AAV9-mediated SH3TC2 gene replacement therapy targeted to Schwann cells for the treatment of CMT4C

Type 4C Charcot-Marie-Tooth (CMT4C) demyelinating neuropathy is caused by autosomal recessive SH3TC2 gene mutations. SH3TC2 is highly expressed in myelinating Schwann cells. CMT4C is a childhood-onset progressive disease without effective treatment. Here, we generated a gene therapy for CMT4C mediated by an adeno-associated viral 9 vector (AAV9) to deliver the human SH3TC2 gene in the Sh3tc2-/- mouse model of CMT4C. We used a minimal fragment of the myelin protein zero (Mpz) promoter (miniMpz), which was cloned and validated to achieve Schwann cell-targeted expression of SH3TC2. Following the demonstration of AAV9-miniMpz.SH3TC2myc vector efficacy to re-establish SH3TC2 expression in the peripheral nervous system, we performed an early as well as a delayed treatment trial in Sh3tc2-/- mice. We demonstrate both after early as well as following late treatment improvements in multiple motor performance tests and nerve conduction velocities. Moreover, treatment led to normalization of the organization of the nodes of Ranvier, which is typically deficient in CMT4C patients and Sh3tc2-/- mice, along with reduced ratios of demyelinated fibers, increased myelin thickness and reduced g-ratios at both time points of intervention. Taken together, our results provide a proof of concept for an effective and potentially translatable gene replacement therapy for CMT4C treatment.

Gene replacement therapy in two Golgi-retained CMT1X mutants before and after the onset of demyelinating neuropathy

X-linked Charcot-Marie-Tooth disease type 1 (CMT1X) is a demyelinating neuropathy resulting from loss-of-function mutations affecting the GJB1/connexin 32 (Cx32) gene. We previously showed functional and morphological improvement in Gjb1-null mice following AAV9-mediated delivery of human Cx32 driven by the myelin protein zero (Mpz) promoter in Schwann cells. However, CMT1X mutants may interfere with virally delivered wild-type (WT) Cx32. To confirm the efficacy of this vector also in the presence of CMT1X mutants, we delivered AAV9-Mpz-GJB1 by lumbar intrathecal injection in R75W/Gjb1-null and N175D/Gjb1-null transgenic lines expressing Golgi-retained mutations, before and after the onset of the neuropathy. Widespread expression of virally delivered Cx32 was demonstrated in both genotypes. Re-establishment of WT Cx32 function resulted in improved muscle strength and increased sciatic nerve motor conduction velocities in all treated groups from both mutant lines when treated before as well as after the onset of the neuropathy. Furthermore, morphological analysis showed improvement of myelination and reduction of inflammation in lumbar motor roots and peripheral nerves. In conclusion, this study provides proof of principle for a clinically translatable gene therapy approach to treat CMT1X before and after the onset of the neuropathy, even in the presence of endogenously expressed Golgi-retained Cx32 mutants.

Mitofusin 1 overexpression rescues the abnormal mitochondrial dynamics caused by the Mitofusin 2 K357T mutation in vitro

BACKGROUND AND AIMS

Mitofusin 1 (MFN1) and MFN2 are outer mitochondrial membrane fusogenic proteins regulating mitochondrial network morphology. MFN2 mutations cause Charcot-Marie-Tooth type 2A (CMT2A), an axonal neuropathy characterized by mitochondrial fusion defects, which in the case of a GTPase domain mutant, were rescued following wild-type MFN1/2 (MFN1/2WT ) overexpression. In this study, we compared the therapeutic efficiency between MFN1WT and MFN2WT overexpression in correcting mitochondrial defects induced by the novel MFN2K357T mutation located in the highly conserved R3 region.

METHODS

Constructs expressing either MFN2K357T , MFN2WT , or MFN1WT under the ubiquitous chicken β-actin hybrid (CBh) promoter were generated. Flag or myc tag was used for their detection. Differentiated SH-SY5Y cells were single transfected with MFN1WT , MFN2WT , or MFN2K357T , as well as double transfected with MFN2K357T /MFN2WT or MFN2K357T /MFN1WT .

RESULTS

SH-SY5Y cells transfected with MFN2K357T exhibited severe perinuclear mitochondrial clustering with axon-like processes devoid of mitochondria. Single transfection with MFN1WT resulted in a more interconnected mitochondrial network than transfection with MFN2WT , accompanied by mitochondrial clusters. Double transfection of MFN2K357T with either MFN1WT or MFN2WT resolved the mutant-induced mitochondrial clusters and led to detectable mitochondria throughout the axon-like processes. MFN1WT showed higher efficacy than MFN2WT in rescuing these defects.

INTERPRETATION

These results further demonstrate the higher potential of MFN1WT over MFN2WT overexpression to rescue CMT2A-induced mitochondrial network abnormalities due to mutations outside the GTPase domain. This higher phenotypic rescue conferred by MFN1WT , possibly due to its higher mitochondrial fusogenic ability, may be applied to different CMT2A cases regardless of the MFN2 mutation type.

Preliminary In Vitro and In Vivo Insights of In Silico Candidate Repurposed Drugs for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease and is the most common type of dementia. Although a considerably large amount of money has been invested in drug development for AD, no disease modifying treatment has been detected so far. In our previous work, we developed a computational method to highlight stage-specific candidate repurposed drugs against AD. In this study, we tested the effect of the top 13 candidate repurposed drugs that we proposed in our previous work in a severity stage-specific manner using an in vitro BACE1 assay and the effect of a top-ranked drug from the list of our previous work, tetrabenazine (TBZ), in the 5XFAD as an AD mouse model. From our in vitro screening, we detected 2 compounds (clomiphene citrate and Pik-90) that showed statistically significant inhibition against the activity of the BACE1 enzyme. The administration of TBZ at the selected dose and therapeutic regimen in 5XFAD in male and female mice showed no significant effect in behavioral tests using the Y-maze and the ELISA immunoassay of Aβ40. To our knowledge, this is the first time the drug tetrabenazine has been tested in the 5XFAD mouse model of AD in a sex-stratified manner. Our results highlight 2 drugs (clomiphene citrate and Pik-90) from our previous computational work for further investigation.

