Wound Healing and Aging

CCN1 is predominantly elevated in human skin dermis by solar-simulated ultraviolet irradiation and accumulated in dermal extracellular matrix

Skin primarily comprises a collagen-rich extracellular matrix (ECM) that provides structural and functional support to the skin. Aging causes progressive loss and fragmentation of dermal collagen fibrils, leading to thin and weakened skin (Dermal aging). We previously reported that CCN1 is elevated in naturally aged human skin, photoaged human skin, and acute UV-irradiated human skin dermal fibroblasts in vivo. Elevated CCN1 alters the expression of numerous secreted proteins that have deleterious effects on the dermal microenvironment, impairing the structural integrity and function of the skin. Here we show that CCN1 is predominantly elevated in the human skin dermis by UV irradiation and accumulated in the dermal extracellular matrix. Laser capture microdissection indicated that CCN1 is predominantly induced in the dermis, not in the epidermis, by acute UV irradiation in human skin in vivo. Interestingly, while UV-induced CCN1 in the dermal fibroblasts and in the medium is transient, secreted CCN1 accumulates in the ECM. We explored the functionality of the matrix-bound CCN1 by culturing dermal fibroblasts on an acellular matrix plate that was enriched with a high concentration of CCN1. We observed that matrix-bound CCN1 activates integrin outside-in signaling resulting in the activation of FAK and its downstream target paxillin and ERK, as well as elevated MMP-1 and inhibition of collagen, in human dermal fibroblasts. These data suggest that accumulation of CCN1 in the dermal ECM is expected to progressively promote the aging of the dermis and thereby negatively impact the function of the dermis.

Age-related downregulation of CCN2 is regulated by cell size in a YAP/TAZ-dependent manner in human dermal fibroblasts: impact on dermal aging

CCN2, a member of the CCN family of matricellular proteins, is a key mediator and biomarker of tissue fibrosis. We previously reported that CCN2 is significantly reduced in aged human dermis, which contributes to dermal aging through the downregulation of collagen production, the major structural protein in the skin. In this study, we investigated the underlying mechanisms of the age-related downregulation of CCN2 in human skin dermal fibroblasts. Dermal fibroblasts isolation and laser-capture microdissection‒coupled RT-PCR from human skin confirmed that age-related reduction of CCN2 expression is regulated by epigenetics. Mechanistic investigation revealed that age-related reduction of CCN2 is regulated by impaired dermal fibroblast spreading/cell size, which is a prominent feature of aged dermal fibroblasts in vivo. Gain-of-function and loss-of-function analysis confirmed that age-related downregulation of CCN2 is regulated by YAP/TAZ in response to reduced cell size. We further confirmed that restoration of dermal fibroblast size rapidly reversed the downregulation of CCN2 in a YAP/TAZ-dependent manner. Finally, we confirmed that reduced YAP/TAZ nuclear staining is accompanied by loss of CCN2 in aged human skin in vivo. Our data reveal a mechanism by which age-related reduction in fibroblast spreading/size drives YAP/TAZ-dependent downregulation of CCN2 expression, which in turn contributes to loss of collagen in aged human skin.

Age-related elevation of HGF is driven by the reduction of fibroblast size in a YAP/TAZ/CCN2 axis-dependent manner

BACKGROUND

Aged human skin is primarily attributable to the loss of collagen. Hepatocyte growth factor (HGF) acts as an anti-fibrotic factor by suppression of collagen production. In aged human skin, HGF is elevated in dermal fibroblasts and thus contributes to dermal aging (thin dermis) by suppression of collagen production.

OBJECTIVE

We aimed to investigate the underlying mechanisms of age-related elevation of HGF expression.

METHODS

Collagen fibrils in the aged skin dermis are fragmented and disorganized, which impairs collagen-fibroblast interaction, resulting in reduced fibroblast spreading and size. To explore the connection between reduced dermal fibroblast size and age-related elevation of HGF expression, we manipulate dermal fibroblast size, and cell-size dependent regulation of HGF was investigated by laser capture microdissection, immunostaining, capillary electrophoresis immunoassay, and quantitative RT-PCR.

RESULTS

We found that reduced fibroblast size is responsible for age-related elevation of HGF expression. Further investigation indicated that cell size-dependent upregulation of HGF expression was mediated by impeded YAP/TAZ nuclear translocation and their target gene, CCN2. Conversely, restoration of dermal fibroblast size rapidly reversed cell-size-dependent upregulation of HGF in a YAP/TAZ-dependent manner. Finally, we confirmed that elevated HGF expression is accompanied by the reduced expression of YAP/TAZ and CCN2 in the aged human skin in vivo.

CONCLUSION

Age-related elevation of HGF is driven by the reduction of fibroblast size in a YAP/TAZ/CCN2 axis-dependent manner. These data reveal a novel mechanism by which reduction of fibroblast size upregulates HGF expression, which in turn contributes to loss of collagen, a prominent feature of aged human skin.

Dermal Fibroblast CCN1 Expression in Mice Recapitulates Human Skin Dermal Aging

The aging process deleteriously alters the structure and function of dermal collagen. These alterations result in thinning, fragility, wrinkles, laxity, impaired wound healing, and a microenvironment conducive to cancer. However, the key factors responsible for these changes have not been fully elucidated, and relevant models for the study of skin aging progression are lacking. CCN1, a secreted extracellular matrix‒associated matricellular protein, is elevated in dermal fibroblasts in aged human skin. Toward constructing a mouse model to study the key factors involved in skin-aging progression, we demonstrate that transgenic mice, with selective expression of CCN1 in dermal fibroblasts (COL1A2-CCN1), display accelerated skin dermal aging. The aged phenotype in COL1A2-CCN1 mice resembles aged human dermis: the skin is wrinkled and the dermis is thin and composed of loose, disorganized, and fragmented collagen fibrils. These dermal alterations reflect reduced production of collagen due to impaired TGFβ signaling and increased expression of matrix metalloproteinases driving the induction of c-Jun/activator protein-1. Importantly, similar mechanisms drive human dermal aging. Taken together, the data demonstrate that elevated expression of CCN1 by dermal fibroblasts functions as a key mediator of dermal aging. The COL1A2-CCN1 mouse model provides a novel tool for understanding and studying the mechanisms of skin aging and age-related skin disorders.

