Effect of HIV-1-related protein expression on cardiac and skeletal muscles from transgenic rats

Abstract

Background: Human immunodeficiency virus type 1 (HIV-1) infection and the consequent acquired immunodeficiency syndrome (AIDS) has protean manifestations, including muscle wasting and cardiomyopathy, which contribute to its high morbidity. The pathogenesis of these myopathies remains partially understood, and may include nutritional deficiencies, biochemical abnormalities, inflammation, and other mechanisms due to viral infection and replication. Growing evidence has suggested that HIV-1-related proteins expressed by the host in response to viral infection, including Tat and gp120, may also be involved in the pathophysiology of AIDS, particularly in cells or tissues that are not directly infected with HIV-1. To explore the potentially independent effects of HIV-1-related proteins on heart and skeletal muscles, we used a transgenic rat model that expresses several HIV-1-related proteins (e.g., Tat, gp120, and Nef). Outcome measures included basic heart and skeletal muscle morphology, glutathione metabolism and oxidative stress, and gene expressions of atrogin-1, muscle ring finger protein-1 (MuRF-1) and Transforming Growth Factor-beta1 (TGFbeta1), three factors associated with muscle catabolism.

Results: Consistent with HIV-1 associated myopathies in humans, HIV-1 transgenic rats had increased relative heart masses, decreased relative masses of soleus, plantaris and gastrocnemius muscles, and decreased total and myosin heavy chain type-specific plantaris muscle fiber areas. In both tissues, the levels of cystine (Cyss), the oxidized form of the anti-oxidant cysteine (Cys), and Cyss:Cys ratios were significantly elevated, and cardiac tissue from HIV-1 transgenic rats had altered glutathione metabolism, all reflective of significant oxidative stress. In HIV-1 transgenic rat hearts, MuRF-1 gene expression was increased. Further, HIV-1-related protein expression also increased atrogin-1 (approximately 14- and approximately 3-fold) and TGFbeta1 (approximately 5-fold and approximately 3-fold) in heart and plantaris muscle tissues, respectively.

Conclusion: We provide compelling experimental evidence that HIV-1-related proteins can lead to significant cardiac and skeletal muscle complications independently of viral infection or replication. Our data support the concept that HIV-1-related proteins are not merely disease markers, but rather have significant biological activity that may lead to increased oxidative stress, the stimulation of redox-sensitive pathways, and altered muscle morphologies. If correct, this pathophysiological scheme suggests that the use of dietary thiol supplements could reduce skeletal and cardiac muscle dysfunction in HIV-1-infected individuals.

Figure 1

Gross pathology of heart and plantaris muscles from HIV-1 transgenic rats. (A) Relative heart masses from HIV-1 transgenic rats were increased compared to controls. In addition to this cardiac tissue defect, several skeletal muscles from HIV-1 transgenic rats were atrophied, including gastrocnemius (gastroc), soleus, and plantaris. (B) Specifically, the cross-sectional areas (CSA) of total and myosin heavy chain (MHC) isoform type-specific (i.e., slow, hybrid or fast MHC isoforms) from plantaris fibers were reduced in HIV-1 transgenic rats. Data in panel A represented as milligram of tissue weight divided by body mass in grams. Bar in panel B = 100 μm. *, p ≤ 0.05 vs. control.

Figure 2

GSH and Cys pools in heart tissues from HIV-1 transgenic rats. High performance liquid chromatography was performed on heart tissues to detect levels of the thiol pairs GSH and GSSG, and Cys and Cyss. HIV-1-related protein expression had no effect on GSH or GSSG levels (A and B), but did increase the overall oxidative state of the GSH pool (C). In contrast, Cys levels were reduced and Cyss levels were elevated in heart tissues from HIV-1 transgenic rats compared to controls (D and E, respectively). Therefore, the Cyss:Cys ratio, a marker of the overall oxidative state of the Cys pool, was significantly increased in HIV-1 transgenic rat hearts (F). *, p ≤ 0.05 vs. control.

Figure 3

GSH and Cys pools in plantaris muscles from HIV-1 transgenic rats. High performance liquid chromatography was performed on plantaris muscles to detect levels of the thiol pairs GSH and GSSG, and Cys and Cyss. HIV-1-related protein expression increased the levels of GSSG (B) and Cyss (E) compared to controls. Surprisingly, GSH levels were markedly increased in plantaris muscles from HIV-1 transgenic rats (A), which served to normalize the overall oxidative state of the GSH pool (C). In contrast, the overall oxidative state of the Cys pool was significantly increased in HIV-1 transgenic rat plantaris muscles (F). *, p ≤ 0.05 vs. control.

Figure 4

Atrogin-1, MuRF-1 and TGFβ₁ mRNA expression patterns in cardiac and plantaris tissues from HIV-1 transgenic rats. Gene expression levels of several catabolic factors including, atrogin-1, MuRF-1 and TGFβ₁, were markedly increased in HIV-1 transgenic rat heart tissues compared to controls (A-C, respectively). Similarly, mRNA expression levels of atrogin-1 and TGFβ₁ were increased in plantaris muscles from HIV-1 transgenic rats compared to controls (D and F, respectively), however, no changes were detected in the levels of MuRF-1 (E). *, p ≤ 0.05 vs. control.