Widespread disturbance in extracellular matrix collagen biomarker responses to teriparatide therapy in osteogenesis imperfecta.

Osteogenesis imperfecta (OI), a heritable disorder caused by abnormalities in synthesis or processing of type I collagen, is characterized by skeletal fragility. Type I collagen interacts with multiple components of the extracellular matrix (ECM) including other collagens types. Thus, alterations in structure or quantity may broadly affect ECM homeostasis. In fact, while OI is clinically categorized by severity of bone disease, patients can also present with extra-skeletal manifestations, including the pulmonary, muscle and cardiovascular systems. Parathyroid hormone (PTH) is a regulator of skeletal homeostasis but the receptor for PTH/PTH1R is expressed in a variety of other tissues. Given interactions between type I collagen with other collagens in the ECM and the potential for PTH action on tissues beyond the skeleton, we explored whether serum levels of non-type I collagens are altered in response to teriparatide (human parathyroid hormone 1-34). We measured biomarkers of collagens II, III, IV, V, and VI in serum from individuals with type I and types III/IV OI in response to an 18 month course of teriparatide or placebo. These results were compared to similar biomarker measures in postmenopausal (PM) women without OI treated with teriparatide. In type I OI, teriparatide therapy increased concentrations of biomarkers of collagens II, III, IV, V, and VI. In individuals with types III/IV OI these biomarker changes in response to teriparatide were blunted, as we previously reported with collagen I biomarkers during teriparatide therapy. In contrast to OI, in PM women there were no effects of teriparatide on the collagen biomarkers we assessed (II, V, and VI). These findings suggest that in OI teriparatide therapy has abnormal effects on the homeostasis of many ECM collagens likely derived from skeletal as well as extra-skeletal tissues.

Inhibition of myostatin prevents microgravity-induced loss of skeletal muscle mass and strength.

The microgravity conditions of prolonged spaceflight are known to result in skeletal muscle atrophy that leads to diminished functional performance. To assess if inhibition of the growth factor myostatin has potential to reverse these effects, mice were treated with a myostatin antibody while housed on the International Space Station. Grip strength of ground control mice increased 3.1% compared to baseline values over the 6 weeks of the study, whereas grip strength measured for the first time in space showed flight animals to be -7.8% decreased in strength compared to baseline values. Control mice in space exhibited, compared to ground-based controls, a smaller increase in DEXA-measured muscle mass (+3.9% vs +5.6% respectively) although the difference was not significant. All individual flight limb muscles analyzed (except for the EDL) weighed significantly less than their ground counterparts at the study end (range -4.4% to -28.4%). Treatment with myostatin antibody YN41 was able to prevent many of these space-induced muscle changes. YN41 was able to block the reduction in muscle grip strength caused by spaceflight and was able to significantly increase the weight of all muscles of flight mice (apart from the EDL). Muscles of YN41-treated flight mice weighed as much as muscles from Ground IgG mice, with the exception of the soleus, demonstrating the ability to prevent spaceflight-induced atrophy. Muscle gene expression analysis demonstrated significant effects of microgravity and myostatin inhibition on many genes. Gamt and Actc1 gene expression was modulated by microgravity and YN41 in opposing directions. Myostatin inhibition did not overcome the significant reduction of microgravity on femoral BMD nor did it increase femoral or vertebral BMD in ground control mice. In summary, myostatin inhibition may be an effective countermeasure to detrimental consequences of skeletal muscle under microgravity conditions.

Sustained Klotho delivery reduces serum phosphate in a model of diabetic nephropathy.