Soybean protein-derived peptide nutriment increases negative nitrogen balance in burn injury-induced inflammatory stress response in aged rats through the modulation of white blood cells and immune factors

BACKGROUND

As an important nutrient, soybean protein-derived peptides (SPP) affect the immune function of animals.

OBJECTIVE

This study describes the effects of nutrient supplementation with SPP on the negative nitrogen balance in the burn injury-induced inflammatory response of aged rats.

DESIGN

Soybean protein isolate (SPI) was hydrolyzed to obtain SPP. A negative nitrogen-balance aged rat model and a major full-thickness 30% total body surface area (TBSA) burn-injury rat model were utilized.

RESULTS

The results show that SPP can increase the speed and ability of inflammatory stress by adjusting white blood cell counts. Soybean protein-derived peptides significantly increased serum immunoglobulin M (IgM), immunoglobulin G (IgG) and immunoglobulin A (IgA) levels; significantly decreased serum interleukin-1 beta (IL-β), tumor necrosis factor-alpha (TNF-α) and regulated upon activation normal T-cell expressed and secreted (RANTES) levels. These results give conclusive evidence that SPP has a significantly positive effect in improving the immune function on the condition of negative nitrogen balance with burn-injury, and reducing excessive inflammation.

CONCLUSIONS

Nutrient supplementation of SPP can, therefore, be used as an adjuvant treatment to inhibit the development and severity of inflammatory reactions caused by burns, providing a novel therapy for the treatment and positive prognosis of burn patients.

Palaeoepidemiology in extinct vertebrate populations: factors influencing skeletal health in Jurassic marine reptiles

Palaeoepidemiological studies related to palaeoecology are rare, but have the potential to provide information regarding ecosystem-level characteristics by measuring individual health. In order to assess factors underlying the prevalence of pathologies in large marine vertebrates, we surveyed ichthyosaurs (Mesozoic marine reptiles) from the Posidonienschiefer Formation (Early Jurassic: Toarcian) of southwestern Germany. This Formation provides a relatively large sample from a geologically and geographically restricted interval, making it ideal for generating baseline data for a palaeoepidemiological survey. We examined the influence of taxon, anatomical region, body size, ontogeny and environmental change, as represented by the early Toarcian Oceanic Anoxic Event, on the prevalence of pathologies, based on a priori ideas of factors influencing population skeletal health. Our results show that the incidence of pathologies is dependent on taxon, with the small-bodied genus Stenopterygius exhibiting fewer skeletal pathologies than other genera. Within Stenopterygius, we detected more pathologies in large adults than in smaller size classes. Stratigraphic horizon, a proxy for palaeoenvironmental change, did not influence the incidence of pathologies in Stenopterygius. The quantification of the occurrence of pathologies within taxa and across guilds is critical to constructing more detailed hypotheses regarding changes in the prevalence of skeletal injury and disease through Earth history.

Actin cytoskeleton assembly regulates collagen production via TGF-β type II receptor in human skin fibroblasts

The dermal compartment of skin is primarily composed of collagen-rich extracellular matrix (ECM), which is produced by dermal fibroblasts. In Young skin, fibroblasts attach to the ECM through integrins. During ageing, fragmentation of the dermal ECM limits fibroblast attachment. This reduced attachment is associated with decreased collagen production, a major cause of skin thinning and fragility, in the elderly. Fibroblast attachment promotes assembly of the cellular actin cytoskeleton, which generates mechanical forces needed for structural support. The mechanism(s) linking reduced assembly of the actin cytoskeleton to decreased collagen production remains unclear. Here, we report that disassembly of the actin cytoskeleton results in impairment of TGF-β pathway, which controls collagen production, in dermal fibroblasts. Cytoskeleton disassembly rapidly down-regulates TGF-β type II receptor (TβRII) levels. This down-regulation leads to reduced activation of downstream effectors Smad2/Smad3 and CCN2, resulting in decreased collagen production. These responses are fully reversible; restoration of actin cytoskeleton assembly up-regulates TβRII, Smad2/Smad3, CCN2 and collagen expression. Finally, actin cytoskeleton-dependent reduction of TβRII is mediated by induction of microRNA 21, a potent inhibitor of TβRII protein expression. Our findings reveal a novel mechanism that links actin cytoskeleton assembly and collagen expression in dermal fibroblasts. This mechanism likely contributes to loss of TβRII and collagen production, which are observed in aged human skin.

Age-related reduction of dermal fibroblast size upregulates multiple matrix metalloproteinases as observed in aged human skin in vivo

BACKGROUND

Fragmentation of collagen fibrils, the major structure protein in skin, is a hallmark of dermal ageing. Matrix metalloproteinases (MMPs) are largely responsible for the fragmentation of collagen fibrils.

OBJECTIVES

To quantify gene expression of all 23 known mammalian MMPs in sun-protected young and aged human skin in vivo and to investigate the potential mechanism underlying age-related alteration of multiple MMPs.

METHODS

MMP mRNA expression levels and MMP activity in sun-protected young and aged human skin in vivo were determined by real-time reverse transcription polymerase chain reaction (RT-PCR) and in situ zymography, respectively. The relative contributions to elevated MMPs in epidermis and dermis were quantified by laser capture microdissection coupled real-time RT-PCR. Dermal fibroblast morphology and collagen fibril fragmentation in human skin in vivo were assessed by second-harmonic generation microscopy and atomic force microscopy, respectively. In vitro cell morphology was assessed by CellTracker® fluorescent dye (Molecular Probes, Eugene, OR, U.S.A.) and phalloidin staining. Protein levels were determined by ProteinSimple capillary electrophoresis immunoassay (ProteinSimple, Santa Clare, CA, U.S.A.).

