Mechanisms of cytomegalovirus-accelerated vascular disease: induction of paracrine factors that promote angiogenesis and wound healing

Abstract

Human cytomegalovirus (HCMV) is associated with the acceleration of a number of vascular diseases such as atherosclerosis, restenosis, and transplant vascular sclerosis (TVS). All of these diseases are the result of either mechanical or immune-mediated injury followed by inflammation and subsequent smooth muscle cell (SMC) migration from the vessel media to the intima and proliferation that culminates in vessel narrowing. A number of epidemiological and animal studies have demonstrated that CMV significantly accelerates TVS and chronic rejection (CR) in solid organ allografts. In addition, treatment of human recipients and animals alike with the antiviral drug ganciclovir results in prolonged survival of the allograft, indicating that CMV replication is a requirement for acceleration of disease. However, although virus persists in the allograft throughout the course of disease, the number of directly infected cells does not account for the global effects that the virus has on the acceleration of TVS and CR. Recent investigations of up- and downregulated cellular genes in infected allografts in comparison to native heart has demonstrated that rat CMV (RCMV) upregulates genes involved in wound healing (WH) and angiogenesis (AG). Consistent with this result, we have found that supernatants from HCMV-infected cells (HCMV secretome) induce WH and AG using in vitro models. Taken together, these findings suggest that one mechanism for HCMV acceleration of TVS is mediated through induction of secreted cytokines and growth factors from virus-infected cells that promote WH and AG in the allograft, resulting in the acceleration of TVS. We review here the ability of CMV infection to alter the local environment by producing cellular factors that act in a paracrine fashion to enhance WH and AG processes associated with the development of vascular disease, which accelerates chronic allograft rejection.

Figure 1. HCMV Secretome Mediates EC Tubule Formation

(A) Quantitation of two parameters of angiogenesis, lumen formation and number of branch points at 24 hours post plating on matrigel in the presence of control supernatants (SFM alone or SFM + HS/ECGS) and test supernatants conditioned by factors secreted by Mock- and HCMV-infected cells. (B) Low power images of EC differentiation on matrigel. (C) High power images, conditions as for (B), illustrating the integrity of individual tubules. (D) Tubule survival after 2 weeks on matrigel in the presence of SFM plus HS/ECGS or supernatant conditioned by HCMV-infected cells.

Figure 2. HCMV Secretome Mediates EC Wound Healing

Wound healing activity of the HCMV secretome. EC were grown to confluence on ECIS arrays and exposed to test supernatants prior to electrical wounding. Wound healing, as indicated by increasing resistance, is plotted as a function of time. Healing traces for duplicate wells are shown for the HSV-1 Secretome (yellow), mock (green), HCMV (red), or UV-inactivated HCMV (light blue). Controls traces include a negative control (SSFM; pink), a positive control (Complete SFM; dark blue) and an unwounded control (black). Cells exposed to the HCMV secretome show wound repair within 6–10 hrs, whereas cells exposed to the HSV-1 or mock secretomes repopulate the wound inefficiently, indicating that the production of wound healing factors is specific for HCMV infections.