine is frequently used in Alzheimer's disease models due to its protective effects. Metal cation dyshomeostasis is an important etiological factor for Alzheimer's disease. Transthyretin protein is thought to act as a transporter for the Aβ protein that accumulates in the brain and is eliminated in the liver and kidneys via the LRP-1 receptor. However, the effect of taurine on this mechanisms is not fully known.

METHODS

30 male rats, aged 28 ± 4 months, were divided into 5 groups (n = 6) as follows: control group, sham group, Aβ 1-42 group, taurine group and taurine+Aβ 1-42 group. Oral taurine pre-supplementation was given as 1000 mg/kg-body weight/day for 6 weeks to taurine and taurine+Aβ 1-42 groups.

RESULTS

Plasma copper, heart transthyretin and Aβ 1-42, brain and kidney LRP-1 levels were found to be decreased in the Aβ 1-42 group. Brain transthyretin was higher in taurine+Aβ 1-42 group and brain Aβ 1-42 was higher in Aβ 1-42 and taurine+Aβ 1-42 groups.

CONCLUSION

Taurine pre-supplementation maintained cardiac transthyretin levels, decreased cardiac Aβ 1-42 levels and increased brain and kidney LRP-1 levels. Taurine may have a potential to be used as a protective agent for aged people at high risk for Alzheimer's disease.

Epigenetic Silencing of LRP2 Is Associated with Dedifferentiation and Poor Survival in Multiple Solid Tumor Types

More than 80% of human cancers originate in epithelial tissues. Loss of epithelial cell characteristics are hallmarks of tumor development. Receptor-mediated endocytosis is a key function of absorptive epithelial cells with importance for cellular and organismal homeostasis. LRP2 (megalin) is the largest known endocytic membrane receptor and is essential for endocytosis of various ligands in specialized epithelia, including the proximal tubules of the kidney, the thyroid gland, and breast glandular epithelium. However, the role and regulation of LRP2 in cancers that arise from these tissues has not been delineated. Here, we examined the expression of LRP2 across 33 cancer types in The Cancer Genome Atlas. As expected, the highest levels of LRP2 were found in cancer types that arise from LRP2-expressing absorptive epithelial cells. However, in a subset of tumors from these cancer types, we observed epigenetic silencing of LRP2. LRP2 expression showed a strong inverse correlation to methylation of a specific CpG site (cg02361027) in the first intron of the LRP2 gene. Interestingly, low expression of LRP2 was associated with poor patient outcome in clear cell renal cell carcinoma, papillary renal cell carcinoma, mesothelioma, papillary thyroid carcinoma, and invasive breast carcinoma. Furthermore, loss of LRP2 expression was associated with dedifferentiated histological and molecular subtypes of these cancers. These observations now motivate further studies on the functional role of LRP2 in tumors of epithelial origin and the potential use of LRP2 as a cancer biomarker.

The role of lipocalin 2 in brain injury and recovery after ischemic and hemorrhagic stroke

Ischemic and hemorrhagic stroke (including intracerebral hemorrhage, intraventricular hemorrhage, and subarachnoid hemorrhage) is the dominating cause of disability and death worldwide. Neuroinflammation, blood-brain barrier (BBB) disruption, neuronal death are the main pathological progress, which eventually causes brain injury. Increasing evidence indicated that lipocalin 2 (LCN2), a 25k-Da acute phase protein from the lipocalin superfamily, significantly increased immediately after the stroke and played a vital role in these events. Meanwhile, there exists a close relationship between LCN2 levels and the worse clinical outcome of patients with stroke. Further research revealed that LCN2 elimination is associated with reduced immune infiltrates, infarct volume, brain edema, BBB leakage, neuronal death, and neurological deficits. However, some studies revealed that LCN2 might also act as a beneficial factor in ischemic stroke. Nevertheless, the specific mechanism of LCN2 and its primary receptors (24p3R and megalin) involving in brain injury remains unclear. Therefore, it is necessary to investigate the mechanism of LCN2 induced brain damage after stroke. This review focuses on the role of LCN2 and its receptors in brain injury and aiming to find out possible therapeutic targets to reduce brain damage following stroke.

Alterations in circulating levels of vitamin D binding protein, total and bioavailability of vitamin D in diabetic retinopathy patients

AIMS

This study aimed to investigate the association between circulating levels of vitamin D binding protein (VDBP) and its genotypes and diabetic retinopathy risk.

METHODS

This case-control study recruited 154 patients with type 2 diabetes mellitus; 62 with diabetic retinopathy (DR) and 92 without DR and diabetic nephropathy (DN). Circulating levels of 25-hydroxyvitamin D3 and VDBP levels were measured in the patients. The genotype and phenotype of VDBP were evaluated based on two common VDBP variations; rs7041 and rs4588.

RESULTS

Serum levels of VDBP were significantly lower in patients with DR than in patients without DR and/or DN (Ln-VDBP (μg/ml): 6.14 ± 0.92 vs. 6.73 ± 1.45, p = 0.001) even after adjustment for age, sex, body mass index, disease duration, estimated glomerular filtration rate (eGFR), HbA1C, insulin therapy profile, and serum levels of 25(OH)D. The distribution of VDBP phenotypes and genotypes in the two studied groups were nearly the same, and the distribution was similar to that of the general population.

CONCLUSIONS

In this study, we found the association between lower circulating levels of VDBP and risk of DR. However, the precise mechanism linking these two remains unknown. Further and more in-depth research is needed to find out the underlying causes of the relationship.

