Tau pathology reduction with SM07883, a novel, potent, and selective oral DYRK1A inhibitor: A potential therapeutic for Alzheimer's disease

Dual-specificity tyrosine phosphorylation-regulated kinase-1A (DYRK1A) is known to phosphorylate the microtubule-associated tau protein. Overexpression is correlated with tau hyperphosphorylation and neurofibrillary tangle (NFT) formation in Alzheimer's disease (AD). This study assessed the potential of SM07883, an oral DYRK1A inhibitor, to inhibit tau hyperphosphorylation, aggregation, NFT formation, and associated phenotypes in mouse models. Exploratory neuroinflammatory effects were also studied. SM07883 specificity was tested in a kinase panel screen and showed potent inhibition of DYRK1A (IC50  = 1.6 nM) and GSK-3β (IC50  = 10.8 nM) kinase activity. Tau phosphorylation measured in cell-based assays showed a reduction in phosphorylation of multiple tau epitopes, especially the threonine 212 site (EC50  = 16 nM). SM07883 showed good oral bioavailability in multiple species and demonstrated a dose-dependent reduction of transient hypothermia-induced phosphorylated tau in the brains of wild-type mice compared to vehicle (47%, p < 0.001). Long-term efficacy assessed in aged JNPL3 mice overexpressing the P301L human tau mutation (3 mg/kg, QD, for 3 months) exhibited significant reductions in tau hyperphosphorylation, oligomeric and aggregated tau, and tau-positive inclusions compared to vehicle in brainstem and spinal cord samples. Reduced gliosis compared to vehicle was further confirmed by ELISA. SM07883 was well tolerated with improved general health, weight gain, and functional improvement in a wire-hang test compared to vehicle-treated mice (p = 0.048). SM07883, a potent, orally bioavailable, brain-penetrant DYRK1A inhibitor, significantly reduced effects of pathological tau overexpression and neuroinflammation, while functional endpoints were improved compared to vehicle in animal models. This small molecule has potential as a treatment for AD.

Modulation of the Wnt pathway through inhibition of CLK2 and DYRK1A by lorecivivint as a novel, potentially disease-modifying approach for knee osteoarthritis treatment

OBJECTIVES

Wnt pathway upregulation contributes to knee osteoarthritis (OA) through osteoblast differentiation, increased catabolic enzymes, and inflammation. The small-molecule Wnt pathway inhibitor, lorecivivint (SM04690), which previously demonstrated chondrogenesis and cartilage protection in an animal OA model, was evaluated to elucidate its mechanism of action.

DESIGN

Biochemical assays measured kinase activity. Western blots measured protein phosphorylation in human mesenchymal stem cells (hMSCs), chondrocytes, and synovial fibroblasts. siRNA knockdown effects in hMSCs and BEAS-2B cells on Wnt pathway, chondrogenic genes, and LPS-induced inflammatory cytokines was measured by qPCR. In vivo anti-inflammation, pain, and function were evaluated following single intra-articular (IA) lorecivivint or vehicle injection in the monosodium iodoacetate (MIA)-induced rat OA model.

RESULTS

Lorecivivint inhibited intranuclear kinases CDC-like kinase 2 (CLK2) and dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A). Lorecivivint inhibited CLK2-mediated phosphorylation of serine/arginine-rich (SR) splicing factors and DYRK1A-mediated phosphorylation of SIRT1 and FOXO1. siRNA knockdowns identified a role for CLK2 and DYRK1A in Wnt pathway modulation without affecting β-catenin with CLK2 inhibition inducing early chondrogenesis and DYRK1A inhibition enhancing mature chondrocyte function. NF-κB and STAT3 inhibition by lorecivivint reduced inflammation. DYRK1A knockdown was sufficient for anti-inflammatory effects, while combined DYRK1A/CLK2 knockdown enhanced this effect. In the MIA model, lorecivivint inhibited production of inflammatory cytokines and cartilage degradative enzymes, resulting in increased joint cartilage, decreased pain, and improved weight-bearing function.

