# The DNA Methylation–Autophagy Axis: A Driver of MSC Fate Imbalance in Skeletal Aging and Osteoporosis

## TL;DR

Aging causes bone marrow stem cells to form fat instead of bone, and this shift is linked to DNA methylation and autophagy working together in a harmful cycle.

## Contribution

This paper identifies a bidirectional feedback loop between DNA methylation and autophagy that drives MSC fate imbalance in aging and osteoporosis.

## Key findings

- Promoter hypermethylation of autophagy and osteogenesis genes suppresses autophagy and osteoblast function.
- Reduced autophagy limits methyl donor availability and epigenetic regulator turnover, worsening DNA methylation.
- This cycle increases oxidative stress, inflammation, and fat formation while impairing bone remodeling.

## Abstract

With aging, the differentiation potential of bone marrow mesenchymal stem cells (MSCs) shifts from osteogenic (bone-forming) to adipogenic (fat-forming) fates, contributing to the development of osteoporosis. This transformation is governed by two key processes: DNA methylation, which regulates gene expression by controlling whether genes are turned on or off, and autophagy, the cell’s waste disposal system that maintains cellular quality. In this review, we explain how DNA methylation and autophagy interact in a bidirectional feedback loop. Excessive DNA methylation can silence genes essential for autophagic function and osteogenesis, while compromised autophagic activity leads to metabolic disruption, resulting in the accumulation of epigenetic regulators that further exacerbate DNA methylation. This vicious cycle increases oxidative stress and inflammation, accelerating bone loss. Understanding this “methylation–autophagy axis” opens new therapeutic avenues, including the use of epigenetic modulators, metabolic and autophagy activators (e.g., targeting AMP-activated protein kinase (AMPK)–mechanistic target of rapamycin (mTOR)–transcription factor EB (TFEB) signaling), and bone-targeted drug delivery systems or combination therapies.

Age-related osteoporosis is driven in part by senescence-associated rewiring of bone marrow mesenchymal stem cells (MSCs) from osteogenic toward adipogenic fates. Accumulating evidence indicates that epigenetic drift and reduced autophagy are not isolated lesions but are mechanistically coupled through a bidirectional DNA methylation and autophagy axis. Here, we summarize how promoter hypermethylation of genes involved in autophagy and osteogenesis suppresses autophagic flux and osteoblast lineage transcriptional programs. Conversely, autophagy insufficiency reshapes the methylome by limiting methyl donor availability, most notably S-adenosylmethionine (SAM), and by reducing the turnover of key epigenetic regulators, including DNA methyltransferases (DNMTs), ten-eleven translocation (TET) dioxygenases, and histone deacetylases (HDACs). This self-reinforcing circuitry exacerbates mitochondrial dysfunction, oxidative stress, and inflammation driven by the senescence-associated secretory phenotype (SASP), thereby stabilizing adipogenic bias and progressively impairing marrow niche homeostasis and bone remodeling. We further discuss therapeutic strategies to restore balance within this axis, including selective modulation of epigenetic enzymes; activation of AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) signaling with downstream engagement of Unc-51-like autophagy-activating kinase 1 (ULK1) and transcription factor EB (TFEB); targeting sirtuin pathways; mitochondria- and autophagy-supportive natural compounds; and bone-targeted delivery approaches or rational combination regimens.