RNA-Seq reveals the functional specificity of epididymal caput, corpus, and cauda genes of cattleyak

The first filial generation of the cattleyaks demonstrates hybrid vigor; however, the male cattleyaks are infertile and restrict productivity and breeding. The discovery of genes in a segment-specific approach offers valuable information and understanding concerning fertility status, yet the biology of cattleyak epididymis is still progressing. Comparative transcriptome analysis was performed on segment pairs of cattleyak epididymis. The caput versus corpus epididymis provided the highest (57.8%) differentially expressed genes (DEGs), corpus versus cauda (25.1%) followed, whereas caput versus cauda pair (17.1%) had the least DEGs. The expression levels of genes coding EPHB6, TLR1, MUC20, MT3, INHBB, TRPV5, EI24, PAOX, KIF12, DEPDC5, and KRT25, which might have the potentials to regulate the homeostasis, innate immunity, differentiation, motility, transport, and sperm maturation-related function in epididymal cells, were downregulated in the distal segment of epididymis. Top enriched KEGG pathways included mTOR, axon guidance, and taste transduction signaling pathways. EIF4B, EPHB6, and TAS2R42 were enriched in the pathways, respectively. Identifying key, new, and unexplored DEGs among the epididymal segments and further analyzing them could boost cattleyak fertility by maximizing sperm quality from genetically better sires and also facilitate better understanding of the epididymal biology.

Functions of the (pro)renin receptor (Atp6ap2) at molecular and system levels: pathological implications in hypertension, renal and brain development, inflammation, and fibrosis

The (pro)renin receptor [(P)RR, Atp6ap2] was initially discovered as a membrane-bound binding partner of prorenin and renin. A soluble (P)RR has additional paracrine effects and is involved in metabolic syndrome and kidney damage. Meanwhile it is clear that most of the effects of the (P)RR are independent of prorenin. In the kidney, (P)RR plays an important role in renal dysfunction by activating proinflammatory and profibrotic molecules. In the brain, (P)RR is expressed in cardiovascular regulatory nuclei and is linked to hypertension. (P)RR is known to be an essential component of the v-ATPase as a key accessory protein and plays an important role in kidney, brain and heart via regulating the pH of the extracellular space and intracellular compartments. V-ATPase and (P)RR together act on WNT and mTOR signalling pathways, which are responsible for cellular homeostasis and autophagy. (P)RR through its role in v-ATPase assembly and function is also important for fast recycling endocytosis by megalin. In the kidney, megalin together with v-ATPase and (P)RR is crucial for endocytic uptake of components of the RAS and their intracellular processing. In the brain, (P)RR, v-ATPases and megalin are important regulators both during development and in the adult. All three proteins are associated with diseases such as XLMR, XMRE, X-linked parkinsonism and epilepsy, cognitive disorders with Parkinsonism, spasticity, intellectual disability, and Alzheimer's Disease which are characterized by impaired neuronal function and/or neuronal loss. The present review focusses on the relevant effects of Atp6ap2 without assigning them necessarily to the RAS. Mechanistically, many effects can be well explained by the role of Atp6ap2 for v-ATPase assembly and function. Furthermore, application of a soluble (P)RR analogue as new therapeutic option is discussed.

Inflammation-like changes in the urothelium of Lifr-deficient mice and LIFR-haploinsufficient humans with urinary tract anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of end-stage kidney disease in children. While the genetic aberrations underlying CAKUT pathogenesis are increasingly being elucidated, their consequences on a cellular and molecular level commonly remain unclear. Recently, we reported rare heterozygous deleterious LIFR variants in 3.3% of CAKUT patients, including a novel de novo frameshift variant, identified by whole-exome sequencing, in a patient with severe bilateral CAKUT. We also demonstrated CAKUT phenotypes in Lifr-/- and Lifr+/- mice, including a narrowed ureteric lumen due to muscular hypertrophy and a thickened urothelium. Here, we show that both in the ureter and bladder of Lifr-/- and Lifr+/- embryos, differentiation of the three urothelial cell types (basal, intermediate and superficial cells) occurs normally but that the turnover of superficial cells is elevated due to increased proliferation, enhanced differentiation from their progenitor cells (intermediate cells) and, importantly, shedding into the ureteric lumen. Microarray-based analysis of genome-wide transcriptional changes in Lifr-/- versus Lifr+/+ ureters identified gene networks associated with an antimicrobial inflammatory response. Finally, in a reverse phenotyping effort, significantly more superficial cells were detected in the urine of CAKUT patients with versus without LIFR variants indicating conserved LIFR-dependent urinary tract changes in the murine and human context. Our data suggest that LIFR signaling is required in the epithelium of the urinary tract to suppress an antimicrobial response under homeostatic conditions and that genetically induced inflammation-like changes underlie CAKUT pathogenesis in Lifr deficiency and LIFR haploinsufficiency.

Maternal preconception PFOS exposure of Drosophila melanogaster alters reproductive capacity, development, morphology and nutrient regulation

Perfluorooctanesulfonic acid (PFOS) is a persistent synthetic surfactant widely detected in the environment. Developmental PFOS exposures are associated with low birth weight and chronic exposures increase risk for obesity and type 2 diabetes. As an obesogen, PFOS poses a major public health exposure risk and much remains to be understood about the critical windows of exposure and mechanisms impacted, especially during preconception. Here, we leverage evolutionarily conserved pathways and processes in the fruit fly Drosophila melanogaster (wild-type Canton-S and megalin-UAS RNAi transgenic fly lines) to investigate the window of maternal preconception exposure to PFOS on reproductive and developmental toxicity, and examine receptor (megalin)-mediated endocytosis of nutrients and PFOS into the oocyte as a potential mechanism. Preconception exposure to 2 ng PFOS/female resulted in an internal concentration of 0.081 ng/fly over two days post exposure, no mortality and reduced megalin transcription. The number of eggs laid 1-3 days post exposure was reduced and contained 0.018 ng PFOS/egg. Following heat shock, PFOS was significantly reduced in eggs from megalin-knockdown transgenic females. Cholesterol and triglycerides were increased in eggs laid immediately following PFOS exposure by non-heat shocked transgenic females whereas decreased cholesterol and increased protein levels were found in eggs laid by heat shocked transgenic females. Preconception exposure likewise increased cholesterol in early emerging wildtype F1 adults and also resulted in progeny with a substantial developmental delay, a reduction in adult weights, and altered transcription of Drosophila insulin-like peptide genes. These findings support an interaction between PFOS and megalin that interferes with normal nutrient transport during oocyte maturation and embryogenesis, which may be associated with later in life developmental delay and reduced weight.

