Co-stimulatory effect of TLR2 and TLR4 stimulation on megakaryocytic development is mediated through PI3K/NF-ĸB and XBP-1 loop.

Toll-like receptors (TLRs) are a class of proteins (patterns recognition receptors-PRRs) capable of recognizing molecules frequently found in pathogens (that are so-called pathogen-associated molecular patterns-PAMPs), they play a key role in the initiation of innate immune response by detecting PAMPs. Our findings show that the functional effects of TLRs co-stimulation on megakaryocytopoiesis. A single cell may receive multiple signal inputs and we consider that multiple TLRs are likely triggered during infection by multiple PAMPs that, in turn, might be involved in infection driven megakaryocytopoiesis, and the present study provide the evidence for the megakaryocytic effects of TLRs co-stimulation.

Endoplasmic reticulum stress induced apoptosis and caspase activation is mediated through mitochondria during megakaryocyte differentiation.

Megakaryocytopoiesis involves the process of the development of hematopoietic stem cells into megakaryocytes (MKs), which are the specialized cells responsible for the production of blood platelets. Platelets are one of the crucial factors for hemostasis and thrombosis. In terminally differentiated MKs, many molecular process such as caspase activation and a massive cytoskeletal rearrangement drive the formation of cytoplasmic extensions called proplatelets. These cytoplasmic extensions packed with granules and organelles are then released from the bone marrow into the blood circulation as platelets. Classically, caspase activation is associated with apoptosis and recent reports suggest their involvement in cell differentiation and maturation. There is no clear evidence about the stimulus for caspase activation during megakaryocyte development. In the current study, we attempted to understand the importance of endoplasmic reticulum stress in the caspase activation during megakaryocyte maturation. We used human megakaryoblstic cell line (Dami cells) as an experimental model. We used PMA (Phorbol 12-myristate 13 acetate) to induce megakaryocytic differentiation to understand the involvement of ER stress and caspase activation during MK maturation. Further, we used Thapsigargin, a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) as a positive control to induce ER stress. We observed larger and adherent cells with the increased expression of megakaryocytic markers (CD41 and CD61) and UPR markers in PMA or Thapsigargin treated cells as compared to control. Also, Thapsigargin treatment induced increased caspase activity and PARP cleavage. The increased expression of megakaryocyte maturation markers alongside with ER stress and caspase activation suggests the importance of ER stress in caspase activation during MK maturation.

Long non-coding RNA: Classification, biogenesis and functions in blood cells.

While there exist some long non-coding RNAs (lncRNAs) that are structurally similar to mRNAs (capped, spliced, poly a tail), not all of the lncRNAs exhibit these features. Structurally, lncRNAs are classified under the regulatory non-coding RNAs category these lncRNA molecules operate as signals, decoys, guides, and scaffolds. In eukaryotes, lncRNAs are transcribed by RNA Polymerase II and RNA Polymerase III at several loci of the genome. Unlike other protein-coding mRNAs, lncRNAs exhibit functional uniqueness by participating in and modulating the various cellular processes such as, histone modification, DNA methylation, and cellular transcription (Wei et al., 2017). LncRNA alters chromatin structure and DNA accessibility, thereby regulating patterns of gene expression (Wang et al., 2011b). Disordered lncRNA with quantitative or qualitative alterations lead to the progression of numerous diseases including blood associated diseases. LncRNAs not only regulate lineage commitment such as cardiovascular lineage but also contribute for the hematopoietic stem cell development with a significant role in myeloid and lymphoid lineage commitment. However, the key molecular functions of lncRNAs in hematopoiesis are still unclear, particularly, their functional role during megakaryocyte development from hematopoietic stem cells (HSCs) is largely unexplored. This review summarizes the current status of knowledge on lncRNAs classification, biogenesis and its role in blood cells.