Linear growth failure results from a broad spectrum of systemic and local disorders that can generate chronic musculoskeletal disability. Current bone lengthening protocols involve invasive surgeries or drug regimens, which are only partially effective. Exposure to warm ambient temperature during growth increases limb length, suggesting that targeted heat could noninvasively enhance bone elongation. We tested the hypothesis that daily heat exposure on one side of the body unilaterally increases femoral and tibial lengths. Mice (N ¼ 20) were treated with 40˚C unilateral heat for 40 min/day for 14 days post-weaning. Non-treated mice (N ¼ 6) served as controls. Unilateral increases in ear (8.8%), hindfoot (3.5%), femoral (1.3%), and tibial (1.5%) lengths were obtained. Tibial elongation rate was > 12% greater (15 mm/day) on the heat-treated side. Extremity lengthening correlated with temperature during treatment. Body mass and humeral length were unaffected. To test whether differences persisted in adults, mice were examined 7-weeks post-treatment. Ear area, hindfoot, femoral, and tibial lengths were still significantly increased $6%, 3.5%, 1%, and 1%, respectively, on the heat-treated side. Left-right differences were absent in non-treated controls, ruling out inherent side asymmetry. This model is important for designing noninvasive heat-based therapies to potentially combat a range of debilitating growth impediments in children. ß

BackgroundPerturbations in abdominal fat secreted adipokines play a key role in metabolic syndrome. This process is further altered during the aging process, probably due to alterations in the preadipocytes (aka. stromal vascular fraction cells-SVF cells or adipose derived stem cells-ASCs) composition and/or function. Since microRNAs regulate genes involved both in development and aging processes, we hypothesized that the impaired adipose function with aging is due to altered microRNA regulation of adipogenic pathways in SVF cells.Methodology and Principal FindingsAlterations in mRNA and proteins associated with adipogenic differentiation (ERK5 and PPARg) but not osteogenic (RUNX2) pathways were observed in SVF cells isolated from visceral adipose tissue with aging (6 to 30 mo) in female Fischer 344 x Brown Norway Hybrid (FBN) rats. The impaired differentiation capacity with aging correlated with altered levels of miRNAs involved in adipocyte differentiation (miRNA-143) and osteogenic pathways (miRNA-204). Gain and loss of function studies using premir or antagomir-143 validated the age associated adipocyte dysfunction.Conclusions and SignificanceOur studies for the first time indicate a role for miRNA mediated regulation of SVF cells with aging. This discovery is important in the light of the findings that dysfunctional adipose derived stem cells contribute to age related chronic diseases.

Limb length inequality is a potentially disabling condition with few noninvasive treatment options. Our lab has previously shown that unilateral heat increases bone elongation rate, suggesting that temperature therapy could be a non‐surgical way to promote limb length equalization. Treatment age is important because we have shown that temperature effects occur primarily when growth is most rapid. We compared heat effects on limb lengthening during early (3‐5 weeks age) and late (5‐7 weeks age) phases of post‐weaning growth in mice (N=24). We tested the hypothesis that heat‐induced limb elongation varies with postnatal growth rate. Female mice (N=6 per age) were treated with 40C unilateral heat for 40 minutes per day for 14 days. Controls (N=6 per age) were not treated. Tibial elongation rate, measured by fluorochrome labeling, was over two‐fold greater during the early phase. Bone elongation rate reflected overall body growth rate, with lower absolute heat‐induced differences during the later phase. Relative increases in extremity length on the heat‐treated side were similar during early and late phases, suggesting that a heat‐induced growth response is still possible during later postnatal growth. These results are important for designing therapies to treat children with linear growth disorders at different stages of development by demonstrating that treatments may not be restricted to early growth phases. Supported by ASBMR GAP, WV‐NASA, UK‐CCTS (NIH UL1TR000117), and NIH/NIAMS R15AR067451‐01.

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Limb length inequality is prevalent in nearly 90% of the population. Differences of 20mm can cause gait asymmetry and chronic back pain. Surgical treatments are invasive and alternatives are needed. Exposure to warm ambient temperature accelerates limb elongation in mice, suggesting that targeted heat could be a noninvasive way to promote limb length equalization. We tested the hypothesis that daily heat exposure on one side of the body will unilaterally increase limb length. Female mice (N=6) were treated with 40C unilateral heat for 40 minutes per day for 14 days post‐weaning. Controls (N=6) were not treated. Femur length was increased 1.3% on the heat‐treated side. Tibial elongation rate, measured by oxytetracycline labeling, was increased >12%. Body mass was unaffected. Histological analysis revealed morphological differences in the growth plate. To validate a protein assay for the next step, we developed western blotting methods to asses IGF‐I activation in whole proximal tibias. We show that IGF‐I (100ng/ml) stimulates Akt phosphorylation after 90 minutes in culture, suggesting that this method will be effective for measuring IGF‐I signaling in heat‐treated bones. This model will be important for elucidating mechanisms of heat‐enhanced growth. Our findings are relevant for the development of non‐invasive heat‐based therapies to increase length of specific bones without surgery. Grant Funding Source: Supported by NASA WV Space Grant Consortium and UK CCTS (NIH UL1TR000117)