A dominant-negative pleiotrophin mutant introduced by homologous recombination leads to germ-cell apoptosis in male mice

Single-cell RNA sequencing reveals transcriptomic landscape and potential targets for human testicular ageing

STUDY QUESTION

What is the molecular landscape underlying the functional decline of human testicular ageing?

SUMMARY ANSWER

The present study provides a comprehensive single-cell transcriptomic atlas of testes from young and old humans and offers insights into the molecular mechanisms and potential targets for human testicular ageing.

WHAT IS KNOWN ALREADY

Testicular ageing is known to cause male age-related fertility decline and hypogonadism. Dysfunction of testicular cells has been considered as a key factor for testicular ageing.

STUDY DESIGN, SIZE, DURATION

Human testicular biopsies were collected from three young individuals and three old individuals to perform single-cell RNA sequencing (scRNA-seq). The key results were validated in a larger cohort containing human testicular samples from 10 young donors and 10 old donors.

PARTICIPANTS/MATERIALS, SETTING, METHODS

scRNA-seq was used to identify gene expression signatures for human testicular cells during ageing. Ageing-associated changes of gene expression in spermatogonial stem cells (SSCs) and Leydig cells (LCs) were analysed by gene set enrichment analysis and validated by immunofluorescent and functional assays. Cell-cell communication analysis was performed using CellChat.

MAIN RESULTS AND THE ROLE OF CHANCE

The single-cell transcriptomic landscape of testes from young and old men was surveyed, revealing age-related changes in germline and somatic niche cells. In-depth evaluation of the gene expression dynamics in germ cells revealed that the disruption of the base-excision repair pathway is a prominent characteristic of old SSCs, suggesting that defective DNA repair in SSCs may serve as a potential driver for increased de novo germline mutations with age. Further analysis of ageing-associated transcriptional changes demonstrated that stress-related changes and cytokine pathways accumulate in old somatic cells. Age-related impairment of redox homeostasis in old LCs was identified and pharmacological treatment with antioxidants alleviated this cellular dysfunction of LCs and promoted testosterone production. Lastly, our results revealed that decreased pleiotrophin signalling was a contributing factor for impaired spermatogenesis in testicular ageing.

LARGE SCALE DATA

The scRNA-seq sequencing and processed data reported in this paper were deposited at the Genome Sequence Archive (https://ngdc.cncb.ac.cn/), under the accession number HRA002349.

LIMITATIONS, REASONS FOR CAUTION

Owing to the difficulty in collecting human testis tissue, the sample size was limited. Further in-depth functional and mechanistic studies are warranted in future.

WIDER IMPLICATIONS OF THE FINDINGS

These findings provide a comprehensive understanding of the cell type-specific mechanisms underlying human testicular ageing at a single-cell resolution, and suggest potential therapeutic targets that may be leveraged to address age-related male fertility decline and hypogonadism.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Key Research and Development Program of China (2022YFA1104100), the National Natural Science Foundation of China (32130046, 82171564, 82101669, 82371611, 82371609, 82301796), the Natural Science Foundation of Guangdong Province, China (2022A1515010371), the Major Project of Medical Science and Technology Development Research Center of National Health Planning Commission, China (HDSL202001000), the Open Project of NHC Key Laboratory of Male Reproduction and Genetics (KF202001), the Guangdong Province Regional Joint Fund-Youth Fund Project (2021A1515110921, 2022A1515111201), and the China Postdoctoral Science Foundation (2021M703736). The authors declare no conflict of interest.

Dissecting the spermatogonial stem cell niche using spatial transcriptomics

Spermatogonial stem cells (SSCs) in the testis support the lifelong production of sperm. SSCs reside within specialized microenvironments called "niches," which are essential for SSC self-renewal and differentiation. However, our understanding of the molecular and cellular interactions between SSCs and niches remains incomplete. Here, we combine spatial transcriptomics, computational analyses, and functional assays to systematically dissect the molecular, cellular, and spatial composition of SSC niches. This allows us to spatially map the ligand-receptor (LR) interaction landscape in both mouse and human testes. Our data demonstrate that pleiotrophin regulates mouse SSC functions through syndecan receptors. We also identify ephrin-A1 as a potential niche factor that influences human SSC functions. Furthermore, we show that the spatial re-distribution of inflammation-related LR interactions underlies diabetes-induced testicular injury. Together, our study demonstrates a systems approach to dissect the complex organization of the stem cell microenvironment in health and disease.

