Absence of human herpesvirus 8 in lung tissues from Japanese patients with primary pulmonary hypertension

The burden of pulmonary hypertension in resource-limited settings

Pulmonary vascular disease (PVD) is a significant global health problem and accounts for a substantial portion of cardiovascular disease in the developing world. Although there have been considerable advances in therapeutics for pulmonary arterial hypertension, over 97% of the disease burden lies within the developing world where there is limited access to health care and pharmaceuticals. The causes of pulmonary arterial hypertension differ between industrialized and developing nations. Infectious diseases-including schistosomiasis human immunodeficiency virus, and rheumatic fever-are common causes of PVD, as are hemoglobinopathies, and untreated congenital heart disease. High altitude and exposure to household air pollutants also contribute to a significant portion of PVD cases. Although diagnosis of pulmonary arterial hypertension requires the use of imaging and invasive hemodynamics, access to equipment may be limited. PVD therapies may be prohibitively expensive and limited to a select few. Prevention is therefore important in limiting the global PVD burden.

HIV infection and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but severe disease that results from chronic obstruction of small pulmonary arteries, leading to right ventricular failure and, ultimately, death. One established risk factor for the development of PAH is HIV infection. In comparison with the incidence of idiopathic PAH in the general population (1-2 per million), HIV-infected patients have a 2500-fold increased risk of developing PAH. The presence of PAH is an independent risk factor for mortality in patients with HIV infection, and in most cases death is causally related to PAH rather than to other complications of HIV infection. This article will focus on HIV-PAH with special considerations to epidemiology, pathogenesis, clinical presentation, diagnostic approach and available treatments.

Mediators involved in HIV-related pulmonary arterial hypertension

HIV-related pulmonary arterial hypertension (PAH) is one of the long-term complications of HIV infection that has become increasingly apparent in recent years. The clinical presentation and underlying pathology of PAH in HIV is similar to that in other forms of the disease, although there are data to suggest subtle differences, such as a greater inflammatory component in the HIV-related form. Advances continue to be made in defining the underlying pathogenesis of PAH, but the overall processes leading to vascular dysfunction and remodeling remain unclear. It would appear that PAH has a multifactorial etiology, with various risk factors--probably acting on an underlying genetic predisposition--that lead to the pulmonary vascular dysfunction that characterizes the disease. A range of growth factors, chemokines, cytokines and other inflammatory mediators, together with mediators involved in vasoconstriction and dilation, have been implicated in the pulmonary vascular remodeling resulting from this dysfunction. An increased understanding of the processes and factors involved in PAH has led to the development of new therapeutic strategies that have improved the management of various forms of PAH, including PAH associated with HIV (HIV-PAH). Recent results from studies into other potential mediators of PAH offer the possibility of new targets for therapy in this progressive and serious condition.

Role of HIV and human herpesvirus-8 infection in pulmonary arterial hypertension

BACKGROUND

Previous work has found a high prevalence of pulmonary arterial hypertension in HIV-infected persons, but establishment of a causal relationship has been limited by the lack of well characterized contemporaneous HIV-uninfected comparator groups. Among HIV-uninfected persons, human herpesvirus-8 (HHV-8) has also been linked to pulmonary arterial hypertension (PAH), but whether this relationship occurs among HIV-infected persons - who have among the highest prevalence of HHV-8 infection - has not been examined.

METHODS AND RESULTS

We echocardiographically calculated pulmonary artery systolic pressure and measured HHV-8 antibodies in HIV-infected and HIV-uninfected adults. Among the 196 HIV-infected participants, the median pulmonary artery systolic pressure (PASP) was 27.5 mmHg and 35.2% had PASP greater than 30 mmHg. This compared to a median of 22 mmHg among 52 HIV-uninfected participants in whom 7.7% had a PASP greater than 30 mmHg (P < 0.001). After adjustment for injecting drug and stimulant use, smoking, age, and gender, HIV-infected participants had 5.1 mmHg higher mean PASP and seven fold greater odds of having a PASP greater than 30 mmHg (P < 0.001). Although we found no association between HHV-8 and PAH among all HIV-infected participants, a borderline relationship was present when restricting to those without risk factors for PAH.

CONCLUSION

HIV-infected persons have a high prevalence of elevated PASP, which is independent of other risk factors for PAH. This suggests a causal role of HIV in PAH and emphasizes the need to understand the natural history of PAH in this setting. A role for HHV-8 infection in PAH remains much less definitive.