RESULTS

Multiple MMPs are elevated in aged human skin dermis. Increased MMP activity and collagen fibril fragmentation were observed in aged skin dermis. As dermal fibroblasts are the major MMP-producing cells in the dermis, reduction of dermal fibroblast size, which is observed in aged human skin, contributes to the elevation of age-related multiple MMPs. Reduction of fibroblast size upregulates c-Jun/c-Fos and activates AP-1.

CONCLUSIONS

Combined actions of the wide variety of MMPs that are constitutively elevated in aged dermis may be involved in the progressive degradation of dermal collagen fibrils. Age-related elevations of multiple MMPs are likely to be a result of the reduction of fibroblast size via activation of AP-1.

3D In vitro model of the re-epithelialization phase in the wound-healing process

Keratinocytes of the basal layer function are to maintain tissue homoeostasis and to fulfil skin repair in response to an external aggression. In wound-healing, during re-epithelialization phase, epithelial precursor cells gradually migrate from the edges of the wound. The epidermal reconstruction model called standard model allows the vertical skin regeneration process (proliferation/differentiation) to being investigated, and keratinocyte function in preserving skin homoeostasis to being assessed. Here, we developed and characterized a 3D migration model, which introduces a step of keratinocytes migration such as the one observed in the phase of re-epithelialization in wound-healing process. We validated the added value and the discriminative potential of this model by demonstrating pro-epithelializing effects of compounds. This new model allows the role of keratinocytes in different biomechanical and environmental requests to being better understood, and brings a new tool for compound screening and the study of mechanisms involved in skin regeneration.

Cell-size-dependent upregulation of HGF expression in dermal fibroblasts: Impact on human skin connective tissue aging

BACKGROUND

Aged human skin is primarily attributable to loss of collagen, the main structural component of skin. Hepatocyte growth factor (HGF) acts as an anti-fibrotic factor by suppression of collagen production. It is not known whether HGF is involved in age-related collagen deficit in human skin.

OBJECTIVE

The objective of this study was to investigate the expression of HGF in human skin, and the underlying mechanisms of age-related elevation of HGF expression.

METHODS

The expression of HGF in young (25±5years, six subjects) and aged (75±6years, six subjects) human skin was determined by laser capture microdissection (LCM) coupled real-time PCR and immunohistology. The underlying mechanisms of age-related elevation of HGF were investigated by reducing dermal fibroblast size, which is a prominent feature of aged skin fibroblast in vivo.

RESULTS

HGF is predominantly expressed in human skin dermal fibroblasts, the major cells responsible for collagen production, and is significantly elevated in aged human skin in vivo. Mechanistically, reduced fibroblast size, which is a prominent feature of aged skin fibroblasts in vivo, is responsible for age-related elevation of HGF expression. Cell-size-dependent upregulation of HGF expression is driven by increased c-Jun and impaired TGF-β signaling. Restoration of fibroblast size normalizes increased c-Jun expression and impaired TGF-β signaling, and thus reversed the elevated HGF expression. Finally, we confirmed that application of retinoid (ROL), which has been shown to improve aged human skin, significantly reduced elevated HGF mRNA expression in aged human skin in vivo (78±4years, six subjects).

CONCLUSION

These data reveal a novel mechanism by which reduction of fibroblast size upregulates HGF expression, which in turn contributes to loss of collagen, a prominent feature of aged skin.

Reduced cell cohesiveness of outgrowths from eccrine sweat glands delays wound closure in elderly skin

Human skin heals more slowly in aged vs. young adults, but the mechanism for this delay is unclear. In humans, eccrine sweat glands (ESGs) and hair follicles underlying wounds generate cohesive keratinocyte outgrowths that expand to form the new epidermis. Here, we compared the re‐epithelialization of partial‐thickness wounds created on the forearm of healthy young (< 40 yo) and aged (> 70 yo) adults. Our results confirm that the outgrowth of cells from ESGs is a major feature of repair in young skin. Strikingly, in aged skin, although ESG density is unaltered, less than 50% of the ESGs generate epithelial outgrowths during repair (vs. 100% in young). Surprisingly, aging does not alter the wound‐induced proliferation response in hair follicles or ESGs. Instead, there is an overall reduced cohesiveness of keratinocytes in aged skin. Reduced cell–cell cohesiveness was most obvious in ESG‐derived outgrowths that, when present, were surrounded by unconnected cells in the scab overlaying aged wounds. Reduced cell–cell contact persisted during the repair process, with increased intercellular spacing and reduced number of desmosomes. Together, reduced outgrowths of ESG (i) reduce the initial number of cells participating in epidermal repair, (ii) delay wound closure, and (iii) lead to a thinner repaired epidermis in aged vs. young skin. Failure to form cohesive ESG outgrowths may reflect impaired interactions of keratinocytes with the damaged ECM in aged skin. Our findings provide a framework to better understand the mediators of delayed re‐epithelialization in aging and further support the importance of ESGs for the repair of human wounds.

Pretibial wounds: a review of current practice

Pretibial wounds are often associated with prolonged wound healing, particularly in the elderly female population. The wounds characteristically have either a proximally or distally based flap. Delayed wound healing has been attributed to flap necrosis and poor blood supply to this area. The aim of this review article is to examine the vascular anatomy, pathology and management options of patients with pretibial wounds.

[Characteristics of aging skin]

The change in the population's age structure in most industrial countries, as in Germany, requires geriatric medicine to play an increasingly important role. Dermatology also has to meet the new challenges by expert discussion and ethical considerations. The physiological aging process is influenced by intrinsic and extrinsic factors and causes a variety of morphological and functional alterations in the skin. Those alterations are the cause for an increasing prevalence of many dermatoses. Infections, wound healing disorders, inflammatory diseases, tumors and associated paraneoplastic syndromes are of particular importance. The structural and functional characteristics of aging skin in combination with the reduced mobility and declining cognitive abilities in elder patients require specific recommendations for skin protection as well as qualified advice about topical and systemic use of medications.