Charcot-Marie-Tooth neuropathies: current gene therapy advances and the route towards translation

Charcot-Marie-Tooth (CMT) neuropathies are a group of genetically and phenotypically heterogeneous disorders that predominantly affect the peripheral nervous system. Unravelling the genetic and molecular mechanisms, as well as the cellular effects of CMT mutations has facilitated the development of promising gene therapy approaches. Proposed gene therapy treatments for CMTs include virally or non-virally mediated gene replacement, addition, silencing, modification and editing of genetic material. For most CMT neuropathies gene- and disease- and even mutation- specific therapy approaches targeting the neuronal axon or myelinating Schwann cells may be needed, due to the diversity of underlying cellular and molecular-genetic mechanisms. The efficiency of gene therapies to improve the disease phenotype has been tested mostly in vitro and in in vivo rodent models that reproduce different molecular and pathological aspects of CMT neuropathies. In the next stage, bigger animal models, in particular non-human-primates, provide important insights into the translatability of the proposed administration and dosing, demonstrating scale-up potential and safety. The path towards clinical trials is faced with further challenges, but is becoming increasingly feasible owing to the progress and knowledge gained from clinical applications of gene therapies for other neurological disorders, as well as the emergence of sensitive outcome measures and biomarkers in patients with CMT neuropathies. This article is protected by copyright. All rights reserved.

Glial Gap Junction Pathology in the Spinal Cord of the 5xFAD Mouse Model of Early-Onset Alzheimer's Disease

Gap junctions (GJs) are specialized transmembrane channels assembled by two hemi-channels of six connexin (Cx) proteins that facilitate neuroglial crosstalk in the central nervous system (CNS). Previous studies confirmed the crucial role of glial GJs in neurodegenerative disorders with dementia or motor dysfunction including Alzheimer's disease (AD). The aim of this study was to examine the alterations in astrocyte and related oligodendrocyte GJs in association with Aβ plaques in the spinal cord of the 5xFAD mouse model of AD. Our analysis revealed abundant Aβ plaque deposition, activated microglia, and astrogliosis in 12-month-old (12M) 5xFAD mice, with significant impairment of motor performance starting from 3-months (3M) of age. Additionally, 12M 5xFAD mice displayed increased immunoreactivity of astroglial Cx43 and Cx30 surrounding Aβ plaques and higher protein levels, indicating upregulated astrocyte-to-astrocyte GJ connectivity. In addition, they demonstrated increased numbers of mature CC1-positive and precursor oligodendrocytes (OPCs) with higher immunoreactivity of Cx47-positive GJs in individual cells. Moreover, total Cx47 protein levels were significantly elevated in 12M 5xFAD, reflecting increased oligodendrocyte-to-oligodendrocyte Cx47-Cx47 GJ connectivity. In contrast, we observed a marked reduction in Cx32 protein levels in 12M 5xFAD spinal cords compared with controls, while qRT-PCR analysis revealed a significant upregulation in Cx32 mRNA levels. Finally, myelin deficits were found focally in the areas occupied by Aβ plaques, whereas axons themselves remained preserved. Overall, our data provide novel insights into the altered glial GJ expression in the spinal cord of the 5xFAD model of AD and the implicated role of GJ pathology in neurodegeneration. Further investigation to understand the functional consequences of these extensive alterations in oligodendrocyte-astrocyte (O/A) GJ connectivity is warranted.

Efficacy of AAV serotypes to target Schwann cells after intrathecal and intravenous delivery

To optimize gene delivery to myelinating Schwann cells we compared clinically relevant AAV serotypes and injection routes. AAV9 and AAVrh10 vectors expressing either EGFP or the neuropathy-associated gene GJB1/Connexin32 (Cx32) under a myelin specific promoter were injected intrathecally or intravenously in wild type and Gjb1-null mice, respectively. Vector biodistribution in lumbar roots and sciatic nerves was higher in AAVrh10 injected mice while EGFP and Cx32 expression rates and levels were similar between the two serotypes. A gradient of biodistribution away from the injection site was seen with both intrathecal and intravenous delivery, while similar expression rates were achieved despite higher vector amounts injected intravenously. Quantified immune cells in relevant tissues were similar to non-injected littermates. Overall, AAV9 and AAVrh10 efficiently transduce Schwann cells throughout the peripheral nervous system with both clinically relevant routes of administration, although AAV9 and intrathecal injection may offer a more efficient approach for treating demyelinating neuropathies.

Dysregulation of Blood-Brain Barrier and Exacerbated Inflammatory Response in Cx47-Deficient Mice after Induction of EAE

Induction of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), in connexin 32 (Cx32) or Cx47 knockout (KO) mice with deficiency in oligodendrocyte gap junctions (GJs) results in a more severe disease course. In particular, Cx47 KO EAE mice experience an earlier EAE onset and more pronounced disease severity, accompanied by dysregulated pro-inflammatory responses preceding the disease manifestations. In this study, analysis of relevant pro-inflammatory cytokines in wild type EAE, Cx32 KO EAE, and Cx47 KO EAE mice revealed altered expression of Vcam-1 preceding EAE [7 days post injection (dpi)], of Ccl2 at the onset of EAE (12 dpi), and of Gm-csf at the peak of EAE (24 dpi) in Cx47 KO EAE mice. Moreover, Cx47 KO EAE mice exhibited more severe blood-spinal cord barrier (BSCB) disruption, enhanced astrogliosis with defects in tight junction formation at the glia limitans, and increased T-cell infiltration prior to disease onset. Thus, Cx47 deficiency appears to cause dysregulation of the inflammatory profile and BSCB integrity, promoting early astrocyte responses in Cx47 KO EAE mice that lead to a more severe EAE outcome. Further investigation into the role of oligodendrocytic Cx47 in EAE and multiple sclerosis pathology is warranted.

Emerging Therapies for Charcot-Marie-Tooth Inherited Neuropathies

Inherited neuropathies known as Charcot-Marie-Tooth (CMT) disease are genetically heterogeneous disorders affecting the peripheral nerves, causing significant and slowly progressive disability over the lifespan. The discovery of their diverse molecular genetic mechanisms over the past three decades has provided the basis for developing a wide range of therapeutics, leading to an exciting era of finding treatments for this, until now, incurable group of diseases. Many treatment approaches, including gene silencing and gene replacement therapies, as well as small molecule treatments are currently in preclinical testing while several have also reached clinical trial stage. Some of the treatment approaches are disease-specific targeted to the unique disease mechanism of each CMT form, while other therapeutics target common pathways shared by several or all CMT types. As promising treatments reach the stage of clinical translation, optimal outcome measures, novel biomarkers and appropriate trial designs are crucial in order to facilitate successful testing and validation of novel treatments for CMT patients.

Novel GJA1/Cx43 Variant Associated With Oculo-Dento-Digital Dysplasia Syndrome: Clinical Phenotype and Cellular Mechanisms

Oculodentodigital dysplasia syndrome is associated with numerous pathogenic variants in GJA1, the gene encoding connexin43 gap junction protein. A novel in-frame deletion (p.Lys134del) was found in our clinic. The patient showed all the typical dysmorphic features of the syndrome. The functional consequences of this variant were also studied in an in vitro system. Cells expressed significantly less number of gap junction plaques with a great number of them retained intracellularly.

