Cerebrospinal fluid contains biologically active bone morphogenetic protein-7

Deciphering the impact of cerebrospinal fluid on stem cell fate as a new mechanism to enhance clinical therapy development

Neural stem cells (NSCs) hold a very significant promise as candidates for cell therapy due to their robust neuroprotective and regenerative properties. Preclinical studies using NSCs have shown enough encouraging results to perform deeper investigations into more potential clinical applications. Nevertheless, our knowledge regarding neurogenesis and its underlying mechanisms remains incomplete. To understand them better, it seems necessary to characterize all components of neural stem cell niche and discover their role in physiology and pathology. Using NSCs in vivo brings challenges including limited cell survival and still inadequate integration within host tissue. Identifying overlooked factors that might influence these outcomes becomes pivotal. In this review, we take a deeper examination of the influence of a fundamental element that is present in the brain, the cerebrospinal fluid (CSF), which still remains relatively unexplored. Its role in neurogenesis could be instrumental to help find novel therapeutic solutions for neurological disorders, eventually advancing our knowledge on central nervous system (CNS) regeneration and repair.

SCO-spondin, a giant matricellular protein that regulates cerebrospinal fluid activity

Cerebrospinal fluid is a clear fluid that occupies the ventricular and subarachnoid spaces within and around the brain and spinal cord. Cerebrospinal fluid is a dynamic signaling milieu that transports nutrients, waste materials and neuroactive substances that are crucial for the development, homeostasis and functionality of the central nervous system. The mechanisms that enable cerebrospinal fluid to simultaneously exert these homeostatic/dynamic functions are not fully understood. SCO-spondin is a large glycoprotein secreted since the early stages of development into the cerebrospinal fluid. Its domain architecture resembles a combination of a matricellular protein and the ligand-binding region of LDL receptor family. The matricellular proteins are a group of extracellular proteins with the capacity to interact with different molecules, such as growth factors, cytokines and cellular receptors; enabling the integration of information to modulate various physiological and pathological processes. In the same way, the LDL receptor family interacts with many ligands, including β-amyloid peptide and different growth factors. The domains similarity suggests that SCO-spondin is a matricellular protein enabled to bind, modulate, and transport different cerebrospinal fluid molecules. SCO-spondin can be found soluble or polymerized into a dynamic threadlike structure called the Reissner fiber, which extends from the diencephalon to the caudal tip of the spinal cord. Reissner fiber continuously moves caudally as new SCO-spondin molecules are added at the cephalic end and are disaggregated at the caudal end. This movement, like a conveyor belt, allows the transport of the bound molecules, thereby increasing their lifespan and action radius. The binding of SCO-spondin to some relevant molecules has already been reported; however, in this review we suggest more than 30 possible binding partners, including peptide β-amyloid and several growth factors. This new perspective characterizes SCO-spondin as a regulator of cerebrospinal fluid activity, explaining its high evolutionary conservation, its apparent multifunctionality, and the lethality or severe malformations, such as hydrocephalus and curved body axis, of knockout embryos. Understanding the regulation and identifying binding partners of SCO-spondin are crucial for better comprehension of cerebrospinal fluid physiology.

Bone morphogenetic proteins (BMPs) in the central regulation of energy balance and adult neural plasticity

The current worldwide obesity pandemic highlights a need to better understand the regulation of energy balance and metabolism, including the role of the nervous system in controlling energy intake and energy expenditure. Neural plasticity in the hypothalamus of the adult brain has been implicated in full-body metabolic health, however, the mechanisms surrounding hypothalamic plasticity are incompletely understood. Bone morphogenetic proteins (BMPs) control metabolic health through actions in the brain as well as in peripheral tissues such as adipose, together regulating both energy intake and energy expenditure. BMP ligands, receptors, and inhibitors are found throughout plastic adult brain regions and have been demonstrated to modulate neurogenesis and gliogenesis, as well as synaptic and dendritic plasticity. This role for BMPs in adult neural plasticity is distinct from their roles in brain development. Existing evidence suggests that BMPs induce weight loss through hypothalamic pathways, and part of the mechanism of action may be through inducing neural plasticity. In this review, we summarize the data regarding how BMPs affect neural plasticity in the adult mammalian brain, as well as the relationship between central BMP signaling and metabolic health.

