Akt-mediated mitochondrial metabolism regulates proplatelet formation and platelet shedding post vasopressin exposure

Multimodal discovery of bavachinin A: A natural FLT3 agonist for treating thrombocytopenia

BACKGROUND

Radiation-induced thrombocytopenia (RIT) poses a serious risk to patients with cancer undergoing radiotherapy and leads to hemorrhage and mortality. Unfortunately, effective treatment options for RIT are currently limited.

PURPOSE

This study aimed to discover active compound from Fructus Psoraleae, a traditional Chinese medicine recognized for its hemostatic properties, and to elucidate its mechanism of action in the treatment of RIT.

METHODS

The efficacy of Fructus Psoraleae in treating thrombocytopenia was assessed using network pharmacology. A drug-screening model was built using a naive Bayes algorithm to determine the effective compounds in Fructus Psoraleae. Giemsa staining and flow cytometry were used to evaluate the effects of bavachinin A on megakaryocytes (MK) differentiation. RIT and thrombopoietin (TPO) receptor (c-MPL) knockout (c-MPL-/-) mice were used to assess the therapeutic efficacy of bavachinin A in mitigating thrombocytopenia. Tg (cd41:eGFP) zebrafish were used to investigate the effect of bavachinin A on thrombopoiesis. RNA sequencing (RNA-seq), molecular docking simulations, molecular dynamics simulations, drug affinity responsive target stability assay (DARTS), and biolayer interferometry (BLI) were used to elucidate the molecular mechanisms of action of bavachinin A against thrombocytopenia.

RESULTS

In silico analysis using a drug screening model identified bavachinin A as promising candidate compound derived from Fructus Psoraleae. In vitro experiments demonstrated that Bavachinin A induced MK differentiation. In vivo experiments revealed that bavachinin A augmented platelet levels and improved coagulation in RIT mice, facilitated megakaryopoiesis and platelet levels in c-MPL-/- mice, and accelerated thrombopoiesis in zebrafish. Furthermore, RNA-seq, molecular docking simulations, molecular dynamics simulations, DARTS, and BLI demonstrated that bavachinin A bound directly to fms-like tyrosine kinase 3 (FLT3). Notably, blocking FLT3 or phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway hindered bavachinin-A-induced MK differentiation. However, repressing the TPO/c-MPL signaling pathway had no significant effect.

CONCLUSION

Bavachinin A promotes MK differentiation and thrombopoiesis by directly binding to FLT3 and activating PI3K/Akt signaling. Importantly, this effect was not dependent on the conventional TPO/c-MPL signaling pathway. This study underscores the translational potential of bavachinin A as a promising novel therapeutic for thrombocytopenia, offering novel insights into TPO-independent mechanisms of thrombopoiesis and establishing a robust multimodal approach for drug discovery.

Regulating mitochondrial oxidative phosphorylation and MAPK signaling: wedelolactone as a novel therapeutic for radiation-induced thrombocytopenia

Introduction

Radiation-induced thrombocytopenia (RIT) is a serious complication of cancer radiotherapy, for which therapeutic options are limited. This study investigates wedelolactone (WED), a metabolite of a botanical drug, as a potential treatment for RIT.

Methods

In vitro experiments were conducted using Meg-01 and K562 cell lines to evaluate the effects of WED on megakaryocyte differentiation and maturation. Flow cytometry and phalloidin staining were employed to assess the expression of megakaryocyte-specific markers CD41 and CD61, as well as nuclear polyploidization. A mouse model of RIT was established to assess the efficacy of WED in restoring platelet counts and regulating hematopoiesis. RNA sequencing and western blot analyses were performed to explore the underlying molecular mechanisms.

Results

In vitro experiments revealed that WED enhanced megakaryocyte differentiation in a dose-dependent manner, increasing the expression of lineage-specific markers CD41 and CD61, and promoting polyploidization and cytoskeletal reorganization. In vivo, WED significantly restored platelet counts in the mouse model of RIT and promoted the production of hematopoietic stem cells (HSCs), megakaryocytes, and reticulated platelets. RNA sequencing and western blot revealed that WED-induced megakaryocyte differentiation involves the regulation of mitochondrial oxidative phosphorylation mediated by the AMPK signaling pathway and activation of the MAPK signaling pathway. Inhibition of mitochondrial oxidative phosphorylation or MAPK signaling suppressed WED-induced megakaryocyte differentiation, highlighting the central role of these pathways.

Discussion

These findings indicate that WED could be a promising therapeutic candidate for RIT, acting through the modulation of oxidative phosphorylation and MAPK signaling pathways to enhance thrombopoiesis.

