Genomic Regulation of Circadian Variation in Wound Repair Gene Expression

Abstract

Wound healing is a temporally organized biological process influenced by local tissue conditions, systemic metabolism, immune activity, and the circadian clock. Molecular clocks within keratinocytes, fibroblasts, endothelial cells, macrophages, and other repair-associated cells regulate the timing and amplitude of genes involved in inflammation, extracellular matrix remodeling, angiogenesis, epithelial migration, and barrier restoration. Core clock proteins, including CLOCK, BMAL1, PER, CRY, REV-ERB, and ROR family members, interact with chromatin, transcription factors, enhancer regions, and epigenetic machinery to produce daily oscillations in wound-repair gene expression. Disruption of sleep, aging, diabetes, glucocorticoid exposure, shift work, and critical illness may impair these rhythms and contribute to delayed healing. Experimental and translational evidence indicates that the timing of injury, surgery, medication administration, light exposure, nutrition, and topical treatment may influence repair outcomes. This review summarizes the epidemiology, mechanisms, clinical manifestations, diagnostic considerations, management strategies, emerging therapies, and guideline-relevant implications of circadian genomic regulation in wound repair.

Introduction

Wound repair requires coordinated progression through hemostasis, inflammation, proliferation, re-epithelialization, angiogenesis, matrix deposition, and remodeling. These stages are not independent events; they are integrated through cellular communication and regulated gene expression. Circadian biology adds a further layer of organization by controlling when specific repair programs are activated and how strongly they are expressed. Nearly all mammalian cells contain molecular oscillators that generate approximately twenty-four-hour transcriptional cycles, while the suprachiasmatic nucleus synchronizes these peripheral clocks primarily through light-mediated neural and endocrine signals.

In skin and other barrier tissues, circadian regulation affects cell-cycle activity, DNA repair, oxidative stress responses, immune trafficking, and tissue metabolism. The clinical importance of this system is increasingly recognized because wounds that appear morphologically similar may heal at different rates depending on age, comorbidity, sleep pattern, treatment timing, and systemic circadian disruption. Understanding genomic regulation may therefore improve risk stratification and support chronobiologically informed wound care.

Epidemiology / Disease Burden

Acute traumatic, surgical, and chronic wounds represent a substantial burden for hospitals, outpatient services, and patients. Chronic wounds associated with diabetes, venous disease, arterial insufficiency, pressure, neuropathy, and inflammatory disorders are particularly difficult to treat and may result in infection, hospitalization, amputation, functional decline, and reduced quality of life. Delayed healing also increases the duration of antimicrobial exposure, dressing use, clinical visits, and occupational disability.

The contribution of circadian disruption is likely underrecognized. Modern healthcare environments commonly involve nocturnal procedures, irregular feeding, prolonged artificial light exposure, sleep fragmentation, and rotating clinical schedules. Older adults and critically ill patients often experience profound attenuation of circadian amplitude. Diabetes and obesity can alter clock-gene expression through metabolic inflammation and insulin resistance, while glucocorticoids, sedatives, and vasopressors may affect peripheral clock synchronization. These factors may compound established biological risks and help explain interindividual variation in healing time.

Pathophysiology

The molecular clock is built around transcriptional and translational feedback loops. CLOCK and BMAL1 form a transcriptional complex that activates Period and Cryptochrome genes through E-box elements. PER and CRY proteins subsequently inhibit CLOCK-BMAL1 activity, creating a negative feedback cycle. REV-ERB and ROR nuclear receptors regulate BMAL1 transcription through ROR response elements and connect the clock to lipid metabolism, inflammation, and cellular differentiation. These oscillators interact with tissue-specific transcription factors, chromatin remodelers, histone-modifying enzymes, and noncoding RNAs.

In keratinocytes, circadian mechanisms influence proliferation, migration, oxidative stress tolerance, and epidermal barrier restoration. BMAL1 loss or reduced clock amplitude may impair coordinated epithelial closure and alter the expression of genes involved in cytoskeletal remodeling and junctional integrity. Fibroblast clocks regulate collagen production, transforming growth factor signaling, matrix metalloproteinase activity, and extracellular matrix maturation. In endothelial cells, rhythmic control of vascular signaling can affect angiogenesis and perfusion of granulation tissue.

Immune cells also exhibit circadian variation. Macrophage polarization, neutrophil recruitment, cytokine production, and pathogen responses can change across the day. Excessive or prolonged inflammation is a recognized mechanism of chronic wound persistence, and clock disruption may shift the balance toward sustained inflammatory signaling. Circadian regulation also intersects with hypoxia-inducible pathways, nuclear factor kappa B, glucocorticoid receptors, insulin signaling, and mitochondrial metabolism. Consequently, altered clock gene expression may influence multiple stages of healing rather than a single molecular pathway.

Risk Factors

Important risk factors for impaired circadian regulation and delayed repair include advanced age, diabetes mellitus, obesity, malnutrition, chronic kidney disease, vascular insufficiency, smoking, sleep apnea, depression, chronic pain, and prolonged hospitalization. Shift work and irregular sleep-wake schedules may reduce the amplitude and stability of peripheral clocks. Excessive nighttime light exposure can suppress melatonin and weaken central-to-peripheral synchronization. Recurrent infection, systemic inflammation, and severe physiological stress may further uncouple cellular oscillators.

Medication-related factors are also relevant. Systemic corticosteroids influence clock-controlled transcription and immune activity, while sedatives and analgesics may disrupt sleep architecture. Some antihypertensive, metabolic, and anti-inflammatory therapies have time-dependent effects that could influence tissue repair. The clinical significance of these interactions varies by drug, dose, disease state, and treatment schedule, so chronotherapy should not be applied without pharmacologic and clinical justification.