Reactivation of γHV68 induces neointimal lesions in pulmonary arteries of S100A4/Mts1-overexpressing mice in association with degradation of elastin

S100A4/Mts-overexpressing mice have thick elastic laminae and mild pulmonary arterial hypertension (PAH), and the occasional older mouse develops occlusive neointimal lesions and perivascular inflammation. We hypothesized that a vasculotropic virus could induce neointimal lesions in the S100A4/Mts1 mouse by facilitating breakdown of elastin and migration and proliferation of smooth muscle cells. To test this hypothesis, we infected S100A4/Mts1 mice with gammaherpesvirus 68 (γHV68). We observed, 6 mo after γHV68 [4 × 103 plaque-forming units (PFU)], perivascular inflammation in 10/15 S100A4/Mts1 mice and occlusive neointimal formation in 3/10 mice, accompanied by striking degradation of elastin. We then compared the early response after high-dose γHV68 (4 × 106 PFU) in C57Bl/6 and S100A4/Mts1 mice. In S100A4/Mts1 mice only, significant PAH, muscularization of distal vessels, and elastase activity were observed 6 wk after γHV68. These features resolved by 3 mo without neointimal formation. We therefore infected mice with the M1-γHV68 strain that reactivates from latency with higher efficiency and observed neointimal lesions at 3 mo in 2/5 C57Bl/6 (5–9% of vessels) and in 5/5 S100A4/Mts1 mice (13–40% of vessels) accompanied by mild PAH, heightened lung elastase activity, and intravascular viral expression. This suggested that enhanced generation of elastin peptides in S100A4/Mts1 mice may promote increased viral entry in the vessel wall. Using S100A4/Mts1 PA organ culture, we showed, in response to elastase activity, heightened production of elastin peptides associated with invasion of inflammatory cells and intravascular viral antigen. We therefore propose that early viral access to the vessel wall may be a critical determinant of the extent of vascular pathology following reactivation.

Pathogenic mechanisms of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a complex disease that causes significant morbidity and mortality and is clinically characterized by an increase in pulmonary vascular resistance. The histopathology is marked by vascular proliferation/fibrosis, remodeling, and vessel obstruction. Development of PAH involves the complex interaction of multiple vascular effectors at all anatomic levels of the arterial wall. Subsequent vasoconstriction, thrombosis, and inflammation ensue, leading to vessel wall remodeling and cellular hyperproliferation as the hallmarks of severe disease. These processes are influenced by genetic predisposition as well as diverse endogenous and exogenous stimuli. Recent studies have provided a glimpse at certain molecular pathways that contribute to pathogenesis; these have led to the identification of attractive targets for therapeutic intervention. We will review our current understanding of the mechanistic underpinnings of the genetic and exogenous/acquired triggers of PAH. The resulting imbalance of vascular effectors provoking pathogenic vascular changes will also be discussed, with an emphasis on common and overarching regulatory pathways that may relate to the primary triggers of disease. The current conceptual framework should allow for future studies to refine our understanding of the molecular pathogenesis of PAH and improve the therapeutic regimen for this disease.

Activation of proMMP-2 and Src by HHV8 vGPCR in human pulmonary arterial endothelial cells

Idiopathic pulmonary arterial hypertension (iPAH) is associated with human herpesvirus 8 (HHV8) infection and demonstrates pathological angiogenesis similar to that observed with another HHV8-linked disease, namely Kaposi Sarcoma (KS). Importantly, the HHV8 encoded viral G-protein-coupled receptor (vGPCR) induces KS lesions in a murine model. Investigating the impact of vGPCR expression on the angiogenic activity of human pulmonary arterial endothelial cells (HPAEC) can yield insight into the pathobiology of HHV8-associated vascular disorders, particularly PAH. Cultured HPAECs were transduced with retroviral vectors carrying either control or vGPCR coding regions. vGPCR expression selectively activated matrix metalloproteinase (MMP)-2, a pivotal matrix modulating enzyme during angiogenesis. A membrane type 1 MMP (MT1-MMP) neutralizing antibody and the tissue inhibitor of metalloproteinases-2 (TIMP-2) independently blocked vGPCR-induced MMP-2 activation. vGPCR expression concordantly promoted MMP-2 activation by increasing MT1-MMP expression while decreasing TIMP-2 expression. vGPCR activated Src kinase as demonstrated by phosphorylation of Src and its substrate focal adhesion kinase (FAK). vGPCR promoted angiogenesis of HPAECs as demonstrated by a substantial increase in tubulogenesis in vitro. The Src inhibitors PP2 and SU6656 significantly diminished vGPCR-induced MMP-2 activation and tubulogenesis. Our findings indicate that vGPCR induces MMP-2 activation in HPAECs through regulation of MT1-MMP and TIMP-2 expression. vGPCR activates Src and inhibition of such activation abrogates proMMP-2 activation and in vitro angiogenesis induced by vGCPR. The current study implicates vGPCR as an etiological agent in iPAH and identifies Src and MMP-2 as potential therapeutic targets in HHV8 associated KS and iPAH.