Zmpste24-/- mouse model for senescent wound healing research

BACKGROUND

The graying of our population has motivated the authors to better understand age-related impairments in wound healing. To increase research throughput, the authors hypothesized that the Hutchinson-Gilford progeria syndrome Zmpste24-deficient (Zmpste24(-/-)) mouse could serve as a model of senescent wound healing.

METHODS

Using a stented excisional wound closure model, the authors tested this hypothesis on 8-week-old male Zmpste24(-/-) mice (n = 25) and age-matched male C57BL/6J wild-type mice (n = 25). Wounds were measured photogrammetrically and harvested for immunohistochemistry, enzyme-linked immunosorbent assay, and quantitative real-time polymerase chain reaction, and circulating vasculogenic progenitor cells were measured by flow cytometry.

RESULTS

Zmpste24(-/-) mice had a significant delay in wound closure compared with wild-type mice during the proliferative/vasculogenic phase. Zmpste24(-/-) wounds had decreased proliferation, increased 8-hydroxy-2'-deoxyguanosine levels, increased proapoptotic signaling (i.e., p53, PUMA, BAX), decreased antiapoptotic signaling (i.e., Bcl-2), and increased DNA fragmentation. These changes correlated with decreased local vasculogenic growth factor expression, decreased mobilization of bone marrow-derived vasculogenic progenitor cells, and decreased new blood vessel formation. Age-related impairments in wound closure are multifactorial.

CONCLUSIONS

The authors' data suggest that the Hutchinson-Gilford progeria syndrome Zmpste24(-/-) progeroid syndrome shares mechanistic overlap with normal aging and therefore might provide a uniquely informative model with which to study age-associated impairments in wound closure.

Nutritional therapy for burns in children and adults

Burns are a serious injury that requires optimal nutritional support. This review discusses the nutritional care for adults and children with major burns. A burned patient's metabolism is greatly accelerated with increased requirements for energy, carbohydrates, proteins, fats, vitamins, minerals, and antioxidants. Early nutrition by parenteral and enteral feedings is vital. Careful assessment of the nutritional state of the burn patient is also important to reduce infection, recovery time, and long-term sequelae.

Exercise accelerates cutaneous wound healing and decreases wound inflammation in aged mice

The purpose of this study was to determine the effect of exercise on wound healing and inflammation in young (3 mo) and old (18 mo) female BALB/cByJ mice. Mice were assigned to either exercise or sedentary control (control) groups. The exercise group mice were run on a motorized treadmill at a moderate intensity 30 min/day for 8 days. All mice were given four full-thickness dermal wounds, and the rate of wound closure was assessed daily for 10 days. Four months later, the aged mice were rerandomized to treatment, wounded again in different locations, and wounds were harvested at 1, 3, or 5 days postwounding. Wound tissue was analyzed for IL-1beta, IL-6, keratinocyte chemoattractant (KC), monocyte chemoattractant protein-1 (MCP-1), and TNF-alpha protein. Myeloperoxidase (MPO) activity and F4/80 mRNA were assessed as an indirect measure of neutrophil and macrophage content, respectively. There was a trend (P = 0.10) for exercise to reduce wound size in young mice, and exercise significantly (P < 0.05) decreased wound size in old mice. TNF-alpha, KC, and MCP-1 were significantly (P < 0.05) lower in wounds from exercised old mice compared with control. No group differences were found for wound IL-1beta or IL-6, MPO activity, or F4/80 mRNA. Our data suggest that exercise accelerates the wound healing process in old mice. This improved healing response in the old mice may be the result of an exercise-induced anti-inflammatory response in the wound.

William J. Cunliffe Scientific Awards. Characteristics and pathomechanisms of endogenously aged skin

The skin, being in direct contact with several environmental factors (e.g. UV irradiation), does not only undergo endogenous aging, which has to do with the 'biological clock' of the skin cells per se, but also exogenous aging. While exogenous skin aging has been extensively studied, the pathomechanisms of endogenous skin aging remain far less clear. Endogenous skin aging reflects reduction processes, which are common in internal organs. These processes include cellular senescence and decreased proliferative capacity, decrease in cellular DNA repair capacity and chromosomal abnormalities, loss of telomeres, point mutations of extranuclear mtDNA, oxidative stress and gene mutations. As a consequence, aged skin in nonexposed areas shows typical characteristics including fine wrinkles, dryness, sallowness and loss of elasticity. Recent data have illustrated that lack of hormones occurring with age may also contribute to the aging phenotype. Improvement of epidermal skin moisture, elasticity and skin thickness, enhanced production of surface lipids, reduction of wrinkle depth, restoration of collagen fibers and increase of the collagen III/I ratio have been reported after hormone replacement therapy or local estrogen treatment in postmenopausal women. Furthermore, an in vitro model of endogenous skin aging consisting of human SZ95 sebocytes which were incubated under a hormone-substituted environment illustrated that hormones at age- and sex-specific levels were able to alter the development of cells by regulating their transcriptome. In conclusion, among other factors the hormone environment plays a distinct role in the generation of aged skin.

Prevalence of somatic small fiber neuropathy in obesity

BACKGROUND

Somatic cutaneous small sensory fiber neuropathy (SSFN) can be an early manifestation of impaired glucose tolerance and diabetes mellitus and/or insulin resistance among obese subjects and is often associated with pain, wound occurrence and impaired wound healing. It is yet unclear as to whether SSFN is prevalent among obese individuals without glucose and/or insulin dysregulation despite abundant evidence of delayed wound healing.

OBJECTIVE

To observe whether there is hypofunctioning of stimulated capsaicin-sensitive cutaneous nerves (small sensory fibers) in obese subjects with/without hyperglycemia and hyperinsulinemia.

