Sirt3-CD38 Axis Drives Mitochondrial Failure in Aging Hearts via Calcium Overload
New research reveals how loss of Sirt3 activates CD38, depletes NAD, and floods mitochondria with calcium—fueling cardiac hypertrophy.
Summary
Researchers used Sirt3-knockout mice and H9C2 cell models to show that Sirt3 deficiency—mirroring normal aging—triggers a cascade in which the NAD-consuming enzyme CD38 accumulates, depleting NAD and generating cyclic ADP-ribose. This metabolite drives calcium overload in mitochondria via upregulated MCU (mitochondrial calcium uniporter), collapsing membrane potential and elevating reactive oxygen species. A multi-omics approach combining RNA-seq, proteomics, and metabolomics confirmed disrupted oxidative phosphorylation and cAMP signaling. Critically, a CD38 inhibitor (78C) reversed mitochondrial dysfunction in Sirt3-knockdown cells, restoring membrane potential and reducing ROS and calcium overload—pointing to the Sirt3–CD38 axis as a druggable target in age-related cardiac hypertrophy.
Detailed Summary
Cardiac hypertrophy—abnormal thickening of heart muscle—is increasingly recognized as an age-related condition driven partly by mitochondrial dysfunction and calcium dysregulation. Sirtuin-3 (Sirt3), an NAD-dependent deacetylase residing in mitochondria, declines with age alongside its cofactor NAD, but the precise mechanism linking Sirt3 loss to mitochondrial calcium overload remained unclear. This study systematically maps that pathway using a multi-omics strategy and pharmacological rescue experiments.
The research team employed 12-week-old Sirt3-knockout (ko) mice as an age-related cardiac hypertrophy model. Hematoxylin and eosin (HE) staining revealed significantly increased myofiber thickness in Sirt3 ko hearts, while transmission electron microscopy (TEM) showed grossly abnormal mitochondrial ultrastructure compared to wild-type controls. RNA-sequencing, 4D label-free proteomics, and metabolomics were then applied to the same heart tissue to identify key molecular drivers. The integrated multi-omics analysis identified CD38—another major NAD-consuming enzyme—as upregulated in Sirt3-deficient hearts. Pathway enrichment (GO and KEGG) linked CD38 metabolites, specifically cyclic ADP-ribose (cADPR), to disrupted cAMP signaling and impaired oxidative phosphorylation (OXPHOS) complex subunit expression, including mt-Nd1, mt-Co2, mt-Atp6, Ndufv1, Sdhc, and Uqcrc2.
In vitro studies in H9C2 cardiomyoblasts with Sirt3 siRNA knockdown validated these findings. Sirt3-depleted cells showed elevated intracellular and mitochondrial ROS (measured by DCFH-DA and MitoSox), dissipated mitochondrial membrane potential (JC-1 assay), upregulated MCU expression, and calcium overload in both cytoplasm and mitochondria (Fluo-4 and Rhod2). When cells were treated with the selective CD38 inhibitor 78C (5 nM), all of these parameters were significantly attenuated—ROS declined, membrane potential was restored, and mitochondrial calcium overload was reversed—demonstrating that CD38 activity is the critical intermediary between Sirt3 loss and mitochondrial dysfunction.
The mechanistic picture that emerges is: Sirt3 deficiency → CD38 upregulation → NAD depletion and cADPR accumulation → cAMP-pathway dysregulation → MCU overexpression → mitochondrial calcium overload → ETC dysfunction and ROS burst. Western blot and qPCR confirmed reduced expression of key OXPHOS subunits (MT-CO1, MT-ATP8, ATP5A1) in Sirt3 ko hearts, consistent with proteomics data. These findings establish the Sirt3–CD38 axis as a central regulator of mitochondrial health in the aging heart and suggest that CD38 inhibition could be a viable therapeutic strategy for age-related cardiac hypertrophy.
Key Findings
- Sirt3-knockout mice develop cardiac hypertrophy with thickened myofibers and severely disrupted mitochondrial ultrastructure.
- Multi-omics identified CD38 as the primary NAD consumer upregulated when Sirt3 is absent, linking NAD depletion to cAMP dysregulation.
- Sirt3 knockdown in H9C2 cells increased mitochondrial and intracellular ROS, collapsed membrane potential, and upregulated MCU-driven calcium overload.
- CD38 inhibitor 78C reversed mitochondrial calcium overload, ROS elevation, and membrane potential loss caused by Sirt3 deficiency.
- OXPHOS complex subunits (MT-CO1, MT-ATP8, ATP5A1, Ndufv1) were consistently downregulated in Sirt3-deficient hearts across proteomic and transcriptomic data.
Methodology
Sirt3-knockout C57BL/6J mice (12 weeks) served as the in vivo cardiac hypertrophy model, with HE staining and TEM for morphology. Multi-omics profiling (RNA-seq on Illumina NovaSeq, 4D label-free proteomics via timsTOF Pro, and UHPLC-Q-TOF metabolomics) was performed on n=3 WT vs. n=3 Sirt3 ko hearts. In vitro validation used H9C2 cells with Sirt3 siRNA knockdown and CD38 inhibitor 78C, assessed by flow cytometry for ROS, mitochondrial membrane potential, and calcium levels.
Study Limitations
The in vivo model relies on germline Sirt3 knockout, which does not fully recapitulate the gradual age-related Sirt3 decline in humans. The study used H9C2 rat cardiomyoblasts rather than primary human cardiomyocytes, and sample sizes were small (n=3 per group). No in vivo pharmacological rescue with CD38 inhibitors was performed, leaving the translational efficacy unconfirmed in an animal model.
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