LRP2 controls sonic hedgehog-dependent differentiation of cardiac progenitor cells during outflow tract formation

Conotruncal malformations are a major cause of congenital heart defects in newborn infants. Recently, genetic screens in humans and in mouse models have identified mutations in LRP2, a multi-ligand receptor, as a novel cause of a common arterial trunk, a severe form of outflow tract (OFT) defect. Yet, the underlying mechanism why the morphogen receptor LRP2 is essential for OFT development remained unexplained. Studying LRP2-deficient mouse models, we now show that LRP2 is expressed in the cardiac progenitor niche of the anterior second heart field (SHF) that contributes to the elongation of the OFT during separation into aorta and pulmonary trunk. Loss of LRP2 in mutant mice results in the depletion of a pool of sonic hedgehog-dependent progenitor cells in the anterior SHF due to premature differentiation into cardiomyocytes as they migrate into the OFT myocardium. Depletion of this cardiac progenitor cell pool results in aberrant shortening of the OFT, the likely cause of CAT formation in affected mice. Our findings identified the molecular mechanism whereby LRP2 controls the maintenance of progenitor cell fate in the anterior SHF essential for OFT separation, and why receptor dysfunction is a novel cause of conotruncal malformation.

Molecular Diversification of the Seminal Fluid Proteome in a Recently Diverged Passerine Species Pair

Seminal fluid proteins (SFPs) mediate an array of postmating reproductive processes that influence fertilization and fertility. As such, it is widely held that SFPs may contribute to postmating, prezygotic reproductive barriers between closely related taxa. We investigated seminal fluid (SF) diversification in a recently diverged passerine species pair (Passer domesticus and Passer hispaniolensis) using a combination of proteomic and comparative evolutionary genomic approaches. First, we characterized and compared the SF proteome of the two species, revealing consistencies with known aspects of SFP biology and function in other taxa, including the presence and diversification of proteins involved in immunity and sperm maturation. Second, using whole-genome resequencing data, we assessed patterns of genomic differentiation between house and Spanish sparrows. These analyses detected divergent selection on immunity-related SF genes and positive selective sweeps in regions containing a number of SF genes that also exhibited protein abundance diversification between species. Finally, we analyzed the molecular evolution of SFPs across 11 passerine species and found a significantly higher rate of positive selection in SFPs compared with the rest of the genome, as well as significant enrichments for functional pathways related to immunity in the set of positively selected SF genes. Our results suggest that selection on immunity pathways is an important determinant of passerine SF composition and evolution. Assessing the role of immunity genes in speciation in other recently diverged taxa should be prioritized given the potential role for immunity-related proteins in reproductive incompatibilities in Passer sparrows.

The role of lipocalin-2 in age-related macular degeneration (AMD)

Lipocalins are a family of secreted adipokines which play important roles in various biological processes. Lipocalin-2 (LCN-2) has been shown to be involved in acute and chronic inflammation. This particular protein is critical in the pathogenesis of several diseases including cancer, diabetes, obesity, and multiple sclerosis. Herein, we discuss the general molecular basis for the involvement of LCN-2 in acute infections and chronic disease progression and also ascertain the probable role of LCN-2 in ocular diseases, particularly in age-related macular degeneration (AMD). We elaborate on the signaling cascades which trigger LCN-2 upregulation in AMD and suggest therapeutic strategies for targeting such pathways.

Megalin: A bridge connecting kidney, the renin-angiotensin system, and atherosclerosis

Megalin is a member of the low-density lipoprotein receptor superfamily. It has been recognized as an endocytic receptor for a large spectrum of ligands. As a consequence, megalin regulates homeostasis of many molecules and affects multiple physiological and pathophysiological functions. The renin-angiotensin system is a hormonal system. A number of studies have reported contributions of the renin-angiotensin system to atherosclerosis. There is evolving evidence that megalin is a regulator of the renin-angiotensin system, and contributes to atherosclerosis. This brief review provides contemporary insights into effects of megalin on renal functions, the renin-angiotensin system, and atherosclerosis.

Cancer gene mutations in congenital pulmonary airway malformation patients

Background

Newborns affected with congenital pulmonary airway malformations (CPAMs) may present with severe respiratory distress or remain asymptomatic. While surgical resection is the definitive treatment for symptomatic CPAMs, prophylactic elective surgery may be recommended for asymptomatic CPAMs owing to the risk of tumour development. However, the implementation of prophylactic surgery is quite controversial on the grounds that more evidence linking CPAMs and cancer is needed. The large gap in knowledge of CPAM pathogenesis results in uncertainties and controversies in disease management. As developmental genes control postnatal cell growth and contribute to cancer development, we hypothesised that CPAMs may be underlain by germline mutations in genes governing airways development.

Methods

Sequencing of the exome of 19 patients and their unaffected parents.

Results

A more than expected number of mutations in cancer genes (false discovery rate q-value <5.01×10⁻⁵) was observed. The co-occurrence, in the same patient, of damaging variants in genes encoding interacting proteins is intriguing, the most striking being thyroglobulin (TG) and its receptor, megalin (LRP2). Both genes are highly relevant in lung development and cancer.

Conclusions

The overall excess of mutations in cancer genes may account for the reported association of CPAMs with carcinomas and provide some evidence to argue for prophylactic surgery by some surgeons.

Congenital pulmonary airway malformation (CPAM) patients have more than expected numbers of damaging variants in genes involved in lung carcinoma; this may provide evidence for clinicians choosing to adopt prophylactic excision in CPAMhttp://ow.ly/h1AE30n4DIe

Investigating the RAS can be a fishy business: interdisciplinary opportunities using Zebrafish

The renin-angiotensin system (RAS) is highly conserved, and components of the RAS are present in all vertebrates to some degree. Although the RAS has been studied since the discovery of renin, its biological role continues to broaden with the identification and characterization of new peptides. The evolutionarily distant zebrafish is a remarkable model for studying the kidney due to its genetic tractability and accessibility for in vivo imaging. The zebrafish pronephros is an especially useful kidney model due to its structural simplicity yet complex functionality, including capacity for glomerular and tubular filtration. Both the pronephros and mesonephros contain renin-expressing perivascular cells, which respond to RAS inhibition, making the zebrafish an excellent model for studying the RAS. This review summarizes the physiological and genetic tools currently available for studying the zebrafish kidney with regards to functionality of the RAS, using novel imaging techniques such as SPIM microscopy coupled with targeted single cell ablation and synthesis of vasoactive RAS peptides.

