Critical Role of Mitochondrial Damage in Determining Outcome of Macrophage Infection with Mycobacterium tuberculosis

Abstract

Human macrophages (Mφ) respond to Mycobacterium tuberculosis (Mtb) infection by undergoing apoptosis, a cornerstone of effective antimycobacterial host defense. Virulent mycobacteria override this reaction by inducing necrosis leading to uncontrolled Mtb replication. Accordingly, Mφ death induced by inoculation with Mtb had the characteristics of apoptosis and necrosis and correlated with moderate increase of mitochondrial permeability transition (MPT), mitochondrial cytochrome c release, and caspase-9 and -3 activation. We hypothesized that changes in intramitochondrial Ca2+ concentration ([Ca2+]m) determine whether Mφ undergo either apoptosis or necrosis. Therefore, we induced mechanism(s) leading to predominant apoptosis or necrosis by modulating [Ca2+]m and examined their physiological consequences. Adding calcium ionophore A23187 to Mφ inoculated with Mtb further increased calcium flux into the cells which is thought to lead to increased [Ca2+]m, blocked necrosis, stabilized MPT, decreased mitochondrial cytochrome c release, lowered caspase activation, and accompanied effective antimycobacterial activity. In contrast, Mφ infected with Mtb in presence of the mitochondrial calcium uniporter inhibitor ruthenium red showed increased mitochondrial swelling and cytochrome c release and decreased MPT and antimycobacterial activity. Thus, in Mtb-infected Mφ, high levels of mitochondrial membrane integrity, low levels of caspase activation, and diminished mitochondrial cytochrome c release are hallmarks of apoptosis and effective antimycobacterial activity. In contrast, breakdown of mitochondrial membrane integrity and increased caspase activation are characteristic of necrosis and uncontrolled Mtb replication.

A Mechanism of Virulence: Virulent Mycobacterium tuberculosis Strain H37Rv, but Not Attenuated H37Ra, Causes Significant Mitochondrial Inner Membrane Disruption in Macrophages Leading to Necrosis

“…After release into the cytosol, cytochrome c forms a complex containing Apaf-1, ATP, and procaspase-9, resulting in the activation of downstream caspases (12) and apoptosis. Cytosolic cytochrome c also binds to inositol (1,4,5) triphosphate receptors of the endoplasmatic reticulum, amplifying the Ca 2ϩ release from the endoplasmatic reticulum (30) that causes mitochondrial Ca 2ϩ influx necessary for induction of apoptosis (31). In contrast to apoptosis, necrosis is a consequence of the opening of the MPT pore (32).…”

“…M were cultured at a density of 1.5 ϫ 10 6 mononuclear cells/2 ml/well in 6-well cluster plates (Corning Glass) (5). The cells were infected with H37Rv at an MOI of 10:1 for 6, 12, and 48 h, washed with ice-cold PBS, and treated with 50 g/ml digitonin in PBS in the presence of protease inhibitor mixture (Roche) for 5 min on ice.…”

“…Mononuclear cells from peripheral blood of healthy donors under informed consent and harvested under guidelines approved by the Brigham and Women's Hospital Human Studies Committee were isolated, as previously described (5). M were cultured for 7 days in IMDM (Invitrogen Life Technologies) containing 10% human AB serum (Gemini Bio-Products) and challenged with varying MOI of Mtb, as described.…”

Differential co-expression network analysis for identification of functional modules in HIV infection and tubercolosis-HIV co-infection

“…Mycobacterium causes mitochondrial outer membrane permeabilization characterized by cytochrome c release from the mitochondrial inter-membrane space and apoptosis. Duan et al (2002) and Chen et al (2006) have reported that mycobacterial infection affects mitochondrial function. 22,23 There is consistent evidence for a central role of mitochondrial dysfunction in these pathologies.…”

“…Duan et al (2002) and Chen et al (2006) have reported that mycobacterial infection affects mitochondrial function. 22,23 There is consistent evidence for a central role of mitochondrial dysfunction in these pathologies. 24 Nucleotide reverse transcriptase inhibitors (NRTIs) have been described to be primarily responsible for mitochondrial dysfunction in adipose tissue and liver.…”