Altered Expression of Glial Gap Junction Proteins Cx43, Cx30, and Cx47 in the 5XFAD Model of Alzheimer's Disease

Glial gap junction proteins, called connexins (Cxs), form gap junctions in the central nervous system (CNS) to allow the bidirectional cytosolic exchange of molecules between adjacent cells. Their involvement in inheritable diseases and the use of experimental animal models that closely mimic such diseases revealed the critical role of glial GJs in myelination and homeostasis. Cxs are also implicated in acquired demyelinating disorders, such as Multiple Sclerosis (MS) and Alzheimer's disease (AD). Animal and human studies have revealed a role of the astrocytic Cx43 in the progression of AD but the role of Cx47, which is the main partner of Cx43 in the astrocyte-oligodendrocyte GJs is still unknown. The aim of this study was to investigate the astrocytic connexins, Cx43 and Cx30 in relation to oligodendrocytic Cx47 in the cortex and thalamus of the 5XFAD mouse model of AD. The model was characterized by increased Aβ deposition, gliosis, neuronal loss, and memory impairment. Compared to wild-type mice, Cx43 and Cx30 showed increased immunoreactivity in older 5XFAD mice, reflecting astrogliosis, while Cx47 immunoreactivity was reduced. Moreover, Cx47 GJ plaques showed reduced colocalization with Cx43 plaques. Oligodendrocyte precursor cells (OPCs) and mature oligodendrocyte populations were also depleted, and myelin deficits were observed. Our findings indicate reduced astrocyte-oligodendrocyte gap junction connectivity and possibly a shift in Cx43 expression toward astrocyte-astrocyte gap junctions and/or hemichannels, that could impair oligodendrocyte homeostasis and myelination. However, other factors, such as Aβ toxicity, could directly affect oligodendrocyte survival in AD. Our study provides evidence that Cxs might have implications in the progression of AD, although the role of oligodendrocyte Cxs in AD requires further investigation.

Gene therapy approaches targeting Schwann cells for demyelinating neuropathies

Charcot-Marie-Tooth disease (CMT) encompasses numerous genetically heterogeneous inherited neuropathies, which together are one of the commonest neurogenetic disorders. Axonal CMT types result from mutations in neuronally expressed genes, whereas demyelinating CMT forms mostly result from mutations in genes expressed by myelinating Schwann cells. The demyelinating forms are the most common, and may be caused by dominant mutations and gene dosage effects (as in CMT1), as well as by recessive mutations and loss of function mechanisms (as in CMT4). The discovery of causative genes and increasing insights into molecular mechanisms through the study of experimental disease models has provided the basis for the development of gene therapy approaches. For demyelinating CMT, gene silencing or gene replacement strategies need to be targeted to Schwann cells. Progress in gene replacement for two different CMT forms, including CMT1X caused by GJB1 gene mutations, and CMT4C, caused by SH3TC2 gene mutations, has been made through the use of a myelin-specific promoter to restrict expression in Schwann cells, and by lumbar intrathecal delivery of lentiviral viral vectors to achieve more widespread biodistribution in the peripheral nervous system. This review summarizes the molecular-genetic mechanisms of selected demyelinating CMT neuropathies and the progress made so far, as well as the remaining challenges in the path towards a gene therapy to treat these disorders through the use of optimal gene therapy tools including clinically translatable delivery methods and adeno-associated viral (AAV) vectors.

Gene replacement therapy after neuropathy onset provides therapeutic benefit in a model of CMT1X

X-linked Charcot-Marie-Tooth disease (CMT1X), one of the commonest forms of inherited demyelinating neuropathy, results from GJB1 gene mutations causing loss of function of the gap junction protein connexin32 (Cx32). The aim of this study was to examine whether delayed gene replacement therapy after the onset of peripheral neuropathy can provide a therapeutic benefit in the Gjb1-null/Cx32 knockout model of CMT1X. After delivery of the LV-Mpz.GJB1 lentiviral vector by a single lumbar intrathecal injection into 6-month-old Gjb1-null mice, we confirmed expression of Cx32 in lumbar roots and sciatic nerves correctly localized at the paranodal myelin areas. Gjb1-null mice treated with LV-Mpz.GJB1 compared with LV-Mpz.Egfp (mock) vector at the age of 6 months showed improved motor performance at 8 and 10 months. Furthermore, treated mice showed increased sciatic nerve conduction velocities, improvement of myelination and reduced inflammation in lumbar roots and peripheral nerves at 10 months of age, along with enhanced quadriceps muscle innervation. Plasma neurofilament light (NEFL) levels, a clinically relevant biomarker, were also ameliorated in fully treated mice. Intrathecal gene delivery after the onset of peripheral neuropathy offers a significant therapeutic benefit in this disease model, providing a proof of principle for treating patients with CMT1X at different ages.

Gene replacement therapy in a model of Charcot-Marie-Tooth 4C neuropathy

Charcot-Marie-Tooth disease type 4C is the most common recessively inherited demyelinating neuropathy that results from loss of function mutations in the SH3TC2 gene. Sh3tc2-/- mice represent a well characterized disease model developing early onset progressive peripheral neuropathy with hypo- and demyelination, slowing of nerve conduction velocities and disturbed nodal architecture. The aim of this project was to develop a gene replacement therapy for treating Charcot-Marie-Tooth disease type 4C to rescue the phenotype of the Sh3tc2-/- mouse model. We generated a lentiviral vector LV-Mpz.SH3TC2.myc to drive expression of the human SH3TC2 cDNA under the control of the Mpz promoter specifically in myelinating Schwann cells. The vector was delivered into 3-week-old Sh3tc2-/- mice by lumbar intrathecal injection and gene expression was assessed 4-8 weeks after injection. Immunofluorescence analysis showed presence of myc-tagged human SH3TC2 in sciatic nerves and lumbar roots in the perinuclear cytoplasm of a subset of Schwann cells, in a dotted pattern co-localizing with physiologically interacting protein Rab11. Quantitative PCR analysis confirmed SH3TC2 mRNA expression in different peripheral nervous system tissues. A treatment trial was initiated in 3 weeks old randomized Sh3tc2-/- littermate mice which received either the full or mock (LV-Mpz.Egfp) vector. Behavioural analysis 8 weeks after injection showed improved motor performance in rotarod and foot grip tests in treated Sh3tc2-/- mice compared to mock vector-treated animals. Moreover, motor nerve conduction velocities were increased in treated Sh3tc2-/- mice. On a structural level, morphological analysis revealed significant improvement in g-ratios, myelin thickness, and ratios of demyelinated fibres in lumbar roots and sciatic nerves of treated Sh3tc2-/- mice. Finally, treated mice also showed improved nodal molecular architecture and reduction of blood neurofilament light levels, a clinically relevant biomarker for axonal injury/degeneration. This study provides a proof of principle for viral gene replacement therapy targeted to Schwann cells to treat Charcot-Marie-Tooth disease type 4C and potentially other similar demyelinating inherited neuropathies.