Maternal-fetal cholesterol transport in the second half of mouse pregnancy does not involve LDL receptor-related protein 2

AIM

LDL receptor-related protein type 2 (LRP2) is highly expressed on both yolk sac and placenta. Mutations in the corresponding gene are associated with severe birth defects in humans, known as Donnai-Barrow syndrome. We here characterized the contribution of LRP2 and maternal plasma cholesterol availability to maternal-fetal cholesterol transport and fetal cholesterol levels in utero in mice.

METHODS

Lrp2^+/- mice were mated heterozygously to yield fetuses of all three genotypes. Half of the dams received a 0.5% probucol-enriched diet during gestation to decrease maternal HDL cholesterol. At E13.5, the dams received an injection of D7-labelled cholesterol and were provided with 1-¹³ C acetate-supplemented drinking water. At E16.5, fetal tissues were collected and maternal cholesterol transport and fetal synthesis quantified by isotope enrichments in fetal tissues by GC-MS.

RESULTS

The Lrp2 genotype did not influence maternal-fetal cholesterol transport and fetal cholesterol. However, lowering of maternal plasma cholesterol levels by probucol significantly reduced maternal-fetal cholesterol transport. In the fetal liver, this was associated with increased cholesterol synthesis rates. No indications were found for an interaction between the Lrp2 genotype and maternal probucol treatment.

CONCLUSION

Maternal-fetal cholesterol transport and endogenous fetal cholesterol synthesis depend on maternal cholesterol concentrations but do not involve LRP2 in the second half of murine pregnancy. Our results suggest that the mouse fetus can compensate for decreased maternal cholesterol levels. It remains a relevant question how the delicate system of cholesterol transport and synthesis is regulated in the human fetus and placenta.

Placental Origins of Chronic Disease

Epidemiological evidence links an individual's susceptibility to chronic disease in adult life to events during their intrauterine phase of development. Biologically this should not be unexpected, for organ systems are at their most plastic when progenitor cells are proliferating and differentiating. Influences operating at this time can permanently affect their structure and functional capacity, and the activity of enzyme systems and endocrine axes. It is now appreciated that such effects lay the foundations for a diverse array of diseases that become manifest many years later, often in response to secondary environmental stressors. Fetal development is underpinned by the placenta, the organ that forms the interface between the fetus and its mother. All nutrients and oxygen reaching the fetus must pass through this organ. The placenta also has major endocrine functions, orchestrating maternal adaptations to pregnancy and mobilizing resources for fetal use. In addition, it acts as a selective barrier, creating a protective milieu by minimizing exposure of the fetus to maternal hormones, such as glucocorticoids, xenobiotics, pathogens, and parasites. The placenta shows a remarkable capacity to adapt to adverse environmental cues and lessen their impact on the fetus. However, if placental function is impaired, or its capacity to adapt is exceeded, then fetal development may be compromised. Here, we explore the complex relationships between the placental phenotype and developmental programming of chronic disease in the offspring. Ensuring optimal placentation offers a new approach to the prevention of disorders such as cardiovascular disease, diabetes, and obesity, which are reaching epidemic proportions.

Transcriptome analysis illuminates the nature of the intracellular interaction in a vertebrate-algal symbiosis

During embryonic development, cells of the green alga Oophila amblystomatis enter cells of the salamander Ambystoma maculatum forming an endosymbiosis. Here, using de novo dual-RNA seq, we compared the host salamander cells that harbored intracellular algae to those without algae and the algae inside the animal cells to those in the egg capsule. This two-by-two-way analysis revealed that intracellular algae exhibit hallmarks of cellular stress and undergo a striking metabolic shift from oxidative metabolism to fermentation. Culturing experiments with the alga showed that host glutamine may be utilized by the algal endosymbiont as a primary nitrogen source. Transcriptional changes in salamander cells suggest an innate immune response to the alga, with potential attenuation of NF-κB, and metabolic alterations indicative of modulation of insulin sensitivity. In stark contrast to its algal endosymbiont, the salamander cells did not exhibit major stress responses, suggesting that the host cell experience is neutral or beneficial.

α-amanitin resistance in Drosophila melanogaster: A genome-wide association approach

We investigated the mechanisms of mushroom toxin resistance in the Drosophila Genetic Reference Panel (DGRP) fly lines, using genome-wide association studies (GWAS). While Drosophila melanogaster avoids mushrooms in nature, some lines are surprisingly resistant to α-amanitin—a toxin found solely in mushrooms. This resistance may represent a pre-adaptation, which might enable this species to invade the mushroom niche in the future. Although our previous microarray study had strongly suggested that pesticide-metabolizing detoxification genes confer α-amanitin resistance in a Taiwanese D. melanogaster line Ama-KTT, none of the traditional detoxification genes were among the top candidate genes resulting from the GWAS in the current study. Instead, we identified Megalin, Tequila, and widerborst as candidate genes underlying the α-amanitin resistance phenotype in the North American DGRP lines, all three of which are connected to the Target of Rapamycin (TOR) pathway. Both widerborst and Tequila are upstream regulators of TOR, and TOR is a key regulator of autophagy and Megalin-mediated endocytosis. We suggest that endocytosis and autophagy of α-amanitin, followed by lysosomal degradation of the toxin, is one of the mechanisms that confer α-amanitin resistance in the DGRP lines.

Membrane dynamics in mammalian embryogenesis: Implication in signal regulation

Eukaryotes have evolved an array of membrane compartments constituting secretory and endocytic pathways that allow the flow of materials. Both pathways perform important regulatory roles. The secretory pathway is essential for the production of extracellular, secreted signal molecules, but its function is not restricted to a mere route connecting intra- and extracellular compartments. Post-translational modifications also play an integral function in the secretory pathway and are implicated in developmental regulation. The endocytic pathway serves as a platform for relaying signals from the extracellular stimuli to intracellular mediators, and then ultimately inducing signal termination. Here, we discuss recent studies showing that dysfunction in membrane dynamics causes patterning defects in embryogenesis and tissue morphogenesis in mammals.

