Takeru Hamashima

Inflammation-induced endothelial cell-derived extracellular vesicles modulate the cellular status of pericytes

Emerging lines of evidence have shown that extracellular vesicles (EVs) mediate cell-to-cell communication by exporting encapsulated materials, such as microRNAs (miRNAs), to target cells. Endothelial cell-derived EVs (E-EVs) are upregulated in circulating blood in different pathological conditions; however, the characteristics and the role of these E-EVs are not yet well understood. In vitro studies were conducted to determine the role of inflammation-induced E-EVs in the cell-to-cell communication between vascular endothelial cells and pericytes/vSMCs. Stimulation with inflammatory cytokines and endotoxin immediately induced release of shedding type E-EVs from the vascular endothelial cells, and flow cytometry showed that the induction was dose dependent. MiRNA array analyses revealed that group of miRNAs were specifically increased in the inflammation-induced E-EVs. E-EVs added to the culture media of cerebrovascular pericytes were incorporated into the cells. The E-EV-supplemented cells showed highly induced mRNA and protein expression of VEGF-B, which was assumed to be a downstream target of the miRNA that was increased within the E-EVs after inflammatory stimulation. The results suggest that E-EVs mediate inflammation-induced endothelial cell-pericyte/vSMC communication, and the miRNAs encapsulated within the E-EVs may play a role in regulating target cell function. E-EVs may be new therapeutic targets for the treatment of inflammatory diseases.

PDGFR-β as a positive regulator of tissue repair in a mouse model of focal cerebral ischemia

Although platelet-derived growth factors (PDGFs) and receptors (PDGFRs) are abundantly expressed in the central nervous system, their functions largely remain elusive. We investigated the role of PDGFR-β in tissue responses and functional recovery after photothrombolic middle cerebral artery occlusion (MCAO). In the normal adult mouse brain, PDGFR-β was mainly localized in neurons and in pericyte/vascular smooth muscle cells (PC/vSMCs). From 3 to 28 days after MCAO, postnatally induced systemic PDGFR-β knockout mice (Esr-KO) exhibited the delayed recovery of body weight and behavior, and larger infarction volume than controls. In Esr-KO, PC/vSMC coverage was decreased and vascular leakage of infused fluorescent-labeled albumin was extensive within the ischemic lesion, but not in the uninjured cerebral cortex. Angiogenesis levels were comparable between Esr-KO and controls. In another PDGFR-β conditional KO mouse (Nestin-KO), PDGFR-β was deleted in neurons and astrocytes from embryonic day 10.5, but was preserved in PC/vSMCs. After MCAO, vascular leakage and infarction volume in Nestin-KO were worse than controls, but partly improved compared with Esr-KO. Astroglial scar formation in both Esr-KO and Nestin-KO was similarly reduced compared with controls after MCAO. These data suggested that PDGFR-β signaling is crucial for neuroprotection, endogenous tissue repair, and functional recovery after stroke by targeting neurons, PC/vSMCs, and astrocytes.

Neuroprotective effects of PDGF against oxidative stress and the signaling pathway involved

The neuroprotective effects of platelet‐derived growth factor (PDGF) and the major signaling pathways involved in these were examined using primary cultured mouse cortical neurons subjected to H2O2‐induced oxidative stress. The specific function of the PDGF β‐receptor (PDGFR‐β) was examined by the selective deletion of the corresponding gene using the Cre‐loxP system in vitro. In wild‐type neurons, PDGF‐BB enhanced the survival of these neurons and suppressed H2O2‐induced caspase‐3 activation. The prosurvival effect of PDGF‐AA was less than that of PDGF‐BB. PDGF‐BB highly activated Akt, extracellular signal‐regulated kinase (ERK), c‐jun amino‐terminal kinase (JNK) and p38. PDGF‐AA activated these molecules at lesser extent than PDGF‐BB. In particular, PDGF‐AA induced activation of Akt was at very low level. The neuroprotective effects of PDGF‐BB were antagonized by inhibitors of phosphatidylinositol 3‐kinase (PI3‐K), mitogen‐activated protein kinase kinase (MEK), JNK and p38. The PDGFR‐β‐depleted neurons showed increased vulnerability to oxidative stress, and less responsiveness to PDGF‐BB‐induced cytoprotection and signal activation, in which Akt activation was most strongly suppressed. After all, these results demonstrated the neuroprotective effects of PDGF and the signaling pathways involved against oxidative stress. The effects of PDGF‐BB were more potent than those of PDGF‐AA. This might be due to the activation and additive effects of two PDGFRs after PDGF‐BB stimulation. Furthermore, the PI3‐K/Akt pathway that was deduced to be preferentially activated by PDGFR‐β may explain the potent effects of PDGF‐BB.

