Intracellular bacteria hijack ER-Golgi transport to facilitate infection

An emerging infectious disease, human granulocytic anaplasmosis (HGA) caused by infection with Anaplasma phagocytophilum (Aph), is first in mortality among tickborne diseases, and second in prevalence only to Lyme disease. Aph causes systemic infection by effectively replicating within membrane-bound inclusions/vacuoles of granulocytes and endothelial cells by subverting innate immune mechanisms and exploiting host nutrients. Therefore, understanding Aph machinery and mechanisms essential for this process in the context of the host response will inform the design of potential therapeutic/prophylactic targets. Aph have a Type IV secretion system (T4SS), similar to the virB/virD system, which allows pathogens to manipulate host cells viaT4SS effectors. We identified a new T4SS effector, endoplasmic reticulum (ER)-Golgi exit site (ERES) protein of Anaplasma (EgeA), and two host cell receptors of EgeA that are ERES proteins: Transport and Golgi organization protein 1 (TANGO1) and Sec1 family domain-containing protein 1 (SCFD1). EgeA, TANGO1, and SCFD1 are all required for Aph infection of human cells and appear to localize to Aph inclusions. On the peripheral ER, ERES exists as specialized domains in a dispersed pattern. At ERESs, vesicles bud off and fuse with cis-Golgi. TANGO1 proteins organize the early secretory pathway from the ER to cis-Golgi to sort cargoes that are too bulky or secreted in volumes too great to use generic mechanisms. Thus, our first hypothesis is EgeA facilitates ER nutrient delivery to Aph inclusions by redirecting TANGO1 and SCFD1 protein transport/ER exit machinery to Aph inclusions. TANGO1 functions to relieve ER traffic jams due to bulky cargo retention at ERES. Thus, our second hypothesis is EgeA alleviates ER stress via TANGO1-mediated ER protein exit. In this proposal, we will test these hypotheses in three major stages: In Aim 1 we will elucidate how EgeA hijacks TANGO1- and SCFD1-mediated protein transport machinery at ERES to deliver ER nutrients to Aph inclusions by assessing EgeA domains interacting with host molecules at ERES and inclusions and binding affinities of host molecules and spatial topology between ERES and Aph inclusions, and EgeA-dependency of delivery. In Aim 2 we will analyze how EgeA interacts with host protein components to modulate ER stress in Aph-infected cells and the unfolded protein response (UPR) signaling pathway. In Aim 3, we will test if EgeA functions and Aph infection can be blocked by intracellular delivery of lipid nanoparticle-encapsulated anti-EgeA nanobody mRNA in cell culture and in mice. The proposed studies will be crucial to understanding biomolecular mechanisms of EgeA functions in Aph infection. Impact: By ascertaining how intracellular Aph acquires ER nutrients and modulates ER stress and the UPR, infection may be pharmacologically or immunologically inhibitable, yielding new and innovative approaches to reduce human risk of acquiring or developing severe HGA. Further, the results will reveal a mechanism of TANGO1 and SCFD1 modulation in ERES transport and ER stress with an exogenous molecule, benefiting the broader fields of infectious diseases and ER homeostasis. Project Number: 1R01AI190088-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: YASUKO RIKIHISA | Institution: OHIO STATE UNIVERSITY, Columbus, OH | Award Amount: $670,881 | Activity Code: R01 | Study Section: Bacterial-Host Interactions Study Section [BHI] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01AI19008801A1