Common arterial trunk and ventricular non-compaction in Lrp2 knockout mice indicate a crucial role of LRP2 in cardiac development

Lipoprotein-related receptor protein 2 (LRP2) is important for development of the embryonic neural crest and brain in both mice and humans. Although a role in cardiovascular development can be expected, the hearts of Lrp2 knockout (KO) mice have not yet been investigated. We studied the cardiovascular development of Lrp2 KO mice between embryonic day 10.5 (E10.5) and E15.5, applying morphometry and immunohistochemistry, using antibodies against Tfap2α (neural crest cells), Nkx2.5 (second heart field), WT1 (epicardium derived cells), tropomyosin (myocardium) and LRP2. The Lrp2 KO mice display a range of severe cardiovascular abnormalities, including aortic arch anomalies, common arterial trunk (persistent truncus arteriosus) with coronary artery anomalies, ventricular septal defects, overriding of the tricuspid valve and marked thinning of the ventricular myocardium. Both the neural crest cells and second heart field, which are essential for the lengthening and growth of the right ventricular outflow tract, are abnormally positioned in the Lrp2 KO. This explains the absence of the aorto-pulmonary septum, which leads to common arterial trunk and ventricular septal defects. Severe blebbing of the epicardial cells covering the ventricles is seen. Epithelial-mesenchymal transition does occur; however, there are fewer WT1-positive epicardium-derived cells in the ventricular wall as compared to normal, coinciding with the myocardial thinning and deep intertrabecular spaces. LRP2 plays a crucial role in cardiovascular development in mice. This corroborates findings of cardiac anomalies in humans with LRP2 mutations. Future studies should reveal the underlying signaling mechanisms in which LRP2 is involved during cardiogenesis.

Summary: This paper sheds a new light on the role of the second heart field and neural crest cells in outflow tract formation in the mouse embryo. Depletion of the LPR2 results in a disturbed contribution pattern and subsequent common arterial trunk.

Mono-2-ethylhexyl phthalate (MEHP) alters histiotrophic nutrition pathways and epigenetic processes in the developing conceptus

Histiotrophic nutrition pathways (HNPs) are processes by which the organogenesis-stage conceptus obtains nutrients, amino acids, vitamins and cofactors required for protein biosynthesis and metabolic activities. Nutrients are captured from the maternal milieu as whole proteins and cargoes via receptor-mediated endocytosis in the visceral yolk sac (VYS), degraded by lysosomal proteolysis and delivered to the developing embryo (EMB). Several nutrients obtained by HNPs are required substrates for one-carbon (C1) metabolism and supply methyl groups required for epigenetic processes, including DNA and histone methylation. Increased availability of methyl donors has been associated with reduced risk for neural tube defects (NTDs). Here, we show that mono-2-ethylhexyl phthalate (MEHP) treatment (100 or 250μM) alters HNPs, C1 metabolism and epigenetic programming in the organogenesis-stage conceptus. Specifically, 3-h MEHP treatment of mouse EMBs in whole culture resulted in dose-dependent reduction of HNP activity in the conceptus. To observe nutrient consequences of decreased HNP function, C1 components and substrates and epigenetic outcomes were quantified at 24h. Treatment with 100-μM MEHP resulted in decreased dietary methyl donor concentrations, while treatment with 100- or 250-μM MEHP resulted in dose-dependent elevated C1 products and substrates. In MEHP-treated EMBs with NTDs, H3K4 methylation was significantly increased, while no effects were seen in treated VYS. DNA methylation was reduced in MEHP-treated EMB with and without NTDs. This research suggests that environmental toxicants such as MEHP decrease embryonic nutrition in a time-dependent manner and that epigenetic consequences of HNP disruption may be exacerbated in EMB with NTDs.

Lipid transport to avian oocytes and to the developing embryo

Studies of receptor-mediated lipoprotein metabolic pathways in avian species have revealed that physiological intricacies of specific cell types are highly analogous to those in mammals. A prime example for the power of comparative studies across different animal kingdoms, elucidated in the chicken, is that the expression of different lipoprotein receptors in somatic cells and oocytes are the key to oocyte growth. In avian species, yolk precursor transport from the hen's liver to rapidly growing oocytes and the subsequent transfer of yolk nutrients via the yolk sac to the developing embryo are highly efficient processes. Oocytes grow from a diameter of 5 mm to 2.5-3 cm in only 7 days, and the yolk sac transfers nutrients from the yolk stored in the mature oocyte to the embryo within just 2 weeks. The underlying key transport mechanism is receptor-mediated endocytosis of macromolecules, i.e., of hepatically synthesized yolk precursors for oocyte growth, and of mature yolk components for embryo nutrition, respectively. Recently, the receptors involved, as well as the role of lipoprotein synthesis in the yolk sac have been identified. As outlined here, lipoprotein degradation/resynthesis cycles and the expression of lipoprotein receptors are not only coordinated with the establishment of the follicular architecture embedding the oocyte, but also with the generation of the yolk sac vasculature essential for nutrient transfer to the embryo.

Deficits in receptor-mediated endocytosis and recycling in cells from mice with Gpr107 locus disruption

GPR107 is a type III integral membrane protein that was initially predicted to be a member of the family of G-protein-coupled receptors. This report shows that deletion of Gpr107 leads to an embryonic lethal phenotype that is characterized by a reduction in cubilin transcript abundance and a decrease in the representation of multiple genes implicated in the cubilin-megalin endocytic receptor complex (megalin is also known as LRP2). Gpr107-null fibroblast cells exhibit reduced transferrin internalization, decreased uptake of low-density lipoprotein (LDL) receptor-related protein-1 (LRP1) cargo and resistance to toxins. Colocalization studies and proteomic analyses suggest that GPR107 associates with clathrin and the retromer protein VPS35 and that GPR107 might be responsible for the return of receptors to the plasma membrane from endocytic compartments. The highly selective deficits observed in Gpr107-null cells indicate that GPR107 interacts directly or indirectly with a limited subset of surface receptors.