Traumatic brain injury enhances the formation of heterotopic ossification around the hip: an animal model study

INTRODUCTION

The incidence of heterotopic ossification (HO) is at its highest when trauma of the hip or pelvis concurs with traumatic brain injury (TBI). The pathogenic mechanisms underlying the neurogenic enhancement of the formation of HO remain, however, poorly understood. Hence, the goal of the present study was to develop a novel small animal model that combines hip and brain trauma that can prove the enhancement of HO around the hip after TBI.

MATERIALS AND METHODS

Forty male Wistar rats were divided into four groups, to undergo hip surgery alone (group 1), hip surgery + moderate TBI (group 2), hip surgery + severe TBI (group 3) and only severe TBI (group 4). The femoral canal was reamed up to 2 mm and a muscle lesion was made to simulate hip surgery. An established controlled cortical impact model was used to create a TBI. Twelve weeks after surgery, the hip with the proximal half of the femur and the pelvic bone was removed and subjected to micro-computed tomography (µCT) analysis. A quantitative analysis using a modified Brooker score as well as a quantitative analysis using a bone-to-tissue ratio was used.

RESULTS

No HO could be found in all the ten animals that did not undergo hip surgery (group 4). In the animals that did undergo surgery to the hip, no HO was found in only one animal (group 1). All the other animals developed HO. In this study, significantly more HO was found in animals that underwent an additional severe TBI.

CONCLUSION

The newly developed rat model, with a combined hip and brain trauma, showed an enhancement of the HO formation around the hip after severe TBI.

Brain Ventricular System and Cerebrospinal Fluid Development and Function: Light at the End of the Tube: A Primer with Latest Insights

The brain ventricular system is a series of connected cavities, filled with cerebrospinal fluid (CSF), that forms within the vertebrate central nervous system (CNS). The hollow neural tube is a hallmark of the chordate CNS, and a closed neural tube is essential for normal development. Development and function of the ventricular system is examined, emphasizing three interdigitating components that form a functional system: ventricle walls, CSF fluid properties, and activity of CSF constituent factors. The cellular lining of the ventricle both can produce and is responsive to CSF. Fluid properties and conserved CSF components contribute to normal CNS development. Anomalies of the CSF/ventricular system serve as diagnostics and may cause CNS disorders, further highlighting their importance. This review focuses on the evolution and development of the brain ventricular system, associated function, and connected pathologies. It is geared as an introduction for scholars with little background in the field.

Reestablishment of Energy Balance in a Male Mouse Model With POMC Neuron Deletion of BMPR1A

The regulation of energy balance involves complex processes in the brain, including coordination by hypothalamic neurons that contain pro-opiomelanocortin (POMC). We previously demonstrated that central bone morphogenetic protein (BMP) 7 reduced appetite. Now we show that a type 1 BMP receptor, BMPR1A, is colocalized with POMC neurons and that POMC-BMPR1A-knockout (KO) mice are hyperphagic, revealing physiological involvement of BMP signaling in anorectic POMC neurons in the regulation of appetite. Surprisingly, the hyperphagic POMC-BMPR1A-KO mice exhibited a lack of obesity, even on a 45% high-fat diet. This is because the brown adipose tissue (BAT) of KO animals exhibited increased sympathetic activation and greater thermogenic capacity owing to a reestablishment of energy balance, most likely stemming from a compensatory increase of BMPR1A in the whole hypothalamus of KO mice. Indeed, control animals given central BMP7 displayed increased energy expenditure and a specific increase in sympathetic nerve activity (SNA) in BAT. In these animals, pharmacological blockade of BMPR1A-SMAD signaling blunted the ability of BMP7 to increase energy expenditure or BAT SNA. Together, we demonstrated an important role for hypothalamic BMP signaling in the regulation of energy balance, including BMPR1A-mediated appetite regulation in POMC neurons as well as hypothalamic BMP-SMAD regulation of the sympathetic drive to BAT for thermogenesis.

