Norihiko Maeda

Prostaglandin E2 stimulates collagen and non-collagen protein synthesis and prolyl hydroxylase activity in osteoblastic clone MC3T3-E1 cells

We investigated the stimulative effect of prostaglandin E2 (PGE2) on an osteoblastic cell line, clone MC3T3-E1, in serum-free medium. PGE2 elevated collagen and non-collagen protein syntheses in a dose-related fashion up to 2 micrograms/ml, the maximal increases being 2- and 3-fold, respectively, over that in the control. Its stimulative effect was evident as early as 12 h. PGE2 slightly increased DNA content, but its effect was less than that on collagen and non-collagen protein syntheses. Moreover, PGE stimulated an increase in prolyl hydroxylase activity with a maximal effect at 1-2 micrograms/ml, the activity being 15-fold over that of the control. These results strongly indicate that PGE2 directly enhances total protein synthesis including that of collagen in osteoblasts in vitro, suggesting its direct effect on bone formation in vivo as well.

Effect of 1,25-dihydroxyvitamin D3 on alkaline phosphatase activity and collagen synthesis in osteoblastic cells, clone MC3T3-El1

A stimulative effect of 1,25-dihydroxyvitamin D3 was tested on osteoblastic cells, clone MC3T3-E1, cultured in serum-free medium with 0.1% bovine serum albumin. This steroid increased alkaline phosphatase activity in a dose-related fashion. The steroid also stimulated dose-dependently collagen and non-collagen protein syntheses, their maximal effects being observed at 12 and 24 h, respectively. The incorporation of [3H]-proline into collagen or non-collagen protein in cells exposed to this steroid for 12 h was 2.9 or 1.9-fold over that of control cultures, respectively. These results strongly indicate the stimulative effects of 1,25-dihydroxyvitamin D3 on the differentiation of osteoblasts in vitro.

Effect of transferrin on alkaline phosphatase activity and collagen synthesis in osteoblastic cells derived from newborn mouse calvaria

The effect of transferrin was tested on osteoblastic cells (clone MC3T3-E1) cultured in serum-free medium containing 1% bovine serum albumin (BSA). Transferrin (Tf) stimulated increases of protein content and protein synthesis, but not of DNA content and cell number, in the cells. This protein also increased alkaline phosphatase activity and collagen synthesis in combination with 1% BSA. Actinomycin D and cycloheximide inhibited alkaline phosphatase activity induced by Tf, suggesting that Tf may enhance de novo synthesis of the enzyme. These results indicate that Tf may be involved in differentiation of osteoblastic cells, but not in their proliferation, in vitro.

Developmental changes in the activities of prolinase and prolidase in rat salivary glands, and the effect of thyroxine administration

SummaryAs the salivary glands are interesting tissues to study proliferation, we studied the activities of prolinase and prolidase using Pro-Ala and Pro-Hyp as substrates, respectively, in developing rat salivary glands between day 1 and week 10 after birth. Developmental changes of prolinase activity in the submandibular and sublingual glands were similar to those in the parotid gland, which steadily increased and reached the adult level by 20–25 days after birth. However, the changes in the activity of prolidase in the submandibular and sublingual glands were different from those in the parotid gland: the activity in the parotid gland slowly increased with maturation and reached a maximum level on day 30, but the activity in the submandibular and sublingual glands continuously increased with maturation. When thyroxine was injected every two days from day 1 to day 19, both enzyme activities were induced precociously in the parotid gland but not in the submandibular and sublingual glands. On the study of regional distribution in rat tissues, the correlation coefficient between prolinase and prolidase activities was high in the peripheral but not high in the brain regions.These results indicate that the physiological roles of prolinase and prolidase are very similar but not the same.

Postnatal Development and Aging of Muscle Spindles in the Mouse Masseter Muscle and Effects of a Fine-Grained Diet on Them

Neuromuscular spindles of skeletal muscles of vertebrates are encapsulated stretch receptors with structurally specialized intrafusal muscle fibers, innervated with sensory and fusimotor nerve endings (Barker and Cope, 1962; Boyd, 1962; Matthews, 1964; Barker et al., 1972). There are many detailed studies on the development of muscle spindles in several animal species and man (Sutton, 1915; Tello, 1917, 1922; Cuajunco 1927, 1940; Hewer, 1935; Zelena, 1957, 1959, 1976; Mavrinskaia, 1960; Bowden, 1963; Schiaffino and Pierobon Bormioli, 1976). Those earlier works showed that the most important event during the development of muscle spindles was the arrival of the sensory nerve fibers into the muscle, and the event occurred in the early stage of gestation. Muscle spindle formation is initiated by the primary afferent nerve contact with a bundle of developing myotubes. In some species, muscle spindle formation is completed during the intrauterine period, but in rats the onset of muscle spindle differentiation is observed to occur at a late stage of gestation (Zelena, 1957, 1959; Marchand and Eldred, 1969; Landon, 1972; Milburn, 1973); and the formation of rat muscle spindles is completed early postnatally.

Postnatal Development of Muscle Spindles and Extrafusal Muscle Fibers in the Mouse Temporal Muscle and Dietary Effect

In 1985, Maeda et al. found that the formation of annulospiral endings in the masseter muscle of developing mice continued after weaning and was completed by the 50th postnatal day. Moreover, Maeda et al. (1987) reported that a long-term intake of a fine-grained diet resulted in degeneration of annulospiral endings of muscle spindles in the masseter muscle of mice.