Expression and immunolocalisation of the endocytic receptors megalin and cubilin in the human yolk sac and placenta across gestation

Megalin and cubilin are multifunctional endocytic receptors associated with many transporting epithelia. They play an essential role in transport of nutrients through the visceral yolk sac of rodents during embryogenesis. Here, we immunolocalise them to the endodermal layer of the human yolk sac, and to the syncytiotrophoblast and cytotrophoblast cells of placental villi. In villi, the protein level of both receptors increased with gestation. The mRNA for megalin remained constant, while that encoding cubilin increased with gestation. These results suggest megalin and cubilin may be important in human maternal–fetal transfer, and that they increase across gestation to facilitate this function.

Inhibition of proteolysis in histiotrophic nutrition pathways alters DNA methylation and one-carbon metabolism in the organogenesis-stage rat conceptus

Epigenetic modifications, including DNA methylation, contribute to the transcriptional regulation of developmental genes that control growth and differentiation during embryogenesis. The methyl donor, S-adenosylmethionine (SAM), is biosynthesized from methionine and adenosine triphosphate by methionine adenosyltransferase 2a (Mat2a) in the one-carbon (C1) metabolism pathway. SAM biosynthesis requires a steady supply of nutrients, vitamins and cofactors obtained by the developing conceptus through histiotrophic nutrition pathways (HNPs). The visceral yolk sac (VYS) captures proteins and their substrate cargos by receptor-mediated endocytosis and degrades them using lysosomal proteases. We hypothesize that leupeptin, a protease inhibitor, reduces the availability of methionine and C1 substrates, restricting SAM biosynthesis and altering patterns of DNA methylation. Rat conceptuses were exposed to 50 and 100 μM leupeptin in whole embryo culture for periods of 26 h from gestational day (GD) 10 or 6 h on GD11. After 6 h on GD11, the 100-μM leupeptin treatment significantly decreased methionine in embryo (EMB) and VYS, reduced Mat2a protein levels and inhibited Mat2a specific activity, all of which produced a significant 52% reduction of SAM in the VYS. The 50- and 100-μM leupeptin treatments significantly decreased global methylation levels by 6%-9% in EMB and by 11%-15% in VYS following both 6- and 26-h exposure periods. This study demonstrates that HNP disruption alters C1 activity and significantly reduces global DNA methylation during organogenesis. Because epigenetic reprogramming is crucial for normal differentiation and growth, these findings suggest a possible mechanism through which nutrients and environmental factors may alter early developmental regulation.

N-glycoproteome of E14.Tg2a mouse embryonic stem cells

E14.Tg2a mouse embryonic stem (mES) cells are a widely used host in gene trap and gene targeting techniques. Molecular characterization of host cells will provide background information for a better understanding of functions of the knockout genes. Using a highly selective glycopeptide-capture approach but ordinary liquid chromatography coupled mass spectrometry (LC-MS), we characterized the N-glycoproteins of E14.Tg2a cells and analyzed the close relationship between the obtained N-glycoproteome and cell-surface proteomes. Our results provide a global view of cell surface protein molecular properties, in which receptors seem to be much more diverse but lower in abundance than transporters on average. In addition, our results provide a systematic view of the E14.Tg2a N-glycosylation, from which we discovered some striking patterns, including an evolutionarily preserved and maybe functionally selected complementarity between N-glycosylation and the transmembrane structure in protein sequences. We also observed an environmentally influenced N-glycosylation pattern among glycoenzymes and extracellular matrix proteins. We hope that the acquired information enhances our molecular understanding of mES E14.Tg2a as well as the biological roles played by N-glycosylation in cell biology in general.

The developing chicken yolk sac acquires nutrient transport competence by an orchestrated differentiation process of its endodermal epithelial cells

During chicken yolk sac (YS) growth, mesodermal cells in the area vasculosa follow the migrating endodermal epithelial cell (EEC) layer in the area vitellina. Ultimately, these cells form the vascularized YS that functions in nutrient transfer to the embryo. How and when EECs, with their apical aspect directly contacting the oocytic yolk, acquire the ability to take up yolk macromolecules during the vitellina-to-vasculosa transition has not been investigated. In addressing these questions, we found that with progressive vascularization, the expression level in EECs of the nutrient receptor triad, LRP2-cubilin-amnionless, changes significantly. The receptor complex, competent for uptake of yolk proteins, is produced by EECs in the area vasculosa but not in the area vitellina. Yolk components endocytosed by LRP2-cubilin-amnionless, preformed and newly formed lipid droplets, and yolk-derived very low density lipoprotein, shown to be efficiently endocytosed and lysosomally processed by EECs, probably provide substrates for resynthesis and secretion of nutrients, such as lipoproteins. In fact, as directly demonstrated by pulse-chase experiments, EECs in the vascularized, but not in the avascular, region efficiently produce and secrete lipoproteins containing apolipoprotein A-I (apoA-I), apoB, and/or apoA-V. In contrast, perilipin 2, a lipid droplet-stabilizing protein, is produced exclusively by the EECs of the area vitellina. These data suggest a differentiation process that orchestrates the vascularization of the developing YS with the induction of yolk uptake and lipoprotein secretion by EECs to ensure embryo nutrition.

Megalin mediates transepithelial albumin clearance from the alveolar space of intact rabbit lungs

The alveolo-capillary barrier is effectively impermeable to large solutes such as proteins. A hallmark of acute lung injury/acute respiratory distress syndrome is the accumulation of protein-rich oedema fluid in the distal airspaces. Excess protein must be cleared from the alveolar space for recovery; however, the mechanisms of protein clearance remain incompletely understood. In intact rabbit lungs 29.8 ± 2.2% of the radio-labelled alveolar albumin was transported to the vascular compartment at 37°C within 120 min, as assessed by real-time measurement of 125I-albumin clearance from the alveolar space. At 4°C or 22°C significantly lower albumin clearance (3.7 ± 0.4 or 16.2 ± 1.1%, respectively) was observed. Deposition of a 1000-fold molar excess of unlabelled albumin into the alveolar space or inhibition of cytoskeletal rearrangement or clathrin-dependent endocytosis largely inhibited the transport of 125I-albumin to the vasculature, while administration of unlabelled albumin to the vascular space had no effect on albumin clearance. Furthermore, albumin uptake capacity was measured as about 0.37 mg ml−1 in cultured rat lung epithelial monolayers, further highlighting the (patho)physiological relevance of active alveolar epithelial protein transport. Moreover, gene silencing and pharmacological inhibition of the multi-ligand receptor megalin resulted in significantly decreased albumin binding and uptake in monolayers of primary alveolar type II and type I-like and cultured lung epithelial cells. Our data indicate that clearance of albumin from the distal air spaces is facilitated by an active, high-capacity, megalin-mediated transport process across the alveolar epithelium. Further understanding of this mechanism is of clinical importance, since an inability to clear excess protein from the alveolar space is associated with poor outcome in patients with acute lung injury/acute respiratory distress syndrome.