DESIGN, SETTING AND PARTICIPANTS

Fifty-eight morbidly obese and 15 lean subjects were recruited for small fiber testing of the forearm in a cross-sectional study. Hyperglycemia was observed in 35 obese subjects. Of 25 obese subjects, hyperinsulinemia was noted in 15, 14 of which were hyperglycemic. No subjects demonstrated symptoms/signs of neuropathy over the hairy skin of the forearm. In fact, a neurological examination revealed that 37 subjects were asymptomatic in the legs and only four complained of a neuropathic pain in the foot. Virtually all subjects were exposed to a set of capsaicin-sensitive tests and measures which were identified by capsaicin desensitization procedures. These tests, conducted while in a supine position in bed at the Banner Good Samaritan Medical Center, Phoenix, examined the two principle roles of cutaneous SSFs, namely conveying pain signals to the CNS and controlling local neurogenic vasodilatation (flare; axon-reflex).

MAIN OUTCOME MEASURES

Heat-induced pain was assessed by verbal reports of sensation after accommodation and heat-, capsaicin-, and transcutneous stimulation- induced blood flow was measured by laser Doppler flowmetry with probes placed at the site of stimulation and 1 cm remote from the site, the latter to evaluate flare latency and intensity of flare.

RESULTS

Significant depression of pain and flare responses were observed in the obese subjects in all but one test. Decreased pain and flare responses were noted in all subjects without hyperglycemia and hyperinsulinemia. Age negatively correlated with capsaicin-induced flare in both the obese and normal groups.

CONCLUSION

SSFN was prevalent in the cohort of morbidly obese subjects in a skin area without neurological symptoms or signs and in subjects with/without hyperglycemia and hyperinsulinemia. SSFN may be a serious factor in observations of impaired wound healing among obese subjects, a particularly worrisome problem in an obese aging population given the propensity for small fiber impairment in aging subjects. Small fiber impairment in the younger obese population may signal an early aging phenomenon.

Inflammation and remodelling in the ageing airway

WHAT WE NEED TO KNOW: What changes occur in atopic and non-atopic airway inflammation in asthma with increasing age? What is the relationship between wound healing and airway remodelling in older subjects? What is the response to anti-inflammatory therapy in older subjects? What is the basis of the "overlap syndrome" with chronic obstructive pulmonary disease in older people with asthma, in whom smoking contributes to airway disease? WHAT WE NEED TO DO: Identify the contribution of immunological mechanisms to asthma in ageing. Determine the extent to which airway remodelling plays a role in airflow obstruction in older people, specifically reversible components. Reduce the impact of smoking in young people with asthma.

Impact of aging on gene expression in a rat model of ischemic cutaneous wound healing

BACKGROUND

Tissue ischemia and aging are independent features associated with the healing impairment of cutaneous wounds. However, the pathophysiology of these processes as they relate to impaired-healing wounds is poorly understood.

MATERIALS AND METHODS

A single full-thickness biopsy wound was made on both ears of young (3-6 month) and aged (>24 month) Fisher rats. One ear was rendered ischemic by transection of the vasculature at the ear base, while the other ear served as an internal nonischemic control. Wounds were harvested from 3 to 7 days and were evaluated histologically for either granulation tissue formation and epithelialization. Total RNA from wounds harvested at postoperative day 7 was probed using a nylon-based cDNA array to assess global genetic expression alterations.

RESULTS

Healing in the rat ear model is impaired by both ischemia and advanced age as measured by granulation tissue formation and wound epithelialization. Granulation tissue formation was affected to a greater degree by ischemia than age (-58% versus -21%, respectively) while epithelialization displayed an opposite response (-17% versus -53%, respectively). Global analysis of gene expression suggests that ischemia engenders a marked increase in genes displaying altered expression in aged animals compared to young animals. Importantly, all possible alterations in gene expression are found in samples from aged ischemic wounds, indicating that gene regulation is not simply depressed by advanced age.

CONCLUSIONS

Wound epithelialization appears to be affected to a greater degree by advanced age than by ischemia. The results demonstrate the distinctive phenotype presented by the clinically relevant combination of age and ischemia in an in vivo model of cutaneous wound healing.

Non-ablative scar revision using a long pulsed frequency doubled Nd:YAG laser

OBJECTIVE

Unsightly scars often are the only reminder of a previous surgical or traumatic wound. Surgical or ablative scar revision is sought by patients, sometimes unnecessarily. When the aesthetic drawback is mainly a result of hypervascularity or hyperpigmentation, these problems can be specifically targeted with a wavelength that is well absorbed by the two above mentioned chromophores. Some degree of epidermal tightening can also be achieved, which is sometimes useful in slightly atrophic scars. The average improvement after 2-3 sessions was 81% (75%-100%) clearance, as judged by an independent observer who reviewed pre- and post-treatment photographs. No undesired effects were reported. All our patients were satisfied and required no further treatment.

METHODS

Selective photothermolysis by means of a long pulsed frequency doubled Nd:YAG laser (DioLite 532, IRIDEX Corporation, Mountain View, CA, USA) was used to eliminate the unsightly vascular and pigmented components of 23 mature scars (scars older than 2 years) in 22 consecutive patients. Energy densities of 17-22 j/cm2 were used with a 500 micron spot, or 65-90 j/cm2 with a 200 micron spot.

RESULTS

overall scar clearance averaged 81% after 2.4 treatments. Facial scars showed the best clearance averaging 94% after 2 treatments. Inframammary scars were the most difficult to clear averaging 46%. Postoperative undesired effects were immediate erythema and swelling that subsided within 2-10 hours and microcrusting on 19/22 (88%) patients that resolved within one week. No other temporary or permanent undesired effects such as purpura, hypo- or hyperpigmentation were noticed, even in patients with darker skin types.

