When the Body Cannot Finish Repair

Bioenergetic Constraints, Extracellular Matrix Aging, and the Loss of Recovery

How a new review of neurovascular ageing strengthens a broader perspective on extracellular matrix dysregulation, cellular senescence, and incomplete tissue recovery.

Aging Is Not Simply About Accumulating Damage

Why do our blood vessels become stiffer, our tissues lose structural integrity, and our organs become less capable of recovering from injury as we age?

The conventional explanation emphasizes accumulated molecular damage, chronic inflammation, mitochondrial dysfunction, cellular senescence, and deterioration of the extracellular matrix (ECM)—the structural network surrounding and supporting our cells.

These processes are closely interconnected. But an important question remains: What causes initially protective and adaptive responses to become persistent, dysfunctional, and ultimately damaging?

In our previous discussions of aging from a bioenergetic perspective, we proposed that the answer may lie partly in the progressive inability to complete recovery.

The body continuously responds to stress, adapts to changing conditions, removes damaged components, and rebuilds functional structures. All these activities require coordinated energy supply, metabolic resources, and cellular communication.

When adaptive demands persist or the capacity to complete recovery becomes insufficient, temporary responses may become chronic. Tissue remodeling remains unfinished, inflammatory signaling continues, and structural abnormalities accumulate.

A recent review published in GeroScience by Bindal and colleagues (2026), titled Sonic hedgehog–matrix metalloproteinase crosstalk in neurovascular ageing and stroke: A potential mechanistic link, provides an interesting molecular example of this broader concept.

Although the authors focus on specific signaling pathways in brain blood vessels, their discussion illustrates how disturbed coordination between tissue protection, degradation, and regeneration may contribute to aging.

The Extracellular Matrix Is More Than Structural Support

The extracellular matrix is often described as the scaffolding that holds our cells and tissues together.

It contains structural components such as collagen, elastin, and proteoglycans, providing mechanical stability while allowing tissues to remain flexible and responsive.

However, the ECM is not a passive structure.

It is continuously maintained, degraded, reconstructed, and reorganized according to physiological needs.

Following injury, for example, damaged matrix components must be removed, inflammatory responses coordinated, and new structural material produced and organized. The resulting tissue must regain sufficient integrity and function.

This process involves two complementary activities:

• Degradation and clearance: Removal of damaged or unnecessary structures to create space for repair.

• Restoration and remodeling: Synthesis, organization, and stabilization of functional tissue.

Both are necessary. Excessive degradation can weaken tissues, while excessive or disorganized deposition can produce stiffness and fibrosis.

Successful recovery therefore requires more than stimulating repair or suppressing inflammation. It requires completing the entire remodeling process.

Importantly, this is not energetically free.

Cells must maintain their metabolism, produce and process new structural proteins, regulate enzymes, control oxidative stress, and coordinate activity with neighboring cells.

This raises an important possibility: Could some age-related ECM abnormalities represent the structural consequences of recovery processes that were initiated but never adequately completed?

What the New Review Reveals About Neurovascular Aging

Bindal and colleagues examine the interactions between two important molecular systems within the neurovascular unit—the coordinated network of endothelial cells, astrocytes, pericytes, neurons, and supporting structures that regulates cerebral circulation and blood–brain barrier function.

The first is Sonic hedgehog (Shh) signaling, which contributes to vascular protection, endothelial stability, neural stem-cell regulation, angiogenesis, and tissue repair.

The second involves matrix metalloproteinases (MMPs), enzymes that degrade and remodel extracellular matrix components.

Under healthy conditions, these systems contribute to maintaining vascular integrity and facilitating appropriate remodeling.

However, aging is associated with mitochondrial dysfunction, oxidative stress, chronic inflammation, and cellular senescence. These disturbances may impair protective Shh signaling while promoting excessive or persistent MMP activity, particularly MMP-2 and MMP-9.

The consequences can include:

• Breakdown of the blood–brain barrier.

• Degradation of vascular basement membranes and tight-junction proteins.

• Increased inflammatory cell infiltration.

• Impaired communication between neurons and blood vessels.

• Reduced cerebral perfusion and microvascular stability.

• Diminished capacity for tissue repair after stroke.

The review also describes a potentially important reciprocal interaction.

MMP-2 can degrade SCUBE2, an extracellular protein involved in presenting Shh signals to target cells. This may further weaken protective Shh signaling.

Conversely, Shh signaling can influence MMP expression and activity, although the direction of this effect depends on the cellular and physiological context.

Together, these observations suggest a potentially self-reinforcing disturbance in which excessive remodeling damages the vascular environment while weakened protective signaling limits restoration.

The authors appropriately emphasize that direct evidence establishing this coordinated interaction in the aging neurovascular unit remains limited. Much of the available evidence comes from experimental models of injury, development, or cellular signaling.

Nevertheless, the proposed mechanism provides a useful example of how multiple aging-associated disturbances may converge on ECM dysfunction.

The Bioenergetic Perspective: Why Recovery May Become Incomplete

Our previously published bioenergetic impedance framework approaches aging from a complementary direction.

