The cellular dynamics responsible for induction of birth defects following Human Cytomegalovirus (HCMV) congenital infections are unclear. Annually, 1% of newborns are congenitally infected with HCMV. Five to 10% of these infants are symptomatic at birth, displaying a broad spectrum of central and peripheral nervous system (CNS and PNS) disorders including microcephaly, mental retardation, and sensorineural hearing loss (SNHL). The most severe manifestations may be due to lytic infection of neural progenitor cells (NPCs), as seen in tissue culture. The improper/abnormal differentiation of infected NPCs and neurons may also contribute to birth defects. The host immune response to HCMV infection may impact delicate CNS and PNS tissues during gestation. However, the development of SNHL during early childhood in infants asymptomatic at birth is perplexing. For the thousands of children and their families affected annually there is a critical need to determine the source of HCMV-induced birth defects to aid in their prevention and treatment. Our long term goal is to translate our in vitro tissue culture findings into elucidating HCMV's cellular interactions contributory to HCMV-induced birth defects. Our objective in this proposal is to determine if HCMV's specific interactions at two chromosome 1 loci, and the resulting downregulation of nidogen 1 (NID1) at 1q42 and myelin protein zero (MPZ) at 1q23, promote malfunctions in the CNS and PNS. We find expression of both proteins is downregulated in infected clinical tissue samples. NID1 is essential to the developing brain for neuronal migration and neural network excitability and plasticity. We find expressed NID1 protein is actively degraded post infection. Expression of the HCMV tegument protein pp71 induces breaks at both sites and downregulates NID1. pp71 and the insulator protein CTCF are bound at the 1q42 breaksite and the NID1 promoter. NID1 protein levels are also reduced after infection with a pp71 deletion virus (AD169del71), indicating at least one additional viral protein regulates NID1. HCMV targets NID1 with two viral proteins via two pathways suggesting NID1's elimination delivers strong selective advantage to the virus. MPZ is the principal nerve sheath protein of the PNS. Mutations in MPZ are causally linked to late onset SNHL. MPZ expression being limited solely to Schwann cells of the PNS, which seems unlikely could offer any selective advantage to the virus, is strong evidence that MPZ regulation is off-target. Deficiencies in NID1 and MPZ could have severe ramifications during development. We hypothesize HCMV specifically downregulates NID1 to promote dispersal of infected cells via remodeling of the extracellular matrix in infected blood vessels and that similarity in sequence shared between the 1q42 and1q23 sites leads to an off-target interaction with the 1q23 locus, downregulating MPZ, potentially leading to SNHL. We will determine 1) how HCMV downregulates NID1, 2) the benefit HCMV derives from this downregulation, 3) if MPZ is regulated in the same manner and 4) what are the ramifications of NID and MPZ downregulation?
Human Cytomegalovirus is a leading cause of birth defects. Those defects can dramatically impact the lives of the children (and their parents) that suffer from them. My research is aimed at understanding the underlying mechanisms involved in the development of those defects to ameliorate and, hopefully, prevent their occurrence.