Regulatory role of oligodendrocyte gap junctions in inflammatory demyelination

Gap junctions (GJs) coupling oligodendrocytes to astrocytes and to other oligodendrocytes are formed mainly by connexin47 (Cx47) and a smaller portion by connexin32 (Cx32). Mutations in both connexins cause inherited demyelinating disorders, but their expression is also disrupted in multiple sclerosis (MS). To clarify whether the loss of either Cx47 or Cx32 could modify the outcome of inflammation and myelin loss, we induced experimental autoimmune encephalomyelitis (EAE) in fully backcrossed Cx32 knockout (KO) and Cx47KO mice and compared their outcome with wild type (WT, C57BI/6 N) mice. Cx47KO EAE mice developed the most severe phenotype assessed by clinical scores and behavioral testing, followed by Cx32KO and WT mice. Cx47KO more than Cx32KO EAE mice developed more microglial activation, myelin, and axonal loss than did WT mice. Oligodendrocyte apoptosis and precursor proliferation was also higher in Cx47KO than in Cx32KO or WT EAE mice. Similarly, blood-spinal cord barrier (BSCB) disruption and inflammatory infiltrates of macrophages, T- and B-cells were more severe in Cx47KO than either Cx32KO or WT EAE groups. Finally, expression profiling revealed that several proinflammatory cytokines were higher at the peak of inflammation in the Cx47KO mice and persisted at later stages of EAE in contrast to reduction of their levels in WT EAE mice. Thus, loss of oligodendrocyte GJs aggravates BSCB disruption and inflammatory myelin loss, likely due to dysregulation of proinflammatory cytokines. This mechanism may play an important role in MS brain with reduced connexin expression, as well as in patients with inherited mutations in oligodendrocyte connexins and secondary inflammation.

Intrathecal gene therapy in mouse models expressing CMT1X mutations

Gap junction beta-1 (GJB1) gene mutations affecting the gap junction protein connexin32 (Cx32) cause the X-linked Charcot-Marie-Tooth disease (CMT1X), a common inherited neuropathy. Targeted expression of virally delivered Cx32 in Schwann cells following intrathecal injection of lentiviral vectors in the Cx32 knockout (KO) mouse model of the disease has led to morphological and functional improvement. To examine whether this approach could be effective in CMT1X patients expressing different Cx32 mutants, we treated transgenic Cx32 KO mice expressing the T55I, R75W or N175D CMT1X mutations. All three mutants were localized in the perinuclear compartment of myelinating Schwann cells consistent with retention in the ER (T55I) or Golgi (R75W, N175D) and loss of physiological expression in the non-compact myelin. Following intrathecal delivery of the GJB1 gene we detected the virally delivered wild-type (WT) Cx32 in non-compact myelin of T55I KO mice, but only rarely in N175D KO or R75W KO mice, suggesting dominant-negative effects of the R75W and N175D mutants but not of the T55I mutant on co-expressed WT Cx32. GJB1 treated T55I KO mice showed improved motor performance, lower ratios of abnormally myelinated fibers and reduction of inflammatory cells in spinal roots and peripheral nerves compared with mock-treated littermates. Either partial (N175D KO) or no (R75W KO) improvement was observed in the other two mutant lines. Thus, certain CMT1X mutants may interfere with gene addition therapy for CMT1X. Whereas gene addition can be used for non-interfering CMT1X mutations, further studies will be needed to develop treatments for patients harboring interfering mutations.

Golgi-retained Cx32 mutants interfere with gene addition therapy for CMT1X

Numerous GJB1 gene mutations cause the X-linked form of Charcot-Marie-Tooth disease (CMT1X). GJB1 encodes connexin32 (Cx32), which forms trans-myelin gap junctions in Schwann cells. Most GJB1 mutations result in loss-of-function mechanisms, supporting the concept of gene replacement therapy. However, interactions between delivered wild type and endogenously expressed mutant Cx32 may potentially occur in the setting of gene replacement therapy. In order to screen for possible interactions of several representative CMT1X mutants with wild type Cx32 that may interfere with the functional gap junction formation, we established an in vitro screening method co-expressing in HeLa cells wild type Cx32 and one of eight different Cx32 mutants including A39P, A39V, T55I, R75W, M93V, L143P, N175D and R183S. Some of the Golgi-retained mutants hindered gap junction plaque assembly by Cx32 on the cell membrane, while co-immunoprecipitation analysis revealed a partial interaction of wild type protein with Golgi-retained mutants. Dye transfer studies confirmed that Golgi-retained R75W, M93V and N175D but not endoplasmic reticulum-retained T55I had a negative effect on wild type Cx32 function. Finally, in vivo intraneural delivery of the gene encoding the wild type Cx32 in mice bearing either the T55I or R75W mutation on Cx32 knockout background showed that virally delivered protein was correctly localized in mice expressing the endoplasmic reticulum-retained T55I whereas it did not traffic normally in mice expressing the Golgi-retained R75W. Thus, certain Golgi-retained Cx32 mutants may interfere with exogenously delivered Cx32. Screening for mutant-wild type Cx32 interactions should be considered prior to planning gene addition therapy for CMT1X.

Gene therapy targeting oligodendrocytes provides therapeutic benefit in a leukodystrophy model

Pelizaeus-Merzbacher-like disease or hypomyelinating leukodystrophy-2 is an autosomal recessively inherited leukodystrophy with childhood onset resulting from mutations in the gene encoding the gap junction protein connexin 47 (Cx47, encoded by GJC2). Cx47 is expressed specifically in oligodendrocytes and is crucial for gap junctional communication throughout the central nervous system. Previous studies confirmed that a cell autonomous loss-of-function mechanism underlies hypomyelinating leukodystrophy-2 and that transgenic oligodendrocyte-specific expression of another connexin, Cx32 (GJB1), can restore gap junctions in oligodendrocytes to achieve correction of the pathology in a disease model. To develop an oligodendrocyte-targeted gene therapy, we cloned the GJC2/Cx47 gene under the myelin basic protein promoter and used an adeno-associated viral vector (AAV.MBP.Cx47myc) to deliver the gene to postnatal Day 10 mice via a single intracerebral injection in the internal capsule area. Lasting Cx47 expression specifically in oligodendrocytes was detected in Cx47 single knockout and Cx32/Cx47 double knockout mice up to 12 weeks post-injection, including the corpus callosum and the internal capsule but also in more distant areas of the cerebrum and in the spinal cord. Application of this oligodendrocyte-targeted somatic gene therapy at postnatal Day 10 in groups of double knockout mice, a well characterized model of hypomyelinating leukodystrophy-2, resulted in significant improvement in motor performance and coordination at 1 month of age in treated compared to mock-treated mice, as well as prolonged survival. Furthermore, immunofluorescence and morphological analysis revealed improvement in demyelination, oligodendrocyte apoptosis, inflammation, and astrogliosis, all typical features of this leukodystrophy model in both brain and spinal cord. Functional dye transfer analysis confirmed the re-establishment of oligodendrocyte gap junctional connectivity in treated as opposed to untreated mice. These results provide a significant advance in the development of oligodendrocyte-cell specific gene therapy. Adeno-associated viral vectors can be used to target therapeutic expression of a myelin gene to oligodendrocytes. We show evidence for the first somatic gene therapy approach to treat hypomyelinating leukodystrophy-2 preclinically, providing a potential treatment for this and similar forms of leukodystrophies.

