BSTRACTAlthough extracellular matrix (ECM) stiffness is an important aspect of the extracellular microenvironment and is known to direct the lineage specification of stem cells and affect cancer progression, the molecular mechanisms that sense ECM stiffness have not yet been elucidated. In this study, we show that the proline-rich linker (PRL) region of vinculin and the PRL-region-binding protein vinexin are involved in sensing the stiffness of ECM substrates. A rigid substrate increases the level of cytoskeleton-associated vinculin, and the fraction of vinculin stably localizing at focal adhesions (FAs) is larger on rigid ECM than on soft ECM. Mutations in the PRL region or the depletion of vinexin expression impair these responses to ECM stiffness. Furthermore, vinexin depletion impairs the stiffness-dependent regulation of cell migration. These results suggest that the interaction of the PRL region of vinculin with vinexin a plays a crucial role in sensing ECM stiffness and in mechanotransduction.

Diabetes, trauma, and insufficient intraoperative irrigation of the surgical wound were independent and direct risk factors for surgical site infection following spine surgery. To prevent surgical site infection in spine surgery, it is important to control the perioperative serum glucose levels in patients with diabetes, avoid any delay of surgery in patients with trauma, and decrease intraoperative contamination by irrigating > 2000 ml/hour of saline in all patients.

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Shortly after birth, mammalian cardiomyocytes irreversibly exit from the cell cycle and become terminally differentiated. The cellular mechanisms responsible for the cessation of cell division and terminal differentiation of cardiomyocytes soon after birth have intrigued developmental biologists as well as cardiovascular physicians, but the genetic cues for the irreversible exit from the cell cycle soon after birth remain largely unknown. We examined whether and if so how oxidative stress to mammalian hearts during fetal-neonatal transition produces changes in the proliferative activity and terminal differentiation of cardiomyocytes. Scavenging of reactive oxygen species (ROS) during fetal-neonatal transition, especially after birth, resulted in an increase in the proliferative activity and a decrease in the ratio of binucleated cardiomyocytes. Exposure to ROS in cultured cardiomyocytes increased the activity of p38 MAPK and the expression of connexin 43 (Cx43). Not only knockdown of Cx43 using siRNA but also the inhibition of p38 MAPK activity resulted in a significant decrease in the production of ROS in cardiomyocytes, suggesting that the signaling pathway ROS-p38 MAPK-Cx43 (especially, Cx43 at mitochondria, mtCx43) constituted a closed regulatory system with positive feedback. In addition, continuous scavenging of ROS or suppression of p38 MAPK activity for 4 days after birth resulted in a significant decrease in the expression of mtCx43 and in the number of binucleated cardiomyocytes. This study demonstrated that the ROS-induced formation of a positive-feedback loop ROS-p38 MAPK-mtCx43 for the sustained activation of p38 MAPK soon after birth possibly contributes to the loss of cell division and binucleation in mammalian cardiomyocytes.

Gap junctions are intercellular channels that connect the cytoplasm of adjacent cell. Gap junctional intercellular communication has long been postulated to contribute to the maintenance of tissue homeostasis. Recent studies, however, have demonstrated that connexins, gap junction proteins, are involved in the regulation of a variety of cellular functions other than intercellular communication. Although, in neonatal rat ventricular myocytes, connexin-40, -43, and -45 are all expressed, connexin43 (Cx43) is the primary subtype. In this study, we examined whether and if so how the knockdown of a gap junction protein Cx43 with siRNA produced changes in the proliferative activity of neonatal cardiomyocytes. Cx43-knockdown resulted in a significant increase in the proliferation of cardiomyocytes. To clarify the mechanisms behind this increase, we investigated whether the activity of mitogen-activated protein kinases (MAPKs) changed on knockdown of Cx43. The knockdown decreased the expression of phosphorylated p38 (p-p38) MAPK. In addition, treatment of cardiomyocytes with a p38 MAPK inhibitor significantly increased the proliferative activity. Cultures were then co-treated with an inhibitor of p38 MAPK and fibroblast growth factor-1 (FGF1), since Cx43-knockdown significantly increased cytosolic FGF1 expression as well. The co-treatment enhanced the proliferation of cardiomyocytes compared with the treatment with the p38 MAPK inhibitor alone. Taken together, the present study demonstrated that Cx43-knockdown produced a significant increase in the proliferation of neonatal cardiomyocytes.

