TY - JOUR T1 - Altering lipid droplet homeostasis affects <em>Coxiella burnetii</em> intracellular growth JF - bioRxiv DO - 10.1101/112300 SP - 112300 AU - Minal Mulye AU - Brianne Zapata AU - Stacey D. Gilk Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/03/01/112300.abstract N2 - Coxiella burnetii is an obligate intracellular bacterial pathogen and a causative agent of culture-negative endocarditis. While C. burnetii initially infects alveolar macrophages, it has also been found in lipid droplet (LD)-containing foamy macrophages in the cardiac valves of endocarditis patients. In addition, transcriptional studies of C. burnetii-infected macrophages reported differential regulation of the LD coat protein-encoding gene perilipin 2 (plin-2). To further investigate the relationship between LDs and C. burnetii, we compared LD numbers in mock-infected and C. burnetii-infected alveolar macrophages using fluorescence microscopy. Compared to only 10% of mock-infected cells, 50% of C. burnetii-infected cells had more than 50 LDs/cell as early as 24 hours post-infection, indicating a significant increase in LDs in infected cells. Increased LDs required the C. burnetii Type 4B Secretion System (T4BSS), a major virulence factor that manipulates host cellular processes by secreting bacterial effector proteins into the host cell cytoplasm. To determine the importance of LDs during C. burnetii infection, we assessed the effect of manipulating LD homeostasis on C. burnetii intracellular growth. Surprisingly, blocking LD formation with the pharmacological inhibitors triascin C or T863, or knocking out acyl-CoA transferase-1 (acat-1) in alveolar macrophages, increased C. burnetii growth at least 2-fold. Conversely, preventing LD lipolysis by inhibiting adipose triglyceride lipase (ATGL) with atglistatin almost completely blocked bacterial growth, suggesting LD breakdown is essential for C. burnetii. Together these data suggest that LDs are detrimental to C. burnetii and maintenance of LD homeostasis, possibly via the T4BSS, is critical for bacterial growth.IMPORTANCE Host neutral lipid storage organelles known as lipid droplets (LDs) serve as a source of energy, nutrients, or signaling lipids during infection with intracellular bacteria, such as Mycobacterium spp., and Chlamydia spp. LDs have also been associated with infection of the intracellular bacterial pathogen Coxiella burnetii, a significant cause of culture-negative infectious endocarditis. Although C. burnetii was found in LD-rich foam macrophages in endocarditis patients, little is known about the host LD-C. burnetii relationship. We demonstrated a C. burnetii Type 4B Secretion System (T4BSS)-dependent LD accumulation in macrophages, suggesting that the T4BSS plays a key role in regulating host cell LD formation or breakdown. Further, manipulation of LD homeostasis significantly affected C. burnetii intracellular growth, indicating LDs play an important role during C. burnetii infection. Since C. burnetii endocarditis has a 19% mortality rate even in treated patients, exploring the LD-C. burnetii association might identify novel therapeutic targets. ER -