CONCLUSIONS

Lorecivivint inhibition of CLK2 and DYRK1A suggested a novel mechanism for Wnt pathway inhibition, enhancing chondrogenesis, chondrocyte function, and anti-inflammation. Lorecivivint shows potential to modify structure and improve symptoms of knee OA.

β1 Integrin as a Xenoantigen in Fetal Porcine Mesencephalic Cells Transplanted into the Rat Brain

Xenografts of fetal porcine mesencephalic cells implanted into the rat striatum are generally rejected within several weeks. The fetal donor mesencephalon predominantly consists of neurons, but also contains microglial and endothelial cells, which are more immunogenic. In the present work, we investigated the occurrence of donor endothelial cells in grafts of porcine mesencephalic cells implanted into the rat striatum. Pig endothelial cells were monitored by immunochemical methods, using a monoclonal antibody (mAb) that recognizes a peptidic epitope of the porcine β1 integrin, and isolectin IB4, for the staining of the Galα1,3Gal epitope. The analysis also involved the detection of the pig hyaluronate receptor CD44, and the cell adhesion molecule CD31. The anti-β1 integrin mAb revealed endothelial-like cells in grafts of porcine mesencephalic cells as soon as 1 week after implantation. A similar staining pattern was obtained with the IB4 lectin. Unlike aortic endothelial cells, these pig brain-derived endothelial-like cells were not recognized by the anti-CD44 antibody. They also failed to express the CD31 adhesion molecule, a fact which suggests that they remained poorly mature, even in grafts maintained during 45 days in immunosuppressed rats. Interestingly, a strong expression of β1 integrin immunoreactivity was noticed in a large proportion (80%) of the cells freshly dissociated from the fetal pig mesencephalic tissue. The immunoreactivity decreased progressively after transplantation of the cells into the rat brain. This observation suggests that dissociated neuroblasts are capable of a temporary expression of β1 integrin. This molecule is known to participate in the process of cell sorting and migration in the developing brain. Hence, its expression could be the hallmark of a rescue mechanism triggered by the disruption of the cell/matrix interactions during the dissociation of the fetal mesencephalon. This disruption might account for part of the dramatic cell death process that occurs during the manipulation of the donor tissue.

Shear stress induces Gαq/11 activation independently of G protein-coupled receptor activation in endothelial cells

Mechanochemical signal transduction occurs when mechanical forces, such as fluid shear stress, are converted into biochemical responses within the cell. The molecular mechanisms by which endothelial cells (ECs) sense/transduce shear stress into biological signals, including the nature of the mechanosensor, are still unclear. G proteins and G protein-coupled receptors (GPCRs) have been postulated independently to mediate mechanotransduction. In this study, we used in situ proximity ligation assay (PLA) to investigate the role of a specific GPCR/Gα_q/11 pair in EC shear stress-induced mechanotransduction. We demonstrated that sphingosine 1-phosphate (S1P) stimulation causes a rapid dissociation at 0.5 min of Gα_q/11 from its receptor S1P₃, followed by an increased association within 2 min of GPCR kinase-2 (GRK2) and β-arrestin-1/2 with S1P₃ in human coronary artery ECs, which are consistent with GPCR/Gα_q/11 activation and receptor desensitization/internalization. The G protein activator AlF₄ resulted in increased dissociation of Gα_q/11 from S1P₃, but no increase in association between S1P₃ and either GRK2 or β-arrestin-1/2. The G protein inhibitor guanosine 5'-(β-thio) diphosphate (GDP-β-S) and the S1P₃ antagonist VPC23019 both prevented S1P-induced activation. Shear stress also caused the rapid activation within 7 s of S1P₃/Gα_q/11 There were no increased associations between S1P₃ and GRK2 or S1P₃ and β-arrestin-1/2 until 5 min. GDP-β-S, but not VPC23019, prevented dissociation of Gα_q/11 from S1P₃ in response to shear stress. Shear stress did not induce rapid dephosphorylation of β-arrestin-1 or rapid internalization of S1P₃, indicating no GPCR activation. These findings suggest that Gα_q/11 participates in the sensing/transducing of shear stress independently of GPCR activation in ECs.

