Aging model for unexposed human dermis

Morphometric analysis of dermal collagen fibers in normal human skin as a function of age

A quantitative study of dermal collagen as a function of age was carried out by computerized digital image analysis. Fast Green-Syrius Red stained sections were obtained of skin biopsies taken from the upper inner arm of 33 healthy women and 38 healthy men. The Leitz texture Analysis System (Leitz-TAS) and mathematical morphology (Serra, 1982) were used for the evaluation of the data. Collagen was studied in the superficial dermis and also in the reticular dermis using the same program. There were significant correlations, firstly between the percentage of collagen measured by the morphometric method and the concentration of collagen analysed biochemically (microg/mm(2) of tissue section) (r = 0.79, p < 0.001) and secondly between the decreased concentration of collagen and age (r = 0.58, p < 0.05). The morphometrical measurements have shown that the relative percentage of collagen bundles (surface of collagen fibers as a function of the dermal area analyzed) was 93.35% in the superficial dermis and 89.2% in the reticular dermis. Although this value is higher than the chemically determined ratio of collagen to other proteins (over 70%), this may be due to the relatively uniform distribution pattern of (type I and III) collagen through the dermis covering most other components of the skin. As the collagen fiber density per unit dermal surface did not change with age, the decrease in collagen content of the skin may be ascribed to the loss of about 6% of dermal mass per decade (Branchet, 1990), although large individual variations exist. The histogram of the diameter distribution of collagen fiber bundles of the reticular dermis showed thinner diameters in persons between 20 and 40 years of age than in older persons. The histogram of the distribution of interfiber spaces did not show any variation with age in the superficial dermis, while in the reticular dermis there was a predominance of smaller interspaces in persons older than 50 years.

Elastic fibers in normal human skin. variations with age: a morphometric analysis

A quantitative study of dermal elastic fibers was carried out by computerized digital image analysis. Sections of skin biopsies taken from the upper inner arm of 33 healthy women and 38 healthy men were stained by a selective procedure for elastic fibers. The Leitz texture analysis system (Leitz-Tas) and mathematical morphology were used for the evaluation of the data. Distinct programs were used for the vertical superficial elastic fibers and for the mature elastic fibers of the reticular dermis. For elastic fibers of the superficial dermis there was no significant variation with age or sex for total area occupied by the fibers or for the total number of fibers per unit skin area or total fiber length. The distribution of the relative fiber number as a function of their length showed that about 80% of the fibers had a length of 0-20 microm, with no detectable age- or sex-dependent variation. The distribution of fiber number frequency as a function of fiber diameter did not show any significant variation with sex or age, either. The relative area of mature elastic fibers increased significantly with age after the sixth decade of life. The total number (Nt) of these fibers did not show however any significant variation with age or sex: Nt per mm(2) of skin surface was 3220+/-660 (S.D.). We found for all age groups a significant increase of total fiber length by comparing persons between 20 and 30 years with those above 60 years. There was, however, no significant variations according to age or sex for the frequency distribution of mature elastic fiber length and diameter. As a significant decrease with age of the dermal thickness was also found in males and females, the loss of elastic fibers with age is mainly due to a loss of skin thickness (skin volume) with age. This loss is about 30% at 50 years and nearly 50% at 80 years. Loss of skin elasticity with age can be due to loss of cells (fibroblasts), to a decrease of their biosynthetic activity and to qualitative modifications of extracellular matrix macromolecules.

Mechanical properties of skin and responsiveness of slowly adapting type I mechanoreceptors in rats at different ages

Slowly adapting type I (s.a. I) cutaneous mechanoreceptors were studied in young (3-4 months old) and adult (9-11 months old) rats. Trains of thirty repetitive mechanical stimuli with 0.1 s rise time, 1.9 s plateau phase, and 0.7 s interstimulus interval were applied. A feed-back mechanism maintained the force of stimulation at 20 mN during the plateau phases of stimuli and the contact force between stimuli at 0.5 mN. During the first few stimuli in a train residual indentation at contact force increased rapidly. Maximal indentation required to maintain the force of stimulation of 20 mN increased as well but to a smaller extent. Thus, the stroke amplitudes of individual stimuli decreased with increasing stimulus number. All displacement values in the group of adult rats were consistently reduced to 62 +/- 3% of the respective values in the group of young rats, indicating a linear decrease in skin compliance in the force range of 0.5-20 mN. Nervous responses to individual stimuli decreased from about 200 impulses for stimulus number 1 to about 60 impulses for stimulus number 30. Significant differences in the number of impulses between young and adult rats were observed from stimulus number 9 to number 16 only. It is concluded that the design of the s.a. I receptor allows maintained high tactile sensitivity in response to force-related stimuli irrespective of age-induced changes in mechanical properties of the skin and underlying tissues.

The aging face. Why changes occur, how to correct them

Most changes that occur in the aging face are related to gravity working on skin that is becoming progressively thinner, drier, and less elastic. Exposure to sunlight hastens these changes, and protection from the sun is the only proved way to delay them. Dermabrasion, chemabrasion, and collagen implant (Zyderm) injection are safe and effective nonsurgical procedures that can improve the appearance of the aging face. Plastic surgical procedures to remove excess skin at the upper eyelids, raise the eyebrows, tighten the lower lids, and elevate the nasal tip can provide functional as well as cosmetic improvement.

The role of limited cell replicative capacity in pathological age change. A review

Physiological functions are carried out by differentiated cells, with finite lifespans, which age and need to be replaced. In young individuals, tissue functions are sustained at optimal levels because cellular dysfunction and cell loss are balanced by the emergence of newly differentiated cells as stem cells and their partially differentiated descendants replicate. However, with the passage of time the mitotic rates of these cells diminish. Eventually, replications occur too infrequently to offset the loss. It is at this point that the tissue begins to show structural changes and declining function which, as they become pervasive, are identified as "ageing". In this paper the theory is set forth that: (1) Diminishing mitotic activity in older tissues results from limited stem cell replicative capacity. (2) All stem cells, regardless of tissue, exhibit similar replicative patterns over time, progressing from the actively proliferating to the nonproliferating state. However, stem cells in different kinds of tissue have different rates of replicative decline, with the result that some tissues show age earlier than others. (3) The combination of two cellular properties--differentiated cell ageing and limited stem cell replicative capacity--is sufficient to establish the framework in which other pathological changes characteristic of aged people and animals take place.