Low-density lipoprotein receptor-related protein 2 gene is associated with egg-quality traits in dwarf layers

Some members of the low-density lipoprotein receptor (LDLR) family play important roles in the regulation of lipoprotein metabolism and egg quality traits. Low-density lipoprotein receptor-related protein 2 (LRP2) gene belongs to the LDLR super family, and widely expresses in many tissues. This work identified and genotyped 1 single-nucleotide polymorphism (SNP), T14347C, at 3'-UTR of the LRP2 using matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS), and analyzed the effects of the SNP (T14347C) on egg-quality traits in 544 dwarf hens from 44 sire families. Frequencies of this SNP in the studied population did not agree with the Hardy-Weinberg equilibrium (P < 0.0001). Egg weight, albumen weight, albumen height, and albumen ratio of the TT genotype were significantly higher than those of the CC genotype (P < 0.05), whereas eggshell ratio of the TT genotype was significantly lower than that of the CC genotype (P < 0.05). The relative expression level of the LRP2 gene in the magnum was determined by real-time quantitative PCR. The gene expression of genotype CC individuals was significantly higher than that of TT and CT birds (P < 0.05). By combining both genetic effects and expression analyses results, we propose that the LRP2 gene is a good candidate gene, exhibiting a key role in albumen formation processes.

Sonic Hedgehog on microparticles and neovascularization

Neovascularization represents a pivotal process consisting in the development of vascular network during embryogenesis and adult life. Postnatally, it arises mainly through angiogenesis, which has physiological and pathological roles in health and disease. Blood vessel formation results as tightly regulated multistep process which needs coordination and precise regulation of the balance of proangiogenic and antiangiogenic factors. Sonic Hedgehog (SHH), a morphogen belonging to Hedgehog (HH) family proteins, is implicated in a remarkably wide variety of process, including vessel development. Recent evidence demonstrate that, in addition to the classic factors, microvesicles (MVs), both microparticles (MPs) and exosomes, small vesicles released distinct cellular compartments, are involved in modulation of neovascularization. MPs generated from T lymphocytes undergoing both activation and apoptosis harbor at their surface SHH and play a crucial role in modulation of neovascularization. They are able to modulate the different steps implicated in angiogenesis process in vitro and to enhance postischemic neovascularization in vivo. As the consequence, we suggest that the MPs carrying SHH contribute to generation of a vascular network and may represent a new therapeutic approach to treat pathologies associated with failed angiogenesis.

Retinal proliferation response in the buphthalmic zebrafish, bugeye

The zebrafish retina regenerates in response to acute retinal lesions, replacing damaged neurons with new neurons. In this study we test the hypothesis that chronic stress to inner retinal neurons also triggers a retinal regeneration response in the bugeye zebrafish. Mutations in the lrp2 gene in zebrafish are associated with a progressive eye phenotype (bugeye) that models several risk factors for human glaucoma including buphthalmos (enlarged eyes), elevated intraocular pressure (IOP), and upregulation of genes related to retinal ganglion cell pathology. The retinas of adult bugeye zebrafish showed high rates of ongoing proliferation which resulted in the production of a small number of new retinal neurons, particularly photoreceptors. A marker of mechanical cell stress, Hsp27, was strongly expressed in inner retinal neurons and glia of bugeye retinas. The more enlarged eyes of individual bugeye zebrafish showed disrupted retinal lamination, and a persistent reduced density of neurons in the ganglion cell layer (GCL), although total numbers of GCL neurons were higher than in control eyes. Despite the presence of a proliferative response to damage, the adult bugeye zebrafish remained behaviorally blind. These findings suggest the existence of an unsuccessful regenerative response to a persistent pathological condition in the bugeye zebrafish.

Morphogen gradients: from generation to interpretation

Morphogens are long-range signaling molecules that pattern developing tissues in a concentration-dependent manner. The graded activity of morphogens within tissues exposes cells to different signal levels and leads to region-specific transcriptional responses and cell fates. In its simplest incarnation, a morphogen signal forms a gradient by diffusion from a local source and clearance in surrounding tissues. Responding cells often transduce morphogen levels in a linear fashion, which results in the graded activation of transcriptional effectors. The concentration-dependent expression of morphogen target genes is achieved by their different binding affinities for transcriptional effectors as well as inputs from other transcriptional regulators. Morphogen distribution and interpretation are the result of complex interactions between the morphogen and responding tissues. The response to a morphogen is dependent not simply on morphogen concentration but also on the duration of morphogen exposure and the state of the target cells. In this review, we describe the morphogen concept and discuss the mechanisms that underlie the generation, modulation, and interpretation of morphogen gradients.

The bugeye mutant zebrafish exhibits visual deficits that arise with the onset of an enlarged eye phenotype

PURPOSE

The bugeye mutant has an enlarged eye phenotype, presumably because of elevated intraocular pressure. Since elevated intraocular pressure is a significant risk factor for glaucoma, the bugeye zebrafish mutant may be a model organism for the disease.

METHODS

The optomotor response (OMR) was used to assess visual responsiveness in both larval and adult zebrafish. Electroretinograms (ERGs) were recorded to measure outer retinal function, and histologic analyses were performed on WT and mutant eyes.