Reproductive Suppression Caused by Spermatogenic Arrest: Transcriptomic Evidence from a Non-Social Animal

Reproductive suppression is an adaptive strategy in animal reproduction. The mechanism of reproductive suppression has been studied in social animals, providing an essential basis for understanding the maintenance and development of population stability. However, little is known about it in solitary animals. The plateau zokor is a dominant, subterranean, solitary rodent in the Qinghai-Tibet Plateau. However, the mechanism of reproductive suppression in this animal is unknown. We perform morphological, hormonal, and transcriptomic assays on the testes of male plateau zokors in breeders, in non-breeders, and in the non-breeding season. We found that the testes of non-breeders are smaller in weight and have lower serum testosterone levels than those of breeders, and the mRNA expression levels of the anti-Müllerian hormone (AMH) and its transcription factors are significantly higher in non-breeder testes. Genes related to spermatogenesis are significantly downregulated in both meiotic and post-meiotic stages in non-breeders. Genes related to the meiotic cell cycle, spermatogenesis, flagellated sperm motility, fertilization, and sperm capacitation are significantly downregulated in non-breeders. Our data suggest that high levels of AMH may lead to low levels of testosterone, resulting in delayed testicular development, and physiological reproductive suppression in plateau zokor. This study enriches our understanding of reproductive suppression in solitary mammals and provides a basis for the optimization of managing this species.

Ptn functions downstream of C/EBPβ to mediate the effects of cAMP on uterine stromal cell differentiation through targeting Hand2 in response to progesterone

Ptn is a pleiotropic growth factor involving in the regulation of cellular proliferation and differentiation, but its biological function in uterine decidualization remains unknown. Here, we showed that Ptn was highly expressed in the decidual cells, and could induce the proliferation of uterine stromal cells and expression of Prl8a2 and Prl3c1 which were two well-established differentiation markers for decidualization, suggesting an important role of Ptn in decidualization. In the uterine stromal cells, progesterone stimulated the expression of Ptn accompanied with an accumulation of intracellular cAMP level. Silencing of Ptn impeded the induction of progesterone and cAMP on the differentiation of uterine stromal cells. Administration of PKA inhibitor H89 resulted in a blockage of progesterone on Ptn expression. Further analysis evidenced that regulation of progesterone and cAMP on Ptn was mediated by C/EBPβ. During in vitro decidualization, knockdown of Ptn could weaken the up-regulation of Prl8a2 and Prl3c1 elicited by C/EBPβ overexpression, while constitutive activation of Ptn reversed the repressive effects of C/EBPβ siRNA on the expression of Prl8a2 and Prl3c1. Meanwhile, Ptn might mediate the regulation of C/EBPβ on Hand2 which was a downstream target of Ptn in the differentiation of uterine stromal cells. Attenuation of Ptn or C/EBPβ by specific siRNA blocked the stimulation of Hand2 by progesterone and cAMP. Collectively, Ptn may play a vital role in the progesterone-induced decidualization pathway.

Differential gene expression profiling of enriched human spermatogonia after short- and long-term culture

This study aimed to provide a molecular signature for enriched adult human stem/progenitor spermatogonia during short-term (<2 weeks) and long-term culture (up to more than 14 months) in comparison to human testicular fibroblasts and human embryonic stem cells. Human spermatogonia were isolated by CD49f magnetic activated cell sorting and collagen(-)/laminin(+) matrix binding from primary testis cultures obtained from ten adult men. For transcriptomic analysis, single spermatogonia-like cells were collected based on their morphology and dimensions using a micromanipulation system from the enriched germ cell cultures. Immunocytochemical, RT-PCR and microarray analyses revealed that the analyzed populations of cells were distinct at the molecular level. The germ- and pluripotency-associated genes and genes of differentiation/spermatogenesis pathway were highly expressed in enriched short-term cultured spermatogonia. After long-term culture, a proportion of cells retained and aggravated the "spermatogonial" gene expression profile with the expression of germ and pluripotency-associated genes, while in the majority of long-term cultured cells this molecular profile, typical for the differentiation pathway, was reduced and more genes related to the extracellular matrix production and attachment were expressed. The approach we provide here to study the molecular status of in vitro cultured spermatogonia may be important to optimize the culture conditions and to evaluate the germ cell plasticity in the future.