Distinctive subcellular Akt-1 responses to shear stress in endothelial cells

Endothelial cells undergo a rapid cell-cell junction inclination following exposure to atheroprotective unidirectional flow. In contrast, atherosclerotic lesions correlate with a heterogeneous distribution of the junctional wall inclination in cells exposed to time-varying, reversing, and oscillatory flow as well as to low mean shear stress. However, the underlying biochemical events by which endothelial cells distinctively respond to unidirectional versus flow reversal remain unclear. Here, we show that the subcellular distribution of flow-induced Akt-1 phosphorylation in endothelial cells lining the mouse aorta varies depending on local hemodynamics. Activated Akt-1 accumulated in perinuclear areas of cells in regions predisposed to disturbed flow but were localized at the cell-cell junction in regions of high unidirectional laminar shear stress. In flow-adapted human endothelial cells, reversal in flow direction was associated within minutes with a subcellular concentration of phosphorylated Akt-1 at the upstream edge of cells. Interestingly, oscillatory flow (with a zero mean shear stress) failed to activate Akt-1, whereas a unidirectional pulsatile flow of similar amplitude induced an increase in Akt-1 phosphorylation. Finally, silencing of the G protein αq/11 subunit abrogated both flow-induced Akt-1 and GSK-3β activation. Together, these results characterize the existence of a Gαq/11-mediated Akt-1 signaling pathway that is dynamically responsive to flow direction, thereby offering a novel approach to regulating EC dysfunctions in regions subjected to flow reversal.

Nitric oxide synthase dysfunction contributes to impaired cerebroarteriolar reactivity in experimental cerebral malaria

Cerebrovascular dysfunction plays a key role in the pathogenesis of cerebral malaria. In experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA, cerebrovascular dysfunction characterized by vascular constriction, occlusion and damage results in impaired perfusion and reduced cerebral blood flow and oxygenation, and has been linked to low nitric oxide (NO) bioavailability. Here, we directly assessed cerebrovascular function in ECM using a novel cranial window method for intravital microscopy of the pial microcirculation and probed the role of NOS isoforms and phosphorylation patterns in the impaired vascular responses. We show that pial arteriolar responses to endothelial NOS (eNOS) and neuronal NOS (nNOS) agonists (Acetylcholine (ACh) and N-Methyl-D-Aspartate (NMDA)) were blunted in mice with ECM, and could be partially recovered by exogenous supplementation of tetrahydrobiopterin (BH4). Pial arterioles in non-ECM mice infected by Plasmodium berghei NK65 remained relatively responsive to the agonists and were not significantly affected by BH4 treatment. These findings, together with the observed blunting of NO production upon stimulation by the agonists, decrease in total NOS activity, augmentation of lipid peroxidation levels, upregulation of eNOS protein expression, and increase in eNOS and nNOS monomerization in the brain during ECM development strongly indicate a state of eNOS/nNOS uncoupling likely mediated by oxidative stress. Furthermore, the downregulation of Serine 1176 (S1176) phosphorylation of eNOS, which correlated with a decrease in cerebrovascular wall shear stress, implicates hemorheological disturbances in eNOS dysfunction in ECM. Finally, pial arterioles responded to superfusion with the NO donor, S-Nitroso-L-glutathione (GSNO), but with decreased intensity, indicating that not only NO production but also signaling is perturbed during ECM. Therefore, the pathological impairment of eNOS and nNOS functions contribute importantly to cerebrovascular dysfunction in ECM and the recovery of intrinsic functionality of NOS to increase NO bioavailability and restore vascular health represents a target for ECM treatment.

Early VEGFR2 activation in response to flow is VEGF-dependent and mediated by MMP activity

Although several potential mechanosensors/mechanotransducers have been proposed, the precise mechanisms by which ECs sense and respond to mechanical forces and translate them into biochemical signals remains unclear. Here, we report that two major ligand-dependent tyrosine autophosphorylation sites of VEGFR2, Y1175 and Y1214, are rapidly activated by shear stress in human coronary artery endothelial cells (HCAECs). Neutralizing antibody against VEGFR2 not only abrogates flow-induced phosphorylation of these tyrosine residues, but also has a marked inhibitory effect on downstream eNOS activation. In situ proximity ligation assay revealed that VEGF and VEGFR2 are closely associated in HCAECs, and more importantly, this association is increased with flow. Finally, we show that flow-induced VEGFR2 activation is attenuated in the presence of the broad spectrum matrix metalloproteinase (MMP) inhibitor, GM6001. Taken together, our results suggest that a ligand-dependent mechanism involving the activity of MMPs plays a key role in the early, shear stress-induced activation of VEGFR2.

