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Macrophages lacking TSC2 have mTORC1-dependent increased GPNMB and ameliorate ventricular dysfunction/remodeling
Mohammad Keykhaei1, Navid Koleini1, Mariam Meddeb1
1Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Ross Building Rm 858, 720 Rutland Avenue, Baltimore, MD, 21205, USA.
Abstract:
Macrophages (MΦ) modulate myocardial inflammation and repair after ischemia-reperfusion (I/R) injury. The mechanistic target of rapamycin (mTOR) regulates MΦ phenotype and functionality, but studies conflict regarding its pro- or anti-inflammatory role. To test this, myeloid TSC2 depleted (MΦTSC2-/-) mice were generated by crossing Lys2Cre with TSC2flx/flx. In vitro, bone marrow-derived MΦTSC2-/- vs. control MΦ had greater mTORC1 and less mTORC2 activity coupled with differential responses to pro- or anti-inflammatory ligands. These disparities were eliminated by inhibiting mTORC1 with rapamycin. MΦTSC2-/- mice had substantially less cardiac dysfunction and ventricular remodeling after I/R, with reduced lung edema and activation of stress/pro fibrotic genes. These differences were eliminated by treating mice with rapamycin, supporting mTORC1 dependence. Post I/R MΦTSC2-/- myocardium had fewer pro-inflammatory (CCR2+MHC-IIhi) MΦ, LY6C+ monocytes, LY6G + neutrophils, and CD8+ T cells at 5-days post-I/R, and fewer CCR2+ but more CCR2- MΦ 2-wks after I/R. Synthesis of glycoprotein nonmetastatic melanoma protein B (GPNMB), a MΦ secreted anti-inflammatory protein was greater in MΦTSC2-/- macrophages and myocardium after I/R in an mTORC1 dependent manner. Thus, constitutive mTORC1 activation in MΦ depresses pro-inflammatory cell infiltration, increases GPNMB protein expression, and preserves heart function following I/R. This reveals beneficial effects of a MΦ-dependent mTORC1-GPNMB cascade on the post I/R heart.
Insights
Constitutive mTORC1 activation in macrophages reduces inflammation and preserves heart function after ischemia-reperfusion injury. This involves increased GPNMB expression and decreased pro-inflammatory cell infiltration, highlighting a beneficial MΦ-mTORC1-GPNMB cascade.
Area of Science:
- Cardiovascular Research
- Immunology
- Cellular Signaling
Background:
- Macrophages (MΦ) play a critical role in myocardial inflammation and repair following ischemia-reperfusion (I/R) injury.
- The mechanistic target of rapamycin (mTOR) pathway influences MΦ phenotype, but its specific role in I/R injury remains debated.
- Understanding mTOR's impact on MΦ is crucial for developing targeted therapies for cardiac I/R injury.
Purpose of the Study:
- To investigate the role of constitutive mTORC1 activation in macrophages on cardiac I/R injury.
- To determine the effects of modulating mTOR activity on MΦ phenotype, inflammatory responses, and cardiac function post-I/R.
- To elucidate the downstream mechanisms, including GPNMB expression, involved in MΦ-mediated cardiac protection.
Main Methods:
- Generated myeloid-specific TSC2-deficient (MΦTSC2-/-) mice by crossing Lys2Cre with TSC2flx/flx mice.
- Assessed mTORC1 and mTORC2 activity in MΦTSC2-/- versus control MΦ in vitro.
- Evaluated cardiac function, ventricular remodeling, inflammatory cell infiltration, and GPNMB expression in MΦTSC2-/- mice subjected to I/R, with and without rapamycin treatment.
Main Results:
- MΦTSC2-/- exhibited enhanced mTORC1 activity and altered responses to inflammatory stimuli in vitro, which were reversed by rapamycin.
- MΦTSC2-/- mice showed significantly reduced cardiac dysfunction, ventricular remodeling, and lung edema after I/R.
- Rapamycin treatment abrogated the protective effects in MΦTSC2-/- mice, confirming mTORC1 dependence. Reduced pro-inflammatory cell infiltration and increased GPNMB expression were observed in MΦTSC2-/- post-I/R.
- Increased GPNMB, an anti-inflammatory protein, was found in MΦTSC2-/- macrophages and myocardium post-I/R, dependent on mTORC1.
Conclusions:
- Constitutive mTORC1 activation in macrophages attenuates cardiac I/R injury by reducing pro-inflammatory cell infiltration.
- The MΦ-dependent mTORC1-GPNMB cascade enhances the expression of the anti-inflammatory protein GPNMB, contributing to cardiac protection post-I/R.
- Targeting the MΦ mTORC1-GPNMB pathway represents a potential therapeutic strategy for mitigating myocardial damage after I/R injury.
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