Rather than starting with individual molecular pathways, it asks whether the physiological system retains sufficient capacity to support its ongoing adaptive and restorative demands.

Cells require more than the availability of oxygen and nutrients. These resources must be delivered, processed, converted into usable energy, and appropriately allocated among competing functions.

Bioenergetic impedance describes constraints that interfere with this coordinated throughput.

Such constraints may arise at multiple levels, including circulation, cellular substrate handling, mitochondrial processing, redox regulation, and interactions among tissues and organs.

The neurovascular system illustrates this particularly well.

With aging, cerebral vessels may become stiffer, endothelial function deteriorates, capillary regulation becomes impaired, and the ability to match blood flow to neuronal activity declines.

Consequently, even when oxygen and nutrients are available in the circulation, their effective delivery to metabolically active brain tissue may become constrained.

The review highlights an especially interesting phenomenon: following ischemic injury, energy-depleted pericytes may remain contracted, contributing to persistent capillary obstruction even after larger blood vessels have been reopened.

This is known as the no-reflow phenomenon.

It illustrates why restoring blood flow at one level does not necessarily restore effective tissue perfusion.

From the bioenergetic perspective, impaired circulation is not merely a vascular consequence of aging. It can become an additional constraint on the energy supply required for cellular maintenance and repair.

This creates the possibility of a reinforcing cycle:

Impaired perfusion → constrained cellular bioenergetics → inadequate repair → persistent vascular dysfunction → further impaired perfusion.

The review does not directly test this entire causal sequence. However, its observations are consistent with the existence of such interacting constraints.

From Adaptive Remodeling to Persistent Damage

One particularly important finding discussed in the review concerns the timing of MMP activity following stroke.

During acute ischemic injury, excessive MMP activation contributes to blood–brain barrier disruption, edema, and secondary tissue damage.

Experimental MMP inhibition during this phase can reduce injury.

However, MMPs also participate in subsequent angiogenesis, extracellular matrix remodeling, and tissue repair.

The authors describe animal experiments in which delayed MMP inhibition interfered with neurovascular remodeling and worsened functional recovery.

This observation illustrates an important physiological principle:

A biological response that contributes to injury during one phase may be essential for recovery during another.

The problem is therefore not simply whether MMP activity is increased or decreased.

The more important questions are whether it is appropriately regulated, whether protective and regenerative processes remain functional, and whether remodeling can progress toward completion.

From our recovery-dynamics perspective, the process can be understood as:

Stress or injury → adaptive response → tissue remodeling → structural restoration → resolution.

When demands persist or restorative capacity becomes inadequate, the sequence may be interrupted:

Stress or injury → persistent adaptation → incomplete remodeling → unresolved structural abnormalities → further physiological stress.

This distinction helps explain why simply suppressing a pathway associated with damage may not always restore function.

Restoration requires coordinated progression through the appropriate phases of recovery.

Cellular Senescence, Persistent Inflammation, and ECM Aging

Our earlier discussions also connected ECM dysregulation with cellular senescence.

Senescence is frequently described as a hallmark of aging, but it can initially serve protective functions.

Cells experiencing significant stress or damage may enter cell-cycle arrest, limiting inappropriate proliferation while participating in tissue repair and immune communication.

Through the senescence-associated secretory phenotype (SASP), these cells release inflammatory mediators, growth factors, and matrix-remodeling enzymes.

When appropriately regulated, such signaling can help recruit immune cells, coordinate tissue reconstruction, and facilitate the removal of damaged cells.

However, when senescent cells persist because clearance or tissue resolution is incomplete, their continued secretory activity may become detrimental.

Persistent SASP signaling can sustain inflammation, promote excessive proteolysis, alter collagen organization, and contribute to fibrosis or structural instability.

The Bindal review identifies cellular senescence and chronic inflammation as potential contributors to increased MMP activity and reduced protective Shh signaling.

This connects two aging-associated processes that are often discussed separately: cellular senescence and extracellular matrix dysregulation.

From our perspective, both may become manifestations of unresolved adaptation.

Senescence can help contain damage and coordinate repair. ECM remodeling can remove damaged structures and prepare tissues for restoration.

But when the signals persist without successful completion, the same protective programs may become sources of chronic dysfunction.

Bioenergetic limitations could contribute to this transition by constraining cellular maintenance, immune clearance, and restorative activity. Persistent injury signals, epigenetic alterations, and other regulatory disturbances may also contribute.

Thus, inadequate bioenergetic support is a proposed contributing mechanism, not an established universal explanation for persistent senescence or ECM pathology.

ECM Dysregulation as a Structural Record of Incomplete Recovery

This brings us back to our earlier interpretation of extracellular matrix aging.

The ECM is continuously shaped by the history of cellular activity.

Every episode of injury, inflammation, adaptation, and repair can influence its composition, organization, and mechanical properties.

When recovery is completed, tissues may regain their previous functional state or establish a sufficiently stable new one.

When recovery remains incomplete, structural changes may persist.

Depending on the affected tissue and biological context, these changes may appear as fibrosis, increased stiffness, excessive matrix degradation, loss of elasticity, or disorganized connective tissue.

Crucially, these structural abnormalities can subsequently alter how cells behave.