Idiopathic pulmonary arterial hypertension in Dutch Caucasian patients is not associated with human herpes virus-8 infection

Samples of lung tissue, taken at time of lung transplant, from 13 Dutch Caucasian patients with idiopathic pulmonary arterial hypertension (iPAH) and 14 patients with non-idiopathic PAH were studied for the presence of human herpes virus-8 (HHV-8). By immunohistochemical staining, in none of patients expression of HHV-8 latency-associated nuclear antigen 1 (LANA-1) was demonstrated. Using two nested polymerase chain reactions (PCR) to amplify part of the open reading frame (ORF) 65 and ORF 73, we failed to detect HHV-8 DNA in all samples studied. These results argue strongly against a role for HHV-8 in the pathogenesis of iPAH.

Occult lymphadenopathic Kaposi's sarcoma associated with severe pulmonary hypertension: A clinical hint about the potential role of HHV-8 in HIV-related pulmonary hypertension?

Severe pulmonary hypertension (PH) mimicking idiopathic PH is an increasingly recognized complication of human immunodeficiency virus (HIV) infection. PH shares several histopathologic features with Kaposi's sarcoma (KS), the most common malignancy in AIDS patients, and molecular evidence of the vasculotropic Kaposi's sarcoma-associated herpesvirus or human herpesvirus 8 (HHV-8) has been found in the lung tissue of patients with the disease. Although the prevalence of HHV-8 infection is increased among HIV-infected patients, no clinical association between KS and PH has ever been reported. Herein, we described a 30-year-old HIV-infected female co-infected with HHV-8 who developed severe PH coincident with occult KS. The clinical presentation of KS was unusual and remained masqueraded for years as an indolent cervical lymphadenopathy, without the typical cutaneous lesions. This is the first ever-reported case of PH associated with KS. Although the co-occurrence of both diseases in this patient could have been just a coincidence, the observation may also indicate that a relationship between HHV-8 infection and HIV-associated PH exists. Coinfection with HHV-8 and occult lymphadenopatic KS should be considered in HIV-infected patients developing PH.

The pleiotropic effects of Kaposi's sarcoma herpesvirus

Kaposi's sarcoma herpesvirus (KSHV), or human herpesvirus 8 (HHV8), is an essential factor in the pathogenesis of Kaposi's sarcoma (KS), multicentric Castleman's disease (MCD), and primary effusion lymphoma (PEL). Case reports suggest an occasional involvement in bone marrow hypoplasia and haemophagocytic syndrome, but other disease associations are unconfirmed or controversial. KSHV-associated disease is of particular importance in immunosuppressed individuals, in particular in patients with HIV infection and transplant recipients. KSHV establishes a latent infection in the majority of infected cells in KS, MCD, and PEL, but lytic replication occurs in a small fraction of infected cells. Viral proteins expressed during both the latent and the lytic phase of the viral life cycle contribute to the pathogenesis of KSHV-associated diseases.

Absence of Kaposi's sarcoma-associated herpesvirus in patients with pulmonary arterial hypertension

RATIONALE

In addition to Kaposi's sarcoma, Kaposi's sarcoma-associated herpesvirus (KSHV or HHV-8) has been associated with two other diseases: primary effusion lymphoma and the plasma cell variant of multicentric Castleman's disease. Recently, evidence of KSHV infection was reported in plexiform lesions of idiopathic pulmonary arterial hypertension (IPAH) as well as in adjacent parenchyma and bronchial epithelial cells.

OBJECTIVES

To further investigate a possible association of KSHV and pulmonary arterial hypertension.

METHODS AND MEASUREMENTS

Twenty-six lungs explanted from German patients suffering from IPAH were tested for the presence of KSHV antigen and genomes by immunohistochemistry (IHC) and polymerase chain reaction (PCR).

MAIN RESULTS

When stained with a commercial monoclonal antibody directed against the latency-associated nuclear antigen of KSHV, LANA-1, a positive signal reminiscent of the "speckled" nuclear pattern typical of latently KSHV-infected cells was found in 16 (61.5%) cases. Alveolar and bronchial epithelial cells in areas of unremarkable lung tissue, but not cells within the plexiform lesions, were the predominantly stained cell types. Different KSHV-PCR assays (based on orf26, orfK6, and orf72) performed on samples that had tested positively in IHC, however, could not confirm KSHV infection, indicating that the IHC signal was not due to KSHV infection. One IHC-negative patient tested positive by PCR. A PCR based on consensus degenerate hybrid oligonucleotide primers (CODEHOP) to detect yet unknown gamma-herpesviruses did not reveal any specific sequences.

CONCLUSIONS

KSHV is unlikely to play a role in the pathogenesis of IPAH.