Role of BMP7 in appetite regulation, adipogenesis, and energy expenditure

Bone morphogenetic protein 7 (BMP7), also known as osteogenic protein-1 (OP-1) is a member of Transforming growth factor-β (TGF-β) family of proteins. Bone morphogenetic proteins were discovered in 1965 by Marshal Urist, of which BMP7 is of particular interest in this review being a leptin-independent anorexinogen and having role in energy expenditure in the brown adipose tissue, which makes it a potential target for preventing/treating obesity. As it has been established that Obesity displays a state of leptin-resistance, thus a protein-like BMP7 which acts through a leptin-independent pathway could give new therapeutic directions. This review will also discuss the synthesis and action of BMP7, along with its receptors and signal transduction. A brief note about BMP7-mediated brown fat development and energy balance is also discussed.

In vitro evaluation of TAT-OP1 osteogenic properties and prospects for in vivo applications

So far, osteogenic protein 1 (OP1) is biotechnologically produced and approved for the treatment of human lumbar spine fusion and long bone non-union fractures. When combined with the TAT sequence, it has been demonstrated in vitro to be easily taken up by PC12 neuronal cells and to acquire its biological activity after intracellular refolding. In this study, TAT-OP1 was shown to be a useful strategy to efficiently drive denatured OP1 into mouse MC3T3E1 pre-osteoblasts. The correct in vitro protein refolding was verified by the activation of the BMP cascade, while the osteogenic potential of OP1 was demonstrated by increased expression of alkaline phosphatase, osteonectin and osteocalcin.

Bone morphogenetic protein 7 (BMP7) reverses obesity and regulates appetite through a central mTOR pathway

Body weight is regulated by coordinating energy intake and energy expenditure. Transforming growth factor β (TGFβ)/bone morphogenetic protein (BMP) signaling has been shown to regulate energy balance in lower organisms, but whether a similar pathway exists in mammals is unknown. We have previously demonstrated that BMP7 can regulate brown adipogenesis and energy expenditure. In the current study, we have uncovered a novel role for BMP7 in appetite regulation. Systemic treatment of diet-induced obese mice with BMP7 resulted in increased energy expenditure and decreased food intake, leading to a significant reduction in body weight and improvement of metabolic syndrome. Similar degrees of weight loss with reduced appetite were also observed in BMP7-treated ob/ob mice, suggesting a leptin-independent mechanism utilized by BMP7. Intracerebroventricular administration of BMP7 to mice led to an acute decrease in food intake, which was mediated, at least in part, by a central rapamycin-sensitive mTOR-p70S6 kinase pathway. Together, these results underscore the importance of BMP7 in regulating both food intake and energy expenditure, and suggest new therapeutic approaches for obesity and its comorbidities.

New ependymal cells are born postnatally in two discrete regions of the mouse brain and support ventricular enlargement in hydrocephalus

A heterogeneous population of ependymal cells lines the brain ventricles. The evidence about the origin and birth dates of these cell populations is scarce. Furthermore, the possibility that mature ependymal cells are born (ependymogenesis) or self-renewed (ependymal proliferation) postnatally is controversial. The present study was designed to investigate both phenomena in wild-type (wt) and hydrocephalic α-SNAP mutant (hyh) mice at different postnatal stages. In wt mice, proliferating cells in the ventricular zone (VZ) were only found in two distinct regions: the dorsal walls of the third ventricle and Sylvian aqueduct (SA). Most proliferating cells were monociliated and nestin+, likely corresponding to radial glial cells. Postnatal cumulative BrdU-labeling showed that most daughter cells remained in the VZ of both regions and they lost nestin-immunoreactivity. Furthermore, some labeled cells became multiciliated and GLUT-1+, indicating they were ependymal cells born postnatally. Postnatal pulse BrdU-labeling and Ki-67 immunostaining further demonstrated the presence of cycling multiciliated ependymal cells. In hydrocephalic mutants, the dorsal walls of the third ventricle and SA expanded enormously and showed neither ependymal disruption nor ventriculostomies. This phenomenon was sustained by an increased ependymogenesis. Consequently, in addition to the physical and geometrical mechanisms traditionally explaining ventricular enlargement in fetal-onset hydrocephalus, we propose that postnatal ependymogenesis could also play a role. Furthermore, as generation of new ependymal cells during postnatal stages was observed in distinct regions of the ventricular walls, such as the roof of the third ventricle, it may be a key mechanism involved in the development of human type 1 interhemispheric cysts.