Changes in matrix stiffness and architecture influence cellular mechanosensing, inflammatory responses, vascular function, and the local delivery of oxygen and nutrients.

ECM abnormalities may therefore become both a consequence of impaired recovery and a contributor to further dysfunction.

This is particularly relevant to aging because accumulated structural changes can persist long after the original stressor has disappeared.

In this sense, the ECM may preserve a physical record of previous recovery failures.

The consequences are not limited to the brain. Similar principles may be relevant to vascular stiffness, chronic wounds, fibrotic tissues, degenerative connective tissue changes, and other age-associated conditions, although the underlying mechanisms differ across organs.

This interpretation does not imply that every structural abnormality originates from bioenergetic insufficiency. Genetic disorders, mechanical injury, chronic exposure, and specific inflammatory or metabolic diseases may initiate or independently maintain ECM pathology.

Rather, bioenergetic constraints may influence whether tissues can adequately adapt to those disturbances and complete restoration.

The Self-Reinforcing Nature of Aging

One of the central ideas in our bioenergetic framework is that unresolved adaptation may progressively increase the cost of maintaining physiological function.

Initially, compensatory responses can preserve function despite stress.

Over time, however, persistent inflammation, altered metabolic allocation, senescence, vascular dysfunction, and disorganized ECM remodeling may create additional demands and reduce physiological flexibility.

The system must then devote increasing resources to maintaining an already compromised state.

This produces a possible reinforcing process:

Persistent stress → increased adaptive demands → constrained recovery → residual cellular and structural changes → greater bioenergetic impedance → further recovery difficulty.

ECM remodeling is particularly important because it can convert transient molecular disturbances into lasting structural constraints.

Unlike a short-lived inflammatory signal, a remodeled basement membrane, stiffened vascular wall, or disorganized collagen network may continue influencing tissue function for prolonged periods.

This offers a way to understand how repeated unresolved stress responses might gradually become embedded in tissue architecture.

It also connects ECM abnormalities with other features of aging, including mitochondrial dysfunction, senescence, altered intercellular communication, and loss of regenerative capacity.

These processes need not develop in a fixed sequence, and they cannot all be reduced to energy deficiency. Rather, they can interact to progressively constrain the capacity to restore physiological function.

From the Hallmarks of Aging to Recovery Dynamics

The hallmarks of aging describe important biological changes associated with the aging process.

However, identifying those changes does not necessarily explain why a system moves from successful adaptation toward persistent dysfunction.

Recovery dynamics adds a temporal perspective.

It asks how the organism responds to a disturbance, what resources are mobilized, how compensatory responses evolve, and whether the system can return toward functional stability.

From this perspective, ECM dysregulation is not merely another isolated aging-related abnormality.

It may represent one mechanism by which incomplete recovery becomes structurally persistent, subsequently influencing future responses to stress.

The Bindal review helps illustrate this principle at the neurovascular level.

Shh signaling contributes to protection and regeneration. MMP activity supports necessary matrix turnover. Oxidative stress, chronic inflammation, and senescence can disturb their regulation, while altered matrix integrity compromises circulation and tissue function.

The additional bioenergetic question is whether declining effective energy throughput and restorative capacity help explain why these processes fail to regain balance.

This is a hypothesis that requires direct testing.

Longitudinal studies could investigate whether impaired energetic function and delayed recovery predict persistent MMP activation, reduced Shh responsiveness, incomplete ECM restoration, and subsequent deterioration in neurovascular performance—even after accounting for initial injury severity and inflammatory burden.

Such research could help determine whether recovery dynamics adds explanatory value beyond conventional measures of molecular damage and disease activity.

A Broader Perspective on Healthy Aging

The emerging picture suggests that maintaining health with advancing age may require more than limiting individual damaging pathways.

Physiological function depends on the capacity to respond appropriately to stress, mobilize sufficient resources, complete repair, and resolve responses that are no longer needed.

Inflammation, senescence, and ECM degradation are not inherently harmful. Each can participate in normal adaptation and healing.

Problems arise when these responses become excessive, inappropriate, or persist beyond their useful physiological roles.

The challenge is therefore not simply to suppress damage-associated signals, but to understand the conditions required for successful restoration.

The Shh–MMP review reminds us that tissue protection and remodeling must remain coordinated—and that their balance changes over time.

Our bioenergetic interpretation extends this observation by proposing that adequate energetic throughput, resource allocation, and recovery capacity are important determinants of whether adaptation proceeds toward resolution or becomes chronically constrained.

Perhaps one important dimension of aging is not simply that our tissues sustain more damage, but that they progressively lose the capacity to finish repairing it.

The extracellular matrix may be where some of those unfinished repairs become physically embedded, creating a structural legacy that shapes future tissue function and recovery.

Understanding this relationship may help connect the molecular hallmarks of aging with the dynamic physiology of resilience, restoration, and functional decline.

References

Bindal, P., Kasher, P. R., & Ogawa, S. (2026). Sonic hedgehog–matrix metalloproteinase crosstalk in neurovascular ageing and stroke: A potential mechanistic link. GeroScience. https://doi.org/10.1007/s11357-026-02619-8