Thomas Bosch

Growth regulation in Hydra: Relationship between epithelial cell cycle length and growth rate☆

The relationship between epithelial cell production and growth rate was investigated in Hydra attenuata under different feeding regimes. The increase of epithelial cell number was compared to the duration of the epithelial cell cycle using standard methods of cell cycle analysis. The results indicate that cell cycle changes accompanying changes in feeding regime are not sufficient to explain the altered growth rate. Under heavy feeding regimes, epithelial cell production equals tissue growth rate. At low feeding level or under starvation conditions the epithelial cell cycle lengthens and growth rate of epithelial cell population is slowed. However, the cell cycle changes are insufficient to account for the reduction in tissue growth and thus there is an effective overproduction of epithelial cells amounting to 10% per day. Evidence suggests that these excess cells are phagocytized by neighboring cells in the tissue. Thus phagocytosis is directly or indirectly involved in regulating the growth of hydra tissue.

Stem cells of Hydra magnipapillata can differentiate into somatic cells and germ line cells

We investigated whether all stem cells of Hydra can differentiate both somatic cells and gametes or if a separate germ line exists in these phylogenetically old organisms. The differentiation potential of single stem cells was analyzed by applying a statistical cloning procedure. All stem cell clones were found to differentiate somatic cells. No clone was found to contain stem cells which do not differentiate. Most of the clones could be induced to form gametes. No clone was found that produced gametes only. The results indicate that stem cells are multipotent in the sense that individual stem cells can differentiate into somatic cells as well as germ line cells.

Therapeutic apheresis--state of the art in the year 2005.

Abstract:u2002 Therapeutic apheresis is an extracorporeal blood purification method for the treatment of diseases in which pathological proteins or cells have to be eliminated. Selective plasma processing is more efficient in pathogen removal than unselective plasma exchange and does not require a substitution fluid like albumin. This overview presents the various selective devices for the treatment of plasma (plasmapheresis) and blood cells (leukocyte apheresis). Prospective randomized trials were performed for the treatment of age‐related macular degeneration (Rheopheresis), sudden hearing loss (heparin‐induced lipoprotein precipitation [HELP]), rheumatoid arthritis (Prosorba), dilative cardiomyopathy (Ig‐Therasorb, Immunosorba), acute‐on‐chronic liver failure (molecular adsorbent recirculating system [MARS]), and ulcerative colitis (Cellsorba). Prospective non‐randomized controlled trials were carried out treating hypercholesterolemia (Liposorber) and crossmatch‐positive recipients before kidney transplantation (Immunosorba). Uncontrolled studies were done for ABO‐incompatibility in living donor kidney transplantation (KT) (Glycosorb), acute humoral rejection after KT (Immunosorba) and acute liver failure (Prometheus). According to the 2002 International Apheresis Registry covering 11428 sessions in 811 patients, 79% of the patients showed an improvement of their condition by apheresis and only a few sessions were fraught with adverse effects (AE). The major AE were blood access difficulties (3.1%) and hypotension (1.6%). In summary, therapeutic apheresis is a safe and effective procedure for the treatment of diseases refractory to drug therapy.

Direct Adsorption of Low‐Density Lipoprotein by DALI‐LDL‐Apheresis: Results of a Prospective Long‐term Multicenter Follow‐up Covering 12 291 Sessions