Activation of MAP kinases, Akt and PDGF receptors in injured peripheral nerves

A number of receptor tyrosine kinases (RTKs) and the downstream phosphatidylinositol‐3‐kinase (PI3K)/Akt and mitogen‐activated protein (MAP) kinase signaling pathways have been critically involved in peripheral nerve regeneration. Here, we examined the activation of PI3K/Akt and MAP kinase pathways, and platelet‐derived growth factor receptors (PDGFRs) in the distal segments of crushed rat sciatic nerve from 3 to 28 days after injury. In Western blot analyses, the phosphorylated forms of extracellular signal‐regulated protein kinase (ERK) and c‐Jun NH2‐terminal kinases (JNKs) were highly augmented on days 3 and 7 and on days 7 and 14 after injury, respectively. Phosphorylated Akt and p38 consistently increased from 3 to 28 days after injury. Phosphorylated PDGFR‐α and ‐β were also increased from 3 to 14 days. In the immunohistological analyses, phosphorylated ERK and PDGFR‐α were co‐localized in many activated Schwann cells and regrowing axons 3 days after injury, while PDGFR‐β was localized in a few spindle‐shaped cells. The detected temporal profile of RTK signaling appears to be crucial for the regulation of Schwann cell proliferation and following redifferentiation. Furthermore, the immunohistological studies suggested a role of ERK and PDGFR‐α in axon regeneration as well.

Cognitive and socio-emotional deficits in platelet-derived growth factor receptor-β gene knockout mice.

Platelet-derived growth factor (PDGF) is a potent mitogen. Extensive in vivo studies of PDGF and its receptor (PDGFR) genes have reported that PDGF plays an important role in embryogenesis and development of the central nervous system (CNS). Furthermore, PDGF and the β subunit of the PDGF receptor (PDGFR-β) have been reported to be associated with schizophrenia and autism. However, no study has reported on the effects of PDGF deletion on mice behavior. Here we generated novel mutant mice (PDGFR-β KO) in which PDGFR-β was conditionally deleted in CNS neurons using the Cre/loxP system. Mice without the Cre transgene but with floxed PDGFR-β were used as controls. Both groups of mice reached adulthood without any apparent anatomical defects. These mice were further examined by conducting several behavioral tests for spatial memory, social interaction, conditioning, prepulse inhibition, and forced swimming. The test results indicated that the PDGFR-β KO mice show deficits in all of these areas. Furthermore, an immunohistochemical study of the PDGFR-β KO mice brain indicated that the number of parvalbumin (calcium-binding protein)-positive (i.e., putatively γ-aminobutyric acid-ergic) neurons was low in the amygdala, hippocampus, and medial prefrontal cortex. Neurophysiological studies indicated that sensory-evoked gamma oscillation was low in the PDGFR-β KO mice, consistent with the observed reduction in the number of parvalbumin-positive neurons. These results suggest that PDGFR-β plays an important role in cognitive and socioemotional functions, and that deficits in this receptor may partly underlie the cognitive and socioemotional deficits observed in schizophrenic and autistic patients.

Isoliquiritigenin Attenuates Adipose Tissue Inflammation in vitro and Adipose Tissue Fibrosis through Inhibition of Innate Immune Responses in Mice.