Systemic inflammation disrupts oligodendrocyte gap junctions and induces ER stress in a model of CNS manifestations of X-linked Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth disease (CMT1X) is a common form of inherited neuropathy resulting from different mutations affecting the gap junction (GJ) protein connexin32 (Cx32). A subset of CMT1X patients may additionally present with acute fulminant CNS dysfunction, typically triggered by conditions of systemic inflammation and metabolic stress. To clarify the underlying mechanisms of CNS phenotypes in CMT1X we studied a mouse model of systemic inflammation induced by lipopolysaccharide (LPS) injection to compare wild type (WT), connexin32 (Cx32) knockout (KO), and KO T55I mice expressing the T55I Cx32 mutation associated with CNS phenotypes. Following a single intraperitoneal LPS or saline (controls) injection at the age of 40-60 days systemic inflammatory response was documented by elevated TNF-α and IL-6 levels in peripheral blood and mice were evaluated 1 week after injection. Behavioral analysis showed graded impairment of motor performance in LPS treated mice, worse in KO T55I than in Cx32 KO and in Cx32 KO worse than WT. Iba1 immunostaining revealed widespread inflammation in LPS treated mice with diffusely activated microglia throughout the CNS. Immunostaining for the remaining major oligodendrocyte connexin Cx47 and for its astrocytic partner Cx43 revealed widely reduced expression of Cx43 and loss of Cx47 GJs in oligodendrocytes. Real-time PCR and immunoblot analysis indicated primarily a down regulation of Cx43 expression with secondary loss of Cx47 membrane localization. Inflammatory changes and connexin alterations were most severe in the KO T55I group. To examine why the presence of the T55I mutant exacerbates pathology even more than in Cx32 KO mice, we analyzed the expression of ER-stress markers BiP, Fas and CHOP by immunostaining, immunoblot and Real-time PCR. All markers were increased in LPS treated KO T55I mice more than in other genotypes. In conclusion, LPS induced neuroinflammation causes disruption of the main astrocyte-oligodendrocyte GJs, which may contribute to the increased sensitivity of Cx32 KO mice to LPS and of patients with CMT1X to various stressors. Moreover the presence of an intracellularly retained, misfolded CMT1X mutant such as T55I induces ER stress under inflammatory conditions, further exacerbating oligodendrocyte dysfunction and pathological changes in the CNS.

Oxaliplatin-induced neurotoxicity is mediated through gap junction channels and hemichannels and can be prevented by octanol

Oxaliplatin-induced neurotoxicity (OIN) is a common complication of chemotherapy without effective treatment. In order to clarify the mechanisms of both acute and chronic OIN, we used an ex-vivo mouse sciatic nerve model. Exposure to 25 μM oxaliplatin caused a marked prolongation in the duration of the nerve evoked compound action potential (CAP) by nearly 1200% within 300 min while amplitude remained constant for over 20 h. This oxaliplatin effect was almost completely reversed by the gap junction (GJ) inhibitor octanol in a concentration-dependent manner. Further GJ blockers showed similar effects although with a narrower therapeutic window. To clarify the target molecule we studied sciatic nerves from connexin32 (Cx32) and Cx29 knockout (KO) mice. The oxaliplatin effect and neuroprotection by octanol partially persisted in Cx29 better than in Cx32 KO nerves, suggesting that oxaliplatin affects both, but Cx32 GJ channels more than Cx29 hemichannels. Oxaliplatin also accelerated neurobiotin uptake in HeLa cells expressing the human ortholog of Cx29, Cx31.3, as well as dye transfer between cells expressing the human Cx32, and this effect was blocked by octanol. Oxaliplatin caused no morphological changes initially (up to 3 h of exposure), but prolonged nerve exposure caused juxtaparonodal axonal edema, which was prevented by octanol. Our study indicates that oxaliplatin causes forced opening of Cx32 channels and Cx29 hemichannels in peripheral myelinated fibers leading to disruption of axonal K(+) homeostasis. The GJ blocker octanol prevents OIN at very low concentrations and should be further studied as a neuroprotectant.

Gene delivery targeted to oligodendrocytes using a lentiviral vector

BACKGROUND

Most leukodystrophies result from mutations in genes expressed in oligodendrocytes that may cause autonomous loss of function of cell structural proteins. Therefore, effective gene delivery to oligodendrocytes is necessary to develop future treatments.

MATERIALS

To achieve this, we cloned a lentiviral vector in which the enhanced green fluorescent protein (EGFP) expression was driven by the oligodendrocyte specific 2,3-cyclic nucleotide 3-phosphodiesterase promoter. The vector was inserted into C57BL/6 neonatal mouse brain by combined intraventricular and parenchymal injections.

RESULTS

Assessment of EGFP expression revealed a widespread distribution, specifically in cells of the oligodendrocyte linage, starting from postnatal day 6 (P6) in the subventricular zone and spreading through migrating oligodendrocyte precursors. By P30, it was detectable throughout the brain and persisted for at least 3 months, showing an increase both in the number of expressing cells and in intensity over time. EGFP expression was restricted to oligodendrocyte linage cells. On average, 20.3 ± 2.56% of all oligodendrocytes in different central nervous system areas were EGFP-positive, with regional variations.

CONCLUSIONS

Lentiviral gene delivery using an oligodendrocyte-specific promoter may achieve widespread and long-lasting expression selectively in oligodendrocytes, offering a possibility for gene therapy in certain leukodystrophies, although the relatively low rates of oligodendrocyte transduction are a limitation that remains to be overcome.

Intraneural GJB1 gene delivery improves nerve pathology in a model of X-linked Charcot-Marie-Tooth disease

OBJECTIVE

X-linked Charcot-Marie-Tooth disease (CMT1X) is a common inherited neuropathy caused by mutations in the GJB1 gene encoding the gap junction protein connexin32 (Cx32). Clinical studies and disease models indicate that neuropathy mainly results from Schwann cell autonomous, loss-of-function mechanisms; therefore, CMT1X may be treatable by gene replacement.

