T. Kalle Lundgren

Histone H2AX-dependent GABA A receptor regulation of stem cell proliferation

Stem cell self-renewal implies proliferation under continued maintenance of multipotency. Small changes in numbers of stem cells may lead to large differences in differentiated cell numbers, resulting in significant physiological consequences. Proliferation is typically regulated in the G1 phase, which is associated with differentiation and cell cycle arrest. However, embryonic stem (ES) cells may lack a G1 checkpoint. Regulation of proliferation in the ‘DNA damage’ S/G2 cell cycle checkpoint pathway is known for its role in the maintenance of chromatin structural integrity. Here we show that autocrine/paracrine γ-aminobutyric acid (GABA) signalling by means of GABAA receptors negatively controls ES cell and peripheral neural crest stem (NCS) cell proliferation, preimplantation embryonic growth and proliferation in the boundary-cap stem cell niche, resulting in an attenuation of neuronal progenies from this stem cell niche. Activation of GABAA receptors leads to hyperpolarization, increased cell volume and accumulation of stem cells in S phase, thereby causing a rapid decrease in cell proliferation. GABAA receptors signal through S-phase checkpoint kinases of the phosphatidylinositol-3-OH kinase-related kinase family and the histone variant H2AX. This signalling pathway critically regulates proliferation independently of differentiation, apoptosis and overt damage to DNA. These results indicate the presence of a fundamentally different mechanism of proliferation control in these stem cells, in comparison with most somatic cells, involving proteins in the DNA damage checkpoint pathway.

Development of a bioactive implant for repair and potential healing of cranial defects

The repair of complex craniofacial bone defects is challenging and a successful result is dependent on the size of the defect, quality of the soft tissue covering the defect, and choice of reconstruction method. The objective of this study was to develop a bioactive cranial implant that could provide a permanent reconstructive solution to the patient by stimulating bone healing of the defect. In this paper the authors report on the feasibility and clinical results of using such a newly developed device for the repair of a large traumatic and therapy-resistant cranial bone defect. The patient had undergone numerous attempts at repair, in which established methods had been tried without success. A mosaic-designed device was manufactured and implanted, comprising interconnected ceramic tiles with a defined calcium phosphate composition. The clinical outcome 30 months after surgery revealed a restored cranial vault without postoperative complications. Computed tomography demonstrated signs of bone ingrowth. Examination with combined (18)F-fluoride PET and CT provided further evidence of bone healing of the cranial defect.

Differential expression and dynamic changes of murine NEDD9 in progenitor cells of diverse tissues.

NEDD9 is a scaffolding protein in the integrin signaling pathway that is involved in cell adhesion dynamics. Little is known of the cellular localization of NEDD9 expression during embryonic development. In the present study, we have analyzed NEDD9 mRNA expression in the mouse and identified new relevant expression sites. In addition, we have characterized NEDD9 protein expression pattern for the first time in mammals. At E9.5-E10.5, high levels of Nedd9 and the neurogenic transcription factor neurogenin-2 (Ngn2) were found to largely overlap in two discrete domains of the trunk neural tube along its dorso-ventral axis, with Nedd9 extending to more ventral regions of the ventricular zone and Ngn2 differentially expressed in neuronally committed progenitors of the intermediate zone. At encephalic and trunk levels of the neural tube, NEDD9 was present in Sox2(+) progenitor cell populations mostly generating Ngn2(+) and/or Nurr1(+) cells. A sharp down-regulation of NEDD9 expression was found in cells upon lineage commitment, as observed in Nurr1(+) and Ngn2(+) mesencephalic dopaminergic and brainstem neuronal progenitors. In other tissues/organs, i.e. prospective heart, retina, olfactory epithelium, gonads, cartilage, gut and pituitary gland, NEDD9 was found to be co-expressed with Sox2, RXR alpha and/or Nurr1-like proteins, suggesting that NEDD9 expression is confined to early progenitors involved in diverse organogenesis and that it may depend on the repertoire and levels of retinoic acid co-receptors expressed by those cells.