Age-dependency of insulin-like growth factors, insulin-like growth factor-binding proteins, and acid labile subunit in plasma and wounds of surgical patients

Wound problems are common in the elderly. We hypothesized that age-related decrements in blood levels of components of the insulin-like growth factor (IGF) system are reflected in the wound environment. In this prospective, observational study IGF-I, IGF-II, IGF-binding protein-2, IGF-binding protein-3, and acid labile subunit were measured by immunoassays in the wound fluid and plasma of young (23.5 +/- 3.3 years) and elderly (78.9 +/- 6.2 years) patients before and daily for 4 days after elective surgery. IGFs, IGFBP-3, and acid labile subunit in plasma were significantly lower in the elderly group (p < 0.0001). The decrements of these proteins in plasma were reflected in corresponding decrements of 25-70% in the wound fluid of elderly patients (p < 0.0001). Additionally, bioavailability of IGF-I was less in the aged. The IGF parameters in the wound displayed a constant ratio with those of blood, suggesting that blood contributes a major share of the IGF that enters the wound during the initial phase of healing. The current data adds to accumulating evidence that a decline in the IGF system in aged patients contributes to the healing deficits observed in the elderly.

Effect of age and hypoxia on TGFbeta1 receptor expression and signal transduction in human dermal fibroblasts: impact on cell migration

Wound healing is critically affected by age, ischemia, and growth factors such as TGFbeta1. The combined effect of these factors on fibroblast migration, an essential component of wound healing, is poorly understood. To address this deficiency, we examined expression of TGFbeta receptor type I and II (TGFbetaRI and RII) under normoxia or hypoxia (1% O(2)) in cultured human dermal fibroblasts (HDFs) from young (ages 24-33) and aged (ages 61-73) adults. TGFbetaRI and RII expression was similar in both groups under normoxia. Hypoxia did not alter receptor levels in young HDFs but significantly decreased TGFbetaRI in aged cells (12 and 43%, respectively). Additionally, young cells displayed a 50% increase in activation of p42/p44 mitogen-activated kinase by TGFbeta1 (2-200 pg/ml) under hypoxia while aged cell levels of active p42/p44 decreased up to 24%. To determine functional outcomes of these findings, we measured the migratory capacity of the cells on type I collagen using a gold salt migration assay. Hypoxia increased the migratory index (MI) of young HDFs over normoxia by 30% but had no effect on aged cells. Under normoxia, TGFbeta1 (1-1000 pg/ml) increased young HDF migration in a concentration-dependent manner up to 109% over controls but minimally increased aged HDF migration (37%). Under hypoxia, TGFbeta1 significantly increased young cell MI at all concentrations but was without effect on the aged HDF response. These data demonstrate that aged fibroblasts have an impaired migratory capacity with complete loss of responsiveness to hypoxia and deficits in the migratory and signal transduction responsiveness to TGFbeta1 that may partly explain diminished healing capabilities often observed in aged patients.

Differential involvement of conotoxin-sensitive mechanisms in neurogenic vasodilatation responses: effects of age

During aging there is a decline in sensory nerve function that is associated with reduced neurogenic inflammation and poor wound repair. The cellular mechanism(s) responsible for this decline in function with age is not well understood. We previously reported that sensory nerves in aged rats release sensory neuropeptides preferentially in response to low-frequency (5 Hz) as compared with higher-frequency (15 Hz) antidromic electrical stimulation, and that low-frequency transcutaneous electrical nerve stimulation accelerates wound healing. The present study investigates possible mechanisms for this preferential response. Using laser Doppler techniques, we have measured changes in blood flow in the base of vacuum-induced blisters induced in the rat hind footpad of young and old animals in response to low-frequency (5 Hz) or high-frequency (15 Hz) electrical stimulation (20 V, 2 ms for 1 minute) of the sciatic nerve. The relative contributions of the sensory neuropeptides, substance P and calcitonin gene-related peptide (CGRP), and of N-type voltage-gated calcium channels to the vascular responses were assessed by using the specific receptor antagonists RP67580, which is 2-(1-imino-2-(2 methoxy phyenyl) ethyl)-7,7 diphenyl-4 perhydroisoindolone-(3aR, 7aR); CGRP(8-37); and omega-conotoxin GVIA (Conus geographus), respectively. The results showed a greater involvement of substance P at high-frequency electrical stimulation and of CGRP at low-frequency stimulation. Our finding that omega-conotoxin-sensitive N-type calcium channel function was preserved with age and was only involved in the vascular response to low-frequency electrical stimulation could explain our previous report demonstrating beneficial effects of low-frequency transcutaneous electrical nerve stimulation to wound repair in aged animals. The current results have important practical implications for improving tissue repair in the aged.

Age- and gender-related collagen distribution in human vocal folds

The composition of the lamina propria in human vocal folds has been shown to affect vocal performance. Collagen plays a significant role in the biomechanical effects of the lamina propria. Specifically, it lends tensile strength to the rapidly oscillating fold. We obtained from a state medical examiner 38 larynges from men and women in infant, adult, and geriatric age groups. We stained the vocal folds for collagen using a picric acid stain and studied them using an image analysis system. Distributions of collagen were measured from the superficial to deep layers (from epithelium to vocalis muscle) within the lamina propria. The data showed an increase in collagen content from infant to adult stages. Infant folds had about 51% of the collagen found in all adults and in geriatric patients (p < .001). There was no significant difference between adult and geriatric folds (p < .16). There was, however, a gender difference in the amount of collagen in both adult and geriatric specimens. Female adult and geriatric folds had about 59% of the collagen found in male adult and geriatric folds (p < .001). The distribution pattern of collagen showed that most of the collagen was present in the deep layer. From these data we conclude that there are age-related and gender-related differences between male and female infant, adult, and geriatric vocal folds. Stress-strain performance studies need to be correlated with histologic findings to better study the phonetic implications of these findings.