METHODS

A lentiviral vector LV.Mpz-GJB1 carrying the GJB1 gene under the Schwann cell-specific myelin protein zero (Mpz) promoter was generated and delivered into the mouse sciatic nerve by a single injection immediately distal to the sciatic notch. Enhanced green fluorescent protein (EGFP) reporter gene expression was quantified and Cx32 expression was examined on a Cx32 knockout (KO) background. A gene therapy trial was performed in a Cx32 KO model of CMT1X.

RESULTS

EGFP was expressed throughout the length of the sciatic nerve in up to 50% of Schwann cells starting 2 weeks after injection and remaining stable for up to 16 weeks. Following LV.Mpz-GJB1 injection into Cx32 KO nerves, we detected Cx32 expression and correct localization in non-compact myelin areas where gap junctions are normally formed. Gene therapy trial by intraneural injection in groups of 2-month-old Cx32 KO mice, before demyelination onset, significantly reduced the ratio of abnormally myelinated fibers (p = 0.00148) and secondary inflammation (p = 0.0178) at 6 months of age compared to mock-treated animals.

INTERPRETATION

Gene delivery using a lentiviral vector leads to efficient gene expression specifically in Schwann cells. Restoration of Cx32 expression ameliorates nerve pathology in a disease model and provides a promising approach for future treatments of CMT1X and other inherited neuropathies.

A start codon CMT1X mutation associated with transient encephalomyelitis causes complete loss of Cx32

X-linked Charcot-Marie-Tooth disease (CMTX1) results from numerous mutations in the GJB1 gene encoding the gap junction protein connexin32 (Cx32) and is one of the commonest forms of inherited neuropathy. Owing to the expression of Cx32 not only in Schwann cells but also in oligodendrocytes, a subset of CMT1X patients develops central nervous system (CNS) clinical manifestations in addition to peripheral neuropathy. While most GJB1 mutations appear to cause peripheral neuropathy through loss of Cx32 function, the cellular mechanisms underlying the CNS manifestations remain controversial. A novel start codon GJB1 mutation (p.Met1Ile) has been found in a CMT1X patient presenting with recurrent episodes of transient encephalomyelitis without apparent signs of peripheral neuropathy. In order to clarify the functional consequences of this mutation, we examined the cellular expression of two different constructs cloned from genomic DNA including the mutated start codon. None of the cloned constructs resulted in detectable expression of Cx32 by immunocytochemistry or immunoblot, although mRNA was produced at normal levels. Furthermore, co-expression with the other major oligodendrocyte connexin, Cx47, had no negative effect on GJ formation by Cx47. Finally, lysosomal and proteasomal inhibition in cells expressing the start codon mutant constructs failed to recover any detection of Cx32 as a result of impaired protein degradation. Our results indicate that the Cx32 start codon mutation is equivalent to a complete loss of the protein with failure of translation, although transcription is not impaired. Thus, complete loss of Cx32 function is sufficient to produce CNS dysfunction with clinical manifestations.

Transgenic replacement of Cx32 in gap junction-deficient oligodendrocytes rescues the phenotype of a hypomyelinating leukodystrophy model

Oligodendrocytes are coupled by gap junctions (GJs) formed mainly by connexin47 (Cx47) and Cx32. Recessive GJC2/Cx47 mutations cause Pelizaeus-Merzbacher-like disease, a hypomyelinating leukodystrophy, while GJB1/Cx32 mutations cause neuropathy and chronic or acute-transient encephalopathy syndromes. Cx32/Cx47 double knockout (Cx32/Cx47dKO) mice develop severe CNS demyelination beginning at 1 month of age leading to death within weeks, offering a relevant model to study disease mechanisms. In order to clarify whether the loss of oligodendrocyte connexins has cell autonomous effects, we generated transgenic mice expressing the wild-type human Cx32 under the control of the mouse proteolipid protein promoter, obtaining exogenous hCx32 expression in oligodendrocytes. By crossing these mice with Cx32KO mice, we obtained expression of hCx32 on Cx32KO background. Immunohistochemical and immunoblot analysis confirmed strong CNS expression of hCx32 specifically in oligodendrocytes and correct localization forming GJs at cell bodies and along the myelin sheath. TG(+)Cx32/Cx47dKO mice generated by further crossing with Cx47KO mice showed that transgenic expression of hCx32 rescued the severe early phenotype of CNS demyelination in Cx32/Cx47dKO mice, resulting in marked improvement of behavioral abnormalities at 1 month of age, and preventing the early mortality. Furthermore, TG(+)Cx32/Cx47dKO mice showed significant improvement of myelination compared with Cx32/Cx47dKO CNS at 1 month of age, while the inflammatory and astrogliotic changes were fully reversed. Our study confirms that loss of oligodendrocyte GJs has cell autonomous effects and that re-establishment of GJ connectivity by replacement of least one GJ protein provides correction of the leukodystrophy phenotype.

Disruption of oligodendrocyte gap junctions in experimental autoimmune encephalomyelitis

Gap junctions (GJs) are vital for oligodendrocyte survival and myelination. In order to examine how different stages of inflammatory demyelination affect oligodendrocyte GJs, we studied the expression of oligodendrocytic connexin32 (Cx32) and Cx47 and astrocytic Cx43 in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis (MS) induced by recombinant myelin oligodendrocyte glycoprotein. EAE was characterized by remissions and relapses with demyelination and axonal loss. Formation of GJ plaques was quantified in relation to the lesions and in normal appearing white matter (NAWM). During acute EAE at 14 days postimmunization (dpi) both Cx47 and Cx32 GJs were severely reduced within and around lesions but also in the NAWM. Cx47 was localized intracellularly in oligodendrocytes while protein levels remained unchanged, and this redistribution coincided with the loss of Cx43 GJs in astrocytes. Cx47 and Cx32 expression increased during remyelination at 28 dpi but decreased again at 50 dpi in the relapsing phase. Oligodendrocyte GJs remained reduced even in NAWM, despite increased formation of Cx43 GJs toward lesions indicating astrogliosis. EAE induced in Cx32 knockout mice resulted in an exacerbated clinical course with more demyelination and axonal loss compared with wild-type EAE mice of the same backcross, despite similar degree of inflammation, and an overall milder loss of Cx47 and Cx43 GJs. Thus, EAE causes persistent impairment of both intra- and intercellular oligodendrocyte GJs even in the NAWM, which may be an important mechanism of MS progression. Furthermore, GJ deficient myelinated fibers appear more vulnerable to CNS inflammatory demyelination.

