الفهرس 
SKIN AGINGOnly 14 pages are availabe for public view
Abstract
Skin aging is the end result of both intrinsic aging, which is the result of the passage of time, and photoaging, which refers to alterations in skin structure and function that result from chronic sun exposure, in addition to the passage of time. It is important to distinguish between chronological skin aging and photoaging.
Chronological skin aging can be summarized as atrophy with structural and functional decline of the skin. Sun-protected aged skin is finely wrinkled with exaggeration of facial expression lines, laxity, and pallor.
Extrinsic skin aging involves hypertrophy as an inflammatory, protective response to the damaging effects of UV rays. Photoaging is manifested by xerosis, leathery skin, irregular pigmentation (freckles, lentigines), and more pronounced wrinkling. Telangiectasias, purpura, comedones, and a variety of benign and premalignant skin tumors including seborrheic keratoses, sebaceous gland hyperplasia, and actinic keratoses are frequent findings. UV irradiation from the sun damages human skin, causing it to age prematurely.
Matrix metalloproteinases are an important family of enzymes involved in many different physiological and pathological processes. They also play an important role in various forms of skin aging.
In the past two decades, significant progress has been made on both skin aging and MMP research. Thus it became evident that MMPs play an important part in cutaneous aging as well.
In both extrinsic and intrinsic aging, expression and activation of MMPs can be induced by ROS, which are the products of either the physiological function of the organism or the extrinsic toxic effects like UV irradiation or tobacco smoking.
Matrix metalloproteinases are potent proteases collectively capable of degradation of all kinds of dermal ECM proteins. In parallel with MMP activation, production of MMP inhibitors is suppressed. Upon incomplete repair and chronic imbalance of ECM synthesis and degradation, damage to the collagen and elastic fibers might accumulate and lead to their decomposition, which is the major molecular feature of dermal aging.
This study was carried for assessment of tissue expression of MMP-1 and MMP-9 in aged skin through different age groups.
Thirty subjects were classified into 3 categories representing the forth decade (30-40 years old), the fifth decade (41-50 years old) and beyond the fifth decade (above 50 years old); 10 subjects were included in each category. They had clinical signs of skin aging, with Fitzpatrick skin types III or IV and Glogau’s photoaging classification types I, II or III.A skin punch biopsy (3mm) was taken from the preauricular area of the face of each subject for evaluation of histological changes of tissues that were stained by H&E and immunohistochemical expression of MMP-1 and MMP-9.
Hematoxylin and eosin results showed that in group I, there was a normal epidermis with no evident hyperplasia or pigmentation. The collagen bundles were normal in appearance with no evidence of degeneration with normal vascular plexus. Group II showed evidence of epidermal atrophy with distorted and effaced rete ridges as well as mild increase in epidermal and dermal pigmentation. Group III showed epidermal atrophy ranged from mild to severe, and atrophy of cutaneous appendages. Evident collagen degeneration was also noted, where the bundles were fine and fragmented and disorganized in the dermis. Vascular ectasia was also detected in group III.
Immunohistochemical staining pattern of MMP-1, revealed that, in both epidermis and dermis, group III showed the strongest expression followed by group II and lastly group I . Consequently, group I and group II showed milder expression (50% for both groups) than group III (20%).
Regarding the expression of MMP-9 in the epidermis of the three study groups, the study revealed that, group III showed the modest expression (50%) followed by group II (40%) and lastly group I (30%). Consequently, group I and group II showed milder expression (30% for both groups) than group III (10%). group I and group III showed the strongest expression (40% for both groups). In the dermis, group I and group III showed the modest expression (50%) followed by group II (40%).On the other hand, the three groups showed the same strong expression (30%).
We noticed that the expression of MMP-1 and MMP-9 increased in type III Fitzpatrick skin photo- type cases more than type IV cases and in the skin with type II Glogau’s classification more than that with type I. Furthermore, higher expression of MMP-1 and MMP-9 was noticed in cases with type III Glogau’s classification of group III than the skin with either type I or type II of group I and II cases.
We concluded from the study that, obvious histological changes, and elevated levels and activities of cutaneous MMP-1 and MMP-9 have been demonstrated in skin aging. Furthermore, The MMP expression was shown to be strongly dependent on the skin type. However, a controlled trial on a large scale would be needed to confirm the findings of this study, and targeting these findings in the prevention and treatment of skin aging.