A rat model for human T lymphocyte virus type I-associated myeloneuropathy. down-regulation of bcl-2 expression and increase in sensitivity to TNF-alpha of the spinal oligodendrocytes

Motor behavioral abnormalities and histopathological findings of Wistar rats inoculated with HTLV-1-infected MT2 cells

The objective of the present study was to describe motor behavioral changes in association with histopathological and hematological findings in Wistar rats inoculated intravenously with human T-cell lymphotropic virus type 1 (HTLV-1)-infected MT2 cells. Twenty-five 4-month-old male rats were inoculated with HTLV-1-infected MT2 cells and 13 control rats were inoculated with normal human lymphocytes. The behavior of the rats was observed before and 5, 10, 15, and 20 months after inoculation during a 30-min/rat testing time for 5 consecutive days. During each of 4 periods, a subset of rats was randomly chosen to be sacrificed in order to harvest the spinal cord for histopathological analysis and to obtain blood for serological and molecular studies. Behavioral analyses of the HTLV-1-inoculated rats showed a significant decrease of climbing, walking and freezing, and an increase of scratching, sniffing, biting, licking, and resting/sleeping. Two of the 25 HTLV-1-inoculated rats (8%) developed spastic paraparesis as a major behavioral change. The histopathological changes were few and mild, but in some cases there was diffuse lymphocyte infiltration. The minor and major behavioral changes occurred after 10-20 months of evolution. The long-term observation of Wistar rats inoculated with HTLV-1-infected MT2 cells showed major (spastic paraparesis) and minor motor abnormalities in association with the degree of HTLV-1-induced myelopathy.

Proinflammatory cytokine gene induction by human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 Tax in primary human glial cells

Infection with human T-cell leukemia virus type 1 (HTLV-1) can result in the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease of the central nervous system (CNS). HTLV-2 is highly related to HTLV-1 at the genetic level and shares a high degree of sequence homology, but infection with HTLV-2 is relatively nonpathogenic compared to HTLV-1. Although the pathogenesis of HAM/TSP remains to be fully elucidated, previous evidence suggests that elevated levels of the proinflammatory cytokines in the CNS are associated with neuropathogenesis. We demonstrate that HTLV-1 infection in astrogliomas results in a robust induction of interleukin-1beta (IL-1beta), IL-1alpha, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and IL-6 expression. HTLV encodes for a viral transcriptional transactivator protein named Tax that also induces the transcription of cellular genes. To investigate and compare the effects of Tax1 and Tax2 expression on the dysregulation of proinflammatory cytokines, lentivirus vectors were used to transduce primary human astrocytomas and oligodendrogliomas. The expression of Tax1 in primary human astrocytomas and oligodendrogliomas resulted in significantly higher levels of proinflammatory cytokine gene expression compared to Tax2. Notably, Tax1 expression uniquely sensitized primary human astrocytomas to apoptosis. A Tax2/Tax1 chimera encoding the C-terminal 53 amino acids of the Tax1 fused to the Tax2 gene (Tax(221)) demonstrated a phenotype that resembled Tax1, with respect to proinflammatory cytokine gene expression and sensitization to apoptosis. The patterns of differential cytokine induction and sensitization to apoptosis displayed by Tax1 and Tax2 may reflect differences relating to the heightened neuropathogenicity associated with HTLV-1 infection and the development of HAM/TSP.

Role of neuronal interferon-gamma in the development of myelopathy in rats infected with human T-cell leukemia virus type 1

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of not only adult T-cell leukemia but also HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Among the rat strains infected with HTLV-1, chronic progressive myelopathy, named HAM rat disease, occurs exclusively in WKAH rats. In the present study, we found that HTLV-1 infection induces interferon (IFN)-gamma production in the spinal cords of HAM-resistant strains but not in those of WKAH rats. Neurons were the major cells that produced IFN-gamma in HTLV-1-infected, HAM-resistant strains. Administration of IFN-gamma suppressed expression of pX, the gene critically involved in the onset of HAM rat disease, in an HTLV-1-immortalized rat T-cell line, indicating that IFN-gamma protects against the development of HAM rat disease. The inability of WKAH spinal cord neurons to produce IFN-gamma after infection appeared to stem from defects in signaling through the interleukin (IL)-12 receptor. Specifically, WKAH-derived spinal cord cells were unable to up-regulate the IL-12 receptor beta2 gene in response to IL-12 stimulation. We suggest that the failure of spinal cord neurons to produce IFN-gamma through the IL-12 pathway is involved in the development of HAM rat disease.