Gαq/11-mediated intracellular calcium responses to retrograde flow in endothelial cells

Disturbed flow patterns, including reversal in flow direction, are key factors in the development of dysfunctional endothelial cells (ECs) and atherosclerotic lesions. An almost immediate response of ECs to fluid shear stress is the increase in cytosolic calcium concentration ([Ca(2+)](i)). Whether the source of [Ca(2+)](i) is extracellular, released from Ca(2+) intracellular stores, or both is still undefined, though it is likely dependent on the nature of forces involved. We have previously shown that a change in flow direction (retrograde flow) on a flow-adapted endothelial monolayer induces the remodeling of the cell-cell junction along with a dramatic [Ca(2+)](i) burst compared with cells exposed to unidirectional or orthograde flow. The heterotrimeric G protein-α q and 11 subunit (Gα(q/11)) is a likely candidate in effecting shear-induced increases in [Ca(2+)](i) since its expression is enriched at the junction and has been previously shown to be activated within seconds after onset of flow. In flow-adapted human ECs, we have investigated to what extent the Gα(q/11) pathway mediates calcium dynamics after reversal in flow direction. We observed that the elapsed time to peak [Ca(2+)](i) response to a 10 dyn/cm(2) retrograde shear stress was increased by 11 s in cells silenced with small interfering RNA directed against Gα(q/11). A similar lag in [Ca(2+)](i) transient was observed after cells were treated with the phospholipase C (PLC)-βγ inhibitor, U-73122, or the phosphatidylinositol-specific PLC inhibitor, edelfosine, compared with controls. Lower levels of inositol 1,4,5-trisphosphate accumulation seconds after the onset of flow correlated with the increased lag in [Ca(2+)](i) responses observed with the different treatments. In addition, inhibition of the inositol 1,4,5-trisphosphate receptor entirely abrogated flow-induced [Ca(2+)](i). Taken together, our results identify the Gα(q/11)-PLC pathway as the initial trigger for retrograde flow-induced endoplasmic reticulum calcium store release, thereby offering a novel approach to regulating EC dysfunctions in regions subjected to the reversal of blood flow.

Shear-induced endothelial cell-cell junction inclination

Atheroprone regions of the arterial circulation are characterized by time-varying, reversing, and oscillatory wall shear stress. Several in vivo and in vitro studies have demonstrated that flow reversal (retrograde flow) is atherogenic and proinflammatory. The molecular and structural basis for the sensitivity of the endothelium to flow direction, however, has yet to be determined. It has been hypothesized that the ability to sense flow direction is dependent on the direction of inclination of the interendothelial junction. Immunostaining of the mouse aorta revealed an inclination of the cell-cell junction by 13 degrees in direction of flow in the descending aorta where flow is unidirectional. In contrast, polygonal cells of the inner curvature where flow is disturbed did not have any preferential inclination. Using a membrane specific dye, the angle of inclination of the junction was dynamically monitored using live cell confocal microscopy in confluent human endothelial cell monolayers. Upon application of shear the junctions began inclining within minutes to a final angle of 10 degrees in direction of flow. Retrograde flow led to a reversal of junctional inclination. Flow-induced junctional inclination was shown to be independent of the cytoskeleton or glycocalyx. Additionally, within seconds, retrograde flow led to significantly higher intracellular calcium responses than orthograde flow. Together, these results show for the first time that the endothelial intercellular junction inclination is dynamically responsive to flow direction and confers the ability to endothelial cells to rapidly sense and adapt to flow direction.