RESULTS

At 5 days old, bugeye mutants have an OMR, ERGs, and retinal morphology indistinguishable from those of wild-type (WT) animals. By 2 months of age, bugeye mutants begin to develop an enlarged eye phenotype. At 3 months, some mutants show deficits in the OMR assay, including lower contrast sensitivity. The data suggest that there is a correlation between the size of the enlarged eye and the degree of OMR deficit. Histologic analysis of the bugeye mutant retina revealed decreases in retinal ganglion cell densities by 3 months. By 5 months, the mutant's ERG b-wave had smaller amplitudes and longer latencies at brighter light intensities than those of the WT fish.

CONCLUSION

After phenotypic onset at 3 months, the bugeye mutants begin to develop visual deficits. At 3 months, bugeye mutants exhibit a decrease in retinal cell densities and by 5 months, they show diminished outer retinal function. In summary, the bugeye mutant provides a means of studying glaucoma-associated phenotypes in the zebrafish.

Dynamic changes in leptin distribution in the progression from ovum to blastocyst of the pre-implantation mouse embryo

The hormone leptin, which is primarily produced by adipose tissue, is a critical permissive factor for multiple reproductive events in the mouse, including implantation. In the CD1 strain, maternally derived leptin from the oocyte becomes differentially distributed among the blastomeres of pre-implantation embryos to create a polarized pattern, a feature consistent with a model of development in which blastomeres are biased toward a particular fate as early as the two-cell stage. In this study, we have confirmed that embryonic leptin is of maternal origin and re-examined leptin distribution in two distinct strains in which embryos were derived after either normal ovulation or superovulation. A polarized pattern of leptin distribution was found in the majority of both CD1 and CF1 embryos (79.1 and 76.9% respectively) collected following superovulation but was reduced, particularly in CF1 embryos (29.8%; P<0.0001), after natural ovulation. The difference in leptin asymmetries in the CF1 strain arose between ovulation and the first cleavage division and was not affected by removal of the zona pellucida. The presence or absence of leptin polarization was not linked to differences in the ability of embryos to normally develop to blastocyst. In the early blastocyst, leptin was confined subcortically to trophectoderm, but on blastocoel expansion, it was lost from the cells. Throughout development, leptin co-localized with LRP2, a multi-ligand transport protein, and its patterning resembled that noted for the maternal-effect proteins OOEP, NLRP5, and PADI6, suggesting that it is a component of the subcortical maternal complex with as yet unknown significance in pre-implantation development.

Mutations in zebrafish lrp2 result in adult-onset ocular pathogenesis that models myopia and other risk factors for glaucoma

The glaucomas comprise a genetically complex group of retinal neuropathies that typically occur late in life and are characterized by progressive pathology of the optic nerve head and degeneration of retinal ganglion cells. In addition to age and family history, other significant risk factors for glaucoma include elevated intraocular pressure (IOP) and myopia. The complexity of glaucoma has made it difficult to model in animals, but also challenging to identify responsible genes. We have used zebrafish to identify a genetically complex, recessive mutant that shows risk factors for glaucoma including adult onset severe myopia, elevated IOP, and progressive retinal ganglion cell pathology. Positional cloning and analysis of a non-complementing allele indicated that non-sense mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotype. Lrp2, previously named Megalin, functions as an endocytic receptor for a wide-variety of bioactive molecules including Sonic hedgehog, Bone morphogenic protein 4, retinol-binding protein, vitamin D-binding protein, and apolipoprotein E, among others. Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals—but not all—develop high IOP and severe myopia with obviously enlarged eye globes. This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis. Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

Complex genetic inheritance, including variable penetrance and severity, underlies many common eye diseases. In this study, we present analysis of a zebrafish mutant, bugeye, which shows complex inheritance of multiple ocular phenotypes that are known risk factors for glaucoma, including high myopia, elevated intraocular pressure, and up-regulation of stress-response genes in retinal ganglion cells. Molecular genetic analysis revealed that mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotypes. Lrp2 is a large transmembrane protein expressed in epithelia of the eye. It facilitates transport and clearance of multiple secreted bioactive factors through receptor-mediated endocytosis. Glaucoma, a progressive blinding disorder, usually presents in adulthood and is characterized by optic nerve damage followed by ganglion cell death. In bugeye/lrp2 mutants, ganglion cell death was significantly elevated, but surprisingly moderate, and therefore they do not model this endpoint of glaucoma. As such, bugeye/lrp2 mutants should be considered valuable as a genetic model (A) for buphthalmia, myopia, and regulated eye growth; (B) for identifying genes and pathways that modify the observed ocular phenotypes; and (C) for studying the initiation of retinal ganglion cell pathology in the context of high myopia and elevated intraocular pressure.

Analysis of the expression pattern of the carrier protein transthyretin and its receptor megalin in the human scalp skin and hair follicles: hair cycle-associated changes

Transthyretin is a serum and cerebrospinal fluid protein synthesized early in development by the liver, choroid plexus and several other tissues. It is a carrier protein for the antioxidant vitamins, retinol, and thyroid hormones. Transthyretin helps internalize thyroxine and retinol-binding protein into cells by binding to megalin, which is a multi-ligand receptor expressed on the luminal surface of various epithelia. We investigated the expression of transthyretin and its receptor megalin in the human skin; however, their expression pattern in the hair follicle is still to be elucidated. This study addresses this issue and tests the hypothesis that "the expression of transthyretin and megalin undergoes hair follicle cycle-dependent changes." A total of 50 normal human scalp skin biopsies were examined (healthy females, 53-62 years) using immunofluorescence staining methods and real-time PCR. In each case, 50 hair follicles were analyzed (35, 10, and 5 follicles in anagen, catagen, and telogen, respectively). Transthyretin and megalin were prominently expressed in the human scalp skin and hair follicles, on both gene and protein levels. The concentrations of transthyretin and megalin were 0.12 and 0.03 Ul/ml, respectively, as indicated by PCR. The expression showed hair follicle cycle-associated changes i.e., strong expression during early and mature anagen, very weak expression during catagen and moderate expression during telogen. The expression values of these proteins in the anagen were statistically significantly higher than those of either catagen or telogen hair follicles (P ≤ 0.001). This study provides the first morphologic indication that transthyretin and megalin are variably expressed in the human scalp skin and hair follicles. It also reports variations in the expression of these proteins during hair follicle cycling. The clinical ramifications of these findings are open for further investigations.