The role of mast cells in ischemic and hemorrhagic brain injury

Stroke, ischemic or hemorrhagic, belongs among the foremost causes of death and disability worldwide. Massive brain swelling is the leading cause of death in large hemispheric strokes and is only modestly alleviated by available treatment. Thrombolysis with tissue plasminogen activator (TPA) is the only approved therapy in acute ischemic stroke, but fear of TPA-mediated hemorrhage is often a reason for withholding this otherwise beneficial treatment. In addition, recanalization of the occluded artery (spontaneously or with thrombolysis) may cause reperfusion injury by promoting brain edema, hemorrhage, and inflammatory cell infiltration. A dominant event underlying these phenomena seems to be disruption of the blood-brain barrier (BBB). In contrast to ischemic stroke, no widely approved clinical therapy exists for intracerebral hemorrhage (ICH), which is associated with poor outcome mainly due to the mass effect of enlarging hematoma and associated brain swelling. Mast cells (MCs) are perivascularly located resident inflammatory cells which contain potent vasoactive, proteolytic, and fibrinolytic substances in their cytoplasmic granules. Experiments from our laboratory showed MC density and their state of granulation to be altered early following focal transient cerebral ischemia, and degranulating MCs were associated with perivascular edema and hemorrhage. (I) Pharmacological MC stabilization led to significantly reduced ischemic brain swelling (40%) and BBB leakage (50%), whereas pharmacological MC degranulation raised these by 90% and 50%, respectively. Pharmacological MC stabilization also revealed a 40% reduction in neutrophil infiltration. Moreover, genetic MC deficiency was associated with an almost 60% reduction in brain swelling, 50% reduction in BBB leakage, and 50% less neutrophil infiltration, compared with controls. (II) TPA induced MC degranulation in vitro. In vivo experiments with post-ischemic TPA administration demonstrated 70- to 100-fold increases in hemorrhage formation (HF) compared with controls HF. HF was significantly reduced by pharmacological MC stabilization at 3 (95%), 6 (75%), and 24 hours (95%) of follow-up. Genetic MC deficiency again supported the role of MCs, leading to 90% reduction in HF at 6 and 24 hours. Pharmacological MC stabilization and genetic MC deficiency were also associated with significant reduction in brain swelling and in neutrophil infiltration. Importantly, these effects translated into a significantly better neurological outcome and lower mortality after 24 hours. (III) Finally, in ICH experiments, pharmacological MC stabilization resulted in significantly less brain swelling, diminished growth in hematoma volume, better neurological scores, and decreased mortality. Pharmacological MC degranulation produced the opposite effects. Genetic MC deficiency revealed a beneficial effect similar to that found with pharmacological MC stabilization. In sum, the role of MCs in these clinically relevant scenarios is supported by a series of experiments performed both in vitro and in vivo. That not only genetic MC deficiency but also drugs targeting MCs could modulate these parameters (translated into better outcome and decreased mortality), suggests a potential therapeutic approach in a number of highly prevalent cerebral insults in which extensive tissue injury is followed by dangerous brain swelling and inflammatory cell infiltration. Furthermore, these experiments could hint at a novel therapy to improve the safety of thrombolytics, and a potential cellular target for those seeking novel forms of treatment for ICH.

Functional outcome and health-related quality of life after traumatic brain injury in the framework of the International Classification of Functioning, Disability and Health (ICF)