Isoliquiritigenin (ILG) is a flavonoid derived from Glycyrrhiza uralensis and potently suppresses NLRP3 inflammasome activation resulting in the improvement of diet-induced adipose tissue inflammation. However, whether ILG affects other pathways besides the inflammasome in adipose tissue inflammation is unknown. We here show that ILG suppresses adipose tissue inflammation by affecting the paracrine loop containing saturated fatty acids and TNF-α by using a co-culture composed of adipocytes and macrophages. ILG suppressed inflammatory changes induced by the co-culture through inhibition of NF-κB activation. This effect was independent of either inhibition of inflammasome activation or activation of peroxisome proliferator-activated receptor-γ. Moreover, ILG suppressed TNF-α-induced activation of adipocytes, coincident with inhibition of IκBα phosphorylation. Additionally, TNF-α-mediated inhibition of Akt phosphorylation under insulin signaling was alleviated by ILG in adipocytes. ILG suppressed palmitic acid-induced activation of macrophages, with decreasing the level of phosphorylated Jnk expression. Intriguingly, ILG improved high fat diet-induced fibrosis in adipose tissue in vivo. Finally, ILG inhibited TLR4- or Mincle-stimulated expression of fibrosis-related genes in stromal vascular fraction from obese adipose tissue and macrophages in vitro. Thus, ILG can suppress adipose tissue inflammation by both inflammasome-dependent and -independent manners and attenuate adipose tissue fibrosis by targeting innate immune sensors.

Chromophobe renal cell carcinoma, oncocytic variant: a proposal of a new variant giving a critical diagnostic pitfall in diagnosing renal oncocytic tumors

In chromophobe renal cell carcinoma (RCC), two forms of typical and eosinophilic variants have been reported to date. We have previously reported a new variant of chromophobe RCC, namely an oncocytic variant. However, little is known on the histological features of this variant. In this article, we report such five cases. Macroscopically, the tumor was well demarcated, but unencapsulated. The cut surface of the tumor showed brown in color, but neither hemorrhage nor necrosis was seen. Microscopically, the tumor consisted of predominant tubular configuration with or without various proportion of solid-sheet pattern. In one tumor, tumor cells microscopically invaded branches of renal vein. In addition, the constituting cells were characterized by the oncocytic cytoplasm, trivial to minimal variation in tumor size, indistinct to slightly distinct cell border, centrally located round nuclei and the absence of perinuclear halo. These characteristics entirely resembled renal oncocytoma. However, neoplastic cells immunohistochemically showed the diffuse and strong labeling for cytokeratin 7 and mitochondrial antigen in all cases. In addition, in fluorescence in situ hybridization (FISH) study the loss of more than four chromosomes among chromosomes 7, 10, 13, 17 and 21 was confirmed in all tumors and the diagnosis of chromophobe RCC was rendered. In conclusion, we propose a new variant, namely an oncocytic variant, of chromophobe RCC morphologically resembling renal oncocytoma and biologically showing characteristics of chromophobe RCC, and this recognition is practically crucial in the differential diagnosis from renal oncocytoma.

PDGFRα plays a crucial role in connective tissue remodeling.

Platelet derived growth factor (PDGF) plays a pivotal role in the remodeling of connective tissues. Emerging data indicate the distinctive role of PDGF receptor-α (PDGFRα) in this process. In the present study, the Pdgfra gene was systemically inactivated in adult mouse (α-KO mouse), and the role of PDGFRα was examined in the subcutaneously implanted sponge matrices. PDGFRα expressed in the fibroblasts of Pdgfra-preserving control mice (Flox mice), was significantly reduced in the sponges in α-KO mice. Neovascularized areas were largely suppressed in the α-KO mice than in the Flox mice, whereas the other parameters related to the blood vessels and endothelial cells were similar. The deposition of collagen and fibronectin and the expression of collagen 1a1 and 3a1 genes were significantly reduced in α-KO mice. There was a significantly decrease in the number and dividing fibroblasts in the α-KO mice, and those of macrophages were similar between the two genotypes. Hepatocyte growth factor (Hgf) gene expression was suppressed in Pdgfra-inactivated fibroblasts and connective tissue. The findings implicate the role of PDGFRα-dependent ECM and HGF production in fibroblasts that promotes the remodeling of connective tissue and suggest that PDGFRα may be a relevant target to regulate connective tissue remodeling.