IRAP Drives Ribosomal Degradation to Refuel Energy for Platelet Activation during Septic Thrombosis

Platelets play crucial roles in multiple pathophysiological processes after energy-dependent activation. It is puzzling how such a small cellular debris has abundant energy supply. In this study, it is shown that insulin-regulated aminopeptidase (IRAP), a type II transmembrane protein, is a key regulator for platelet activation by promoting energy regeneration during septic thrombosis. Through interaction with certain endosome membrane proteins, IRAP can not only promote granule release, but also facilitate lysosomal degradation of theoretically discarded ribosomes in an mTORC1- and S-acylation-dependent manner in activated platelets. Plentiful amino acids obtained from IRAP-mediated ribophagy are recruited to aerobic glycolysis and then promote energy metabolism reprogramming, thereby producing abundant energy for platelet life extension and prolonged activation. Consequently, targeted blocking IRAP can dramatically alleviate platelet hyperactivation and septic thrombosis.

Biphasic Effect of Thyroid Hormone on Megakaryopoiesis and Platelet Production

Background: Abnormal platelet counts are frequently observed in patients with thyroid dysfunction; however, the direct impact of thyroid hormones on thrombopoiesis remains largely undefined. Methods: This study elucidates the dose-response effect of the thyroid hormone triiodothyronine (T3) on megakaryocyte (MK) development and thrombopoiesis using both a murine model of hyperthyroidism/hypothyroidism and in vitro cultures of human cord blood CD34+ cell-derived MKs. After the application of inhibitors to MKs, the examination of total and phosphorylated protein levels of the phosphoinositide 3-kinase (PI3K)/AKT pathway was utilized to assess the specific mechanisms of T3 action. The use of autophagy dual-staining lentivirus and transmission electron microscopy was employed to evaluate the impact of T3 on the autophagy flux in MKs. Mouse whole-body irradiation and bone marrow transplantation models are applied to assess the influence of T3 on the recovery of MKs/platelets in vivo. Results: We found that physiological or slightly elevated thyroid hormone levels are essential for sustaining MK development and thrombopoiesis, primarily through the TRα-PI3K/AKT signaling pathway. In contrast, supraphysiological thyroid hormone concentrations induce MK apoptosis via excessive autophagy, thereby reducing platelet production. Conclusions: Here, we present evidence that the thyroid hormone influences MK development and platelet production in a concentration-dependent manner, exhibiting a dualistic role. Our discoveries shed new light on the intricate relationship between thyroid hormones and platelet formation, offering novel perspectives on the pathophysiological consequences of thyroid disorders.

Deficiency of thioredoxin-interacting protein results in age-related thrombocytopenia due to megakaryocyte oxidative stress

BACKGROUND

Platelets are generated from megakaryocytes (MKs), mainly located in the bone marrow (BM). Megakaryopoiesis can be affected by genetic disorders, metabolic diseases, and aging. The molecular mechanisms underlying platelet count regulation have not been fully elucidated.

OBJECTIVES

In the present study, we investigated the role of thioredoxin-interacting protein (TXNIP), a protein that regulates cellular metabolism in megakaryopoiesis, using a Txnip-/- mouse model.

METHODS

Wild-type (WT) and Txnip-/- mice (2-27-month-old) were studied. BM-derived MKs were analyzed to investigate the role of TXNIP in megakaryopoiesis with age. The global transcriptome of BM-derived CD41+ megakaryocyte precursors (MkPs) of WT and Txnip-/- mice were compared. The CD34+ hematopoietic stem cells isolated from human cord blood were differentiated into MKs.

RESULTS

Txnip-/- mice developed thrombocytopenia at 4 to 5 months that worsened with age. During ex vivo megakaryopoiesis, Txnip-/- MkPs remained small, with decreased levels of MK-specific markers. Critically, Txnip-/- MkPs exhibited reduced mitochondrial reactive oxygen species, which was related to AKT activity. Txnip-/- MkPs also showed elevated glycolysis alongside increased glucose uptake for ATP production. Total RNA sequencing revealed enrichment for oxidative stress- and apoptosis-related genes in differentially expressed genes between Txnip-/- and WT MkPs. The effects of TXNIP on MKs were recapitulated during the differentiation of human cord blood-derived CD34+ hematopoietic stem cells.

CONCLUSION

We provide evidence that the megakaryopoiesis pathway becomes exhausted with age in Txnip-/- mice with a decrease in terminal, mature MKs that response to thrombocytopenic challenge. Overall, this study demonstrates the role of TXNIP in megakaryopoiesis, regulating mitochondrial metabolism.