Diabetic nephropathy (DN) is a primary cause of end-stage renal disease and is becoming more prevalent because of the global rise in type 2 diabetes. A model of DN, the db/db uninephrectomized ( db/db-uni) mouse, is characterized by obesity, as well as compromised renal function. This model also manifests defects in mineral metabolism common in DN, including hyperphosphatemia, which leads to severe endocrine disease. The FGF23 coreceptor, α-Klotho, circulates as a soluble, cleaved form (cKL) and may directly influence phosphate handling. Our study sought to test the effects of cKL on mineral metabolism in db/db-uni mice. Mice were placed into either mild or moderate disease groups on the basis of the albumin-to-creatinine ratio (ACR). Body weights of db/db-uni mice were significantly greater across the study compared with lean controls regardless of disease severity. Adeno-associated cKL administration was associated with increased serum Klotho, intact, bioactive FGF23 (iFGF23), and COOH-terminal fragments of FGF23 ( P < 0.05). Blood urea nitrogen was improved after cKL administration, and cKL corrected hyperphosphatemia in the high- and low-ACR db/db-uni groups. Interestingly, 2 wk after cKL delivery, blood glucose levels were significantly reduced in db/db-uni mice with high ACR ( P < 0.05). Interestingly, several genes associated with stabilizing active iFGF23 were also increased in the osteoblastic UMR-106 cell line with cKL treatment. In summary, delivery of cKL to a model of DN normalized blood phosphate levels regardless of disease severity, supporting the concept that targeting cKL-affected pathways could provide future therapeutic avenues in DN. NEW & NOTEWORTHY In this work, systemic and continuous delivery of the "soluble" or "cleaved" form of the FGF23 coreceptor α-Klotho (cKL) via adeno-associated virus to a rodent model of diabetic nephropathy (DN), the db/db uninephrectomized mouse, normalized blood phosphate levels regardless of disease severity. This work supports the concept that targeting cKL-affected pathways could provide future therapeutic avenues for the severe mineral metabolism defects associated with DN.

Alterations in non-type I collagen biomarkers in osteogenesis imperfecta.

Osteogenesis imperfecta [1] is a rare disorder of connective tissue caused by abnormalities in the synthesis or processing of type I collagen. Type I collagen is the most abundant type of collagen and is expressed in almost all connective tissues. Given that type I collagen interacts with other collagens based in the extracellular matrix (ECM), we hypothesized changes in type I collagen in OI would result in perturbations in the homeostasis of other collagen types. We measured serum biomarkers of several non-type I collagens in patients with mild (type I) and moderate-to-severe (type III/IV) OI. Compared to controls, those with moderate-to severe OI had a higher mean level of the synthesis markers of collagen III (ProC3) (P = 0.02), and levels of collagen V (ProC5) (P = 0.07) were slightly, but not significantly, higher. Degradation markers of collage type IV (C4M2) (P = 0.04) and type VI (C6M) (P = 0.003) were also higher. In each case, a test for trend suggested levels were higher in moderate-to-severe OI, intermediate in mild OI, and lowest in controls (P = 0.06-0.002). These changes supports the hypothesis that mutations in type I collagen induce a widespread alteration in the ECM, and that the diverse clinical manifestations of OI reflect an extensive disruption in ECM biology.

Serum Sclerostin Levels in Adults With Osteogenesis Imperfecta: Comparison With Normal Individuals and Response to Teriparatide Therapy.

Sclerostin (SOST), a glycoprotein primarily derived from osteocytes, is an important regulator of bone remodeling. Osteogenesis imperfecta (OI) is a heritable disorder of bone characterized by low bone mass, bone fragility, recurrent fractures, and bone deformities. Altered SOST-mediated signaling may have a role in pathogenesis of type I collagen-related OI; however, this has not been evaluated in humans. We measured serum SOST levels in adults with OI who were enrolled in a randomized, placebo-controlled clinical trial that evaluated the effects of osteoanabolic therapy with teriparatide. Compared with age- and sex-matched control participants, mean SOST levels were lower in those with type I or types III/VI OI (p < 0.0001). Receiver operating curve analysis revealed that sclerostin alone or sclerostin plus bone mineral content discriminated patients with OI from controls (area under the curve 0.80 and 0.87, respectively). SOST levels increased in the group of patients with type I OI during therapy with teriparatide (compared with placebo, p = 0.01). The increase was significant at 6, 12, and 24 months of therapy (p ≤ 0.02) and was apparent as early as 3 months (p = 0.06). The magnitude of increases in SOST levels during therapy was inversely correlated with increases in vertebral volumetric bone mineral density (vBMD). Overall, these results suggest that: 1) SOST regulation is fundamentally altered in osteogenesis imperfecta; 2) serum SOST levels could be a biomarker of OI in adults; and 3) alterations in SOST may help predict the response to anabolic therapies in OI. © 2017 American Society for Bone and Mineral Research.

Loss of inversin decreases transepithelial sodium transport in murine renal cells.