Engineering the recruitment of phosphotyrosine binding domain- containing adaptor proteins reveals distinct roles for RET receptor-mediated cell survival

The RET receptor tyrosine kinase is important for several different biological functions during development. The recruitment at the phosphorylated Tyr1062 site in RET of a number of different phosphotyrosine binding (PTB) domain-containing adaptor proteins, including Shc and Frs2, plays a dominant role for the multiple different biological functions of the RET receptor during development, including stimulation of cell survival. Here, we demonstrate that a competitive recruitment of Shc as opposed to Frs2 mediates the survival signaling arising from RET activation. Based on results from a peptide array, we have genetically engineered the PTB domain binding site of RET to rewire its recruitment of the PTB proteins Shc and Frs2. An engineered RET that has a competitive interaction with Shc at the expense of Frs2, but not a RET receptor that only recruits Frs2, activates cell survival signaling pathways and is protective from cell death in neuronal SK-N-MC cells. Thus, cell type-specific functions involve a competitive recruitment of different PTB adaptor molecules by RET that activate selective signaling pathways.

RET PLCγ Phosphotyrosine Binding Domain Regulates Ca2+ Signaling and Neocortical Neuronal Migration

The receptor tyrosine kinase RET plays an essential role during embryogenesis in regulating cell proliferation, differentiation, and migration. Upon glial cell line-derived neurotrophic factor (GDNF) stimulation, RET can trigger multiple intracellular signaling pathways that in concert activate various downstream effectors. Here we report that the RET receptor induces calcium (Ca2+) signaling and regulates neocortical neuronal progenitor migration through the Phospholipase-C gamma (PLCγ) binding domain Tyr1015. This signaling cascade releases Ca2+ from the endoplasmic reticulum through the inositol 1,4,5-trisphosphate receptor and stimulates phosphorylation of ERK1/2 and CaMKII. A point mutation at Tyr1015 on RET or small interfering RNA gene silencing of PLCγ block the GDNF-induced signaling cascade. Delivery of the RET mutation to neuronal progenitors in the embryonic ventricular zone using in utero electroporation reveal that Tyr1015 is necessary for GDNF-stimulated migration of neurons to the cortical plate. These findings demonstrate a novel RET mediated signaling pathway that elevates cytosolic Ca2+ and modulates neuronal migration in the developing neocortex through the PLCγ binding domain Tyr1015.

Subcellular receptor redistribution and enhanced microspike formation by a Ret receptor preferentially recruiting Dok

Ret is a receptor tyrosine kinase for the GDNF family of ligands and plays important roles during nervous system development for cell proliferation, cell migration and neurite growth. Signaling initiated from intracellular tyrosine 1062, by recruitment of several different phosphotyrosine binding (PTB) proteins (i.e. Shc, Frs2 and Dok), is important for these biological effects. By a single amino acid substitution in the PTB domain binding sequence of Ret, we have rewired the receptor such that it preferentially recruits Dok (Ret(Dok+)) with little or no remaining interactions with Shc and Frs2. Ret(Dok+) displays a sustained MAP kinase activation and a loss of Akt signaling compared to Ret(WT). We show that early events after ligand stimulation of Ret(Dok+) include massive formation of fine microspikes that are believed to be priming structures for neurite growth from the cell soma. The Ret(Dok+) receptors relocated in the membrane compartment into focal clusters at the tip of the microspikes, which was associated with Cdc42 activation. These results suggest that engagement of different adaptor proteins by Ret results in very different downstream signaling and functions within neurons and that Dok recruitment leads to a rapid receptor relocation and formation of microspikes.

