Koichi Nakaoji

Mallotus philippinensis bark extracts promote preferential migration of mesenchymal stem cells and improve wound healing in mice

In the present study, we report the effects of the ethanol extract from Mallotus philippinensis bark (EMPB) on mesenchymal stem cell (MSC) proliferation, migration, and wound healing in vitro and in a mouse model. Chemotaxis assays demonstrated that EMPB acted an MSC chemoattractant and that the main chemotactic activity of EMPB may be due to the effects of cinnamtannin B-1. Flow cytometric analysis of peripheral blood mononuclear cells in EMPB-injected mice indicated that EMPB enhanced the mobilization of endogenous MSCs into blood circulation. Bioluminescent whole-animal imaging of luciferase-expressing MSCs revealed that EMPB augmented the homing of MSCs to wounds. In addition, the efficacy of EMPB on migration of MSCs was higher than that of other skin cell types, and EMPB treatment improved of wound healing in a diabetic mouse model. The histopathological characteristics demonstrated that the effects of EMPB treatment resembled MSC-induced tissue repair. Taken together, these results suggested that EMPB activated the mobilization and homing of MSCs to wounds and that enhancement of MSC migration may improve wound healing.

Oxidative Stress Induces the Formation of D‐Aspartyl Residues in the Elastin Mimic Peptides

Racemization of aspartyl (Asp) residues in peptides and proteins has been considered to be a nonenzymatic chemical reaction which occurs via succinimide formation. However, it has not been known yet what conditions in living body accelerate the inversion of the L‐ to the D‐form. Here, we examined the effect of ultraviolet (UV) exposure or oxidative stress on the formation of D‐Asp residues in the elastin mimic peptides with or without heat treatment. As a result, UV exposure did not affect the D‐Asp formation in peptides. On the other hand, the amount of D‐Asp in heat‐treated peptide solution at the same time as addition of HO. radical, H2O2, and lipid peroxide was significantly increased. These results indicate that the inversion rate to D‐form of Asp residues in skin elastin is accelerated by generation of reactive oxygen species (ROS), and that oxidative stress might be closely related to D‐Asp formation in aging proteins.

Cinnamtannin B-1 Promotes Migration of Mesenchymal Stem Cells and Accelerates Wound Healing in Mice

Substances that enhance the migration of mesenchymal stem cells to damaged sites have the potential to improve the effectiveness of tissue repair. We previously found that ethanol extracts of Mallotus philippinensis bark promoted migration of mesenchymal stem cells and improved wound healing in a mouse model. We also demonstrated that bark extracts contain cinnamtannin B-1, a flavonoid with in vitro migratory activity against mesenchymal stem cells. However, the in vivo effects of cinnamtannin B-1 on the migration of mesenchymal stem cells and underlying mechanism of this action remain unknown. Therefore, we examined the effects of cinnamtannin B-1 on in vivo migration of mesenchymal stem cells and wound healing in mice. In addition, we characterized cinnamtannin B-1-induced migration of mesenchymal stem cells pharmacologically and structurally. The mobilization of endogenous mesenchymal stem cells into the blood circulation was enhanced in cinnamtannin B-1-treated mice as shown by flow cytometric analysis of peripheral blood cells. Whole animal imaging analysis using luciferase-expressing mesenchymal stem cells as a tracer revealed that cinnamtannin B-1 increased the homing of mesenchymal stem cells to wounds and accelerated healing in a diabetic mouse model. Additionally, the cinnamtannin B-1-induced migration of mesenchymal stem cells was pharmacologically susceptible to inhibitors of phosphatidylinositol 3-kinase, phospholipase C, lipoxygenase, and purines. Furthermore, biflavonoids with similar structural features to cinnamtannin B-1 also augmented the migration of mesenchymal stem cells by similar pharmacological mechanisms. These results demonstrate that cinnamtannin B-1 promoted mesenchymal stem cell migration in vivo and improved wound healing in mice. Furthermore, the results reveal that cinnamtannin B-1-induced migration of mesenchymal stem cells may be mediated by specific signaling pathways, and the flavonoid skeleton may be relevant to its effects on mesenchymal stem cell migration.

Radiation-Induced RhoGDIβ Cleavage Leads to Perturbation of Cell Polarity: A Possible Link to Cancer Spreading

The equilibrium between proliferation and apoptosis is tightly balanced to maintain tissue homeostasis in normal tissues and even in tumors. Achieving and maintaining such a balance is important for cancer regrowth and spreading after cytotoxic treatments. Caspase‐3 activation and tumor cell death following anticancer therapy as well as accompanying cell death pathways are well characterized, but their association to homeostasis of cancerous tissue and tumor progression remains poorly understood. Here we proposed a novel mechanism of cancer spreading induced by caspase‐3. RhoGDIβ, known as a direct cleavage substrate of caspase‐3, is overexpressed in many epithelial cancers. The N‐terminal‐truncated RhoGDIβ (ΔN‐RhoGDIβ) is accumulated in caspase‐3‐activated cells. Stable expression of ΔN‐RhoGDIβ in HeLa cells did not induce apoptosis, but impaired directional cell migration in a wound‐healing assay accompanied by a perturbed direction of cell division at the wound edge. Subcellular protein fractionation experiments revealed that ΔN‐RhoGDIβ but not wild‐type RhoGDIβ was present in the detergent‐soluble cytoplasmic and nuclear fractions and preferentially associated with Cdc42. Furthermore, Cdc42 activity was constitutively inhibited by stable expression of ΔN‐RhoGDIβ, resulting in increased radiation‐induced compensatory proliferation linking to RhoA activation. Thus, ΔN‐RhoGDIβ dominant‐negatively regulates Cdc42 activity and contributes to loss of polarity‐related functions. The caspase‐3‐cleaved RhoGDIβ is a possible determinant to promote cancer spreading due to deregulation of directional organization of tumor cell population and inhibition of default equilibrium between proliferation and apoptosis after cytotoxic damage. J. Cell. Physiol. 231: 2493–2505, 2016.