The influence of the reduced thyroid function in mothers during gravidity and lactation on the endochondral bone development in rat offspring during the early postnatal period

U ovom radu je postavljena hipoteza da hipotireoidizam ženki pacova utiče na proces endohondralnog okoštavanja tako što utiče na proliferaciju i diferencijaciju hondrocita, osteoklasta i osteoblasta kod mladunaca. U ogledu su korišćeni mladunci muškog pola (n=36), eutanazirani odmah na rođenju ili sedmog dana starosti, potomci majki (n=24) iz kontrolne grupe i dve tretirane grupe koje su tokom graviditeta i laktacije dobijale nisku (1.5 mg/L), ili visoku (150 mg/L) dozu propiltiouracila (PTU) u vodi za piće. Na osnovu kliničkog stanja, koncentracije tireoidnih hormona i indeksa aktivacije štitaste žlezde utvrđeno je da je niska doza PTU-a prouzrokovala supklinički, a visoka klinički oblik hipotireoidizma i kod majki i kod mladunaca obe starosne grupe. Za analizu proksimalne epifizne ploče mladunaca korišćena je morfometrija, in situ hibridizacija, imunohistohemija, histohemija i elektronska mikroskopija. Hondrociti u zoni rezervne hrskavice i zoni proliferacije su sadržali manju količinu glikogena, najverovatnije su brže proliferisali i imali su manje izraženu autofagnu aktivnost kod mladunaca iz sve četiri tretirane grupe u odnosu na kontrole. Vanćelijski matriks je sadržala manje kolagena tipa 2 i 10, a više glikozaminoglikana. Najizrazitije promene su skraćenje zone hipertrofije hondrocita, smanjena visina i povećanje broja hipertrofisanih hondrocita koji nisu eksprimirali kaspazu 3. U osteoklastima u zoni osifikacije je smanjenja sinteza tartarat rezistentne kisele fosfataze, dok je u osteoblastima smanjena sinteza kiselog proteina matriksa dentina 1 i kolagena tipa 1. To je povezano sa zaostajanjem kalcifikovane hrskavice, smanjenom depozicijom i kalcifikacijom osteoida te formiranjem kraćih a širih trabekula. Sve promene su naročito izražene kod mladunaca sa kliničkim oblikom hipotireoidizmom starih sedam dana. U zaključku, supklinički i klinički hipotireoidizam kod mladunaca na rođenju i sedmog dana starosti najverovatnije stimuliše proliferaciju hondrocita, a usporava diferencijaciju i smanjuje funkcionalnu aktivnost kako hondrocita, tako i osteoklasta i osteoblasta negativno utičući na endohondralno okoštavanje i dužinu tibije.In this work we hypothesized that the hypothyroidism in rat dams, influences the process of offspring endochondral ossification affecting proliferation and differentiation of chondrocytes, osteoclasts and osteoblasts in pups. At the day of birth and seven-day-old male pups (n = 36) derived from control dams and dams treated with a low (1.5 mg/L) or high (150 mg/L) dose of propylthiouracil (PTU) in drinking water during pregnancy and lactation (n = 24), were used. Based on the clinical examination, thyroid hormone concentrations and thyroid activation index, it was found that the low dose of PTU caused subclinical, and the high dose of PTU clinical form of hypothyroidism in both mothers and in pups of both age groups. Morphometry, in situ hybridization, immunohistochemistry, histochemistry and electron microscopy were used to analyze the proximal epiphyseal plates of the pups. Chondrocytes in the reserve cartilage zone and proliferation zone contained a lower amount of glycogen, most likely proliferated faster and had a less pronounced autophagy activity in pups from all four treated groups compared to controls. The extracellular matrix contained less collagen type 2 and 10 and more glycosaminoglycans. The most pronounced changes were the shortening of the hypertrophic zone, the reduced height and the increase in the number of hypertrophic chondrocytes that did not express caspase 3. Ossification zone: low amount of tartrate resistant acid phosphatase, and dentin matrix acid protein-1 and collagen type 1 was synthesized in osteoclasts and osteoblasts, respectively. This was associated with the delay of calcified cartilage resorption, decreased deposition and calcification of osteoid, and the formation of shorter and wider trabeculae. All changes were particularly pronounced in pups with a clinical form of hypothyroidism, seven days old. In conclusion, subclinical and clinical hypothyroidism in pups at the day of birth and seven-day-old, most likely stimulates chondrocyte proliferation. It also slows down differentiation and reduces the functional activity of chondrocyte, osteoclasts and osteoblasts, adversely affecting endochondral ossification and tibia length