Study design: Focus group study Objective: To investigate cell-specific endoplasmic reticulum (ER) stress reactions in contusive spinal cord by evaluating the expression of the glucose-regulated protein 78 (GRP78) and C/EBP homologous transcription factor protein (CHOP) using immunohistochemical staining. Setting: Data were analysed at Tokai University School of Medicine in Japan. Methods: The authors generated rat spinal cord injury (SCI) models using an IH-Impactor (100 kdyne(LI), 200 kdyne (HI)). Rats were killed at 1, 3, 5, 7 and 14 days post operation (dpo). Spinal cord sections were prepared and the expression ratio of GRP78 and CHOP was evaluated in oligodendrocyte precursor cells (OPCs) (NG2 þ ), oligodendrocytes (OLs) (APC þ ), neurons (NeuN þ ) and astrocytes (GFAP þ ) using double immunohistochemical staining. We examined an area 8 mm distal from SCI-epicenter. Results: Compared with the sham group, both injured groups had higher GRP78 expression ratio in contused spinal cord at 1 dpo. GRP78 expression ratio was highest in GFAP þ cells of both groups, and lowest in NG2 þ cells. Although GRP78 was expressed strongly immediately after SCI in the both groups, increased CHOP expression was observed only in the HI group. The CHOP expression in NG2 þ cells was significantly higher than that observed in GFAP þ cells at 5 dpo. Conclusion: Although the ER stress response contributes to cell survival in the low-stress SCI conditions, the ER stress response induces an apoptotic cascade in high-stress SCI conditions. The ER response varies according to cell type, with the highest observed in astrocytes, and the lowest observed in oligodendrocyte precursor cells.

After traumatic spinal cord injury (SCI), endoplasmic reticulum (ER) stress exacerbates secondary injury, leading to expansion of demyelination and reduced remyelination due to oligodendrocyte precursor cell (OPC) apoptosis. Although recent studies have revealed that amiloride controls ER stress and leads to improvement in several neurological disorders including SCI, its mechanism is not completely understood. Here, we used a rat SCI model to assess the effects of amiloride on functional recovery, secondary damage expansion, ER stress-induced cell death and OPC survival. Hindlimb function in rats with spinal cord contusion significantly improved after amiloride administration. Amiloride significantly decreased the expression of the pro-apoptotic transcription factor CHOP in the injured spinal cord and significantly increased the expression of the ER chaperone GRP78, which protects cells against ER stress. In addition, amiloride treatment led to a significant decrease in ER stress-induced apoptosis and a significant increase of NG2-positive OPCs in the injured spinal cord. Furthermore, in vitro experiments performed to investigate the direct effect of amiloride on OPCs revealed that amiloride reduced CHOP expression in OPCs cultured under ER stress. These results suggest that amiloride controls ER stress in SCI and inhibits cellular apoptosis, contributing to OPC survival. The present study suggests that amiloride may be an effective treatment to reduce ER stress-induced cell death in the acute phase of SCI.

Magnesium ions (Mg(2+)) play a fundamental role in cellular function, but the cellular dynamic changes of intracellular Mg(2+) remain poorly delineated. The present study aims to clarify whether the concentration of intracellular Mg(2+) possibly changes cyclically in association with rhythmic contraction and intracellular Ca(2+) oscillation in cultured cardiac myocytes from neonatal rats. To do this, we performed a noise analysis of fluctuations in the concentration of intracellular Mg(2+) in cardiac myocytes. The concentration was estimated by loading cells with either Mg-fluo4/AM or KMG-20/AM. Results revealed that the intensity of Mg-fluo-4 or KMG-20 fluorescence fluctuated cyclically in association with the rhythmic contraction of cardiac myocytes. In addition, the simultaneous measurement of Fura2 and Mg-fluo-4 fluorescence revealed phase differences between the dynamics of the two signals, suggesting that the cyclic changes in the Mg-fluo-4 or KMG-20 fluorescent intensity actually reflected the changes in intracellular Mg(2+). The complete termination of spontaneous rhythmic contractions did not abolish Mg(2+) oscillations, suggesting that the rhythmic fluctuations in intracellular Mg(2+) did not result from mechanical movements. We suggest that the concentration of intracellular Mg(2+) changes cyclically in association with spontaneous, cyclic changes in the concentration of intracellular Ca(2+) of cardiac myocytes. A noise analysis of the fluctuation of subtle changes in fluorescence intensity could contribute to the elucidation of novel functional roles of Mg(2+) in cells.