Earlier studies have shown that removal of the submandibular glands of mice retards the rate of contraction of experimentally induced wounds and that communal licking of wounds accelerates contraction in intact animals [Hutson, J. M., Niall, M., Evans, D. & Fowler, R. (1979) Nature (London) 279, 793-795]. In the light of the observation that nerve growth factor (NGF) is secreted in high concentrations in mouse saliva, we have studied the effect of topically applied high molecular weight nerve growth factor (HMW-NGF) upon the rate of wound contraction in sialoadenectomized animals. Results show that HMW-NGF significantly accelerates the rate of wound contraction and that this phenomenon is probably dependent upon the enzymic activity of the protein. Neither diisopropyl fluorophosphate-inactivated NGF nor 2.5S NGF [isolated according to Bocchini, V. & Angeletti, P. U. (1969) Proc. Natl. Acad. Sci. USA 64, 787-794] displays this biological activity. Thus, it may be that one of the physiological roles of NGF in saliva is to promote wound healing by the licking process.

Circular, full-thickness dermal burn- and freeze-produced wounds were produced in rats to compare the difference in healing between the two types of thermal injuries. Contraction did not occur in wounds (n = 30) caused by freezing, while burn wounds (n = 30) contracted to less than one-third of original size by 21 days after injury. If the centers of the freeze-produced wounds (n = 12) were excised, contraction would then occur and proceed at the same rate as an open wound. Histologically, the degree of initial tissue destruction by the two types of injuries was similar. The burn wound contained only half the amount of collagen found in the freeze-produced wound. There was a greater and more rapid replacement of collagen in the burn wounds. With both injuries, the highest concentration of collagen was found on the fifteenth day and returned to normal by the twenty-eighth day. The burn wound contained three times the amount of collagen in normal skin, while the freeze-produced wound contained only 1 3/4 times the amount in normal skin. Contraction does not seem to occur in the healing of the freeze-injured skin because the slow removal and replacement of the residual matrix prevents contraction.

Overexpression of heat shock protein (HSP)72 is associated with cardioprotection. Hyperthermiainduced HSP72 overexpression is attenuated with senescence. While exercise also increases myocardial HSP72 in young animals, it is unknown whether this effect is attenuated with aging. Therefore, we investigated the effect of aging on exercise-induced myocardial heat shock factor (HSF)-1 activation and HSP72 expression. Male Fischer-344 rats (6 or 24 mo) were randomized to control, exercise, and hyperthermic groups. Exercise consisted of 2 days of treadmill running (60 min/day, ϳ75% maximal oxygen consumption). Hyperthermia, 15 min at ϳ41°C (colonic temperature), was achieved using a temperature-controlled heating blanket. Analyses included Western blotting for myocardial HSP72 and HSF-1, electromobility shift assays for HSF-1 activation, and Northern blotting for HSP72 mRNA. Exercise and hyperthermia increased (P Ͻ 0.05) myocardial HSP72 in both young (Ͼ3.5-and 2.5-fold, respectively) and aged (Ͼ3-and 1.5-fold, respectively) animals. Both exercise and hyperthermic induction of HSP72 was attenuated with age. Myocardial HSF-1 protein, HSF-1 activation, and HSP72 mRNA did not differ with age. These data demonstrate that aging is associated with diminished exercise-induced myocardial HSP72 expression. Mechanisms other than HSF-1 activation and transcription of HSP72 mRNA are responsible for this age-related impairment. stress proteins; cardioprotection; heart; heat shock protein AGING IS A MULTIFACTORIAL PROCESS resulting in damage to molecules, cells, and tissues. Eventually, this damage exceeds the capacity of the organism to adapt and/or repair the damage (49). Cells have evolved complex genetic systems to detect specific forms of stress and activate the expression of genes whose products increase the resistance of the cell to further stress and/or initiate the processes of tissue regeneration. Unfortunately, the expression of many of these genes is attenuated in aging (53, 63). As a consequence, cellular responsiveness to stress diminishes with advancing age.One of the best understood cellular responses to stress has been traditionally called the heat shock response. Cell stresses including heat stress and exercise result in preferential transcription and translation of heat shock proteins (HSPs). Overexpression of 72-kDa HSP (HSP72) is associated with protection of cardiomyocytes from a variety of stresses including myocardial ischemia-reperfusion (I/R) injury (33, 50). Heat stress-induced increases in myocardial HSP72 are associated with reduced myocardial damage after I/R in young animals (12, 13). Furthermore, we and others (14,23,24,43,45,56,60) have shown that endurance exercise elevates myocardial HSP72 and protects against myocardial I/R injury in young adult animals.Evidence indicates that mammalian aging is associated with decreased cellular expression of HSP72 in response to heat stress (6-8, 16, 21, 22, 26, 27, 38, 40-42). At present, the mechanism to explain the agerelated decline in myocardial HSP72 expr...

By using fluorescence and electron microscopy, the endocytic pathway encountered by cell surface components after they had bound wheat germ agglutinin (WGA) was visualized. The majority of these components are thought to consist of sialylated glycoproteins (HMWAG) that represent a subpopulation of the total cell surface proteins but most of the externally disposed plasma membrane proteins of the cell. Examination of semi-thin sections by medium- and high-voltage electron microscopy revealed the three-dimensional organization of vesicular and tubular endosomes. Binding of either fluorescein isothiocyanate-, horseradish peroxidase-, or ferritin-conjugated WGA to cells at 4 degrees C showed that the HMWAG were distributed uniformly over the cell surface. Warming of surface-labeled cells to 37 degrees C resulted in the endocytosis of WGA into peripheral endosomes via invagination of regions of both coated and uncoated membrane. The peripheral endosome appeared as isolated complexes comprising a vesicular element (300-400 nm diam.) surrounded by and continuous with tubular cisternae (45-60 nm diam.), which did not interconnect the endosomes. After 30 min or more label also became localized in a network of anastomosing tubules (45-60 nm diam.) that were located in the centrosomal region of the cell. Endocytosed WGA-HMWAG complexes did not become associated with cisternae of the Golgi apparatus, although tubular and vesicular endosomes were noted in the vicinity of the trans-Golgi region. The accumulation of WGA-HMWAG in the endosomes within the centrosomal region was inhibited when cells were incubated at 18 degrees C. None of these compartments contained acid phosphatase activity, a result that is consistent with other data that the HMWAG do not pass through lysosomes initially. The kinetics of labeling were consistent with the interpretation that recycling of most of the WGA binding surface glycoproteins occurred rapidly from early peripheral endosomes followed by the late trans-Golgi compartment. In conclusion, a portion of cell surface glycoproteins are routed to a complex arrangement of tubular and vesicular compartments following endocytosis that includes a putative post-endosomal, tubular reticulum that appears to be separate from the trans-most Golgi saccule.

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