Rapid changes in shear stress induce dissociation of a G alpha(q/11)-platelet endothelial cell adhesion molecule-1 complex

It has been recently shown that endothelial platelet endothelial cell adhesion molecule-1 (PECAM-1) expression is pro-atherogenic. PECAM-1 is involved in sensing rapid changes in fluid shear stress but the mechanisms for activating signalling complexes at the endothelial cell junction have yet to be elucidated. Additional studies suggest the activation of membrane-bound G proteins G alpha(q/11) also mediate flow-induced responses. Here, we investigated whether PECAM-1 and G alpha(q/11) could act in unison to rapidly respond to fluid shear stress. With immunohistochemistry, we observed a co-localization of G alpha(q/11) and PECAM-1 at the cell-cell junction in the atheroprotected section of mouse aortae. In contrast, G alpha(q/11) was absent from junctions in atheroprone areas as well as in all arterial sections of PECAM-1 knockout mice. In primary human endothelial cells, temporal gradients in shear stress led to a rapid dissociation of the G alpha(q/11)-PECAM-1 complex within 30 s and a partial relocalization of the G alpha(q/11) staining to perinuclear areas within 150 min, whereas transitioning fluid flow devoid of temporal gradients did not disrupt the complex. Inhibition of G protein activation eliminated temporal gradient flow-induced G alpha(q/11)-PECAM-1 dissociation. These results allow us to conclude that G alpha(q/11)-PECAM-1 forms a mechanosensitive complex and its localization suggests the G alpha(q/11)-PECAM-1 complex is a critical mediator of vascular diseases.

PECAM-1 is a critical mediator of atherosclerosis

Atherosclerosis is a chronic inflammatory disease of large arteries in which lesion development preferentially occurs at vessel sites exposed to rapid changes in flow. We have previously shown that platelet endothelial cell adhesion molecule (PECAM-1), a surface receptor of the immunoglobulin superfamily, is involved in mechanosensing of rapid changes in flow. We wondered whether apolipoprotein E deficient (ApoE(-/-)) mice, predisposed to development of atheromas, would be protected from atherosclerosis by deficiency in PECAM-1. Using double knockout (DKO) mice for both PECAM-1 and ApoE (ApoE(-/-)/PECAM-1(-/-)) we found a significant reduction of sudanophilic lesions in their aortae compared to single knockout (SKO) (ApoE(-/-)/PECAM-1(+/+)) mice maintained on a high-fat Western diet. Immunostaining of aortic sinus cross sections demonstrated significantly lower ICAM-1 expression in DKO lesions compared with SKO lesions, and en face preparations of vessel regions subjected to disturbed and laminar flow showed less disruption of junctional connexin 43 in DKO than in SKO mice. Thus, PECAM-1 deficiency reduced the extent of lesions at the aortic arch and the aortic sinus, and lowered atherogenic indices. These results suggest that PECAM-1 is an important factor in the atherogenic changes seen in the ApoE-deficient mouse model and thus should be considered as a potential target for protection against atherosclerosis.

Compartmentalization of TCR repertoire alteration during rejection of an intrabrain xenograft

Xenograft rejections of embryonic pig neural cells implanted into the adult rat striatum occurs within 3-4 weeks, following a dramatic T cell infiltration. Little is known about the cross-talk between the brain and peripheral lymphoid tissues which results in this recruitment and lymphocyte homing. To better characterize the dynamics of the T cell response against xenogeneic neural cells implanted into the brain parenchyma, we used both qualitative and quantitative methods to follow the alterations of the CDR3 length distribution (CDR3-LD) of the TCR (T cell receptor) beta chain in the transplanted striatum and compared this response to that observed in the deep cervical lymph nodes, spleen, and blood. Data showed that the T cell repertoire diversity was highly altered in the recipient brain during xenograft rejection. Comparison of the alterations of the CDR3-LD between several animals revealed a single public alteration in the Vbeta20 family, and many private alterations of the CDR3-LD which differed from one infiltrated brain to another. Alterations of the T cell repertoire were also observed in lymphocytes homed into the deep cervical lymph nodes. However, they differed from the alterations detected in the infiltrated brains. Conversely, no significant alteration of the CDR3-LD was detected in the spleen or in the blood. These data suggest that the deep cervical lymph nodes play an active role in the process of xenograft recognition or/and rejection. However, they also indicate that the fate of T cells homed in the brain and deep cervical lymph nodes differs.

