How Smooth Muscle Cells Change Identity in Aortic Aneurysm

This story is taken from the paper by Honglin Dong et al. For full details, see below.

The aorta is the body’s largest blood vessel, and its strength depends heavily on a special type of cell called vascular smooth muscle cells (VSMCs). In healthy arteries, these cells act like disciplined workers: they contract and relax with every heartbeat, helping the vessel withstand pressure while staying flexible and strong.

In aortic aneurysm, however, the vessel wall weakens and expands dangerously. For years, scientists believed this happened mainly because smooth muscle cells died or because inflammation damaged the tissue. This new study reveals a deeper and more surprising story: many VSMCs don’t simply disappear, they change who they are.

Using single-cell RNA sequencing, researchers analysed thousands of individual cells from healthy and diseased human aortas. Instead of seeing one uniform smooth muscle population, they uncovered several distinct VSMC “identities,” each with different roles in disease.

The loss of the healthy builders

The first group were contractile VSMCs, the healthy cells responsible for strength and elasticity. These cells showed strong connections to each other and to the surrounding tissue and produced very low levels of inflammatory signals.

In aneurysm tissue, these protective cells were reduced. This suggests that as disease develops, normal VSMCs either die or transform into other cell types, weakening the vessel wall’s natural defence.

Repair crews that reshape the wall

Another group of cells resembled fibroblasts, which normally help repair damaged tissue. These fibroblast-like VSMCs produced large amounts of collagen and other structural proteins, likely attempting to patch injured areas of the aorta.

While this may sound helpful, the process is imperfect. These cells also released enzymes that remodel the vessel wall and mild inflammatory signals. Over time, constant remodelling can distort the structure of the aorta, making it stiffer and more fragile rather than stronger.

Stem-like cells with disruptive potential

The researchers also found mesenchymal-like VSMCs: cells that lost their muscle identity and expressed markers seen in stem-like or immature cells. These cells were loosely attached to their surroundings and produced moderate levels of inflammation.

These flexible but unstable cells may act as a transition state, capable of turning into other harmful phenotypes and contributing to vessel weakening.

Muscle cells that behave like immune cells

Perhaps the most striking discovery was the appearance of macrophage-like and T-cell-like VSMCs. These smooth muscle cells began acting like immune cells, producing powerful signals that activate inflammatory cells.

Macrophage-like VSMCs secreted high levels of chemokines and inflammatory factors, driving immune infiltration into the vessel wall. T-cell-like VSMCs showed similar behaviour, amplifying immune responses rather than supporting structure.

Instead of repairing the artery, these cells appear to fuel chronic inflammation, a dystopian positive feedback loop to accelerate aneurysm growth.

What drives these identity changes?

The study also examined transcription factors that act like switches controlling cell identity. Factors such as KLF4, RUNX3, and MAF were strongly linked to specific VSMC phenotypes, particularly the immune-like states.

In addition, cell–cell communication analysis revealed that inflammatory signalling pathways, especially those involving macrophage migration inhibitory factor (MIF), were highly active between different VSMC types. Of course, cells follow instructions, even when they are deraigned and have lost their identity!

Why this matters

This research changes how we think about aortic aneurysm. Rather than a simple loss of smooth muscle cells, the disease involves a complex reprogramming of cells, from contractile and protective to inflammatory and disruptive.

Understanding these transitions opens new possibilities for diagnosis and treatment. Instead of targeting only inflammation or tissue breakdown.

In short, aortic aneurysm is a story of cellular transformation. This study brings us closer to understand how blood vessels lose their strength and how we may stop that process before it becomes life-threatening.

Top figure shows the cells from healthy and aneurysm aortas organized into clusters. Each cluster represents a distinct cell types

Bottom figure separates these same cell groups into healthy (control) and aneurysm samples. This comparison shows that the balance of cell types changes in disease.

Paper: Single-cell RNA sequencing reveals the vascular smooth muscle cell phenotypic landscape in aortic aneurysm

Authors: Genmao Cao, Xuezhen Xuan, Yaling Li, Jie Hu, Ruijing Zhang, Haijiang Jin, and Honglin Dong

Journal: Cell Communication and Signaling (2023) 21:113

DOI: https://doi.org/10.1186/s12964-023-01120-5