Prospectively isolated CD133/CD24-positive ependymal cells from the adult spinal cord and lateral ventricle wall differ in their long-term in vitro self-renewal and in vivo gene expression

In contrast to ependymal cells located above the subventricular zone (SVZ) of the adult lateral ventricle wall (LVW), adult spinal cord (SC) ependymal cells possess certain neural stem cell characteristics. The molecular basis of this difference is unknown. In this study, antibodies against multiple cell surface markers were applied to isolate pure populations of SC and LVW ependymal cells, which allowed a direct comparison of their in vitro behavior and in vivo gene expression profile. Isolated CD133(+)/CD24(+)/CD45(-)/CD34(-) ependymal cells from the SC displayed in vitro self-renewal and differentiation capacity, whereas those from the LVW did not. SC ependymal cells showed a higher expression of several genes involved in cell division, cell cycle regulation, and chromosome stability, which is consistent with a long-term self-renewal capacity, and shared certain transcripts with neural stem cells of the embryonic forebrain. They also expressed several retinoic acid (RA)-regulated genes and responded to RA exposure. LVW ependymal cells showed higher transcript levels of many genes regulated by transforming growth factor-β family members. Among them were Dlx2, Id2, Hey1, which together with Foxg1 could explain their potential to turn into neuroblasts under certain environmental conditions.

Recombinant human TAT-OP1 to enhance NGF neurogenic potential: preliminary studies on PC12 cells

Osteogenic protein 1 (OP1), also known as bone morphogenic protein-7 (BMP7), is a multifunctional cytokine with demonstrated neurogenic potential. As the recombinant OP1 (rhOP1) was shown to provide axonal guidance cues and to prevent the reduction of dendritic growth in the injury-induced cortical cultures, it was suggested that an in vivo efficient rhOP1 delivery could enhance neurite growth and functional reconnectivity in the damaged brain. In the present work, we engineered a chimeric molecule in which rhBMP7 was fused to a protein transduction domain derived from HIV-1 TAT protein to deliver the denatured recombinant BMP7 into cells and obtain its chaperone-mediated folding, circumventing the expensive and not much efficient in vitro refolding procedures. When tested on rat PC12 cells, a widely used in vitro neurogenic differentiation model, the resulting fusion protein (rhTAT-OP1) demonstrated to enter fastly into the cells, lose HIV-TAT sequence and interact with membrane receptors activating BMP pathway by SMAD 1/5/8 phosphorylation. In comparison with nerve growth factor (NGF) and BMP7, it proved itself effective to induce the formation of more organized H and M neurofilaments. Moreover, if used in combination with NGF, it stimulated a significant (P < 0.05) and more precocious dendritic outgrowth with respect to NGF alone. These results indicate that rhTAT-OP1 fused with TAT transduction domain shows neurogenic activity and may be a promising enhancer factor in NGF-based therapies.

The expression of twisted gastrulation in postnatal mouse brain and functional implications

Twisted gastrulation (TWSG1), an extracellular regulator of bone morphogenetic protein (BMP) signaling, is critical for embryonic brain development. Mice deficient in TWSG1 have abnormal forebrain development manifesting as holoprosencephaly. The expression and potential roles of TWSG1 in postnatal brain development are less well understood. We show that Twsg1 is expressed in the adult mouse brain in the choroid plexus (CP), hippocampus, and other regions, with the strongest expression observed in CP. TWSG1 was also detected in a human fetal brain at mid-gestation, with highest levels in the epithelium of CP. Bmp1, Bmp2, Bmp4-Bmp7 as well as BmprIA and BmprII, but not BmprIB, were expressed in CP. BMP antagonists Chordin (Chrd) and Noggin were not detected in CP, however Chrd-like 1 and brain-specific Chrd-like (Brorin) were expressed. Electrophysiological study of synaptic plasticity revealed normal paired-pulse facilitation and long-term potentiation in the CA1 region of hippocampus in Twsg1(-/-) mice. Among the homozygous mutants that survive beyond the first 2 weeks, the prevalence of hydrocephalus was 4.3%, compared to 1.5% in a wild type colony (P=0.0133) between 3 and 10 weeks of life. We detected a high level of BMP signaling in CP in wild type adult mice that was 17-fold higher than in the hippocampus (P=0.005). In contrast, transforming growth factor beta (TGFbeta) signaling was predominant in the hippocampus. Both BMP signaling and the expression of BMP downstream targets Msx1 and Msx2 were reduced in CP in Twsg1(-/-) mice. In summary, we show that Twsg1 is expressed in the adult mouse and human fetal CP. We also show that BMP is a branch of TGFbeta superfamily that is dominant in CP. This presents an interesting avenue for future research in light of the novel roles of CP in neural progenitor differentiation and neuronal repair, especially since TWSG1 appears to be the main regulator of BMP present in CP.