Type II nephronophthisis (NPHP2) is an autosomal recessive renal cystic disorder characterized by mutations in the inversin gene. Humans and mice with mutations in inversin have enlarged cystic kidneys that may be due to fluid accumulation resulting from altered ion transport. To address this, transepithelial ion transport was measured in shRNA-mediated inversin-depleted mouse cortical collecting duct (mCCD) cells. Loss of inversin decreased the basal ion flux in mCCD cells compared with controls. Depletion of inversin decreased vasopressin-induced Na+ absorption but did not alter Cl- secretion by mCCD cells. Addition of amiloride, a specific blocker of the epithelial sodium channel (ENaC), abolished basal ion transport in both inversin knockdown and control cells, indicating ENaC involvement. Transcript levels of ENaC ß-subunit were reduced in inversin-knockdown cells consistent with decreased ENaC activity. Furthermore, Nedd4l (neural precursor cell expressed, developmentally downregulated 4 like), an upstream negative regulator of ENaC, was evaluated. The relative amount of the phosphorylated, inactive Nedd4l was decreased in inversin-depleted cells consistent with decreased ENaC activity. The protein levels of Sgk1 (serum and glucocorticoid-inducible kinase), which phosphorylates Nedd4l, remained unchanged although the transcript levels were increased in inversin-depleted cells. Interestingly, mRNA and protein levels of Crtc2 (Creb-regulated transcription coactivator) kinase, a positive regulator of Sgk1, were decreased in inversin-depleted cells. Together these results suggest that loss of inversin decreases Na+ transport via ENaC, mediated in part by transcriptional and posttranslational regulation of Crtc2/Sgk1/Nedd4l axis as a contributory mechanism for enlarged kidneys in NPHP2.

Chronic Hyperphosphatemia and Vascular Calcification Are Reduced by Stable Delivery of Soluble Klotho.

αKlotho (αKL) regulates mineral metabolism, and diseases associated with αKL deficiency are characterized by hyperphosphatemia and vascular calcification (VC). αKL is expressed as a membrane-bound protein (mKL) and recognized as the coreceptor for fibroblast growth factor-23 (FGF23) and a circulating soluble form (cKL) created by endoproteolytic cleavage of mKL. The functions of cKL with regard to phosphate metabolism are unclear. We tested the ability of cKL to regulate pathways and phenotypes associated with hyperphosphatemia in a mouse model of CKD-mineral bone disorder and αKL-null mice. Stable delivery of adeno-associated virus (AAV) expressing cKL to diabetic endothelial nitric oxide synthase-deficient mice or αKL-null mice reduced serum phosphate levels. Acute injection of recombinant cKL downregulated the renal sodium-phosphate cotransporter Npt2a in αKL-null mice supporting direct actions of cKL in the absence of mKL. αKL-null mice with sustained AAV-cKL expression had a 74%-78% reduction in aorta mineral content and a 72%-77% reduction in mineral volume compared with control-treated counterparts (P<0.01). Treatment of UMR-106 osteoblastic cells with cKL + FGF23 increased the phosphorylation of extracellular signal-regulated kinase 1/2 and induced Fgf23 expression. CRISPR/Cas9-mediated deletion of fibroblast growth factor receptor 1 (FGFR1) or pretreatment with inhibitors of mitogen-activated kinase kinase 1 or FGFR ablated these responses. In summary, sustained cKL treatment reduced hyperphosphatemia in a mouse model of CKD-mineral bone disorder, and it reduced hyperphosphatemia and prevented VC in mice without endogenous αKL. Furthermore, cKL stimulated Fgf23 in an FGFR1-dependent manner in bone cells. Collectively, these findings indicate that cKL has mKL-independent activity and suggest the potential for enhancing cKL activity in diseases of hyperphosphatemia with associated VC.

Novel functions of circulating Klotho.

A significant portion of the key biological functions of αKlotho (αKL) and its cognate ligand Fibroblast growth factor-23 (FGF23) have been revealed through the study of rare diseases of mineral metabolism. These findings have far reaching implications for common disorders such as chronic kidney disease-mineral bone disorder (CKD-MBD). αKL's predominant effect on mineral homeostasis is through its actions in the kidney as a co-receptor for FGF23, however emerging data has shed light on its capacity to act as a circulating factor through the cleavage of the transmembrane form of αKL ('mKL') to produce 'cleaved KL' or 'cKL'. This review summarizes new findings from studies using extended delivery of cKL to mouse models with phenotypes reflecting those arising in CKD-MBD.