Fsh controls gene expression in fish both independently of and through steroid mediation

The mechanisms and the mediators relaying Fsh action on testicular functions are poorly understood. Unlike in mammals, in fish both gonadotropins (Fsh and Lh) are able to efficiently stimulate steroidogenesis, likely through a direct interaction with their cognate receptors present on the Leydig cells. In this context, it is crucial to understand if Fsh effects are mediated through the production of steroids. To address this issue we performed transcriptome studies after in vitro incubations of rainbow trout testis explants in the presence of Fsh alone or in combination with trilostane, an inhibitor of Δ4- steroidogenesis. Trilostane significantly reduced or suppressed the response of many genes to Fsh (like wisp1, testis gapdhs, cldn11, inha, vt1 or dmrt1) showing that, in fish, important aspects of Fsh action follow indirect pathways and require the production of Δ4-steroids. What is more, most of the genes regulated by Fsh through steroid mediation were similarly regulated by Lh (and/or androgens). In contrast, the response to Fsh of other genes was not suppressed in the presence of trilostane. These latter included genes encoding for anti-mullerian hormone, midkine a (pleiotrophin related), angiopoietine-related protein, cyclins E1 and G1, hepatocyte growth factor activator, insulin-like growth factor 1b/3. A majority of those genes were preferentially regulated by Fsh, when compared to Lh, suggesting that specific regulatory effects of Fsh did not depend on steroid production. Finally, antagonistic effects between Fsh and steroids were found, in particular for genes encoding key factors of steroidogenesis (star, hsd3b1, cyp11b2-2) or for genes of the Igf system (igf1b/3). Our study provides the first clear evidence that, in fish, Fsh exerts Δ4-steroid-independent regulatory functions on many genes which are highly relevant for the onset of spermatogenesis.

FSH and LH have common and distinct effects on gene expression in rainbow trout testis

The general rules established from mammalian species for the regulation of spermatogenesis by gonadotropins may not be fully relevant in fish. Particularly, Fsh is as potent as Lh to stimulate steroidogenesis and the Fsh receptor is expressed in Leydig cells. In seasonal breeders, Fsh is likely the major gonadotropin involved in spermatogenesis onset and Lh is required to support spermatogenesis progression and gamete release. However, the genes that relay the action of Fsh and Lh have been poorly investigated in fish. The present study was aimed at identifying gonadotropin-dependent genes expressed in the testis during fish puberty. We cultured pubertal trout testicular explants for 96 h, with or without gonadotropin, and analyzed transcriptome variations using microarrays. Fsh and Lh had similar effects on a large group of genes while other genes were preferentially regulated by one or the other gonadotropin. We showed that most of the responsive genes were expressed in somatic cells and exhibited relevant patterns during the seasonal reproductive cycle. Some genes preferentially modulated by Lh could be involved in testicular cell fate (pvrl1 and bty) or sperm maturation (ehmt2 and racgap1) and will deserve further examination. Besides Fsh's effects on the steroidogenic pathway, our study demonstrates that Fsh coordinates relevant stimulatory and inhibitory paracrine factors known to regulate early germ cell proliferation and differentiation. Some of these genes belong to major regulatory pathways including the Igf pathway (igf1b/igf3 and igfbp6), the Tgfb pathway (amh, inha, inhba, and fstl3), the Wnt pathway (wisp1), and pleiotrophin (mdka).

Expression of the growth factor pleiotrophin and its receptor protein tyrosine phosphatase beta/zeta in the serum, cartilage and subchondral bone of patients with osteoarthritis

OBJECTIVES

Pleiotrophin is a heparin-binding growth factor expressed in embryonic but not mature cartilage, suggesting a role in cartilage development. Elucidation of the molecular changes observed during the remodelling process in osteoarthritis is of paramount importance. This study aimed to investigate serum pleiotrophin levels and expression of pleiotrophin and its receptor protein tyrosine phosphatase beta/zeta in the cartilage and subchondral bone of osteoarthritis patients.

METHODS

Serum samples derived from 16 osteoarthritis patients and 18 healthy donors. Pleiotrophin and receptor protein tyrosine phosphatase beta/zeta in the cartilage and subchondral bone were studied in 29 patients who had undergone total knee or hip replacement for primary osteoarthritis and in 10 control patients without macroscopic osteoarthritis changes.

RESULTS

Serum pleiotrophin levels and expression of pleiotrophin in chondrocytes and subchondral bone osteocytes significantly increased in osteoarthritis patients graded Ahlback II to III. Receptor protein tyrosine phosphatase beta/zeta was mainly detected in the subchondral bone osteocytes of patients with moderate osteoarthritis and as disease severity increased, in the osteocytes and bone lining cells of the distant trabeculae.

CONCLUSIONS

These data render pleiotrophin and receptor protein tyrosine phosphatase beta/zeta promising candidates for further studies towards developing targeted therapeutic schemes for osteoarthritis.

Loss of receptor protein tyrosine phosphatase β/ζ (RPTPβ/ζ) promotes prostate cancer metastasis

BACKGROUND

The role of pleiotrophin and its receptors RPTPβ/ζ and Syndecan-3 during tumor metastasis remains unknown.

RESULTS

RPTPβ/ζ knockdown initiates EMT, promotes pleiotrophin-mediated migration and attachment through Syndecan-3 and induces in vivo metastasis.