Cerebrospinal fluid promotes survival and astroglial differentiation of adult human neural progenitor cells but inhibits proliferation and neuronal differentiation

BACKGROUND

Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Growing evidence suggests an important role of cerebrospinal fluid (CSF) not only on neuroectodermal cells during brain development but also on the survival, proliferation and fate specification of NSCs in the adult brain. Existing in vitro studies focused on embryonic cell lines and embryonic CSF. We therefore studied the effects of adult human leptomeningeal CSF on the behaviour of adult human NSCs (ahNSCs).

RESULTS

Adult CSF increased the survival rate of adult human NSCs compared to standard serum free culture media during both stem cell maintenance and differentiation. The presence of CSF promoted differentiation of NSCs leading to a faster loss of their self-renewal capacity as it is measured by the proliferation markers Ki67 and BrdU and stronger cell extension outgrowth with longer and more cell extensions per cell. After differentiation in CSF, we found a larger number of GFAP+ astroglial cells compared to differentiation in standard culture media and a lower number of beta-tubulin III+ neuronal cells.

CONCLUSIONS

Our data demonstrate that adult human leptomeningeal CSF creates a beneficial environment for the survival and differentiation of adult human NSCs. Adult CSF is in vitro a strong glial differentiation stimulus and leads to a rapid loss of stem cell potential.

Adult cerebrospinal fluid inhibits neurogenesis but facilitates gliogenesis from fetal rat neural stem cells

Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Administration of NSCs into the cerebrospinal fluid (CSF) offers a nontraumatic transplantation method into the brain. However, cell survival and intraparenchymal migration of the transplants are limited. Furthermore, CSF was recently reported to be an important milieu for controlling stem cell processes in the brain. We studied the effects of adult human leptomeningeal CSF on the behavior of fetal rat NSCs. CSF increased survival of NSCs compared with standard culture media during stem cell maintenance and differentiation. The presence of CSF enhanced NSC differentiation, leading to a faster loss of self-renewal capacity and faster and stronger neurite outgrowth. Some of these effects (mainly cell survival, neurite brancing) were blocked by addition of the bone morphogenic protein (BMP) inhibitor noggin. After differentiation in CSF, significantly fewer MAP2ab(+) neurons were found, but there were more GFAP(+) astroglia compared with standard media. By RT-PCR analysis, we determined a decrease of mRNA of the NSC marker gene Nestin but an increase of Gfap mRNA during differentiation up to 72 hr in CSF compared with standard media. Our data demonstrate that adult human leptomeningeal CSF enhances cell survival of fetal rat NSCs during proliferation and differentiation. Furthermore, CSF provides a stimulus for gliogenesis but inhibits neurogenesis from fetal NSCs. Our data suggest that CSF contains factors such as BMPs regulating NSC behavior, and we hypothesize that fast differentiation of NSCs in CSF leads to a rapid loss of migration capacity of intrathecally transplanted NSCs.

Disruption of the neurogenic niche in the subventricular zone of postnatal hydrocephalic hyh mice

Neural stem cells persist after embryonic development in the subventricular zone (SVZ) niche and produce new neural cells during postnatal life; ependymal cells are a key component associated with this neurogenic niche. In the animal model of human hydrocephalus, the hyh mouse, the ependyma of the lateral ventricles is progressively lost during late embryonic and early postnatal life and disappears from most of the ventricular surface throughout its life span. To determine the potential consequences of this loss on the SVZ, we characterized the abnormalities in this neurogenic niche in hyh mice. There was overall disorganization and a marked reduction of proliferative cells in the SVZ of both newborn and adult hyh hydrocephalic mice in vivo; neuroblasts were displaced to the ventricular surface, and their migration through the rostral migratory stream was reduced. The numbers of resident neural progenitor cells in hyh mice were also markedly reduced, but they were capable of proliferating, forming neurospheres, and differentiating into neurons and glia in vitro in a manner indistinguishable from that of wild-type progenitor cells. These findings suggest that the reduction of proliferative activity observed in vivo is not caused by a cell autonomous defect of SVZ progenitors but is a consequence of a reduced number of these cells. Furthermore, the overall tissue disorganization of the SVZ and displacement of neuroblasts imply alterations in the neurogenic niche of postnatal hyh mice.