Gap junction pathology in multiple sclerosis lesions and normal-appearing white matter

Oligodendrocyte gap junctions (GJs) are vital for central nervous system myelination, but their involvement in multiple sclerosis (MS) pathology remains unknown. The aim of this study was to examine alterations of oligodendrocyte and related astrocyte GJs in MS lesions and normal-appearing white matter (NAWM). Post-mortem brain samples from 9 MS and 11 age-matched non-MS control patients were studied. Tissue sections that included both chronic active and inactive lesions were characterized neuropathologically with Luxol Fast Blue staining and immunostaining for myelin oligodendrocyte glycoprotein (MOG) and the microglial marker Iba1. We analyzed the expression of Cx32 and Cx47 in oligodendrocytes and of Cx43, the major astrocytic partner in oligodendrocyte-astrocyte (O/A) GJs by quantitative immunoblot and real-time PCR. Formation of GJ plaques was quantified by immunohistochemistry. Compared to control brains, both Cx32 and Cx47 GJ plaques and protein levels were reduced in and around MS lesions, while Cx43 was increased as part of astrogliosis. In the NAWM, Cx32 was significantly reduced along myelinated fibers whereas Cx47 showed increased expression mainly in oligodendrocyte precursor cells (OPCs). However, OPCs showed only limited connectivity to astrocytes. Cx43 showed modestly increased levels in MS NAWM compared to controls, while GJ plaque counts were unchanged. Our findings indicate that oligodendrocyte GJs are affected not only in chronic MS lesions but also in NAWM, where disruption of Cx32 GJs in myelinated fibers may impair myelin structure and function. Moreover, limited O/A GJ connectivity of recruited OPCs in the setting of persistent inflammation and astrogliosis may prevent differentiation and remyelination.

Angiocidin inhibits breast cancer proliferation through activation of epidermal growth factor receptor and nuclear factor kappa (NF-ĸB)

Angiocidin, a tumor-associated peptide, has been previously shown to inhibit tumor progression by blocking angiogenesis. We now show that angiocidin has a direct inhibitory effect on tumor cell proliferation. MDA-MB-231 breast cancer cells were inhibited from proliferating in the presence of epidermal growth factor (EGF) and angiocidin. Angiocidin transfected breast cancer cells also displayed growth inhibition in vitro and failed to develop significant tumors in mice as compared to vector controls. The anti-proliferative effect of angiocidin was reversed by treating the cells with the epidermal growth factor receptor (EGFR) inhibitor 4557W, a potent tyrosine kinase inhibitor. Consistent with these results, we found that treatment of breast cancer cells with angiocidin induced a 2.3 fold increase in EGFR tyrosine 845 phosphorylation while no change in phosphorylation was observed in the remaining 16 phosphorylation sites of EGFR and those of its family members as measured by a human EGFR phosphorylation array. Treatment of breast cancer cells with angiocidin also resulted in the activation of nuclear factor ĸB (Nf-ĸB) and the de novo up-regulation of many down-stream genes transcribed by Nf-ĸB, including cytokines, inflammatory mediators and the cell cycle inhibitor p21(waf1). Therefore, angiocidin is a peptide that not only inhibits tumor angiogenesis but also directly induces inhibition of tumor growth progression through the activation of EGFR and down-stream genes transcribed by Nf-ĸB.

Molecular mechanisms of gap junction mutations in myelinating cells

There is an emerging group of neurological disorders that result from genetic mutations affecting gap junction proteins in myelinating cells. The X-linked form of Charcot Marie Tooth disease (CMT1X) is caused by numerous mutations in the GJB1 gene encoding the gap junction protein connexin32 (Cx32), which is expressed in both Schwann cells in the PNS and oligodendrocytes in the CNS. Patients with CMT1X present mainly with a progressive peripheral neuropathy, showing mixed axonal and demyelinating features. In many cases there is also clinical or subclinical involvement of the CNS with acute or chronic phenotypes of encephalopathy. Furthermore, mutations in the GJA12/GJC2 gene encoding the gap junction protein Cx47, which is expressed in oligodendrocytes, have been identified in families with progressive leukodystrophy, known as Pelizaeus-Merzbacher-like disease, as well as in patients with hereditary spastic paraplegia. Recent studies have provided insights into the pattern of gap junction protein expression and function in CNS and PNS myelinating cells. Furthermore, in vitro and in vivo disease models have clarified some of the molecular and cellular mechanisms underlying these disorders. Here we provide an overview of the clinical, genetic, and neurobiological aspects of gap junction disorders affecting the nervous system.

Axonal pathology precedes demyelination in a mouse model of X-linked demyelinating/type I Charcot-Marie Tooth neuropathy

The X-linked demyelinating/type I Charcot-Marie-Tooth neuropathy (CMT1X) is an inherited peripheral neuropathy caused by mutations in GJB1, the gene that encodes the gap junction protein connexin32. Connexin32 is expressed by myelinating Schwann cells and forms gap junctions in noncompact myelin areas, but axonal involvement is more prominent in X-linked compared with other forms of demyelinating Charcot-Marie-Tooth disease. To clarify the cellular and molecular mechanisms of axonal pathology in CMT1X, we studied Gjb1-null mice at early stages (i.e. 2-4 months old) of the neuropathy, when there is minimal or no demyelination. The diameters of large myelinated axons were progressively reduced in Gjb1-null mice compared with those in wild-type littermates. Furthermore, neurofilaments were relatively more dephosphorylated and more densely packed starting at 2 months of age. Increased expression of β-amyloid precursor protein, a marker of axonal damage, was also detected in Gjb1-null nerves. Finally, fast axonal transport, assayed by sciatic nerve ligation experiments, was slower in distal axons of Gjb1-null versus wild-type animals with reduced accumulation of synaptic vesicle-associated proteins. These findings demonstrate that axonal abnormalities including impaired cytoskeletal organization and defects in axonal transport precede demyelination in this mouse model of CMT1X.

Connexin32 mutations cause loss of function in Schwann cells and oligodendrocytes leading to PNS and CNS myelination defects

The gap junction (GJ) protein connexin32 (Cx32) is expressed by myelinating Schwann cells and oligodendrocytes and is mutated in X-linked Charcot-Marie-Tooth disease. In addition to a demyelinating peripheral neuropathy, some Cx32 mutants are associated with transient or chronic CNS phenotypes. To investigate the molecular basis of these phenotypes, we generated transgenic mice expressing the T55I or the R75W mutation and an IRES-EGFP, driven by the mouse Cnp promoter. The transgene was expressed in oligodendrocytes throughout the CNS and in Schwann cells. Both the T55I and the R75W mutants were localized in the perinuclear cytoplasm, did not form GJ plaques, and did not alter the expression or localization of two other oligodendrocytic GJ proteins, Cx47 and Cx29, or the expression of Cx29 in Schwann cells. On wild type background, the expression of endogenous mCx32 was unaffected by the T55I mutant, but was partly impaired by R75W. Transgenic mice with the R75W mutation and all mutant animals with Gjb1-null background developed a progressive demyelinating peripheral neuropathy along with CNS myelination defects. These findings suggest that Cx32 mutations result in loss of function in myelinated cells without trans-dominant effects on other GJ proteins. Loss of Cx32 function alone in the CNS causes myelination defects.