CONCLUSION

RPTPβ/ζ plays a suppressor-like role in prostate cancer metastasis.

SIGNIFICANCE

Boosting RPTPβ/ζ or attenuating Syndecan-3 signaling pathways may lead to more effective therapeutic strategies in treating prostate cancer metastasis. Pleiotrophin is a growth factor that induces carcinogenesis. Despite the fact that many published reports focused on the role of pleiotrophin and its receptors, receptor protein tyrosine phosphatase (RPTPβ/ζ), and syndecan-3 during tumor development, no information is available regarding their function in tumor metastasis. To investigate the mechanism through which pleiotrophin regulates tumor metastasis, we used two different prostate carcinoma cell lines, DU145 and PC3, in which the expression of RPTPβ/ζ or syndecan-3 was down-regulated by the RNAi technology. The loss of RPTPβ/ζ expression initiated epithelial-to-mesenchymal transition (EMT) and increased the ability of the cells to migrate and invade. Importantly, the loss of RPTPβ/ζ expression increased metastasis in nude mice in an experimental metastasis assay. We also demonstrate that RPTPβ/ζ counterbalanced the pleiotrophin-mediated syndecan-3 pathway. While the inhibition of syndecan-3 expression inhibited the pleiotrophin-mediated cell migration and attachment through the Src and Fak pathway, the inhibition of RPTPβ/ζ expression increased pleiotrophin-mediated migration and attachment through an interaction with Src and the subsequent activation of a signal transduction pathway involving Fak, Pten, and Erk1/2. Taken together, these results suggest that the loss of RPTPβ/ζ may contribute to the metastasis of prostate cancer cells by inducing EMT and promoting pleiotrophin activity through the syndecan-3 pathway.

Implications of pleiotrophin in human PC3 prostate cancer cell growth in vivo

Pleiotrophin (PTN) is a heparin-binding growth factor with diverse functions related to tumor growth, angiogenesis, and metastasis. Pleiotrophin seems to have a significant role in prostate cancer cell growth and to mediate the stimulatory actions of other factors that affect prostate cancer cell functions. However, all studies carried out up to date are in vitro, using different types of human prostate cancer cell lines. The aim of the present work was to study the role of endogenous PTN in human prostate cancer growth in vivo. For this purpose, human prostate cancer PC3 cells were stably transfected with a plasmid vector, bearing the antisense PTN sequence, in order to inhibit PTN expression (AS-PC3). Migration, apoptosis, and adhesion on osteoblastic cells were measured in vitro. In vivo, PC3 cells were s.c. injected into male NOD/SCID mice, and tumor growth, survival rates, angiogenesis, apoptosis, and the number of metastasis were estimated. Pleiotrophin depletion resulted in a decreased migration capability of AS-PC3 cells compared with the corresponding mock-transfected or the non-transfected PC3 cells, as well as increased apoptosis and decreased adhesiveness to osteoblastic cells in vitro. In prostate cancer NOD/SCID mouse xenografts, PTN depletion significantly suppressed tumor growth and angiogenesis and induced apoptosis of cancer cells. In addition, PTN depletion decreased the number of metastases, providing a survival benefit for the animals bearing AS-PC3 xenografts. Our data suggest that PTN is implicated in human prostate cancer growth in vivo and could be considered a potential target for the development of new therapeutic approaches for prostate cancer.

Pleiotrophin expression and role in physiological angiogenesis in vivo: potential involvement of nucleolin

Background

Pleiotrophin (PTN) is a heparin-binding growth factor with significant role(s) in tumour growth and angiogenesis. Although implication of endogenous PTN has been studied in several in vivo models of tumour angiogenesis, its role in physiological angiogenesis has not been addressed. In the present work, we studied expression and functional significance of endogenous PTN during angiogenesis in the chicken embryo chorioallantoic membrane (CAM).

Methods

Using molecular, cellular and biochemical assays, we studied the expression pattern of PTN in CAM and human endothelial cells and its possible interaction with nucleolin (NCL). CAM cells were transfected with a pCDNA3.1 vector, empty (PC) or containing full length cDNA for PTN in antisense orientation (AS-PTN). Angiogenesis was estimated by measuring total vessel length. In vitro, human endothelial cells migration was studied by using a transwell assay, and down-regulation of NCL was performed by using a proper siRNA.