Provirus expansion and deregulation of apoptosis-related genes in the spinal cord of a rat model for human T-lymphocyte virus type I-associated myeloneuropathy

Apoptosis of the spinal oligodendrocytes is the main factor linked to the pathogenesis of human T-lymphocyte virus type I (HTLV-I)-induced myeloneuropathy in rats (HAM rat). To clarify apoptosis-related mechanisms, expression of apoptosis-related genes in the spinal cord of these rats was chronologically examined by means of a semiquantitative reverse transcriptase-polymerase chain reaction. Provirus expansion and increment of HTLV-I pX mRNA were evident at 7 months after the induced infection. Tumor necrosis factor-alpha increased gradually soon after pX expression. The expression of a major apoptosis-resistant gene, bcl-2, was markedly suppressed at a period of the provirus expansion and bax was also down-regulated. p53 was consistently expressed at high levels. These findings were never observed in spinal cords of HAM-resistant strains with HTLV-I infection even throughout their entire life. Collective evidence suggests that the local provirus expansion and deregulation of apoptosis-related genes, especially down-regulation of bcl-2, may lead to apoptosis of oligodendrocytes, thus being a major pathogenetic pathway in the HTLV-I-induced myeloneuropathy.

Molecular biology of cervical myelopathy and spinal cord injury: role of oligodendrocyte apoptosis

BACKGROUND CONTEXT

Rational design of treatment strategies for cervical myelopathy and spinal cord injury requires a working knowledge of the molecular biology underlying these pathological processes. The cellular process of apoptosis is an important component of tissue and organ development as well as the natural response to disease and injury. Recent studies have convincingly demonstrated that apoptosis also plays a pivotal role in numerous pathological processes, contributing to the adverse effects of various diseases and traumatic conditions. A growing body of evidence has implicated apoptosis as a key determinant of the extent of neurological damage and dysfunction after acute spinal cord injury and in chronic cervical myelopathy.

PURPOSE

To provide clinicians and research investigators interested in spinal cord injury and myelopathy with a practical and up-to-date basic science review of cellular apoptosis in the context of spinal cord pathology.

STUDY DESIGN/SETTING

A review of recently published or presented data from molecular biological, animal model and human clinical studies.

METHODS

A computer-based comprehensive review of the English-language scientific and medical literature was performed in order to identify relevant publications with emphasis given to more recent studies.

RESULTS

Investigation into the role of apoptosis in spinal cord injury and myelopathy has drawn the interest of an increasing number of researchers and has yielded a substantial amount of new information.

CONCLUSIONS

Apoptosis is a fundamental biological process that contributes to preservation of health as well as development of disease. There is now strong evidence to support a significant role for apoptosis in secondary injury mechanisms after acute spinal cord injury as well in the progressive neurological deficits observed in such conditions as spondylotic cervical myelopathy.

Provirus expansion and deregulation of apoptosis-related genes in the spinal cord of a rat model for human T-lymphocyte virus type I-associated myeloneuropathy

Apoptosis of the spinal oligodendrocytes is the main factor linked to the pathogenesis of human T-lymphocyte virus type I (HTLV-I)-induced myeloneuropathy in rats (HAM rat). To clarify apoptosis-related mechanisms, expression of apoptosis-related genes in the spinal cord of these rats was chronologically examined by means of a semiquantitative reverse transcriptase-polymerase chain reaction. Provirus expansion and increment of HTLV-I pX mRNA were evident at 7 months after the induced infection. Tumor necrosis factor-alpha increased gradually soon after pX expression. The expression of a major apoptosis-resistant gene, bcl-2, was markedly suppressed at a period of the provirus expansion and bax was also down-regulated. p53 was consistently expressed at high levels. These findings were never observed in spinal cords of HAM-resistant strains with HTLV-I infection even throughout their entire life. Collective evidence suggests that the local provirus expansion and deregulation of apoptosis-related genes, especially down-regulation of bcl-2, may lead to apoptosis of oligodendrocytes, thus being a major pathogenetic pathway in the HTLV-I-induced myeloneuropathy.

