A novel insertion pathway of mitochondrial outer membrane proteins with multiple transmembrane segments

The central channel Tom40 of the preprotein translocase of outer membrane (TOM) complex is thought to be responsible for the import of virtually all preproteins synthesized outside the mitochondria. In this study, we analyze the topogenesis of the peripheral benzodiazepine receptor (PBR), which integrates into the mitochondrial outer membrane (MOM) through five hydrophobic transmembrane segments (TMSs) and functions in cholesterol import into the inner membrane. Analyses of in vitro and in vivo import into TOM component–depleted mitochondria reveal that PBR import (1) depends on the import receptor Tom70 but requires neither the Tom20 and Tom22 import receptors nor the import channel Tom40, (2) shares the post-Tom70 pathway with the C-tail–anchored proteins, and (3) requires factors of the mitochondrial intermembrane space. Furthermore, membrane integration of mitofusins and mitochondrial ubiquitin ligase, the MOM proteins with two and four TMSs, respectively, proceeds through the same initial pathway. These findings reveal a previously unidentified pathway of the membrane integration of MOM proteins with multiple TMSs

The Role of c-fos in Cell Death and Regeneration of Retinal Ganglion Cells

PURPOSE. To investigate the effect of c-fos on apoptotic cell death and regeneration of damaged retinal ganglion cells (RGCs) in tissue culture of retinal explants. METHODS. Retinas from transgenic mice carrying the exogenous c-fos gene under the control of the interferon (IFN)-␣/␤ inducible Mx-promoter (Mx-c-fos), c-fos-deficient mice, and littermate control mice were dissected and cultured in a threedimensional collagen gel culture system, followed by an analysis of TdT-dUTP terminal nick-end labeling (TUNEL) staining and measurement of neurites that emerged from explants. RESULTS. Compared with littermate control mice, Mx-c-fos transgenic animals showed a higher ratio of TUNEL positivity in the RGC layer from early in the culture period that correlated with the small number of regenerating neurites. In contrast, the c-fos-null mutated mice showed a still-lower ratio of TUNEL-positive cells. Nevertheless, the number of regenerating neurites was significantly lower in the initial phase, although the drastic increase in density of neurite regeneration was observed in the late period of culture. CONCLUSIONS. These findings suggest that c-fos is involved in both apoptotic cell death and regeneration of damaged RGCs. Elucidation of the precise c-fos-mediated cascade involved in RGC apoptosis and regeneration is significant in realizing neuronal survival and regeneration. (Invest Ophthalmol Vis Sci

Inhibition of microRNA-33b in humanized mice ameliorates nonalcoholic steatohepatitis

マイクロRNA-33bの阻害は非アルコール性脂肪肝炎を改善する --核酸医薬による治療応用へ--. 京都大学プレスリリース. 2023-06-13.Nonalcoholic steatohepatitis (NASH) can lead to cirrhosis and hepatocellular carcinoma in their advanced stages; however, there are currently no approved therapies. Here, we show that microRNA (miR)-33b in hepatocytes is critical for the development of NASH. miR-33b is located in the intron of sterol regulatory element–binding transcription factor 1 and is abundantly expressed in humans, but absent in rodents. miR-33b knock-in (KI) mice, which have a miR-33b sequence in the same intron of sterol regulatory element–binding transcription factor 1 as humans and express miR-33b similar to humans, exhibit NASH under high-fat diet feeding. This condition is ameliorated by hepatocyte-specific miR-33b deficiency but unaffected by macrophage-specific miR-33b deficiency. Anti-miR-33b oligonucleotide improves the phenotype of NASH in miR-33b KI mice fed a Gubra Amylin NASH diet, which induces miR-33b and worsens NASH more than a high-fat diet. Anti-miR-33b treatment reduces hepatic free cholesterol and triglyceride accumulation through up-regulation of the lipid metabolism–related target genes. Furthermore, it decreases the expression of fibrosis marker genes in cultured hepatic stellate cells. Thus, inhibition of miR-33b using nucleic acid medicine is a promising treatment for NASH

Phospholipase Cbeta4 and protein kinase Calpha and/or protein kinase CbetaI are involved in the induction of long term depression in cerebellar Purkinje cells.

Activation of the type-1 metabotropic glutamate receptor (mGluR1) signaling pathway in the cerebellum involves activation of phospholipase C (PLC) and protein kinase C (PKC) for the induction of cerebellar long term depression (LTD). The PLC and PKC isoforms that are involved in LTD remain unclear, however. One previous study found no change in LTD in PKCgamma-deficient mice, thus, in the present study, we examined cerebellar LTD in PLCbeta4-deficient mice. Immunohistochemical and Western blot analyses of cerebellum from wild-type mice revealed that PLCbeta1 was expressed weakly and uniformly, PLCbeta2 was not detected, PLCbeta3 was expressed predominantly in caudal cerebellum (lobes 7-10), and PLCbeta4 was expressed uniformly throughout. In PLCbeta4-deficient mice, expression of total PLCbeta, the mGluR1-mediated Ca(2+) response, and LTD induction were greatly reduced in rostral cerebellum (lobes 1-6). Furthermore, we used immunohistochemistry to localize PKCalpha, -betaI, -betaII, and -gamma in mouse cerebellar Purkinje cells during LTD induction. Both PKCalpha and PKCbetaI were found to be translocated to the plasmamembrane under these conditions. Taken together, these results suggest that mGluR1-mediated activation of PLCbeta4 in rostral cerebellar Purkinje cells induced LTD via PKCalpha and/or PKCbetaI