Results

Endogenous PTN mRNA and protein levels, as well as protein levels of its receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) were maximal at early stages, when CAM angiogenesis is active. Application of AS-PTN onto CAM at days of active angiogenesis was not toxic to the tissue and led to dose-dependent decreased expression of endogenous PTN, ERK1/2 activity and angiogenesis. Interestingly, endogenous PTN was also immunolocalized at the endothelial cell nucleus, possibly through interaction with NCL, a protein that has a significant role in the nuclear translocation of many proteins. Down-regulation of NCL by siRNA in human endothelial cells significantly decreased nuclear PTN, verifying this hypothesis. Moreover, it led to abolishment of PTN-induced endothelial cell migration, suggesting, for the first time, that PTN-NCL interaction has a functional significance.

Conclusions

Expression of endogenous PTN correlates with and seems to be involved in angiogenesis of the chicken embryo CAM. Our data suggest that NCL may have a role, increasing the number of growth factors whose angiogenic/tumorigenic activities are mediated by NCL.

A microarray analysis of the XX Wnt4 mutant gonad targeted at the identification of genes involved in testis vascular differentiation

One of the earliest morphological changes during testicular differentiation is the establishment of an XY specific vasculature. The testis vascular system is derived from mesonephric endothelial cells that migrate into the gonad. In the XX gonad, mesonephric cell migration and testis vascular development are inhibited by WNT4 signaling. In Wnt4 mutant XX gonads, endothelial cells migrate from the mesonephros and form a male-like coelomic vessel. Interestingly, this process occurs in the absence of other obvious features of testis differentiation, suggesting that Wnt4 specifically inhibits XY vascular development. Consequently, the XX Wnt4 mutant mice presented an opportunity to focus a gene expression screen on the processes of mesonephric cell migration and testicular vascular development. We compared differences in gene expression between XY Wnt4+/+ and XX Wnt4+/+ gonads and between XX Wnt4-/- and XX Wnt4+/+ gonads to identify sets of genes similarly upregulated in wildtype XY gonads and XX mutant gonads or upregulated in XX gonads as compared to XY gonads and XX mutant gonads. We show that several genes identified in the first set are expressed in vascular domains, and have predicted functions related to cell migration or vascular development. However, the expression patterns and known functions of other genes are not consistent with roles in these processes. This screen has identified candidates for regulation of sex specific vascular development, and has implicated a role for WNT4 signaling in the development of Sertoli and germ cell lineages not immediately obvious from previous phenotypic analyses.

The large functional spectrum of the heparin-binding cytokines MK and HB-GAM in continuously growing organs: the rodent incisor as a model

The heparin binding molecules MK and HB-GAM are involved in the regulation of growth and differentiation of many tissues and organs. Here we analyzed the expression of MK and HB-GAM in the developing mouse incisors, which are continuously growing organs with a stem cell compartment. Overlapping but distinct expression patterns for MK and HB-GAM were observed during all stages of incisor development (initiation, morphogenesis, cytodifferentiation). Both proteins were detected in the enamel knot, a transient epithelial signaling structure that is important for tooth morphogenesis, and the cervical loop where the stem cell niche is located. The functions of MK and HB-GAM were studied in dental explants and organotypic cultures in vitro. In mesenchymal explants, MK stimulated HB-GAM expression and, vice-versa, HB-GAM upregulated MK expression, thus indicating a regulatory loop between these proteins. BMP and FGF molecules also activated expression of both cytokines in mesenchyme. The proliferative effects of MK and HB-GAM varied according to the mesenchymal or epithelial origin of the tissue. Growth, cytodifferentiation and mineralization were inhibited in incisor germs cultured in the presence of MK neutralizing antibodies. These results demonstrate that MK and HB-GAM are involved in stem cells maintenance, cytodifferentiation and mineralization processes during mouse incisor development.

Transcriptome analysis of differentiating spermatogonia stimulated with kit ligand

Kit ligand (KL) is a survival factor and a mitogenic stimulus for differentiating spermatogonia. However, it is not known whether KL also plays a role in the differentiative events that lead to meiotic entry of these cells. We performed a wide genome analysis of difference in gene expression induced by treatment with KL of spermatogonia from 7-day-old mice, using gene chips spanning the whole mouse genome. The analysis revealed that the pattern of RNA expression induced by KL is compatible with the qualitative changes of the cell cycle that occur during the subsequent cell divisions in type A and B spermatogonia, i.e. the progressive lengthening of the S phase and the shortening of the G2/M transition. Moreover, KL up-regulates in differentiating spermatogonia the expression of early meiotic genes (for instance: Lhx8, Nek1, Rnf141, Xrcc3, Tpo1, Tbca, Xrcc2, Mesp1, Phf7, Rtel1), whereas it down-regulates typical spermatogonial markers (for instance: Pole, Ptgs2, Zfpm2, Egr2, Egr3, Gsk3b, Hnrpa1, Fst, Ptch2). Since KL modifies the expression of several genes known to be up-regulated or down-regulated in spermatogonia during the transition from the mitotic to the meiotic cell cycle, these results are consistent with a role of the KL/kit interaction in the induction of their meiotic differentiation.