The role of the thymus in development of necrotizing arteritis in transgenic rats carrying the env-pX gene of human T-cell leukemia virus type-I

Necrotizing arteritis mimicking polyarteritis nodosa occurred in transgenic rats carrying the env-pX gene of human T-cell leukemia virus type I. To investigate the pathogenesis of necrotizing arteritis in these rats (env-pX rats), adoptive transfers of spleen cells and bone marrow cells were done from env-pX rats before they developed arteritis to nontransgenic rats. Necrotizing arteritis occurred in lethally irradiated nontransgenic rats reconstituted by env-pX spleen cells, thus indicating that the env-pX transgene in affected vessels may not be essential for the development of arteritis. In contrast, arteritis was not induced in nontransgenic recipients by adoptive transfers of env-pX bone marrow cells, which suggested that T cells derived from the env-pX thymus may play a role in the development of arteritis. To clarify if the process of differentiation of T cells in the env-pX thymus is crucial to develop necrotizing arteritis, reciprocal exchange of thymus frameworks was done between env-pX and nontransgenic rats. Necrotizing arteritis occurred in nontransgenic rats with an env-pX thymus framework, whereas development of arteritis was suppressed in env-pX rats in which the thymus framework was replaced with a nontransgenic one. This collective evidence shows that the thymus is directly associated with the development of necrotizing arteritis in env-pX rats.

Clonotypic analysis of T cells accumulating at arthritic lesions in HTLV-I env-pX transgenic rats

Human T cell leukemia virus type I (HTLV-I) env-pX transgenic rats (env-pX rats) develop chronic destructive arthritis resembling rheumatoid arthritis in humans. Immunological characteristics were compared with those of collagen-induced arthritis (CIA). Rheumatoid factor was present in some env-pX rats regardless of the development of arthritis, but not in nontransgenic rats with CIA. All rats with CIA produced anti-type II collagen (IIC) antibody, but never so in env-pX rats with naturally occurring arthritis. Although expansions of oligoclonal T cells were evident in the affected joints, no particular clone was shown to infiltrate into the arthritic lesions in env-pX rats. In contrast to CIA, in which clonal expansions of IIC-specific T cells are implicated, locally expanded T cell clones against various antigens of the joints may play pathogenetic roles in the arthritis seen in env-pX rats. However, complementarity-determining region 3 of the TCR Vbeta gene of T cells accumulating at the affected joints in env-pX rats contained the GGA amino acid sequence, which was reported to be a conserved motif in HTLV-I env-pX transgenic mice with arthritis. These findings suggest that common antigen(s) might be recognized by T cells accumulating at sites of arthritis in both transgenic rats and mice.

Immunological hyperresponsiveness in HTLV-I LTR-env-pX transgenic rats: a prototype animal model for collagen vascular and HTLV-I-related inflammatory diseases

We have earlier reported that diverse collagen vascular diseases, including arthritis, arteritis, thrombosis, myocarditis, myositis, sialo-/dacryoadenitis and dermatitis develop with the advent of autoantibodies in transgenic rats carrying the LTR-env-pX gene of human T lymphocyte virus type I (LTR-env-pX rats). To clarify the pathogenesis of these collagen vascular diseases, immunological features of LTR-env-pX rats were examined. In LTR-env-pX rats affected with these diseases, expression of CD80/86 on both tissue-infiltrating and peripheral T cells increased, compared with findings in non-transgenic rats with experimental inflammatory diseases. CD80/86 was also upregulated on peripheral T cells in LTR-env-pX rats prior to the development of diseases. Lymphocytes from LTR-env-pX rats showed an increase in autologous proliferation and were hyperreactive against several mitogens, including concanavalin A, immobilized anti-CD3 antibodies, and superantigens in vitro. Antigen-specific immune response was also enhanced in LTR-env-pX rats. The collective evidence indicates that lymphocytes of LTR-env-pX rats constitutively express surface molecules related to T cell activation and are immunologically hyperresponsive. Bone marrow cell transfer from LTR-env-pX rats to lethally irradiated non-transgenic rats revealed that these immunologically pre-activated and hyperresponsive lymphocytes play a critical role in the pathogenesis of several collagen vascular diseases, especially of dermatitis in LTR-env-pX rats.