Physiological and Pathological Changes in Levels of the Two Small Stress Proteins, HSP27 and ∝B Crystallin, in Rat Hindlimb Muscles1

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Abstract
The two small stress proteins, HSP27 and ∝B crystallin, are expressed widely in normal rat tissues and abundantly in skeletal muscle. In order to clarify the physiological significance of these stress proteins, the changes in their levels were determined immunochemically, in the slow-twitch soleus muscle and fast-twitch extensor digitorum longus muscle or rectus femoris muscle of growing rats, and in those of adult rats during denervation and tenotomy. HSP27 was quantitated by specific immunoassay, similar to that for aB crystallin, with antibodies raised in rabbits against purified rat HSP27. In adult rats, HSP27 was present at high levels in tissues composed of striated muscle, and it was present at much higher levels in the soleus muscle than in the rectus femoris or extensor digitorum longus muscle, as is ∝B crystallin. However, in rats of perinatal age (from prenatal day 2 to postnatal day 3), levels of HSP27 in the rectus femoris muscle were enhanced like those in the soleus muscle, reaching the maximum levels at postnatal day 3. Thereafter HSP27 in the fast-twitch muscle showed a steep decrease. The increase in ∝B crystallin in the hindlimb muscles was also observed in the perinatal period. However, ∝B crystallin concentrations in the soleus muscle of perinatal rats were as low as those in rectus femoris muscle. The transection of the sciatic nerve resulted in decreases in the levels of HSP27 and aB crystallin in the soleus muscle of adult rats, together with increases in the levels of the two proteins in the extensor digitorum longus muscle. The decrease in HSP27 and aB crystallin in the soleus muscle was also observed after tenotomy. However, there was no increase in the concentrations of the two proteins in the tenotomized extensor digitorum longus muscle. These results suggest that the two small stress proteins in the hindlimb muscle, in particular HSP27, are induced by events associated with birth, and that the expression of HSP27 and ∝B crystallin in the skeletal muscles is controlled similarly in adult rats.

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