A microarray analysis of the XX Wnt4 mutant gonad targeted at the identification of genes involved in testis vascular differentiation

One of the earliest morphological changes during testicular differentiation is the establishment of an XY specific vasculature. The testis vascular system is derived from mesonephric endothelial cells that migrate into the gonad. In the XX gonad, mesonephric cell migration and testis vascular development are inhibited by WNT4 signaling. In Wnt4 mutant XX gonads, endothelial cells migrate from the mesonephros and form a male-like coelomic vessel. Interestingly, this process occurs in the absence of other obvious features of testis differentiation, suggesting that Wnt4 specifically inhibits XY vascular development. Consequently, the XX Wnt4 mutant mice presented an opportunity to focus a gene expression screen on the processes of mesonephric cell migration and testicular vascular development. We compared differences in gene expression between XY Wnt4+/+ and XX Wnt4+/+ gonads and between XX Wnt4+/+ and XX Wnt4+/+ gonads to identify sets of genes similarly upregulated in wildtype XY gonads and XX mutant gonads or upregulated in XX gonads as compared to XY gonads and XX mutant gonads. We show that several genes identified in the first set are expressed in vascular domains, and have predicted functions related to cell migration or vascular development. However, the expression patterns and known functions of other genes are not consistent with roles in these processes. This screen has identified candidates for regulation of sex specific vascular development, and has implicated a role for WNT4 signaling in the development of Sertoli and germ cell lineages not immediately obvious from previous phenotypic analyses.

Pleiotrophin stimulates tyrosine phosphorylation of β-adducin through inactivation of the transmembrane receptor protein tyrosine phosphatase β/ζ

Pleiotrophin (PTN the protein, Ptn the gene) signals through a unique mechanism; it inactivates the tyrosine phosphatase activity of its receptor, the transmembrane receptor protein tyrosine phosphatase (RPTP)beta/zeta, and increases tyrosine phosphorylation of the substrates of RPTPbeta/zeta through the continued activity of a yet to be described protein tyrosine kinase(s) in PTN-stimulated cells. We have now found that the cytoskeletal protein beta-adducin interacts with the intracellular domain of RPTPbeta/zeta in a yeast two-hybrid system, that beta-adducin is a substrate of RPTPbeta/zeta, that beta-adducin is phosphorylated in tyrosine in cells not stimulated by PTN, and that tyrosine phosphorylation of beta-adducin is sharply increased in PTN-stimulated cells, suggesting that beta-adducin is a downstream target of and regulated by the PTN/RPTPbeta/zeta signaling pathway. beta-Catenin was the first downstream target of the PTN/RPTPbeta/zeta signaling pathway to be identified; these data thus also suggest that PTN coordinately regulates steady state levels of tyrosine phosphorylation of the important cytoskeletal proteins beta-adducin and beta-catenin and, through PTN-stimulated tyrosine phosphorylation, beta-adducin may contribute to the disruption of cytoskeletal structure, increased plasticity, and loss of homophilic cell-cell adhesion that are the consequences of PTN stimulation of cells and a characteristic feature of different malignant cells with mutations that activate constitutive expression of the endogenous Ptn gene.

Fyn is a downstream target of the pleiotrophin/receptor protein tyrosine phosphatase β/ζ-signaling pathway: Regulation of tyrosine phosphorylation of Fyn by pleiotrophin

Pleiotrophin (PTN the protein, Ptn the gene) signals downstream targets through inactivation of its receptor, the transmembrane receptor protein tyrosine phosphatase (RPTP)beta/zeta, disrupting the balanced activity of RPTPbeta/zeta and the activity of a constitutively active tyrosine kinase. As a consequence of the inactivation of RPTPbeta/zeta, PTN stimulates a sharp increase in the levels of tyrosine phosphorylation of the substrates of RPTPbeta/zeta in PTN-stimulated cells. We now report that the Src family member Fyn interacts with the intracellular domain of RPTPbeta/zeta in a yeast two-hybrid system. We further demonstrate that Fyn is a substrate of RPTPbeta/zeta, and that tyrosine phosphorylation of Fyn is sharply increased in PTN-stimulated cells. In previous studies, we demonstrated that beta-catenin and beta-adducin are targets of the PTN/RPTPbeta/zeta-signaling pathway and defined the mechanisms through which tyrosine phosphorylation of beta-catenin and beta-adducin disrupts cytoskeletal protein complexes. We conclude that Fyn is a downstream target of the PTN/RPTPbeta/zeta-signaling pathway and suggest that PTN coordinately regulates tyrosine phosphorylation of beta-catenin, beta-adducin, and Fyn through the PTN/RPTPbeta/zeta-signaling pathway and that together Fyn, beta-adducin, and beta-catenin may be effectors of the previously described PTN-stimulated disruption of cytoskeletal stability, increased cell plasticity, and loss of cell-cell adhesion that are characteristic of PTN-stimulated cells and a feature of many human malignant cells in which mutations have established constitutive expression of the Ptn gene.