Functional analysis of platelet-derived growth factor receptor-β in neural stem/progenitor cells

Activation of neural stem/progenitor cells (NSPCs) is a potential therapeutic strategy of neurological disorders. In this study, NSPCs of subventricular zone were isolated and cultured from platelet-derived growth factor-β-receptor-knockout (PDGFR-β(-/-)) mice of postnatal day 1 (P1) and P28, and the roles of PDGFR-β were examined in these cells. In PDGFR-β-preserving control NSPCs, stem cell activities, such as numbers and diameters of secondary neurospheres, cell proliferation and survival rates, were significantly higher in P1 NSPCs than those in P28 NSPCs. In PDGFR-β(-/-) NSPCs, most of these parameters were decreased as compared with age-matched controls. Among them, the decrease of secondary neurosphere formation was most striking in P1 and P28 PDGFR-β(-/-) NSPCs and in P28 control NSPCs as compared with P1 control NSPCs. PCR-array and following quantitative real-time PCR (qRT-PCR) analyses demonstrated that expressions of fibroblast growth factor-2 (FGF2) and exons IV-IX of brain-derived neurotrophic factor (BDNF) were decreased, and noggin was increased in P1 PDGFR-β(-/-) as compared with P1 controls. Addition of BDNF rescued the number and diameter of secondary neurospheres in P1 PDGFR-β(-/-) NSPCs to similar levels as controls. The expressions of PDGFs and PDGFRs in control NSPCs were increased along with the differentiation-induction, where phosphorylated PDGFR-β was co-localized with neuronal and astrocyte differentiation markers. In controls, the neuronal differentiation was decreased, and the glial differentiation was increased from P1 to P28 NSPCs. Compared with P1 controls, neuronal differentiation was reduced in P1 PDGFR-β(-/-) NSPCs, whereas glial differentiation was comparable between the two genotypes. These results suggest that PDGFR-β signaling is important for the self-renewal and multipotency of NSPCs, particularly in neonatal NSPCs. BDNF, FGF2, and noggin may be involved in the effects of PDGFR-β signaling in these cells. Accordingly, the activation of PDGFR-β in NSPCs may be a novel therapeutic strategy of neurological diseases.

PDGFR-β Plays a Key Role in the Ectopic Migration of Neuroblasts in Cerebral Stroke

The neuroprotective agents and induction of endogenous neurogenesis remain to be the urgent issues to be established for the care of cerebral stroke. Platelet‐derived growth factor receptor beta (PDGFR‐β) is mainly expressed in neural stem/progenitor cells (NSPCs), neurons and vascular pericytes of the brain; however, the role in pathological neurogenesis remains elusive. To this end, we examined the role of PDGFR‐β in the migration and proliferation of NSPCs after stroke. A transient middle cerebral‐arterial occlusion (MCAO) was introduced into the mice with conditional Pdgfrb‐gene inactivation, including N‐PRβ‐KO mice where the Pdgfrb‐gene was mostly inactivated in the brain except that in vascular pericytes, and E‐PRβ‐KO mice with tamoxifen‐induced systemic Pdgfrb‐gene inactivation. The migration of the DCX+ neuroblasts from the subventricular zone toward the ischemic core was highly increased in N‐PRβ‐KO, but not in E‐PRβ‐KO as compared to Pdgfrb‐gene preserving control mice. We showed that CXCL12, a potent chemoattractant for CXCR4‐expressing NSPCs, was upregulated in the ischemic lesion of N‐PRβ‐KO mice. Furthermore, integrin α3 intrinsically expressed in NSPCs that critically mediates extracellular matrix‐dependent migration, was upregulated in N‐PRβ‐KO after MCAO. NSPCs isolated from N‐PRβ‐KO rapidly migrated on the surface coated with collagen type IV or fibronectin that are abundant in vascular niche and ischemic core. PDGFR‐β was suggested to be critically involved in pathological neurogenesis through the regulation of lesion‐derived chemoattractant as well as intrinsic signal of NSPCs, and we believe that a coordinated regulation of these molecular events may be able to improve neurogenesis in injured brain for further functional recovery. Stem Cells 2016;34:685–698