Blood T-cell receptor beta chain transcriptome in multiple sclerosis. Characterization of the T cells with altered CDR3 length distribution

Multiple sclerosis is an inflammatory demyelinating disease of the CNS associated with T cells autoreactive for myelin components. In this study, we analysed the T-cell receptor (TCR) usage of the variable beta (Vbeta) chain transcriptome in the blood of multiple sclerosis patients at various stages of the disease using a global and quantitative comparison of the complementarity-determining region 3 length distribution (CDR3-LD) of transcripts of the 26 Vbeta genes. We investigated 35 patients: 12 with a high risk of multiple sclerosis, 10 with clinically definite multiple sclerosis, 13 with a relapsing-remitting worsening and active multiple sclerosis and 13 healthy individuals. Cells bearing the TCR transcripts with altered CDR3-LD were sorted and studied for CD4 or CD8 phenotype, cytokine transcript accumulation and response to human myelin basic protein (MBP). We show that patients from all the groups have a significantly skewed blood T-cell repertoire. Vbeta transcriptome patterns were more altered in patients from the clinically definite multiple sclerosis group and the worsening and active multiple sclerosis group than in the high risk group. The T cells sorted from Vbeta families with altered CDR3-LD concerned both CD4 and CD8 T cells, with a more pronounced skewing in the CD8 compartment. These cells displayed a significantly increased level of interferon-gamma, interleukin-2 and tumour necrosis factor-alpha transcripts compared with their counterparts from the healthy individual group. Furthermore, using interferon-gamma enzyme-linked immunospot (ELISPOT) assays, T cells from four out of seven altered Vbeta families tested from multiple sclerosis patients responded to human MBP, whereas no response was observed with human albumin or with altered Vbeta families from healthy individuals. Our data support the concept of an early autoimmune component in the disease and emphasize the possible involvement of CD8-positive T cells in multiple sclerosis.

Ectopic expression of the TrkA receptor in adult dopaminergic mesencephalic neurons promotes retrograde axonal NGF transport and NGF-dependent neuroprotection

A recombinant adeno-associated virus (rAAV) was used to investigate the impact of an ectopic expression of the NGF high-affinity receptor in adult neurons. The rat TrkA cDNA cloned in a pCMX vector was first tagged with a human c-Myc sequence. The resulting vector was shown to encode a functional receptor which promoted the expression of TrkA immunoreactivity upon transfection of 293 fibroblasts or nnr5 cells, a TrkA-defective variant of PC12 cells. These cells also accumulate TrkA transcripts upon transfection and extended neurites in the presence of NGF. Therefore, the TrkA(myc) cassette was inserted into the pSSV9 plasmid. The new vectors shared properties similar to pCMX TrkA(myc) in 293 and nnr5 cells and enabled the preparation of rAAV TrkA(myc) viruses. Unilateral injection of this rAAV into the substantia nigra (SN) resulted in a protracted expression of TrkA (or c-Myc) immunoreactivity in numerous cell bodies, including tyrosine-hydroxylase (TH)-positive dopaminergic neurons. The presence of TrkA receptors in corresponding striatal dopaminergic endings was demonstrated by the advent of a striato-nigral retrograde axonal transport of (125)I-NGF. Likewise, ectopic expression of TrkA in neurons of the parafascicular thalamic nucleus promoted a striatofuge transport of NGF toward this structure. To investigate whether ectopic expression of TrkA in SN neurons may confer neuroprotection, lesions were induced by 6-hydroxydopamine in striata located ipsilateral to the virus injection site. NGF or vehicle were next delivered dorsally to the virus-treated SN for 2 weeks, before sacrifice and processing of brains for TH-immunohistochemistry. NGF treatment, in contrast to treatment with vehicle, significantly enhanced the number of dopaminergic neurons counted in the lesioned SN. These data suggest that ectopic TrkA can mediate the trophic actions of NGF and influence neuronal plasticity in vivo.