Transcriptomic Analysis of Induced Pluripotent Stem Cells Derived from Patients with Bipolar Disorder from an Old Order Amish Pedigree.

Fibroblasts from patients with Type I bipolar disorder (BPD) and their unaffected siblings were obtained from an Old Order Amish pedigree with a high incidence of BPD and reprogrammed to induced pluripotent stem cells (iPSCs). Established iPSCs were subsequently differentiated into neuroprogenitors (NPs) and then to neurons. Transcriptomic microarray analysis was conducted on RNA samples from iPSCs, NPs and neurons matured in culture for either 2 weeks (termed early neurons, E) or 4 weeks (termed late neurons, L). Global RNA profiling indicated that BPD and control iPSCs differentiated into NPs and neurons at a similar rate, enabling studies of differentially expressed genes in neurons from controls and BPD cases. Significant disease-associated differences in gene expression were observed only in L neurons. Specifically, 328 genes were differentially expressed between BPD and control L neurons including GAD1, glutamate decarboxylase 1 (2.5 fold) and SCN4B, the voltage gated type IV sodium channel beta subunit (-14.6 fold). Quantitative RT-PCR confirmed the up-regulation of GAD1 in BPD compared to control L neurons. Gene Ontology, GeneGo and Ingenuity Pathway Analysis of differentially regulated genes in L neurons suggest that alterations in RNA biosynthesis and metabolism, protein trafficking as well as receptor signaling pathways may play an important role in the pathophysiology of BPD.

Myostatin Neutralization Results in Preservation of Muscle Mass and Strength in Preclinical Models of Tumor-Induced Muscle Wasting.

Skeletal muscle wasting occurs in a great majority of cancer patients with advanced disease and is associated with a poor prognosis and decreased survival. Myostatin functions as a negative regulator of skeletal muscle mass and has recently become a therapeutic target for reducing the loss of skeletal muscle and strength associated with clinical myopathies. We generated neutralizing antibodies to myostatin to test their potential use as therapeutic agents to attenuate the skeletal muscle wasting due to cancer. We show that our neutralizing antimyostatin antibodies significantly increase body weight, skeletal muscle mass, and strength in non-tumor-bearing mice with a concomitant increase in mean myofiber area. The administration of these neutralizing antibodies in two preclinical models of cancer-induced muscle wasting (C26 colon adenocarcinoma and PC3 prostate carcinoma) resulted in a significant attenuation of the loss of muscle mass and strength with no effect on tumor growth. We also show that the skeletal muscle mass- and strength-preserving effect of the antibodies is not affected by the coadministration of gemcitabine, a common chemotherapeutic agent, in both non-tumor-bearing mice and mice bearing C26 tumors. In addition, we show that myostatin neutralization with these antibodies results in the preservation of skeletal muscle mass following reduced caloric intake, a common comorbidity associated with advanced cancer. Our findings support the use of neutralizing antimyostatin antibodies as potential therapeutics for cancer-induced muscle wasting.

Increased brain bio-distribution and chemical stability and decreased immunogenicity of an engineered variant of GDNF.