Traumatic brain injury (TBI) affects people of all ages and is a cause of long-term disability. In recent years, the epidemiological patterns of TBI have been changing. TBI is a heterogeneous disorder with different forms of presentation and highly individual outcome regarding functioning and health-related quality of life (HRQoL). The meaning of disability differs from person to person based on the individual s personality, value system, past experience, and the purpose he or she sees in life. Understanding of all these viewpoints is needed in comprehensive rehabilitation. This study examines the epidemiology of TBI in Finland as well as functioning and HRQoL after TBI, and compares the subjective and objective assessments of outcome. The frame of reference is the International Classification of Functioning, Disability and Health (ICF). The subjects of Study I represent the population of Finnish TBI patients who experienced their first TBI between 1991 and 2005. The 55 Finnish subjects of Studies II and IV participated in the first wave of the international Quality of life after brain injury (QOLIBRI) validation study. The 795 subjects from six language areas of Study III formed the second wave of the QOLIBRI validation study. The average annual incidence of Finnish hospitalised TBI patients during the years 1991-2005 was 101:100 000 in patients who had TBI as the primary diagnosis and did not have a previous TBI in their medical history. Males (59.2%) were at considerably higher risk of getting a TBI than females. The most common external cause of the injury was falls in all age groups. The number of TBI patients ≥ 70 years of age increased by 59.4% while the number of inhabitants older than 70 years increased by 30.3% in the population of Finland during the same time period. The functioning of a sample of 55 persons with TBI was assessed by extracting information from the patients medical documents using the ICF checklist. The most common problems were found in the ICF components of Body Functions (b) and Activities and Participation (d). HRQoL was assessed with the QOLIBRI which showed the highest level of satisfaction on the Emotions, Physical Problems and Daily Life and Autonomy scales. The highest scores were obtained by the youngest participants and participants living independently without the help of other people, and by people who were working. The relationship between the functional outcome and HRQoL was not straightforward. The procedure of linking the QOLIBRI and the GOSE to the ICF showed that these two outcome measures cover the relevant domains of TBI patients functioning. The QOLIBRI provides the patients subjective view, while the GOSE summarises the objective elements of functioning. Our study indicates that there are certain domains of functioning that are not traditionally sufficiently documented but are important for the HRQoL of persons with TBI. This was the finding especially in the domains of interpersonal relationships, social and leisure activities, self, and the environment. Rehabilitation aims to optimize functioning and to minimize the experience of disability among people with health conditions, and it needs to be based on a comprehensive understanding of human functioning. As an integrative model, the ICF may serve as a frame of reference in achieving such an understanding.

Stanniocalcin-1 in cell stress and differentiation

Stanniocalcin-1 (STC-1) is a 56 kD homodimeric protein which was originally identified in bony fish, where it regulates calcium/phosphate homeostasis and protects against toxic hypercalcemia. STC-1 was considered unique to fish until the cloning of cDNA for human STC-1 in 1995 and mouse Stc-1 in 1996. STC-1 is conserved through evolution with human and salmon STC-1 sharing 60% identity and 80% similarity. The surprisingly high homology between mammalian and fish STC-1 and the protective actions of STC-1 in terminally differentiated neurons, originally reported by my colleagues, prompted me to further study the role of STC-1 in cell stress and differentiation. One purpose was to determine whether there is an inter-relationship between terminally differentiated cells and STC-1 expression. The study revealed an accumulation of STC-1 in mature megakaryocytes and adipocytes, i.e. postmitotic cells with limited or lost proliferative capacity. Still proliferating uninduced cells were negative for STC-1 mRNA and protein, whereas differentiating cells accumulated STC-1 in their cytoplasm. Interestingly, in liposarcomas the grade inversely correlated with STC-1 expression. Another aim was to study how STC-1 gene expression is regulated. Given that IL-6 is a cytokine with neuroprotective actions, by unknown mechanisms, we examined whether IL-6 regulates STC-1 gene expression. Treatment of human neural Paju cells with IL-6 induced a dose-dependent upregulation of STC-1 mRNA levels. This induction of STC-1 expression by IL-6 occurred mainly through the MAPK signaling pathway. Furthermore, I studied the role of IL-6-mediated STC-1 expression as a mechanism of cytoprotection conferred by hypoxic preconditioning (HOPC) in brain and heart. My findings show that Stc-1 was upregulated in brain after hypoxia treatment. In the brain of IL-6 deficient mice, however, no upregulation of Stc-1 expression was evident. After induced brain injury the STC-1 response in brains of IL-6 transgenic mice, with IL-6 overexpression in astroglial cells, was stronger than in brains of WT mice. These results indicate that IL-6-mediated expression of STC-1 is one molecular mechanism of HOPC-induced tolerance to brain ischemia. The protection conferred by HOPC in heart occurs during a bimodal time course comprising early and delayed preconditioning. Interestingly, my results showed that the expression of Stc-1 in heart was upregulated in a biphasic manner during HOPC. IL-6 deficient mice did not, however, show a similar biphasic manner of Stc-1 upregulation as did WT mice. Instead, only an early upregulation of Stc-1 expression was evident. The results suggest that the upregulation of Stc-1 during the delayed preconditioning is IL-6-dependent. The upregulated expression of Stc-1 during the early preconditioning, however, is only partly IL-6-dependent and possibly also directly mediated by HIF-1. These findings suggest that STC-1 is a pro-survival protein for terminally differentiated cells and that STC-1 expression may in fact be regulated by stress. In addition, I show that STC-1 gene upregulation, mediated in part by IL-6, is a new mechanism of protection conferred by HOPC in brain and heart. Because of its importance for fundamental biological processes, such as differentiation and cytoprotection, STC-1 may have therapeutic implications for management of stroke, neurodegenerative diseases, cancer, and obesity.