Temporal analysis of cytokine gene expression during infiltration of porcine neuronal grafts implanted into the rat brain

A large array of evidence supports the involvement of infiltrating T lymphocytes in the rejection process of intracerebral neuronal xenografts. Little is known, however, about the molecular mechanisms that drive the recruitment of this cell type. In the present work, we used real-time RT-PCR methodology to investigate the kinetics of cytokine gene expression during the infiltration of fetal porcine neurons (PNEU) implanted into the striatum of LEW.1A rats. T lymphocyte infiltration was followed by measuring the intracerebral levels of transcripts encoding the beta chain of the T cell receptor. These transcripts remained barely detectable until the fourth week (28 days) postimplantation, when a sudden accumulation occurred. Their kinetics, which support previous immunohistochemical observations, indicate that alphabetaT lymphocyte recruitment occurs rapidly after a delay of several weeks in this experimental model. Infiltration of PNEU grafts by T lymphocytes was accompanied by a concomitant, dramatic augmentation of transcripts coding for monocyte chemotactic protein-1 and RANTES (for regulated on activation, normal T cell expressed and secreted), two chemokines targeting this cell type, among others. Likewise, a sudden accumulation of transcripts of proinflammatory lymphokines [interleukin (IL)-1alpha, tumor necrosis factor-alpha, IL-6] as well as Th1 cytokines (IL-2, interferon-gamma) was also detected. In contrast, IL-4, -10, and -13 mRNA remained barely detectable at the different time points. No significant changes were noticed for IL-12 or transforming growth factor-beta transcripts. These data support the concept that T lymphocyte infiltration of PNEU grafts is actively promoted by a local production of chemokines and proinflammatory lymphokines and is based on a Th1 polarization.

Different mechanisms mediate the rejection of porcine neurons and endothelial cells transplanted into the rat brain

In order to investigate the early cellular responses mediating xenograft rejection in the brain, porcine aortic endothelial cells (PAEC) or porcine fetal mesencephalic neurons (PNEU) were transplanted into the striatum of LEW.1A rats. PAEC were detected with a specific anti-beta1 integrin antibody, and PNEU with an anti-porcine neurofilament antibody, or an antibody recognizing the NeuN antigen. PAEC grafts were massively infiltrated within 24 h by OX42-positive cells, which may correspond to polymorphonuclear (PMN) cells or macrophages. At that moment, the graft contained numerous cells expressing the inducible isoform of NO-synthase (iNOS). Infiltration by ED1-positive macrophages was effective after three days. The beta1-integrin labeling decreased from that time-point to day 7 post-implantation, and vanished after 11 days. Although some OX8-positive cells were present around the graft as soon as 3 days after transplantation, cells expressing the T-cell receptor (TCR)-beta chain infiltrated the graft after 7 days and their number remained low. A strong, diffuse OX8-and ED1-positive immunoreactive material remained in the scar up to the third week. In striking contrast, PNEU grafts remained poorly infiltrated by OX42- or ED1-positive cells during the first two weeks. A massive infiltration by macrophages and TCRbeta-positive lymphocytes occurred after 3 weeks. Natural killer (NK) cells were more scarce. The inflammation territory enlarged, and blood vessels were overloaded with macrophages or lymphocytes. Nevertheless, the graft contained NeuN-positive nuclei and neurites harbouring the porcine neurofilament protein. Hence, rejection was not completed at this time-point. These results suggest that the rapid rejection of PAEC is mainly driven by macrophages and possibly PMN cells, unlike PNEU, whose rejection is delayed and also involves lymphocytes. Differences in immunogenicity of grafted cells and/or patterns of production of pro-inflammatory cytokines may account for these contrasted rejection kinetics.

Lower limb bone hemangiomas in children: report of two cases

Hemangiomas of the bone are rare lesions, accounting for approximately 1% of all primary bone tumors. Hemangiomas occur fairly frequently in the vertebral bodies and the skull, but are unusual in other bones. We report two cases of unusual and fairly rare aspects of this vascular tumor in children. Both cases involved recurrences, which led to a wide bone resection in case 1 and to several curettages in case 2. In these two cases the histological type of hemangioma was capillary. In reviewing the literature we found no indication of wide resection of the benign forms in children.