Deleting HDAC9 Gene Slows Fat Tissue Aging and Boosts Mitochondrial Function in Mice
Mice lacking the HDAC9 gene gained less fat with age, accumulated fewer senescent cells, and showed improved mitochondrial respiration in adipose tissue.
Summary
Researchers at Augusta University found that deleting the HDAC9 gene in mice significantly reduced age-related fat tissue deterioration. Older HDAC9 knockout mice gained less weight, accumulated fewer senescent cells in adipose tissue, and showed better mitochondrial function compared to normal aging mice. A key mechanism identified was upregulation of thiosulfate sulfurtransferase (TST), an enzyme that declines with age and appears to protect against cellular senescence. When TST was silenced in fat precursor cells, senescence markers increased, confirming its protective role. These findings suggest HDAC9 inhibition could be a viable strategy to preserve healthy adipose tissue and metabolic function during aging.
Detailed Summary
Adipose tissue aging is a major driver of systemic metabolic decline, characterized by accumulation of senescent cells, chronic low-grade inflammation via the senescence-associated secretory phenotype (SASP), and mitochondrial dysfunction. Despite its importance, the molecular mechanisms governing adipose tissue aging remain poorly understood. This study from the Medical College of Georgia at Augusta University investigated whether HDAC9 — a class IIa histone deacetylase previously shown to suppress adipogenic differentiation — plays a role in these aging processes.
The researchers first established that HDAC9 expression increases with age in mouse adipose tissues, suggesting it may actively contribute to age-related deterioration rather than simply being a bystander. Using global Hdac9 knockout (KO) mice on a C57BL/6 background, housed at thermoneutral temperature on a chow diet, the team compared aging outcomes across multiple age groups against wild-type (WT) littermate controls. Approximately 1-year-old KO mice showed significantly reduced body weight gain and fat mass as measured by whole-body NMR spectroscopy, without changes in lean mass, indicating a specific effect on adiposity rather than general growth suppression.
Senescence burden in adipose tissue was assessed using senescence-associated beta-galactosidase (SABG) staining in whole tissue, the mature adipocyte fraction (MAF), and the stromal vascular fraction (SVF), alongside protein expression of canonical senescence markers p16 and p21. KO mice showed markedly reduced SABG staining and lower p16/p21 expression in aging adipose depots compared to WT controls. Importantly, primary preadipocytes isolated from KO mice also exhibited reduced baseline senescence and were more resistant to stress-induced senescence triggered by hydrogen peroxide (H₂O₂) treatment and UV irradiation, demonstrating a cell-autonomous protective effect of HDAC9 deletion.
RNA sequencing of visceral fat from 10-month-old KO versus WT mice revealed coordinated upregulation of mitochondria-associated gene networks in KO animals. This was corroborated by increased mitochondrial DNA copy number (CoxII/β-globin ratio) and Seahorse XFe24 MitoStress assay results showing elevated basal respiration and proton leak in adipose tissue explants from KO mice. These findings indicate that HDAC9 deletion fundamentally improves mitochondrial biogenesis and respiratory capacity in aging fat tissue.
A particularly novel finding was the identification of thiosulfate sulfurtransferase (TST) as a downstream mediator. TST, an enzyme involved in mitochondrial hydrogen sulfide metabolism, was significantly downregulated in adipose tissues of aging WT mice but was upregulated in KO mice. ChIP assays confirmed that HDAC9 directly regulates TST transcription. Critically, siRNA-mediated silencing of TST in primary preadipocytes increased SABG staining and upregulated p16 and p21 expression, establishing a functional link between the HDAC9-TST axis and cellular senescence. These results position TST as a key effector through which HDAC9 deletion confers protection against adipose tissue aging, opening a new mechanistic pathway for therapeutic targeting.
Key Findings
- HDAC9 protein expression increased progressively with age in mouse adipose tissues, correlating positively with aging-related deterioration
- Approximately 1-year-old Hdac9 KO mice had significantly reduced fat mass by NMR spectroscopy compared to age-matched WT littermates, without changes in lean mass
- SABG staining and p16/p21 protein expression were markedly reduced in adipose tissues (whole tissue, MAF, and SVF) of aging KO versus WT mice
- Primary preadipocytes from KO mice showed reduced baseline senescence and resistance to H₂O₂- and UV-induced senescence compared to WT-derived cells
- RNA-seq of visceral fat from 10-month-old KO mice revealed coordinated upregulation of mitochondria-associated gene sets; mitochondrial DNA copy number was increased in KO adipose tissue
- Seahorse MitoStress assay showed elevated basal respiration and proton leak in adipose tissue explants from KO versus WT mice
- TST expression was reduced in aging WT adipose tissue but upregulated in KO mice; siRNA silencing of TST in preadipocytes increased SABG staining and p16/p21 expression, confirming its anti-senescence role
Methodology
The study used global Hdac9 KO mice (C57BL/6 background) and WT littermate controls, all male unless specified, housed at thermoneutral temperature (27.5–30°C) on chow diet. Senescence was assessed by SABG staining and p16/p21 Western blot in vivo and in vitro (H₂O₂ and UV stress models). Mitochondrial function was measured via Seahorse XFe24 MitoStress assay on adipose tissue explants and mitochondrial DNA copy number by qPCR. Transcriptomic analysis used RNA sequencing of visceral fat from 10-month-old mice with GSEA and KEGG pathway analysis; ChIP assays confirmed HDAC9 binding at the TST promoter.
Study Limitations
The study used global Hdac9 knockout mice, making it impossible to attribute effects specifically to adipose tissue versus other organ systems without conditional knockout models. All primary experiments used male mice, limiting generalizability to females. The study is preclinical and mouse-based; translation to human adipose tissue aging requires validation, and no pharmacological HDAC9 inhibitor was tested, leaving the therapeutic feasibility of targeting HDAC9 in adults unaddressed.
Enjoyed this summary?
Get the latest longevity research delivered to your inbox every week.