Increased keratinocyte proliferation by JUN-dependent expression of PTN and SDF-1 in fibroblasts

In skin, fibroblasts of the connective tissue play a decisive role in epidermal homeostasis and repair by contributing to the regulation of keratinocyte proliferation and differentiation. The AP-1 transcription factor subunit JUN plays a crucial role in this mesenchymal-epithelial interplay by regulating the expression of two critical paracrine-acting cytokines, keratinocyte growth factor (KGF) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We have performed gene expression profiling of wild-type and Jun–/– mouse embryonic fibroblasts to identify additional players involved in this complex network, and have found pleiotrophin (PTN) and the stromal cell-derived factor 1 (SDF-1) as novel JUN-regulated factors. Both cytokines are expressed by dermal fibroblasts in vivo, as shown by semi-quantitative RT-PCR and in situ hybridization on murine skin sections. Using a heterologous feeder layer co-culture system, we demonstrated that PTN and SDF-1 exert a mitogenic effect on primary human keratinocytes. Moreover, SDF-1-induced keratinocyte proliferation could be specifically inhibited by neutralizing antibodies against SDF-1 or its receptor, CXCR4. Consistent with its role in promoting keratinocyte growth, PTN was upregulated during cutaneous wound healing in vivo. Interestingly, co-cultivation with keratinocytes stimulated PTN expression but repressed SDF-1 production in fibroblasts, demonstrating the complexity of the paracrine regulatory cytokine networks that control skin homeostasis and regeneration.

An expression signature classifies chemotherapy-resistant pediatric osteosarcoma

Osteosarcoma is the most common malignant bone tumor in children. Osteosarcoma patients who respond poorly to chemotherapy are at a higher risk of relapse and adverse outcome. Therefore, it was the aim of this study to identify prognostic factors at the time of diagnosis to characterize the genes predictive of poor survival outcome and to identify potential novel therapeutic targets. Expression profiling of 30 osteosarcoma diagnostic biopsy samples, 15 with inferior necrosis following induction chemotherapy (Huvos I/II) and 15 with superior necrosis following induction chemotherapy (Huvos III/IV), was conducted using Affymetrix U95Av2 oligonucleotide microarrays. One hundred and four genes were found to be statistically significant and highly differentially expressed between Huvos I/II and III/IV patients. Statistically significant genes were validated on a small independent cohort comprised of osteosarcoma xenograft tumor samples. Markers of Huvos I/II response predominantly were gene products involved in extracellular matrix (ECM) microenvironment remodeling and osteoclast differentiation. A striking finding was the significant decrease in osteoprotegerin, an osteoclastogenesis inhibitory factor. Additional genes involved in osteoclastogenesis and bone resorption, which were statistically different, include annexin 2, SMAD, PLA2G2A, and TGFbeta1. ECM remodeling genes include desmoplakin, SPARCL1, biglycan, and PECAM. Gene expression of select genes involved in tumor progression, ECM remodeling, and osteoclastogenesis were validated via quantitative reverse transcription-PCR in an independent cohort. We propose that osteosarcoma tumor-driven changes in the bone microenvironment contribute to the chemotherapy-resistant phenotype and offer testable hypotheses to potentially enhance therapeutic response.

De novo t(7;10)(q33;q23) translocation and closely juxtaposed microdeletion in a patient with macrocephaly and developmental delay

We have applied FISH with fully integrated BACs and BAC subfragments assessed in the human genome sequence to a de novo t(7;10)(q33;q23) translocation in a patient with developmental delay and macrocephaly. The translocation breakpoints disrupt the SEC8L1 gene on chromosome 7 and the PTEN gene on chromosome 10. RT-PCR demonstrated chimeric transcripts containing the first 11 exons of SEC8L1 fused to exon 3 of PTEN. In addition to the balanced translocation, we found a 7-Mb deletion in the translocated part of chromosome 7 at 4-Mb distance of the translocation breakpoint. This microdeletion, which disrupts the PTN and TPK1 genes and deletes 29 bonafide genes and the T-cell receptor beta locus, arose in the paternal germline. The patient's phenotype may be caused by a dominant-negative effect of the SEC8L1-PTEN fusion protein and/or haploinsufficiency of the disrupted or deleted genes. Our study demonstrates that de novo translocations can be associated with microdeletions outside the breakpoint region(s), rendering the study and risk estimation of such breakpoints more complicated than previously assumed.