Antioxidant status in delayed healing type of wounds

This investigation studied the contribution of antioxidants in delaying healing in excision cutaneous wounds (8 mm) in diabetic, aged and immunocompromised animals. Skin levels of catalase, glutathione (GSH), ascorbic acid (AA) and vitamin E in streptozotocin-induced diabetic rat were lower as compared to nondiabetics. The 7-d wound tissue of diabetic rats showed an increased vitamin E level along with depleted GSH content. In aged rats (18 months old), higher levels of skin superoxide dismutase (SOD), glutathione peroxidase (Gpx) and thiobarbituric acid reactive substances (TBARS) and lower levels of catalase and GSH were found as compared to their values in young rats (3-4 months old). The levels of SOD, GPx, catalase, AA, GSH and vitamin E in 7-d wound tissue of aged rats were significantly lower in comparison to those in young rats. However, TBARS were elevated in these wound tissues. The non-wounded skin of immunocompromised (athymic) mice showed lower levels of SOD, catalase, and TBARS and higher GSH and GPx levels in comparison to those present in normal mouse skin. Surprisingly, the analysis of 7-d wound tissue showed higher levels of SOD, catalase, GPx, and GSH and lower TBARS level in athymic mice compared to the wound tissue of normal mice. Thus low levels of antioxidants accompanied by raised levels of markers of free radical damage play a significant role in delaying wound healing in aged rats. In diabetic rats reduced glutathione levels may have a contributory role in delaying the healing process. However, in immunocompromised mice the antioxidant status following injury showed an adapted response.

The beneficial effects of recombinant human insulin-like growth factor-I (IGF-I) on wound healing in severely wounded senescent mice

The effects of recombinant insulin-like growth factor I (rIGF-I) on wound healing were tested using senescent and young BDF-1 mice, aged 108 weeks and 10 weeks, respectively. After inflicting a full thickness dermal burn encompassing 15% of the body surface, a skin incision, 2 cm in length, was made in the back. A silicone tube containing a piece of polyvinyl sponge was then implanted into a subcutaneous pocket in the flank to collect body fluid. An osmotic pump was buried in the abdominal subcutaneous tissue for the continuous infusion of rIGF-I, the control being treated with the solvent of IGF-I, physiological saline, only. The administration of IGF-I produced favorable effects on wound healing in the senescent mice, shown by enhanced tensile strength and an elevated concentration in the hydroxyproline of the polyvinyl sponge content. The IGF-I-treated severely wounded senescent mice healed better than their counterparts and their skeletal muscles contained more glutamine. Furthermore, they showed more enhanced cutaneous hypersensitivity towards dinitrofluorobenzene than the controls, suggesting an enhanced grade of cellular immunity. There were no conspicuous differences between the two groups of young mice. These data may suggest the beneficial effects of rIGF-I on wound healing, especially in geriatric surgery.

Effects of aging on neurogenic vasodilator responses evoked by transcutaneous electrical nerve stimulation: relevance to wound healing

We have previously shown an age-related decline in the modulation of skin vascular reactivity by sensory nerves that correlates with a decline in wound repair efficacy. This study was designed to examine the possibility that improving the functional ability of aged sensory nerves using noninvasive transcutaneous electrical nerve stimulation (TENS) could also accelerate tissue repair. TENS of the sciatic nerve, combined with measuring blood flow responses in the rat hind-footpad using laser Doppler flowmetry, was used to establish the vascular effects. Following TENS (using parameters 20V, 5 Hz for 1 min), similar increases in vascular responses were obtained in both young (13.2+/-0.9 cm2) and old rats (11.6+/-2.3 cm2). In contrast, capsaicin-pretreated rats showed markedly diminished responses. Sympathetic fibers did not appear to modulate these sensory nerve responses. In the second part, a thermal wound was induced (using a CO2 laser) in the interscapular region of old rats (under anesthesia). In the active treatment group, TENS was applied twice daily for the initial 5 days, and the sham group received inactive TENS. Using the healing endpoint as the time when full wound contraction occurred, the active group required 14.7+/-0.2 days for complete healing, a significant improvement over the sham group (21.8+/-0.3 days). We contend that low-frequency TENS can improve the vascular response of old rats. In addition, wound healing in aged rats can be accelerated by peripheral activation of sensory nerves at low-frequency electrical stimulation parameters.

Influence of caloric intake on aging and on the response to stressors

Reducing the food intake of rodents to well below that of ad libitum fed animals increases the life span. This action, which gerontologists often refer to as the antiaging action of dietary restriction (DR), is due to the slowing of the aging processes. DR also maintains most physiological processes in a youthful state and delays the occurrence and/or slows the progression of age-associated disease processes. This antiaging action of DR results from the reduced intake of calories. Reduction of the body fat content does not play a causal role in the antiaging action of DR, nor does reduction in the metabolic rate. Alterations in the characteristics of carbohydrate metabolism and of oxidative metabolism in response to DR have been found that are of such a nature that they could, at least in part, underlie the antiaging action. Several theories have recently been proposed in regard to the mechanisms responsible for the antiaging action of DR, but none has been tested by rigorously designed studies. Of these theories, the one that seems most promising is based on the fact that DR protects rats and mice of all ages against the damaging actions of acute stressors. This protective action against stressors may play a major role in the antiaging action of DR.

Abundance of alpha 1(I) and alpha 1(III) procollagen and p21 mRNAs in fibroblasts cultured from fetal and postnatal dermis

The steady-state abundance of alpha 1(I) and alpha 1(III) procollagen mRNAs, p21Sdi1 mRNA, and beta-actin mRNA was determined in 29 skin fibroblast lines established from fetal, young and old donors. Donor ages ranged from 12 gestational weeks to nonagenarian. Adult donors were members of the Baltimore Longitudinal Study of Aging. The abundance of alpha 1(I) procollagen mRNA was decreased in cell lines from both young and old donors compared with fetal lines. Additionally, one alpha 1(I) transcript observed in the fetal lines was not detected in postnatal lines. The abundance of alpha 1(III) procollagen mRNA was decreased in postnatal lines from old donors compared with fetal lines. The abundance of beta-actin mRNA was lower in postnatal lines from both young and old donors compared to fetal lines. These results suggest that cultures of fetal skin fibroblasts exhibit a greater capacity for synthesis of procollagens and beta-actin than postnatal lines. In contrast, the abundance of p21Sdi1 mRNA was elevated in lines established from postnatal donors. These results are consistent with developmental changes in amounts of procollagen, beta-actin and p21.