CNS injury, γ1 laminin, and its KDI peptide

Nisäkkäillä keskushermoston uudistuminen on rajallista. Keskushermostovamman jälkeen aktivoituu monien paranemista edistävien tekijöiden lisäksi myös estäviä tekijöitä. Monella molekyylillä, kuten laminiinilla, on keskushermoston paranemista tehostava vaikutus. Laminiinit ovat myös kehon tyvikalvojen oleellisia rakennuskomponentteja. Keskushermoston laminiinit ovat tärkeitä sikiökehityksen aikana, esimerkiksi hermosäikeiden ohjauksessa. Myöhemmin ne osallistuvat veriaivoesteen ylläpitoon sekä vammojen jälkeiseen kudosreaktioon. Väitöskirjatutkimuksessani olen selvittänyt lamiiniinien, erityisesti γ1 laminiinin ja sen KDI peptidin, ekspressiota keskushermoston vammatilanteissa. Kokeellisessa soluviljelmäasetelmassa, joka simuloi vammautunutta keskushermostoympäristöä, osoitimme että KDI peptidi voimistaa sekä hermosolujen selviytymistä että hermosäikeiden kasvua. Kainihappo on glutamaattianalogi, ja glutamaattitoksisuudella uskotaan olevan tärkeä merkitys keskushermoston eri vamma- ja sairaustilanteissa tapahtuvassa hermosolukuolemassa. Toisessa väitöskirjani osatyössä osoitimme eläinmallissa KDI peptidin suojaavan rotan aivojen hippokampuksen hermosoluja kainihapon aiheuttamalta solutuholta. Elektrofysiologisilla mittauksilla osoitimme kolmannessa osatyössäni, että KDI peptidi estää glutamaattireseptorivirtoja ja suojaa siten glutamaattitoksisuudelta. Aivoveritulpan aiheuttama aivovaurio on yleinen syy aivohalvaukseen. Viimeisessä osatyössäni tutkimme eläinmallissa laminiinien ekspressiota iskemian vaurioittamassa aivokudoksessa. Laminiiniekspression todettiin voimistuvan vaurion jälkeen sekä tyvikalvo- että soluväliainerakenteissa. Vaurion ympärillä havaittiin astrosyyttejä, jotka jo melko aikaisessa vaiheessa vamman jälkeen ekspressoivat γ1 laminiinia ja KDI peptidiä. Tästä voidaan päätellä laminiinien osallistuvan aivoiskeemisen vaurion patofysiologiaan. Yleisesti väitöskirjatyöni kartoitti laminiinien ekspressiota sekä terveessä että vammautuneessa keskushermostossa. Väitöskirjatyöni tukee hypoteesia, jonka mukaan KDI peptidi suojaa keskushermostoa vaurioilta.