Pleiotrophin: a cytokine with diverse functions and a novel signaling pathway

Pleiotrophin (PTN the protein, Ptn the gene) is a 136 amino acid secreted heparin-binding cytokine that signals diverse functions, including lineage-specific differentiation of glial progenitor cells, neurite outgrowth, and angiogenesis. Pleiotrophin gene expression is found in cells in early differentiation during different development periods and upregulated in cells with an early differentiation phenotype in wound repair. The Ptn gene is a protooncogene. It is strongly expressed in different human tumor cells and expression of the Ptn gene in tumor cells in vivo accelerates growth and stimulates tumor angiogenesis. Separate independent domains have been identified in PTN to signal transformation and tumor angiogenesis. Pleiotrophin is the first ligand of any of the known transmembrane tyrosine phosphatases. Pleiotrophin inactivates the receptor protein tyrosine phosphatase (RPTP) beta/zeta. The interaction of PTN and RPTP beta/zeta increases steady-state tyrosine phosphorylation of beta-catenin. Pleiotrophin thus regulates both normal cell functions and different pathological conditions at many levels. It signals these functions through a transmembrane tyrosine phosphatase.

Identification of pleiotrophin as a mesenchymal factor involved in ureteric bud branching morphogenesis

Branching morphogenesis is central to epithelial organogenesis. In the developing kidney, the epithelial ureteric bud invades the metanephric mesenchyme, which directs the ureteric bud to undergo repeated branching. A soluble factor(s) in the conditioned medium of a metanephric mesenchyme cell line is essential for multiple branching morphogenesis of the isolated ureteric bud. The identity of this factor had proved elusive, but it appeared distinct from factors such as HGF and EGF receptor ligands that have been previously implicated in branching morphogenesis of mature epithelial cell lines. Using sequential column chromatography, we have now purified to apparent homogeneity an 18 kDa protein, pleiotrophin, from the conditioned medium of a metanephric mesenchyme cell line that induces isolated ureteric bud branching morphogenesis in the presence of glial cell-derived neurotrophic factor. Pleiotrophin alone was also found to induce the formation of branching tubules in an immortalized ureteric bud cell line cultured three-dimensionally in an extracellular matrix gel. Consistent with an important role in ureteric bud morphogenesis during kidney development, pleiotrophin was found to localize to the basement membrane of the developing ureteric bud in the embryonic kidney. We suggest that pleiotrophin could act as a key mesenchymally derived factor regulating branching morphogenesis of the ureteric bud and perhaps other embryonic epithelial structures.

Enhanced hippocampal long-term potentiation in mice lacking heparin-binding growth-associated molecule

Heparin-binding growth-associated molecule (HB-GAM) (pleiotrophin) is a highly conserved extracellular matrix-associated protein implicated in a diverse range of developmental processes, including the formation and plasticity of neuronal connections. Using gene targeting, we have in the present study created HB-GAM-deficient mice that are viable and fertile and show no gross anatomical abnormalities. The hippocampal structure as well as basal excitatory synaptic transmission in the area CA1 appear normal in the mice lacking HB-GAM. However, hippocampal slices from HB-GAM-deficient mice display a lowered threshold for induction of long-term potentiation (LTP), which reverts back to the wild-type level by application of HB-GAM. HB-GAM expression in hippocampus is activity-dependent and upregulated in several neuropathological conditions. Thus, we suggest that HB-GAM acts as an inducible signal to inhibit LTP in hippocampus.

The lysine-rich C-terminal tail of heparin affin regulatory peptide is required for mitogenic and tumor formation activities

Heparin affin regulatory peptide (HARP) is a 18-kDa heparin-binding polypeptide that is highly expressed in developing tissues and in several primary human tumors. It seems to play a key role in cellular growth and differentiation. In vitro, HARP displays mitogenic, angiogenic, and neurite outgrowth activities. It is a secreted protein that is organized in two beta-sheet domains, each domain containing a cluster of basic residues. To assess determinants involved in the biological activities of HARP, C-terminally truncated proteins were produced in Chinese hamster ovary-K1 cells and tested for their mitogenic, tumor formation in nude mice and neurite outgrowth activities. Our data clearly indicate that the residues 111-136 of the lysine-rich C-terminal domain are involved in the mitogenic and tumor formation activities of HARP. Correlatively, no signal transduction was detected using the corresponding mutant, suggesting the absence of HARP binding to its high affinity receptor. However, this C-terminal domain of HARP is not involved in the neurite outgrowth activity. We also demonstrate that HARP signal peptide cleavage could led to two maturated forms that are both but differentially mitogenic.