The role of oxygen in regulating neural stem cells in development and disease

Oxygen (O2) is a substrate for energy production in the cell and is a rapid regulator of cellular metabolism. Recent studies have also implicated O2 and its signal transduction pathways in controlling cell proliferation, fate, and morphogenesis during the development of many tissues, including the nervous system. O2 tensions in the intact brain are much lower than in room air, and there is evidence that dynamic control of O2 availability may be a component of the in vivo neural stem cell (NSC) niche. At lower O2 tensions, hypoxia-inducible factor 1alpha (HIF1alpha) facilitates signal transduction pathways that promote self-renewal (e.g., Notch) and inhibits pathways that promote NSC differentiation or apoptosis (e.g., bone morphogenetic proteins). Increasing O2 tension degrades HIF1alpha, thus promoting differentiation or apoptosis of NSCs and progenitors. These dynamic changes in O2 tension can be mimicked to optimize ex vivo production methods for cell replacement therapies. Conversely, disrupted O2 availability may play a critical role in disease states such as stroke or brain tumor progression. Hypoxia during stroke activates precursor proliferation in vivo, while glioblastoma stem cells proliferate maximally in a more hypoxic environment than normal stem cells, which may make them resistant to certain anti-neoplastic therapies. These findings suggest that O2 response is central to the normal architecture and dynamics of NSC regulation and in the etiology and treatment of brain diseases.

Hypoxia and HIF1alpha repress the differentiative effects of BMPs in high-grade glioma

Hypoxia commonly occurs in solid tumors of the central nervous system (CNS) and often interferes with therapies designed to stop their growth. We found that pediatric high-grade glioma (HGG)-derived precursors showed greater expansion under lower oxygen tension, typical of solid tumors, than normal CNS precursors. Hypoxia inhibited p53 activation and subsequent astroglial differentiation of HGG precursors. Surprisingly, although HGG precursors generated endogenous bone morphogenetic protein (BMP) signaling that promoted mitotic arrest under high oxygen tension, this signaling was actively repressed by hypoxia. An acute increase in oxygen tension led to Smad activation within 30 minutes, even in the absence of exogenous BMP treatment. Treatment with BMPs further promoted astroglial differentiation or death of HGG precursors under high oxygen tension, but this effect was inhibited under hypoxic conditions. Silencing of hypoxia-inducible factor 1alpha (HIF1alpha) led to Smad activation even under hypoxic conditions, indicating that HIF1alpha is required for BMP repression. Conversely, BMP activation at high oxygen tension led to reciprocal degradation of HIF1alpha; this BMP-induced degradation was inhibited in low oxygen. These results show a novel, mutually antagonistic interaction of hypoxia-response and neural differentiation signals in HGG proliferation, and suggest differences between normal and HGG precursors that may be exploited for pediatric brain cancer therapy.

A rapid and sensitive bioassay for the simultaneous measurement of multiple bone morphogenetic proteins. Identification and quantification of BMP4, BMP6 and BMP9 in bovine and human serum

Background

Bone morphogenetic proteins (BMPs) are pleiotropic members of the TGF-beta superfamily which regulate many biological processes during development and adult tissue homeostasis and are implicated in the pathogenesis of a number of human diseases. Their involvement in both normal and aberrant physiology creates a need for rapid, sensitive and methodologically simple assays to evaluate their activity from a variety of biological samples. Previously alkaline phosphatase based assays, ELISA and luciferase based bioassays have been developed to evaluate either individual or total BMP activity. In this paper, we describe a highly sensitive, rapid and specific cell based assay for the simultaneous quantification of total and isoform specific BMP activity from biological samples.

Results

A C2C12 cell line stably transfected with a reporter plasmid consisting of the BMP response element (BRE) from the Id1 promoter fused to a luciferase reporter gene was generated. Exposure of this cell line to human recombinant BMP2, BMP4, BMP6, BMP7, BMP9 and BMP10 induced the expression of luciferase which was quantified using a luminometer. This assay was specific for BMP activity as the other TGF-β superfamily members TGF-β 1, Nodal and Mullerian Inhibiting Substance (MIS) did not induce the reporter. Pretreatment of samples with isoform specific BMP blocking antibodies coupled with isoform specific titration analysis allowed the simultaneous identification and quantification of BMP4, BMP6 and BMP9 in serum samples.

