Xenophagy in response to Gram-positive Staphylococcus aureus and Gram-negative Salmonella enterica sv. Typhimurium

• Main Author: Radhi, Ohood Aqeed
• Published: University of Strathclyde 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.759474

Autophagy is an important process for cell survival in the human body, which plays a critical role in fighting infections. Some infections exploit the autophagic system and are often promoted by autophagy. Recent evidence has suggested that Staphylococcus aureus has specialised mechanisms to evade xenophagy, thus allowing bacterial survival and replication within autophagosomes, leading to eventual cell death. ULK1 is a serine/threonine kinase that plays an essential role during the early steps of autophagosome biogenesis, but its roles during xenophagy following Staphylococcus aureus infection have been unclear. ULK1 represents an excellent candidate for drug targeting to control autophagy under various settings. This study aimed to investigate the role of autophagy in defence against two disease causing bacteria that are known for their ability to damage cells: Salmonella entericasv. Typhimurium and Staphylococcus aureus. A further aim was to study the role of the ULK1 complex in xenophagy following infection by Staphylococcus aureus and furthermore to test ULK1 inhibitors as a novel therapy to restrict MRSA infection in cells. In addition, in this project, CRISPR genetic selection approaches were developed, aimed to find new host cell genes required for Staphylococcus aureus and Salmonella enterica sv. Typhimurium infection. The results indicated two different roles of autophagy: 1) to provide a protective niche for MRSA, and 2) to provide a mechanism to fight infection by Salmonella enterica sv. Typhimurium. Importantly, treatment of cells with a ULK1/2 small molecule inhibitor strongly inhibited cell killing following infection by MRSA. However, ULK1/2 inhibition made cells more sensitive to cell death following infection by Salmonella enterica sv. Typhimurium. Thus, ULK1 inhibitors may be a novel therapeutic method for fighting infection by MRSA.Also, in this project, we found that screening with a freely available CRISPR-Cas9 library successfully identified the host genes essential for the toxicity of cells by MRSA(NCTC8325) or Salmonella enterica sv. Typhimurium. This was confirmed byfunctional validation and may open the door for novel putative therapeutic targets in future.