Changing the shape of craniofacial bones can profoundly alter ecological function, and understanding how developmental conditions sculpt skeletal phenotypes can provide insight into evolutionary adaptations. Thyroid hormone (TH) stimulates metamorphosis and regulates skeletal morphogenesis across vertebrates. To assess the roles of this hormone in sculpting the craniofacial skeleton of a non-metamorphic vertebrate, we tested zebrafish for developmental periods of TH-induced craniofacial shape change. We analyzed shapes of specific bones that function in prey detection, capture and processing. We quantified these elements from late-larval through adult stages under three developmental TH profiles. Under wild-type conditions, each bone progressively grows allometrically into a mature morphology over the course of postembryonic development. In three of the four bones, TH was required to sculpt an adult shape: hypothyroidism inhibited aspects of shape change, and allowed some components of immature shape to be retained into adulthood. Excess developmental TH stimulated aspects of precocious shape change leading to abnormal morphologies in some bones. Skeletal features with functional importance showed high sensitivities to TH, including the transformator process of the tripus, the mandibular symphysis of the lower jaw, the scutiform lamina of the hyomandibula, and the anterior arm of the pharyngeal jaw. In all, we found that TH is necessary for shaping mature morphology of several essential skeletal elements; this requirement is particularly pronounced during larval development. Altered TH titer leads to abnormal morphologies with likely functional consequences, highlighting the potential of TH and downstream pathways as targets for evolutionary change.

IntroductionType 2 diabetes mellitus (T2DM) is well-known to be associated with normal bone density but, concurrently, low bone turnover and increased risk for fracture. One of the proposed mechanisms is possible derangement in bone precursor cells, which could be represented by deficiencies in circulating osteogenic progenitor (COP) cells and osteoclast precursors (OCP). The objective of our study is to understand whether extent of glycemic control has an impact on these cells, and to identify other factors that may as well.MethodsThis was a secondary analysis of baseline data from 51 male participants, aged 37-65 in an ongoing clinical trial at Michael E. DeBakey VA Medical Center, Houston, Texas, USA. At study entry serum Hemoglobin A1c was measured by high-performance liquid chromatography osteocalcin (OCN) and C-terminal telopeptide of type 1 collagen (CTx) were measured by ELISA, and testosterone and estradiol by liquid-chromatography/mass-spectrometry. Areal bone mineral density (BMD), trabecular bone score and body composition were measured by dual energy x-ray absorptiometry, while COP and OCP were measured by flow cytometry.ResultsWhen adjusted for serum testosterone, parathyroid hormone, and 25-hydroxyvitamin D, those with poor long-term glycemic control had significantly higher percentage of COP (p = 0.04). COP correlated positively with visceral adipose tissue (VAT) volume (r = 0.37, p = 0.01) and negatively with free testosterone (r = -0.28, p = 0.05) and OCN (r = -0.28, p = 0.07), although only borderline for the latter. OCP correlated positively with age, FSH, lumbar spine BMD, and COP levels, and negatively with glucose, triglycerides, and free estradiol. Multivariable regression analyses revealed that, in addition to being predictors for each other, another independent predictor for COP was VAT volume while age, glucose, and vitamin D for OCP.ConclusionOur results suggest that high COP could be a marker of poor metabolic control. However, given the complex nature and the multitude of factors influencing osteoblastogenesis/adipogenesis, it is possible that the increase in COP is a physiologic response of the bone marrow to increased osteoblast apoptosis from poor glycemic control. Alternatively, it is also likely that a metabolically unhealthy profile may retard the development of osteogenic precursors to fully mature osteoblastic cells.

Background An emerging field of research concerns the deleterious effects of type 2 diabetes mellitus (T2DM) on bone. Our group has previously reported a hemoglobin A1c (A1c) threshold of 7% where bone impairment occurs as reflected by reduction in bone turnover markers and deterioration in bone microarchitecture and strength. However, whether poor glycemic control is also associated with underlying derangements in cellular flux remains unclear. Methods Analysis of the baseline data from 42 consecutive men aged 35-65 enrolled in a clinical trial (NCT03887936) at the Michael E DeBakey VA Medical Center, Houston, TX, who were able to provide the outcomes of interest. Inclusion criteria were average fasting morning testosterone from 2 measurements of <300 ng/dl, T2DM and BMI<35 kg/m2. The following variables were assessed: A1c by high performance liquid chromatography; testosterone and estradiol by LC/MS; bone turnover markers and sex hormone binding globulin by ELISA; quantification of osteoblast (OB) progenitors and osteoclast (OC) precursors by flow cytometry; areal bone mineral density (aBMD) and body composition by DXA; and bone microarchitecture and strength by high resolution peripheral quantitative computerized tomography. Results Participants with poorly controlled T2DM (A1c>7%) had significantly lower percent of OB progenitors in circulation than those with A1c≤7% (1.12 ± 0. 079% v 1.47 ± 0.11% of non-B non-T non-NK cells, p=0. 02) when controlling for age, duration of T2DM, free testosterone, and 25-hydroxyvitamin D levels. Higher levels of free testosterone were associated with smaller percentage of OB progenitors (r = -0.31, p = 0. 05). Although the percent of OC precursors in circulation (cells that were dual CD14CD11b+, CD14MCSFR+, or CD14CD120b+) was not significantly related to A1c, it was positively associated with percent of OB progenitors in peripheral blood (r = 0.34, p = 0. 03; r = 0.35, p = 0. 02; r = 0.39, p = 0. 01) respectively. There was a significant positive association between OB progenitors and visceral adipose tissue (VAT) volume (r=0.41, p=0. 009). Although there was no association between osteoblast progenitors and osteocalcin levels (product of mature OBs), osteocalcin negatively correlated with VAT (r=-0.47, p=0. 002). There was no association between OB progenitors and OC precursors with aBMD or bone microarchitecture parameters. Conclusions Poor glycemic control is associated with fewer circulating OB progenitors, as was higher free testosterone levels while the converse was true for VAT. It is possible that the former harms cell viability, while the latter two affect differentiation of OB progenitors into mature OB's; with testosterone promoting, and visceral adipose tissue (via unknown mediators) retarding maturation as suggested by the negative association between osteocalcin and VAT. The positive association between OB progenitors with circulating OC precursors is consistent with the physiologic crosstalk between OB and OC which appears to be preserved in patients with T2D. Presentation: No date and time listed