Conclusion

The assay is rapid (<48 hours) and can be used to simultaneously measure isoform specific and total BMP activity in complex solutions.

The BMP ligand Gbb gates the expression of synaptic homeostasis independent of synaptic growth control

Inhibition of postsynaptic glutamate receptors at the Drosophila NMJ initiates a compensatory increase in presynaptic release termed synaptic homeostasis. BMP signaling is necessary for normal synaptic growth and stability. It remains unknown whether BMPs have a specific role during synaptic homeostasis and, if so, whether BMP signaling functions as an instructive retrograde signal that directly modulates presynaptic transmitter release. Here, we demonstrate that the BMP receptor (Wit) and ligand (Gbb) are necessary for the rapid induction of synaptic homeostasis. We also provide evidence that both Wit and Gbb have functions during synaptic homeostasis that are separable from NMJ growth. However, further genetic experiments demonstrate that Gbb does not function as an instructive retrograde signal during synaptic homeostasis. Rather, our data indicate that Wit and Gbb function via the downstream transcription factor Mad and that Mad-mediated signaling is continuously required during development to confer competence of motoneurons to express synaptic homeostasis.

A rapid and sensitive bioassay to measure bone morphogenetic protein activity

Background

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily and were originally identified as proteins that induce ectopic bone formation. BMPs were shown subsequently to be involved in several biological processes during development and in adult tissues through the regulation of the growth, differentiation and apoptosis of various cell types. An alkaline phosphatase (ALP)-based assay is the most widely used assay to evaluate BMP activity. However, the ALP assay is not rapid and not sensitive enough to measure BMP activity at physiological concentrations. In this paper, we describe a highly sensitive, rapid, and specific cell-based assay for the quantification of BMP activity.

Results

Two cells lines, C2C12 and HepG2 were stably transfected with a reporter plasmid consisting of BMP-responsive elements from the Id1 promoter fused to a luciferase reporter gene. Exposure of cells containing this construct to BMPs induces the expression of luciferase, which can be quantified with a luminometer. The bioassay is specific for BMPs and can detect BMP-4 activity at a concentration as low as 3 pM. Related family members, such as TGF-beta1, TGF-beta2 and TGF-beta3, do not induce the reporter gene.

Conclusion

The assay is rapid (less than 24 hours) and can be used, as described in this paper, to measure BMP activity in complex solutions and in cell culture in a simple and efficient way.

Osteoinductive Effect of Cerebrospinal Fluid from Brain-Injured Patients

Patients with traumatic brain injury (TBI) are predisposed to heterotopic ossification, which is believed to be due to osteoinductive factors released at the site of the brain injury. To date, little is known about the presence of such factors in human cerebrospinal fluid (CSF). This study investigated whether CSF of TBI patients is osteoinductive. In addition, known osteoinductive factors--such as bone morphogenetic protein (BMP)-2, BMP-4, and BMP-7, and S100B--were measured in CSF. Eighty-four consecutive patients were classified according to brain pathology: TBI (n = 11), non-traumatic brain pathology (NTBP) (n = 26), and no brain pathology (control group) (n = 47). The osteoinductive effect of CSF was measured repeatedly in proliferation assays using a fetal human osteoblast cell line. The mean proliferation rate (normalized to the internal negative control) of the TBI, NTBP, and control groups was 138.2% (SD 13.1), 110.0% (SD 22.1), and 118.8% (SD 16.9), respectively. The potentially confounding effect of age was investigated further by restricting the selection of patients for analysis to that of the oldest patient in the TBI group and use of multiple regression analysis. After implementation of both, it was shown that age is highly unlikely to account for the higher rates of proliferation observed among the TBI patients in this study. Of note, the TBI group had a significantly higher mean proliferation rate than the NTBP (p = 0.001) and the control group (p = 0.006). S100B and BMP-2, -4, or -7 concentrations were measured using enzyme-linked immunosorbent assay (ELISA). There was no correlation between proliferation rates and S100B (r = 0.023). Only three of 36 CSF samples had measurable levels of BMP-2 and -7, and none had detectable concentrations of BMP-4. Consequently, it is unlikely that S100B or BMP-2, -4, or -7 are the putative osteoinductive factors. The results indicate that CSF from TBI patients has an osteoinductive effect in vitro. However, the osteoinductive factor has still to be characterized.

