• Cell Membrane Disruption Stimulates NO/PKG Signaling and Potentiates Cell Membrane Repair in Neighboring Cells

      Togo, Tatsuru; McNeil, Paul L.; Department of Cellular Biology and Anatomy (2012-08-7)
      Resealing of a disrupted plasma membrane at the micron-diameter range requires Ca2+-regulated exocytosis. Repeated membrane disruptions reseal more quickly than the initial wound, and this potentiation of membrane resealing persists for at least 24 hours after the initial wound. Long-term potentiation of membrane resealing requires CREB-dependent gene expression, which is activated by the PKC- and p38 MAPK-dependent pathway in a wounded cell. The present study demonstrates that membrane resealing is potentiated in both wounded and neighboring cells in MDCK cells. Wounding of cells expressing CREB133, a mutant variant of CREB, does not show the potentiated response of cell membrane resealing in either wounded or neighboring cells. Furthermore, wounding of cells induces CREB phosphorylation, not only in wounded cells, but also in neighboring cells. Inhibition of the nitric oxide/PKG signaling pathway suppresses CREB phosphorylation in neighboring cells, but not in wounded cells. The potentiation of membrane resealing in neighboring cells is suppressed if the nitric oxide/PKG pathway is inhibited during the initial wound. Together, these results suggest that the nitric oxide/PKG pathway stimulates CREB phosphorylation in neighboring cells so that subsequent cell membrane disruptions of the neighboring cells reseal more quickly.
    • Genetic Ablation of CD68 Results in Mice with Increased Bone and Dysfunctional Osteoclasts

      Ashley, Jason W.; Shi, Zhenqi; Zhao, Haibo; Li, Xingsheng; Kesterson, Robert A.; Feng, Xu; McNeil, Paul L.; Department of Cellular Biology and Anatomy; College of Graduate Studies (2011-10-3)
      CD68 is a member of the lysosome associated membrane protein (LAMP) family that is restricted in its expression to cells of the monocyte/macrophage lineage. This lineage restriction includes osteoclasts, and, while previous studies of CD68 in macrophages and dendritic cells have proposed roles in lipid metabolism, phagocytosis, and antigen presentation, the expression and function of CD68 in osteoclasts have not been explored. In this study, we investigated the expression and localization of CD68 in macrophages and osteoclasts in response to the monocyte/macrophage-colony stimulating factor (M-CSF) and the receptor activator of NF-κB ligand (RANKL). We found that M-CSF stimulates CD68 expression and RANKL alters the apparent molecular weight of CD68 as measured by Western immunoblotting. In addition, we explored the significance of CD68 expression in osteoclasts by generating mice that lack expression of CD68. These mice have increased trabecular bone, and in vitro assessment of CD68â /â osteoclasts revealed that, in the absence of CD68, osteoclasts demonstrate an accumulation of intracellular vesicle-like structures, and do not efficiently resorb bone. These findings demonstrate a role for CD68 in the function of osteoclasts, and future studies will determine the mechanistic nature of the defects seen in CD68â /â osteoclasts.
    • Mitochondrial Dysfunction and Adipogenic Reduction by Prohibitin Silencing in 3T3-L1 Cells

      Liu, Dong; Lin, Yiming; Kang, Ting; Huang, Bo; Xu, Wei; Garcia-Barrio, Minerva; Olatinwo, Moshood; Matthews, Roland; Chen, Yuqing Eugene; Thompson, Winston E.; et al. (2012-03-30)
      Increase in mitochondrial biogenesis has been shown to accompany brown and white adipose cell differentiation. Prohibitins (PHBs), comprised of two evolutionarily conserved proteins, prohibitin-1 (PHB1) and prohibitin-2 (PHB2), are present in a high molecular-weight complex in the inner membrane of mitochondria. However, little is known about the effect of mitochondrial PHBs in adipogenesis. In the present study, we demonstrate that the levels of both PHB1 and PHB2 are significantly increased during adipogenesis of 3T3-L1 preadipocytes, especially in mitochondria. Knockdown of PHB1 or PHB2 by oligonucleotide siRNA significantly reduced the expression of adipogenic markers, the accumulation of lipids and the phosphorylation of extracellular signal-regulated kinases. In addition, fragmentation of mitochondrial reticulum, loss of mitochondrial cristae, reduction of mitochondrial content, impairment of mitochondrial complex I activity and excessive production of ROS were observed upon PHB-silencing in 3T3-L1 cells. Our results suggest that PHBs are critical mediators in promoting 3T3-L1 adipocyte differentiation and may be the potential targets for obesity therapies.