Cell Migration by a FRS2-Adaptor Dependent Membrane Relocation of Ret Receptors

During development neural progenitor cells migrate with extraordinary precision to inhabit tissues and organs far from their initial position. Little is known about the cellular basis for directional guidance by tyrosine kinase receptors (RTKs). RET is a RTK with important functions in guiding the migration of neuronal cells, and RET dysregulation leads to clinical disease such as agangliosis of the colon. We show here that RET migration in neuroepitheliomal and non‐neuronal cells is elicited by the activation of specific signaling pathways initiated by the competitive recruitment of the FRS2 adaptor molecule to tyrosine 1062 (Y1062) in RET. FRS2 selectively recruited RET to focal complexes and led to activation of SRC family kinases and focal adhesion kinase (FAK). Activation of SRC depended on its direct interaction with RET at a different intracellular tyrosine (Y981) and activation of molecular signaling from these two separate sites in concert regulated migration. Our data suggest that an important function for FRS2 is to concentrate RET in membrane foci, leading to an engagement of specific signaling complexes localized in these membrane domains. J. Cell. Biochem. 104: 879–894, 2008.

Solely Penile Skin for Neovaginal Construction in Sex Reassignment Surgery

Background: Gender reassignment surgery due to transsexualism (International Classification of Diseases, Tenth Revision: F64.0) is a procedure becoming increasingly common worldwide as a result of a significant increase in diagnostic incidence. Several methods have been described for this complex surgery, but no internationally agreed upon gold standard exists, in particular with regard to which methods allow for creating a sufficient neovaginal depth. Methods: We use a 2-stage technique using solely penile skin for creating a neovaginal cavity and present the long-term outcome in terms of measured neovaginal depth. Eighty patients were included. Patients’ neovaginal depth was measured in a standardized fashion 6 months or more after initial surgery. Results were compared with published data on female anatomy. Results: The average neovaginal depth achieved was 10.2 cm. Having had a postoperative complication and noncompliance to neovaginal dilatation were both negatively correlated with neovaginal depth, whereas higher body mass index was not. Most patients received a neovaginal depth sufficient for penetrative intercourse and within the range for biological women. Conclusions: Using solely penile skin for the vaginal lining is a satisfactory surgical method to achieve adequate vaginal depth, provided that the postoperative dilatation regimen is followed. This holds true regardless of age or body mass index.

Midface Osteotomies for Feminization of the Facial Skeleton

Summary: Facial feminization surgery is a term to describe the surgical alteration of a masculine facial appearance to a more feminine appearance, which is most commonly performed for male-to-female transsexual individuals. To alter the midfacial relations, segmentalized osteotomies were performed in selected patients expanding on the established techniques for facial feminization surgery. All patients underwent a preoperative 3D computerized tomography scan and 3D photography before and after the surgery. The inclusion of the midface in surgery was determined based on the relative projection and angle of the zygomatic body compared with the supraorbital region (the supraorbital region was reduced in all patients). Patients were prospectively followed up by 3D surface photography and 3D computerized tomography scans. Rotation and advancement of the zygomatic region was found to be an effective way to further feminize the midfacial appearance in selected male-to-female transsexual patients. No major surgical complications occurred. Although somewhat technically challenging, we suggest that midface surgery should be considered for feminizing purposes in order for the patient to achieve a long-term favorable result compared with other alternative methods.

BCG-induced cytokine release in bladder cancer cells is regulated by Ca2+ signaling

Bacillus Calmette–Guérin (BCG) is widely used in the clinic to effectively treat superficial urinary bladder cancer. However, a significant proportion of patients who fail to respond to BCG risk cystectomy or death. Though more than 3 million cancer treatments with BCG occur annually, surprisingly little is known about the initial signaling cascades activated by BCG. Here, we report that BCG induces a rapid intracellular Ca2+ (calcium ion) signal in bladder cancer cells that is essential for activating the transcription factor nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) and for synthesizing and secreting proinflammatory cytokines, including interleukin 8 (IL‐8). A similar Ca2+ response was observed when cells were exposed to the supernatant of BCG. Studying cellular molecular mechanisms involved in the BCG signaling event, we found pivotal roles for phospholipase C and the Toll‐like receptor 4. Further assessment revealed that this signaling pathway induces synthesis of IL‐8, whereas exocytosis appeared to be controlled by global Ca2+ signaling. These results shed new light on the molecular mechanisms underlying BCG treatment of bladder cancer, which can help in improving therapeutic efficacy and reducing adverse side effects.