BMPs, FGF8 and Wnts regulate the differentiation of locus coeruleus noradrenergic neuronal precursors

In the present study, we investigated the involvement of rhombomere 1 patterning proteins in the regulation of the major noradrenergic centre of the brain, the locus coeruleus. Primary cultures of rat embryonic day 13.5 locus coeruleus were treated with fibroblast growth factor-8, noggin and members of the bone morphogenetic and Wnt protein families. We show that bone morphogenetic proteins 2, 5 and 7 increase and noggin decreases the number of tyrosine hydroxylase-positive locus coeruleus neurons. Interestingly, from all Wnts expressed in the first rhombomere by embryonic day 12.5 in the mice, we only found expression of wnt5a mRNA in the vicinity of the locus coeruleus. In agreement with this finding, from all Wnts studied in vitro, only Wnt5a increased the number of tyrosine hydroxylase-positive neurons in locus coeruleus cultures. Finally, we also found that fibroblast growth factor-8 increased the number of tyrosine hydroxylase-positive cells in locus coeruleus cultures. Neither of the identified factors affected the survival of tyrosine hydroxylase-positive locus coeruleus noradrenergic neurons or the proliferation of their progenitors or neurogenesis. Instead, our results suggest that these patterning signals of rhombomere 1 may work to promote the differentiation of noradrenergic progenitors at later stages of development.

Accelerated bone healing and excessive callus formation in patients with femoral fracture and head injury

The effect of head injury on systemic physiology, including bone healing is still a topic of vivid discussion. Whether the observed changes genuinely represent accelerated fracture healing or are a form of local heterotopic ossification remains unclear. We aimed to investigate whether in patients with long bone fractures the presence of head injury is associated with accelerated bone healing and excessive callus formation. In total 67 patients were studied 17 with head injury and 50 without head injury (25 treated with reamed and the other 25 with the unreamed nailing technique). Both groups were comparable in terms of age, sex, ISS. All underwent stabilisation of their femoral fracture with intramedullary nailing. The quantification of fracture healing response was estimated by taking the radiological ratio of the largest diameter of callus formed into two planes and the adjacent normal diameter of femoral canal. The minimum follow up of the patients was 12 months. In patients with head injury, the mean time to fracture union was significantly shorter than either the reamed or unreamed group (10.5 weeks compared with 20.5 and 26.9 weeks, p<0.001). The difference between the mean callus to diaphyseal ratio was statistically significant for both the AP and Lateral projections (AP: mean difference 0.462, 95% CI 0.312 to 0.602, p<0.0001, LAT: mean difference 0.289, 95% CI 0.142 to 0.436, p<0.001) with the head injured patients having more florid callus compared to the control group.

Bone morphogenetic proteins regulate ionotropic glutamate receptors in human retina

Bone morphogenetic proteins (BMPs) are required for the development of retina, but their role in the mature eye is unknown. We therefore examined the expression of BMP-7 in adult human retina and assessed its effects on horizontal cells cultured from adult human retina. BMP-7 expression was detected in all retinal layers, with high levels of expression being present in the inner and outer nuclear layers. Human horizontal cells, found in the inner nuclear layer, possess both AMPA and kainate receptors, and glutamatergic agonists that activate these receptors induce prominent inward currents. Exposure to BMP-7 suppresses the kainate receptor current but enhances the AMPA receptor current. BMP-6, activin, and cartilage-derived morphogenic protein-2 (CDMP-2) have similar effects to BMP-7 and act just as rapidly (< 1 s). In contrast BMP-2 and transforming growth factor-beta2 are inactive. The actions of BMP-7 on both AMPA and kainate receptors were blocked by the nonselective kinase inhibitor, staurosporine. In contrast, the serine/threonine kinase inhibitors blocked only the effects of BMP-7 on the AMPA current. Thus, BMPs rapidly and differentially regulate two ionotropic glutamate receptors through distinct pathways, neither of which involves nuclear regulatory activity. These observations suggest that BMPs might modify synaptic function in the mature nervous system.