The small GTPase RAB18: Insights into cellular steatosis, lipophagy and the non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease is a rapidly growing concern for public health. Its most prevalent marker is steatosis, which is the accumulation of large lipid storage organelles called lipid droplets (LD) in the hepatocytes. RAB18, a member of the Rab family, localizes to the LD membrane. Rab family proteins are regulators of cellular membrane trafficking, therefore RAB18 is expected to play a role regulating LD biology. The presented work aims to elucidate this role as well as the mechanisms behind the localization of RAB18 to the LD membrane. The localization of RAB18 was investigated by overexpressing mutant RAB18 variants in HepG2 cells. RAB18 localization was observed to depend on the reversible cyclical palmitoylation of its C-terminus. Using FRAP experiments, it could be shown that targeting the palmitoylation machinery with small molecule inhibitors modulated RAB18 localization. This coincided with changes in LD size in cells treated with de-palmitoylation inhibitors. An overall increase in LD size was observed in HepG2 cells with RAB18 downregulation. The wild type LD size in these cells was restored by the inhibition of autophagy. This size reduction was due to newly created LDs. Inhibition of autophagy prior to LD accumulation was subsequently tested in vitro on primary human hepatocytes in sandwich culture. Inhibition of autophagy by chloroquine resulted in a dose dependent rise in LD number and a decrease in average LD size in these cells. These effects could be translated to the in vivo situation in mice. Daily chloroquine injection of mice on a steatogenic diet resulted in a significant decrease of LD size in vivo. Conversely, no changes were detected in the blood-values of treated mice compared with the control. This thesis demonstrates, that RAB18 localizes to the LD via a C-terminal acylation cycle. RAB18 reduces the size of LDs by modulating autophagy of newly formed LDs. This mechanism is important for LD number and size regulation in hepatocytes

The alterations of tonus and movements through the interplay between the cerebral hemispheres and the cerebellum

This paper deals with the experimental production of involuntary movenients and abnormal tonus in macaques ( Macacu mulatta ) and their alterations in these animals and in children with cerebral palsy and other cerebral lesions. The first major subdivision of the paper has three parts. The first part describes the effects of lesions in the macaque cerebral hemispheres, ranging from a small destructive lesion in area 4 to an essentially complete bicortectomy. The case histories of a few patients document some of the results. The second part reports the effects of lesions in the macaque cerebellum ranging from small vermal injuries to complete cerebellectomies. The third part is concerned with successive lesions in the cerebellum and cerebral hemispheres of macaques and with planned cerebellar lesions in a few children with grave hypertonicity and marked involuntary movements. This subdivision is illustrated with photographs of the monkeys and the children at various stages of the procedures, photographs of many monkey brains at postmortem, and some photomicrographs showing lesions. The second major subdivision has a discussion of the anatomic and the physiologic bases for the experimental results obtained and for the operations on the children. It correlates the material presented with data from the literature and is illustrated with photomicrographs of degenerated tracts and with diagrams. The paper stresses the balancing of cerebral hemisphere and cerebellar discharges in the regulation of tonus and in the stabilizing of movements. It discusses the possibility of producing more effective tonus by making carefully planned lesions in cerebellar areas of animals or of children with highly handicapping hypertonicity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49991/1/901270502_ftp.pd

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements