Stem cell autotomy and niche interaction in different systems

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes(platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells(GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug. In both, moths and the milkweed bug, GSCs form finger-like projections toward the niche, the apical cells(homologs of the hub cells in Drosophila). Whereas in the milkweed bug the projection terminals remain at the surface of the niche cells, in the gipsy moth they protrude deeply into the singular niche cell. In both cases, the projections undergo serial retrograde fragmentation with progressing signs of autophagy. In the gipsy moth, the autotomized vesicles are phagocytized and digested by the niche cell. In the milkweed bug the autotomized vesicles accumulate at the niche surface and disintegrate. Autotomy and sprouting of new projections appears to occur continuously. The significance of the GSC-niche interactions, however, remains enigmatic. Our concept on the signaling relationship between stem cell-niche in general and GSC and niche(hub cells and cyst stem cells) in particular has been greatly shaped by Drosophila melanogaster. In comparing the interactions of GSCs with their niche in Drosophila with those in species exhibiting GSC autotomy it is obvious that additional or alternative modes of stem cell-niche communication exist. Thus, essential signaling pathways, including niche-stem cell adhesion(E-cadherin) and the direction of asymmetrical GSC division- as they were found in Drosophila- can hardly be translated into the systems where GSC autotomywas reported. It is shown here that the serial autotomy of GSC projections shows remarkable similarities with Wallerian axonal destruction, developmental axon pruning and dying-back degeneration in neurodegenerative diseases. Especially the hypothesis of an existing evolutionary conserved "autodestruction program" in axons that might also be active in GSC projections appears attractive. Investigations on the underlying signaling pathways have to be carried out. There are two other well known cases of programmed cell autotomy: the enucleation of erythroblasts in the process of erythrocyte maturation and the segregation of thousands of thrombocytes(platelets) from one megakaryocyte. Both progenitor cell types- erythroblasts and megakaryocytes- are associated with a niche in the bone marrow, erythroblasts with a macrophage, which they surround, and the megakaryocytes with the endothelial cells of sinusoids and their extracellular matrix. Although the regulatory mechanisms may be specific in each case, there is one aspect that connects all described processes of programmed cell autotomy and neuronal autodestruction: apoptotic pathways play always a prominent role. Studies on the role of male GSC autotomy in stem cell-niche interaction have just started but are expected to reveal hitherto unknown ways of signal exchange. Spermatogenesis in mammals advance our understanding of insect spermatogenesis. Mammal and insect spermatogenesis share some broad principles, but a comparison of the signaling pathways is difficult. We have intimate knowledge from Drosophila, but of almost no other insect, and we have only limited knowledge from mammals. The discovery of stem cell autotomy as part of the interaction with the niche promises new general insights into the complicated stem cell-niche interdependence.

Does Carica papaya leaf-extract increase the platelet count? An experimental study in a murine model

Objective:To investigate the potential role of fresh Carica papaya(C.papaya)leaf extract on haematological and biochemical parameters and toxicological changes in a murine model.Methods:In total 36 mice were used for the trial.Fresh C.papaya leaf extract[0.2 mL(2 g)/mouse]was given only to the test group(18 mice).General behavior,clinical signs and feeding patterns were recorded.Blood and tissue samples were collected at intervals.Haematological parameters including platelet,red blood cell(RBC),white blood cell<(WBC),packed cell volume(PCV),serum biochemistry including serum creatinine,serum glutamic-oxaloacetic transaminase(SCOT)and serum glutamic-pyruvic transaminase(SGPT)were determined.Organs for possible histopathological changes were examined.Results:Neither group exhibited alteration of behavior or reduction in food and water intake.Similarly,no significant changes in SCOT,SGPT and serum creatinine levels were delected in the test group.Histopathological organ changes were not observed in either group of mice except in three liver samples of the test group which had a mild focal necrosis.The platelet count(11.33±0.35)×10~5VμL(P=0.00004)and the RBC count(7.97±0.61)×10~/μL(P=0.00003)were significandy increased in the test group compared to that of the controls.However,WBC count and PCV(%)values were not changed significantly in the test group.The platelet count in the test group started to increase significantly from Day 3(3.4±0.18×10~5/μL),reaching almost a fourfold higher at Day 21(11.3×10~5/μL),while it was 3.8X10^5/μL and 5.5×10~5/μL at Day 3 and Day 21 respectively in the control.Likewise,the RBC count in the test group increased from 6×10~6/μL to 9×10~6/μL at Day 21 while it remained near constant in the control group(6×10~6μL).Conclusions:Fresh C.papaya leaf extract significandy increased the platelet and RBC counts in the test group as compared to controls.Therefore,it is very important to identify those chemicals of C.papaya leaves as it can be recommended to be used as a medication to boost thrombopoiesis and erythropoiesis in humans and in animals in which these cell lineages have been compromised.

Abivertinib inhibits megakaryocyte differentiation and platelet biogenesis

Abivertinib,a third-generation tyrosine kinase inhibitor,is originally designed to target epidermal growth factor receptor(EGFR)-activating mutations.Previous studies have shown that abivertinib has promising antitumor activity and a well-tolerated safety profile in patients with non-small-cell lung cancer.However,abivertinib also exhibited high inhibitory activity against Bruton’s tyrosine kinase and Janus kinase 3.Given that these kinases play some roles in the progression of megakaryopoiesis,we speculate that abivertinib can affect megakaryocyte(MK)differentiation and platelet biogenesis.We treated cord blood CD34+hematopoietic stem cells,Meg-01 cells,and C57BL/6 mice with abivertinib and observed megakaryopoiesis to determine the biological effect of abivertinib on MK differentiation and platelet biogenesis.Our in vitro results showed that abivertinib impaired the CFU-MK formation,proliferation of CD34+HSC-derived MK progenitor cells,and differentiation and functions of MKs and inhibited Meg-01-derived MK differentiation.These results suggested that megakaryopoiesis was inhibited by abivertinib.We also demonstrated in vivo that abivertinib decreased the number of MKs in bone marrow and platelet counts in mice,which suggested that thrombopoiesis was also inhibited.Thus,these preclinical data collectively suggested that abivertinib could inhibit MK differentiation and platelet biogenesis and might be an agent for thrombocythemia.