Hypoxia and tissue destruction in pulmonary TB

Area of Science:

• Pulmonary Medicine
• Infectious Diseases
• Pathology

Background:

• Human tuberculosis (TB) is characterized by lung destruction mediated by matrix metalloproteinases (MMPs).
• The role of tissue hypoxia in human TB lesions and its impact on disease pathology remain unclear.

Purpose of the Study:

• To investigate tissue hypoxia in human TB lesions.
• To determine the influence of hypoxia on matrix metalloproteinase-1 (MMP-1) regulation and its contribution to lung destruction in TB.

Main Methods:

• Positron emission tomography (PET) imaging with [18F]-fluoromisonidazole ([18F]FMISO) was used to assess tissue hypoxia in five TB patients.
• Immunohistochemistry and primary human cell culture models were employed to study MMP-1 regulation under varying oxygen conditions and in response to Mycobacterium tuberculosis (M.tb) infection.
• Small interfering RNA (siRNA) was used to inhibit hypoxia-inducible factor (HIF)-1α.

Main Results:

• PET imaging revealed severe and heterogeneous tissue hypoxia in human TB lesions, particularly around pulmonary cavities.
• Hypoxia significantly upregulated MMP-1 gene expression and secretion in M.tb-infected macrophages and respiratory epithelial cells.
• M.tb infection induced HIF-1α accumulation, which, along with NF-κB, promoted MMP-1 activity. HIF-1α blockade inhibited MMP-1 expression.

Conclusions:

• Human TB lesions are significantly hypoxic.
• Mycobacterium tuberculosis drives HIF-1α accumulation, synergistically increasing collagenase activity and contributing to lung destruction and cavitation.