Several lines of evidence indicate that Glial cell line-derived neurotrophic factor (GDNF) is a trophic factor for dopaminergic neurons. Direct parenchymal administration of GDNF is robustly neuroprotective and neurorestorative in multiple neurotoxin-based animal models (rat and non-human primate (NHP)) of Parkinson's Disease (PD), suggesting its potential as a therapeutic agent. Although small, open-label clinical trials of intra-putamenal administration of bacteria-derived, full length, wild type GDNF (GDNFwt) were efficacious in improving standardized behavioral scores, a double-blinded, randomized controlled trial failed to do so. We hypothesize that the lack of clinical efficacy of GDNFwt in the larger randomized trial was due to poor bio-distribution in the putamen and/or poor chemical stability while in the delivery device for prolonged time periods at 37°C. The development of neutralizing antibodies in some patients may also have been a contributing factor. GDNFv is an engineered form of GDNFwt, expressed and purified from mammalian cells, designed to overcome these limitations, including removal of the N-terminal heparin-binding domain to improve its diffusivity in brain parenchyma by reducing its binding to extracellular matrix (ECM), and key amino acid substitutions to improve chemical stability. Intra-striatal administration of a single injection of GDNFv in the rat produced significantly greater brain distribution than GDNFwt, consistent with reduced binding to ECM. Using liquid chromatography/mass spectrometry (LS/MS) methods GDNFv was shown to have improved chemical stability compared to GDNFwt when stored at 37°C for 4weeks. In addition, GDNFv resulted in lower predicted clinical immunogenicity compared to GDNFwt, as demonstrated by reduced CD4+ T cell proliferation and reduced IL-2-induced secretion in peripheral blood mononucleated cells collected from volunteers representing the world's major histocompatibility complex (MHC) haplotypes. GDNFv was demonstrated to be pharmacologically equivalent to GDNFwt in the key parameters in vitro of GFRα1 receptor binding, c-Ret phosphorylation, neurite outgrowth, and in vivo in its ability to increase dopamine turnover (DA). GDNFv protected dopamine nerve terminals and neurons in a 6-hydroxy-dopamine (6-OHDA) rat model. In summary, we empirically demonstrate the superior properties of GDNFv compared to GDNFwt through enhanced bio-distribution and chemical stability concurrently with decreased predicted clinical immunogenicity while maintaining pharmacological and neurotrophic activity. These data indicate that GDNFv is an improved version of GDNF suitable for clinical assessment as a targeted regenerative therapy for PD.

Myostatin inhibitors as therapies for muscle wasting associated with cancer and other disorders.

PURPOSE OF REVIEW: This review summarizes recent progress in the development of myostatin inhibitors for the treatment of muscle wasting disorders. It also focuses on findings in myostatin biology that may have implications for the development of antimyostatin therapies. RECENT FINDINGS: There has been progress in evaluating antimyostatin therapies in animal models of muscle wasting disorders. Some programs have progressed into clinical development with initial results showing positive impact on muscle volume.In normal mice myostatin deficiency results in enlarged muscles with increased total force but decreased specific force (total force/total mass). An increase in myofibrillar protein synthesis without concomitant satellite cell proliferation and fusion leads to muscle hypertrophy with unchanged myonuclear number. A specific force reduction is not observed when atrophied muscle, the predominant therapeutic target of myostatin inhibitor therapy, is made myostatindeficient.Myostatin has been shown to be expressed by a number of tumor cell lines in mice and man. SUMMARY: Myostatin inhibition remains a promising therapeutic strategy for a range of muscle wasting disorders.

Circulating αKlotho influences phosphate handling by controlling FGF23 production.

The FGF23 coreceptor αKlotho (αKL) is expressed as a membrane-bound protein (mKL) that forms heteromeric complexes with FGF receptors (FGFRs) to initiate intracellular signaling. It also circulates as an endoproteolytic cleavage product of mKL (cKL). Previously, a patient with increased plasma cKL as the result of a translocation [t(9;13)] in the αKLOTHO (KL) gene presented with rickets and a complex endocrine profile, including paradoxically elevated plasma FGF23, despite hypophosphatemia. The goal of this study was to test whether cKL regulates phosphate handling through control of FGF23 expression. To increase cKL levels, mice were treated with an adeno-associated virus producing cKL. The treated groups exhibited dose-dependent hypophosphatemia and hypocalcemia, with markedly elevated FGF23 (38 to 456 fold). The animals also manifested fractures, reduced bone mineral content, expanded growth plates, and severe osteomalacia, with highly increased bone Fgf23 mRNA (>150 fold). cKL activity in vitro was specific for interactions with FGF23 and was FGFR dependent. These results demonstrate that cKL potently stimulates FGF23 production in vivo, which phenocopies the KL translocation patient and metabolic bone syndromes associated with elevated FGF23. These findings have important implications for the regulation of αKL and FGF23 in disorders of phosphate handling and biomineralization.

Transcriptome signature of resistance exercise adaptations: mixed muscle and fiber type specific profiles in young and old adults.

