# Collagen hydroxylation couples NAD+/NADH dynamics to tumor dormancy and reactivation

## TL;DR

The paper shows how collagen hydroxylation affects tumor dormancy and reactivation through NAD+/NADH balance and mitochondrial activity.

## Contribution

The study identifies P4HA2 as a key regulator of tumor dormancy through collagen hydroxylation and NAD+/NADH dynamics.

## Key findings

- P4HA2-mediated proline hydroxylation of collagens sustains dormancy by balancing the NAD+/NADH ratio.
- Loss of P4HA2 disrupts collagen proteostasis and activates ALDH4A1, triggering dormant cell reactivation.
- ALDH4A1 is essential for reactivated dormant cell survival, revealing a metabolic vulnerability.

## Abstract

Metastasis remains the leading cause of cancer-related mortality. Disseminated tumor cells (DTCs) colonize distant organs where they enter a prolonged state of quiescence, named cellular dormancy, within collagen-rich extracellular matrix (ECM) niches. How dormant cells regulate the formation of collagen-rich niches and the mechanisms maintaining collagen proteostasis during dormancy and reactivation are not understood. Here, we identify prolyl hydroxylase P4HA2 as a key regulator of tumor dormancy through its dual role in collagen proline hydroxylation and mitochondrial function. We demonstrate that P4HA2-mediated proline hydroxylation of collagens balances the NAD+/NADH ratio, sustaining dormancy by limiting mitochondrial activity. Loss of P4HA2 disrupts collagen proteostasis, induces autophagy, and activates the proline catabolism enzyme ALDH4A1, lowering the NAD+/NADH ratio, which fuels mitochondrial energetics and triggers DTC awakening. Notably, ALDH4A1 is essential for the survival of these reactivated dormant cells, and its depletion induces apoptosis upon awakening, revealing a metabolic vulnerability in reactivated dormant cells. Our findings establish a previously unrecognized link between collagen homeostasis, NADH metabolism and tumor cell dormancy, unveiling a mechanistic framework for identifying actionable targets to eliminate DTCs and prevent metastatic relapse.