Clinical Features

There is no single bedside sign that specifically identifies circadian dysregulation in a wound. Clinicians may observe delayed epithelialization, persistent inflammation, excessive exudate, recurrent infection, poor granulation, fragile tissue, or prolonged need for advanced dressings. These findings overlap with conventional causes of impaired healing and should not be attributed to circadian mechanisms until vascular, infectious, metabolic, nutritional, pressure-related, and mechanical factors have been evaluated.

Patients may report irregular sleep, nocturnal wakefulness, shift work, daytime fatigue, or variable glucose control. A history of sleep disruption is clinically relevant because it may indicate reduced clock amplitude, neuroendocrine stress, and impaired immune regulation. Temporal patterns in pain, exudate, pruritus, or wound discomfort may provide supportive information, although standardized clinical tools for circadian wound phenotyping remain under development.

Diagnosis

Diagnosis remains primarily clinical and requires systematic assessment of wound size, depth, tissue type, exudate, infection, perfusion, pressure, neuropathy, and healing trajectory. Recommended evaluation commonly includes glycemic assessment, nutritional screening, vascular examination, ankle-brachial or toe-brachial measurements when appropriate, and microbiological testing only when infection is suspected. Biopsy may be indicated for atypical, nonhealing, or suspicious lesions.

Research methods for assessing circadian regulation include serial sampling of clock-gene transcripts, melatonin profiling, actigraphy, sleep diaries, and transcriptomic analysis of wound-edge tissue. These approaches are not yet routine because they require repeated sampling, specialized laboratory methods, and validated reference ranges. Future diagnostic platforms may use minimally invasive molecular signatures to estimate clock phase, circadian amplitude, and the readiness of tissue for repair.

Treatment & Management

Management should begin with established evidence-based wound care. Clinicians should control bleeding, assess perfusion, cleanse appropriately, debride devitalized tissue when indicated, manage infection, maintain a balanced moist environment, relieve pressure, optimize nutrition, and address edema. Diabetes management, smoking cessation, vascular referral, compression therapy for suitable venous disease, and pressure redistribution remain central to outcomes.

Circadian-informed care can be integrated as an adjunct rather than a substitute for standard treatment. Regular sleep-wake timing, adequate nighttime darkness, daytime light exposure, consistent meal timing, mobilization, and reduction of avoidable nocturnal interruptions may support systemic synchronization. Hospital teams should consider whether repeated overnight procedures, unnecessary vital-sign disturbances, or irregular medication schedules are compromising sleep and recovery. Timing of debridement, dressing changes, and surgery may eventually be individualized according to tissue clock phase, but current evidence is insufficient to mandate a universal time of day.

Topical agents, growth factors, cellular therapies, and biomaterials should be selected according to wound type, evidence quality, safety, and cost. Circadian interventions must not delay infection treatment, revascularization, surgical source control, or pressure relief. Patients should be informed that chronobiological strategies are complementary and that commercially promoted clock-modulating products may lack robust clinical validation.

Recent Advances / Emerging Therapies

Recent research has focused on pharmacological modulation of REV-ERB, ROR, and other clock-associated pathways, as well as delivery systems designed to release molecules at specific times. Experimental studies are examining timed administration of anti-inflammatory compounds, metabolic regulators, melatonin-related interventions, and regenerative therapies. Investigators are also evaluating whether engineered scaffolds can provide both structural support and temporal release of growth factors.

Single-cell sequencing, spatial transcriptomics, epigenomic profiling, and organoid models are clarifying how circadian programs differ among keratinocytes, fibroblasts, immune cells, and vascular compartments. These technologies may identify patient-specific molecular phenotypes and therapeutic targets. However, translation remains challenging because animal models may not reproduce human sleep patterns, wound anatomy, comorbidity, or medication exposure. Well-designed clinical trials must evaluate healing rate, infection, pain, recurrence, functional recovery, and safety rather than relying only on molecular endpoints.

Guideline Recommendations

Current wound-care guidelines prioritize comprehensive assessment, perfusion optimization, infection prevention and treatment, pressure redistribution, metabolic control, nutrition, appropriate debridement, and multidisciplinary follow-up. These principles remain the clinical standard for patients with acute and chronic wounds. Although circadian genomic regulation is biologically plausible and supported by growing experimental evidence, routine clock-gene testing and formal chronotherapy are not yet recommended in most clinical guidelines.

Healthcare professionals can reasonably incorporate low-risk supportive measures, including protection of nighttime sleep, exposure to daytime light, regular activity, consistent nutrition, and avoidance of unnecessary schedule disruption. Any medication-timing intervention should follow established pharmacological evidence and patient-specific considerations. Documentation of sleep pattern, shift work, corticosteroid exposure, and hospitalization-related circadian disruption may improve holistic assessment and support future research.

Conclusion

Circadian clocks regulate genomic programs that influence inflammation, epithelial migration, fibroblast activity, angiogenesis, matrix remodeling, and barrier restoration. Disruption of these rhythms may contribute to delayed healing, particularly in patients with diabetes, aging-related vulnerability, sleep disturbance, systemic illness, or prolonged hospitalization. At present, the most appropriate clinical approach is to combine rigorous conventional wound management with practical protection of sleep and circadian stability. Advances in transcriptomics, chronotherapy, and precision medicine may eventually enable treatment timing based on individual tissue clock phase. Further prospective human studies are required before molecular clock testing or targeted clock-modulating therapies can become routine components of wound-care practice.