Abstract:u2002 Direct adsorption of lipoproteins (DALI) is the first low density lipoprotein (LDL)‐apheresis technology by which atherogenic LDL and lipoprotein(a) (Lp(a)) can be selectively removed from whole blood without plasma separation. The present follow‐up was carried out to evaluate the clinical efficacy, selectivity and safety of long‐term DALI apheresis. The follow‐up was carried out in an open, prospective uncontrolled multicenter clinical design. Included were 158 drug‐resistant hypercholesterolemic patients from 28 apheresis centers. These patients underwent 12u2003291 DALI sessions between January 1997 and March 2002. The patients suffered from severe atherosclerosis and their mean LDL‐C was 188u2003mg/dL before the sessions. Mean follow‐up was 25u2003±u200316 (range 1–56) months during which 78u2003±u200353 sessions were carried out. In most treatments, DALI 750 (63%) or DALI 1000 (30%) adsorbers were used. On average, 7423u2003±u20031495u2003mL blood was processed at a flow rate of 84u2003±u200316u2003mL/min in 102u2003±u200325u2003min. Acute reductions by the single DALI sessions averaged 69u2003±u200312% for LDL‐C, 41u2003±u200318% for TG, 15u2003±u200310% for HDL‐C, 19u2003±u200311% for fibrinogen and 62u2003±u200324% for Lp(a) (in patients with Lp(a)u2003>u200330u2003mg/dL). Adverse events were recorded in only 3.9% of the sessions. In this 5‐year follow‐up, long‐term therapy with DALI was safe, effective and selective as LDL‐C and Lp(a) could be reduced by >60% per session in approximately 100u2003min treatment time while HDL‐C decrease and the incidence of AE were low.

State of the art of low-density lipoprotein apheresis in the year 2003.

Abstract:u2002 Low‐density lipoprotein (LDL) apheresis is a last‐resort treatment for hypercholesterolemic patients resistant to conservative lipid‐lowering therapy. In the extracorporeal circuit, LDL, Lp(a) and coagulation factors are selectively eliminated, while the beneficial proteins like high‐density lipoprotein, albumin and immunoglobulins are returned to the patient. Clinical effects of LDL apheresis comprise improvement of symptoms like angina and exercise tolerance, reduction of clinical coronary events like unstable angina, need for angioplasty or bypass operation, myocardial infarction and ultimately coronary mortality. The reduction of atherogenic lipoproteins and of coagulation factors by LDL apheresis (LA) positively influences hemorheology, endothelial function and coronary reserve. In the controlled LAARS, LA significantly improved the electrocardiographic signs of myocardial ischemia in the treadmill test. In angiographically controlled trials such as LARS and L‐CAPS, a reduction of progression of coronary lesions was observed; in favorable cases, regression of the stenoses could be documented. In addition, in the LDL apheresis coronary morphology trial, LA decreased the coronary plaque area. The Hokuriku trial documented a 72% decrease of coronary events (MACE) in the LA group vs. controls treated only by statins. In longitudinal studies, the incidence of MACE after regular LA decreased compared with the preapheresis period in the same patients. Apart from coronary heart disease, recent studies indicate a positive effect of LA also on carotid artery stenoses and peripheral vascular disease. Prospective randomized studies showed the beneficial effects of cascade filtration on age‐related macular degeneration and of heparin‐induced LDL precipitation apheresis on acute inner ear deafness.

Cloning and characterization of BS-cadherin, a novel cadherin from the colonial urochordate Botryllus schlosseri

The genomic DNA for a novel member of the cadherin family (BS-cadherin) was cloned and characterized from the colonial marine invertebrate, Botryllus schlosseri. Using a differential display of mRNA by means of PCR, a small cDNA fragment of 380 nucleotides was found to be specifically expressed in a colony undergoing allogeneic rejection processes, as compared with naive parts of the same genotype. This cDNA fragment was used as a probe to screen a genomic library of Botryllus schlosseri. A genomic fragment containing an ORF of 2718 nucleotides, with no introns, was isolated. The encoded protein exhibits a typical structure of cadherins; an extracellular domain with conserved repeated sequences (cadherin signatures), a single transmembrane domain and a conserved cytoplasmic tail region. The BS-cadherin amino-acid sequence shows 32-35% identity to mature classical cadherins type I, e.g., N-, P- and E-cadherin as well as mature classical cadherins type II, e.g., human cadherin-6, -8 and OB-cadherin. This cadherin represents a new cadherin gene family, evolutionarily distant to all other known classical cadherins.