This investigation examined the effects of acute resistance exercise (RE), progressive resistance training (PRT), and age on the human skeletal muscle Transcriptome. Two cohorts of young and old adults [study A: 24 yr, 84 yr (n = 28); study B: 25 yr, 78 yr (n = 36)] were studied. Vastus lateralis biopsies were obtained pre- and 4 h post-RE in conjunction with the 1st and 36th (last) training session as part of a 12-wk PRT program in study A, whereas biopsies were obtained in the basal untrained state in study B. Additionally, the muscle fiber type specific (MHC I and MHC IIa) Transcriptome response to RE was examined in a subset of young and old women from study A. Transcriptome profiling was performed using HG U133 Plus 2.0 Arrays. The main findings were 1) there were 661 genes affected by RE during the 1st and 36th training bout that correlated with gains in muscle size and strength with PRT (termed the Transcriptome signature of resistance exercise adaptations); 2) the RE gene response was most pronounced in fast-twitch (MHC IIa) muscle fibers and provided additional insight into the skeletal muscle biology affected by RE; 3) skeletal muscle of young adults is more responsive to RE at the gene level compared with old adults and age also affected basal level skeletal muscle gene expression. These skeletal muscle Transcriptome findings provide further insight into the molecular basis of sarcopenia and the impact of resistance exercise at the mixed muscle and fiber type specific level.

Proteomic analysis of demyelinated and remyelinating brain tissue following dietary cuprizone administration.

Cuprizone intoxication is a commonly used model of demyelination that allows the temporal separation of demyelination and remyelination. The underlying biochemical alterations leading to demyelination, using this model, remain unclear and may be multifold. Analysis of proteomic changes within the brains of cuprizone-exposed animals may help elucidate key cellular processes. In the current study, we report the results of the liquid chromatography tandem mass spectrometry analysis of total protein from the brain hemispheres of control and toxin-exposed mice at 6 weeks of exposure and after 3 and 6 weeks of recovery to identify protein changes during the remyelination phase. We found that at 6 weeks of cuprizone exposure, myelin proteins were reduced compared to controls and increased throughout the course of recovery, as expected. In contrast, other protein groups, such as proteins related to mitochondrial function, were increased at 6 weeks of treatment compared to untreated controls and returned toward control levels following withdrawal of toxin. These results suggest that a global proteomic analysis of the brain tissue of cuprizone-treated mice can identify changes related to the demyelination/remyelination process.

RNA helicase Ddx39 is expressed in the developing central nervous system, limb, otic vesicle, branchial arches and facial mesenchyme of Xenopus laevis.

Ddx39, a DEAD-box RNA helicase, is a part of the homeostatic machinery that regulates the switch between cellular proliferation and differentiation. Ddx39 was shown to be differentially regulated in Xenopus laevis using a differential screen of mRNAs from regenerating limbs (King et al., 2003). Here, the expression patterns of Ddx39 in developing limb and nervous system are reported. Ddx39 was detected by RT-PCR in the Xenopus embryo, the earliest stage examined. Localization of the message by whole-mount in situ hybridization at stage 17 showed it to be localized primarily to the developing nervous system. Ddx39 was present in the ventricular region of the developing neural tube up to and including stage 48, and was also localized to the head mesenchyme, pharyngeal arches, and paraxial mesoderm. Strong label was also present in the developing limb buds at stages 48-55. Analysis of expression patterns in cryosections of the developing eye at stage 38 and 47 showed Ddx39 in the ciliary marginal zone (CMZ) adjacent to the neural retina and within the lens epithelium. Ddx39 was also present in the anterior eye during fibroblast growth factor 2 (FGF2)-mediated retinal regeneration. BrDU incorporation analyses and double-label studies with proliferating cell nuclear antigen showed that Ddx39 message was restricted to a subpopulation of proliferating cells in the developing and regenerating optic cup.

MMP-28 as a regulator of myelination.