Influence of age on natural and delayed healing of experimentally-induced gastric ulcers in rats

This study aimed to investigate the effect of age on natural ulcer healing and delayed ulcer healing induced by nonsteroidal antiinflammatory drugs, using a rat model. Gastric ulcers were induced in young, adult, and aged rats using serosal or mucosal (kissing ulcers) application of acetic acid. Rats were treated with indomethacin 1 mg/kg/day subcutaneously or vehicle for two weeks. Ulcers were assessed by macroscopic and histological measurements of ulcer size. Ulcer induction was affected by age. Aged rats developed significantly smaller ulcers when induced by serosal application of acetic acid and significantly larger ulcers from mucosal application of acetic acid. However, measurements of ulcer size from both models showed no age-related differences in natural ulcer healing. Similarly, indomethacin-induced delayed gastric ulcer healing was not effected by age. We conclude that there are age-related differences in the development of gastric ulcers but there are no age-related differences in natural or delayed ulcer healing in rats.

Enhanced cell proliferation and biosynthesis mediate improved wound repair in refed, caloric-restricted mice

Aged mice that have undergone long-term caloric-restriction (CR) have improved health and enhanced longevity in comparison to aged mice that are ad libitum-fed (AL). However, caloric-restriction does not benefit the impaired wound healing of aged mice. To test the hypothesis that CR mice have the capacity for enhanced wound repair, but require a short-term period of additional nutrient intake to show this advantage, we assessed wound healing in CR mice that had been refed (RF) an ad libitum diet for 4 weeks prior to wounding. Two strains of AL young (Y AL) (4-6 months), AL middle-aged (M AL) (15-17 months), and three different, matched cohorts of old mice (O) (30-33 months): O AL, O CR, and O RF were studied. Two full-thickness 4 mm diameter punch biopsy skin wounds were created on the dorsum of each mouse. Animals were sacrificed and wounds were harvested at 1,2,3,5, and 7 days post-wounding. Repair of wounds was slower in O AL and O CR mice compared to Y AL and M AL animals. In contrast, the O RF mice healed similarly to that of the Y AL and M AL mice, as assessed by measures of wound area and histologic criteria. O RF mice demonstrated enhanced synthesis of type I collagen mRNA in comparison to O AL and O CR mice. A greater number of endothelial cells and fibroblasts at the wound edge of the O RF mice exhibited replication in vivo as measured by uptake of BrdU. O RF mice had higher levels of insulin-like binding protein 3 (IGFBP-3). Furthermore, fibroblasts derived from the explant of the punch biopsy of O CR mouse skin revealed enhanced proliferation and contraction in vitro, in comparison to fibroblasts from the O AL mice. In conclusion, O RF mice demonstrate an enhanced capacity to undergo wound repair in comparison to O AL mice. This effect appears to be mediated, in part, by enhanced cell proliferation, contraction, and collagen biosynthesis. In addition, short-term refeeding induced an increase in the serum level of IGFBP-3, the major binding protein for IGF-1. These data confirm that cells from O CR animals have a preserved proliferative, biosynthetic, and contractile capacity, but that an adequate source of nutrients is necessary to demonstrate this advantage in wound healing.

Proliferative responses to platelet-derived growth factor in young and old rat patellar tendon

Musculoskeletal soft tissue repair is often a slow process that may be complicated by aging, thus we investigated the mitogenic response of young and old rat patellar tendon (PT) explants to platelet-derived growth factor-AB (PDGF-AB). Bilateral PT explants from young (4 months) and old (29 or 36 months) rats of two strains (Fisher 344 and Fisher-Brown-Norway) were cultured for 72 h in platelet-poor horse serum in the presence or absence of 100 ng/ml recombinant human PDGF-AB. The explants were radiolabelled with [3H]-TdR for the final 24 h in culture. Tendon cellularity and DNA synthesis data were analyzed by multiple factor ANOVA (age, strain, and side), Mann-Whitney t-test (cellularity and DNA synthesis), and a sign test (proliferative response to PDGF). Tendon cellularity declined significantly with age in both strains (p < 0.05), while both young and old patellar tendon fibroblasts in both strains had a significant (> 100%) increase in DNA synthesis with the addition of PDGF (p < 0.05). Although there was a trend to lower proliferative responses in older tendons, the differences were not significant. Autoradiographic analysis of labeling indices in F344 tendons showed a diminished responsiveness to PDGF (p < 0.04, ANOVA). Strain and side response on a per cell or tissue weight basis were not significant factors. Under appropriate experimental conditions, these two animal models of aging showed declines in responses to high levels of PDGF, suggesting that the PT reflects an age-dependent diminished capacity for wound repair.

Age-related changes in wound healing

Knowledge of the physiology of wound healing, in particular the recovery of the dermal and epidermal compartments and the co-ordination of these processes by the cytokine network, is of great importance to rational wound management. The individual components of the wound healing process have been studied using various in vitro and in vivo models, comparing young, adult and aged individuals. Many of the processes involved in wound healing are impaired in the elderly. However, in elderly patients not suffering from concomitant diseases, the rate of wound healing is normal or only slightly reduced. Various 'systemic factors' (endocrine and haematological diseases, nutritional deficiencies and medications) and 'regional disorders' (vascular and neural diseases) may impair wound healing. These complicating conditions occur more frequently in aged subjects. Failure of wound healing in the elderly is a chronic disabling condition, which occurs frequently in our society, requiring a major investment of medical care.