Clinical Effects of Direct Adsorption of Lipoprotein Apheresis: Beyond Cholesterol Reduction

Abstract: Direct adsorption of lipoproteins (DALI) from whole blood is the first LDL hemoperfusion technique for extracorporeal LDL and Lp(a) elimination without initial plasma separation. Thus, this technique is characterized by high user‐friendliness. In a long‐term multicenter study, LDL and lipoprotein (a) (Lp(a)) reductions were 69% and 64%, respectively, per session. Adverse effects were rare, as 95% of the sessions were uneventful. Biocompatibility studies showed only minor blood–adsorber interactions for most parameters; however, there was a significant bradykinin generation. After a single session, significant reductions of plasma viscosity, erythrocyte aggregation and adhesion molecules were documented. A retrospective analysis of 18 chronic DALI patients revealed that in the majority of patients, symptoms like angina and dyspnea as well as their general status and subjective well‐being improved significantly. Moreover, the objective cardiovascular event rate (MACE) decreased from a total of 26 in the 3‐year period prior to DALI to 6 during a mean follow‐up of 3.8 years during chronic DALI therapy. Thus, the average event rate of 0.48 per patient year at baseline could be significantly reduced to 0.09 (Pu2003<u20030.004) by DALI. This impressive improvement of symptoms and coronary events can hypothetically be related to the improvement of hemorheology and the transformation of unstable into stable plaques by DALI LDL apheresis.

Role of the cellular environment in interstitial stem cell proliferation in Hydra

SummaryThe role of the cellular environment on hydra stem cell proliferation and differentiation was investigated by introduction of interstitial cells into host tissue of defined cellular composition. In epithelial tissue lacking all non-epithelial cells the interstitial cell population did not grow but differentiated into nerve cells and nematocytes. In host tissue with progressively increased numbers of nerve cells growth of the interstitial cell population was positively correlated to the nerve cell density. In agreement with previous observations (Bode et al. 1976), growth of the interstitial cell population was also found to be negatively correlated to the level of interstitial cells present. The strong correlation between the growth of the interstitial cell population and the presence of interstitial cells and nerve cells implies that interstitial cell proliferation is controlled by a feedback signal from interstitial cells and their derivatives. Our results suggest that the cellular environment of interstitial cells provides cues which are instrumental in stem cell decision making.

Plasmapheresis in C4d-positive acute humoral rejection following kidney transplantation: a review of 4 cases.

Abstract:u2003 Acute and chronic rejection after kidney transplantation has long been exclusively attributed to cellular and vascular mechanisms. Modern immunosuppressive therapy, therefore, addresses the cellular immune system. Rising experiences in kidney transplantation in the last few decades have revealed that some types of rejection are refractory to the conventional immunosuppressive treatment. Humoral rejection, which has previously been reported as a crucial factor in hyperacute rejection, is now suspected to play also an important role in acute and chronic rejection. Acute humoral rejection (AHR) is characterized by immunohistochemical detection of C4d deposits in peritubular capillaries. As shown for other antibody‐mediated diseases, such as some autoimmune diseases, plasmapheresis has been suggested to be an efficient therapeutic approach in AHR. We present four patients with C4d‐positive AHR in the early phase after kidney transplantation. In three of the four patients, humoral graft rejection was successfully treated by plasmapheresis. Graft function was significantly improved with a stable long‐term outcome. One patient lost the graft. Although the number of patients with C4d‐positive AHR treated by plasmapheresis is limited, plasma exchange appears to be an efficient and powerful therapeutic approach to control humoral rejection.

Cloning of a ras-related gene from Hydra which responds to head-specific signals

Members of the Ras family of proteins are important components of signal transduction pathways responding to external signals and leading to changes in cell behavior. Analysis of two ras-related genes in the phylogenetically old metazoan Hydra indicates that in normal animals both genes are expressed in all body regions of the polyp. Upon head removal, however, the transcript level of one of the two genes, ras2, decreases rapidly in the upper gastric region which is adjacent to the former head. The decrease is transient and specific for ras2, since no changes could be observed in the transcript level of the related ras1 gene or any other gene. The disappearance of the ras2 mRNA can be prevented completely by brief exposure of decapitated polyps to the protein kinase C activator TPA, which previously was shown to be capable of converting gastric tissue into head tissue [Müller, W.A. In: Othmer, H.G. (Ed.) Experimental and Theoretical Advances in Biological Pattern Formation. Plenum Press, New York, NY, 1993, pp. 237-253]. The finding that Hydra ras2 expression is strongly dependent on a signal from the head provides the first evidence for ras expression being regulated in pattern formation.