BACKGROUND: Matrix metalloproteinase-28 (MMP-28) is a poorly understood member of the matrix metalloproteinase family. Metalloproteinases are important mediators in the development of the nervous system and can contribute to the maturation of the neural micro-environment. RESULTS: MMP-28 added to myelinating rat dorsal root ganglion (DRG) co-cultures reduces myelination and two antibodies targeted to MMP-28 (pAb180 and pAb183) are capable of binding MMP-28 and inhibiting its activity in a dose-dependent manner. Addition of 30 nM pAb180 or pAb183 to rat DRG cultures resulted in the 2.6 and 4.8 fold enhancement of myelination respectively while addition of MMP-28 to DRG co-cultures resulted in enhanced MAPK, ErbB2 and ErbB3 phosphorylation. MMP-28 protein expression was increased within demyelinated lesions of mouse experimental autoimmune encephalitis (EAE) and human multiple sclerosis lesions compared to surrounding normal tissue. CONCLUSION: MMP-28 is upregulated in conditions of demyelination in vivo, induces signaling in vitro consistent with myelination inhibition and, neutralization of MMP-28 activity can enhance myelination in vitro. These results suggest inhibition of MMP-28 may be beneficial under conditions of dysmyelination.

Neural MMP-28 expression precedes myelination during development and peripheral nerve repair.

Mammalian matrix metalloproteinase 28 (MMP-28) is expressed in several normal adult tissues, and during cutaneous wound healing. We show that, in frog and mouse embryos, MMP-28 is expressed predominantly throughout the nervous system. Xenopus expression increases during neurulation and remains elevated through early limb development where it is expressed in nerves. In the mouse, neural expression peaks at embryonic day (E) 14 but remains detectable through E17. During frog hindlimb regeneration XMMP-28 is not initially expressed in the regenerating nerves but is detectable before myelination. Following hindlimb denervation, XMMP-28 expression is detectable along regenerating nerves before myelination. In embryonic rat neuron-glial co-cultures, MMP-28 decreases after the initiation of myelination. Incubation of embryonic brain tissue with purified MMP-28 leads to the degradation of multiple myelin proteins. These results suggest that MMP-28 plays an evolutionarily conserved role in neural development and is likely to modulate the axonal-glial extracellular microenvironment.

Expression of Xenopus XlSALL4 during limb development and regeneration.

The multi-C2H2 zinc-finger domain containing transcriptional regulators of the spalt (SAL) family plays important developmental regulatory roles. In a competitive subtractive hybridization screen of genes expressed in Xenopus laevis hindlimb regeneration blastemas, we identified a SAL family member that, by phylogenetic analysis, falls in the same clade as human SALL4 and have designated it as XlSALL4. Mutations of human SALL4 have been linked to Okihiro syndrome, which includes preaxial (anterior) limb defects. The expression pattern of XlSALL4 transcripts during normal forelimb and hindlimb development and during hindlimb regeneration at the regeneration-competent and regeneration-incompetent stages is temporally and regionally dynamic. We show for the first time that a SAL family member (XlSALL4) is expressed at the right place and time to play a role regulating both digit identity along the anterior/posterior axis and epimorphic limb regeneration.

Identification of genes expressed during Xenopus laevis limb regeneration by using subtractive hybridization.

Suppression polymerase chain reaction-based subtractive hybridization was used to identify genes that are expressed during Xenopus laevis hindlimb regeneration. Subtractions were done by using RNAs extracted from the regeneration-competent stage (stage 53) and regeneration-incompetent stage (stage 59) of limb development. Forward and reverse subtractions were done between stage 53 7-day blastema and stage 53 contralateral limb (competent stage), stage 59 7-day pseudoblastema and stage 59 contralateral limb (incompetent stage), and stage 53 7-day blastema and stage 59 7-day pseudoblastema. Several thousand clones were analyzed from the various subtracted libraries, either by random selection and sequencing (1,920) or by screening subtracted cDNA clones (6,150), arrayed on nylon membranes, with tissue-specific probes. Several hundred clones were identified from the array screens whose expression levels were at least twofold higher in experimental tissue vs. control tissue (e.g., blastema vs. limb) and selected for sequencing. In addition, primers were designed to assay several of the randomly selected clones and used to assess the level of expression of these genes during regeneration and normal limb development. Approximately half of the selected clones were differentially expressed, as expected, including several that demonstrate blastema-specific enhancement of expression. Three distinct categories of expression were identified in our screens: (1) clones that are expressed in both regeneration-competent blastemas and -incompetent pseudoblastemas, (2) clones that are expressed at highest levels in regeneration-competent blastemas, and (3) clones that are expressed at highest levels in regeneration-incompetent pseudoblastemas. Characterizing the role of each of these three categories of genes will be important in furthering our understanding of the process of tissue regeneration.