Impairment of learning and memory in TAG-1 deficient mice associated with shorter CNS internodes and disrupted juxtaparanodes

The cell adhesion molecule TAG-1 is expressed by neurons and glial cells and plays a role in axon outgrowth, migration and fasciculation during development. TAG-1 is also required for the clustering of Kv1.1/1.2 potassium channels and Caspr2 at the juxtaparanodes of myelinated fibers. Behavioral examination of TAG-1 deficient mice (Tag-1(-/-)) showed cognitive impairments in the Morris water maze and novel object recognition tests, reduced spontaneous motor activity, abnormal gait coordination and increased response latency to noxious stimulation. Investigation at the molecular level revealed impaired juxtaparanodal clustering of Caspr2 and Kv1.1/1.2 in the hippocampus, entorhinal cortex, cerebellum and olfactory bulb, with diffusion into the internode. Caspr2 and Kv1.1 levels were reduced in the cerebellum and olfactory bulb. Moreover, Tag-1(-/-) mice had shorter internodes in the cerebral and cerebellar white matter. The detected molecular alterations may account for the behavioural deficits and hyperexcitability in these animals.

Human oligodendrocytes express Cx31.3: function and interactions with Cx32 mutants

Murine oligodendrocytes express the gap junction (GJ) proteins connexin32 (Cx32), Cx47, and Cx29. CNS phenotypes in patients with X-linked Charcot-Marie-Tooth disease may be caused by dominant effects of Cx32 mutations on other connexins. Here we examined the expression of Cx31.3 (the human ortholog of murine Cx29) in human brain and its relation to the other oligodendrocyte GJ proteins Cx32 and Cx47. Furthermore, we investigated in vitro whether Cx32 mutants with CNS manifestations affect the expression and function of Cx31.3. Cx31.3 was localized mostly in the gray matter along small myelinated fibers similar to Cx29 in rodent brain and was co-expressed with Cx32 in a subset of human oligodendrocytes. In HeLa cells Cx31.3 was localized at the cell membrane and appeared to form hemichannels but no GJs. Cx32 mutants with CNS manifestations were retained intracellularly, but did not alter the cellular localization or function of co-expressed Cx31.3. Thus, Cx31.3 shares many characteristics with its ortholog Cx29. Cx32 mutants with CNS phenotypes do not affect the trafficking or function of Cx31.3, and may have other toxic effects in oligodendrocytes.

Cloning and characterization of angiocidin, a tumor cell binding protein for thrombospondin-1

Thrombospondin-1 (TSP-1) is a matrix protein that has been implicated in mechanisms of tumor progression. Our laboratory previously showed that the CSVTCG (cys-ser-val-thr-cys-gly) sequence of TSP-1 functioned as a tumor cell adhesion domain and CSVTCG peptides as well as an anti-peptide antibody possessed anti-metastatic activity in a murine model of lung metastasis. In a subsequent study, a putative TSP-1 binding protein from lung carcinoma was isolated by CSVTCG-peptide affinity chromatography. In this study, we present the full-length cDNA of this binding protein isolated from a prostate cancer cell (PC3-NI) cDNA library. The purified recombinant protein, termed angiocidin, is a potent inhibitor of tumor growth of Lewis Lung carcinoma in vivo and tumor invasion and angiogenesis in vitro. In addition, the recombinant protein inhibits tumor and endothelial cell proliferation and induces apoptosis. The activity of angiocidin both in vivo and in vitro is partially dependent on its TSP-1 binding activity, since an angiocidin deletion mutant missing a high affinity-binding site for TSP-1 failed to inhibit tumor growth in vivo and was less active in its anti-tumor and anti-angiogenic activities in vitro. These results suggest that the anti-tumor activity of TSP-1 reported in many studies may be mediated in part by binding proteins such as angiocidin. Such proteins may function as tumor-suppressor proteins, which limit the growth of tumors by inhibiting angiogenesis and cell matrix interaction.

Mechanisms of thrombospondin-1-mediated metastasis and angiogenesis

The major route of tumor spread is through the bloodstream. Once in circulation, the tumor cells aggregate in clumps with platelets, which enhances the tumor cell survival. The tumor emboli will then adhere to the endothelium and by the release of proteases extravasation of the cells will occur. One of the platelet-secreted proteins is thrombospondin-1. In this article, thrombospondin-1 will be described as a modulator of angiogenesis through its role in regulating endothelial cell apoptosis, protease expression, and vascular endothelial growth factor expression. We hope to convey the idea that activity of thrombospondin-1 in tumor progression is dependent upon its interaction with several host- and tumor-associated proteins.

The role of thrombospondin-1 in tumor progression

The role of thrombospondin-1 (TSP-1) in tumor progression is both complex and controversial. It is clear from the literature that the function of TSP-1 in malignancy depends on the presence of other factors and the level of TSP-1 expression in the tumor tissue. High levels of TSP-1 secreted by tumors, which were engineered to overexpress TSP-1, inhibit tumor growth, while anti-sense inhibition of TSP-1 production in certain tumors also inhibits growth. Clearly, the presence of other factors in these experimental systems must be important. The role of TSP-1 in angiogenesis also depends on the levels of TSP-1, the presence and level of angiogenic stimulators such as basic fibroblast growth factor (bFGF), and the localization of TSP-1 in the tissue. Matrix-bound TSP-1 promotes capillary tube formation in the rat aorta model of angiogenesis, while TSP-1 inhibits bFGF- induced angiogenesis in the rat cornea model. The inhibitory effect also depends on the proteolytic state of TSP-1 since the amino terminus promotes angiogenesis in the cornea model, while the remaining 140-kDa fragment inhibits bFGF-induced angiogenesis. Both the stimulatory and inhibitory effects of TSP-1 are likely due to upregulation of matrix-degrading enzymes and their inhibitors. These enzymes are critical for maintaining optimal matrix turnover during angiogenesis. These varied TSP-1-dependent mechanisms offer new targets for the development of anti-angiogenic therapeutics for the treatment of a variety of cancers, as well as other pathologies involving inappropriate angiogenesis such as diabetic retinopathy.

The role of adhesive proteins in the hematogenous spread of cancer

The understanding of the mechanisms that control metastasis and invasion are critical for the identification of new targets for drug development. In this review we focused on two major pathways that mediate hematogenous cancer spread: the hemostatic system and cell adhesive interactions that lead to tumor invasion and angiogenesis. We describe the contribution of platelets and a number of adhesive proteins as well as their receptors that have recently been shown to play a role in metastasis. In addition, enzymes and their inhibitors that modulate cellular adhesive interactions are described. We hope that this summary will stimulate researchers in this area to focus their efforts on molecules that have recently been discovered. These molecules will not only lead to the fuller understanding of the "soil and seed" hypothesis proposed more than 100 years ago but also provide new therapeutic approaches for the treatment of metastatic disease.