Biology subjects

Baroi, S.

Publications and source records attributed to Baroi, S..

3 recordsLinked to original sources

bioRxiv2026

Osteocytes secrete adiponectin and display adipocyte-like phenotype under control of PPARG nuclear receptor

Osteocytes and adipocytes represent cells with disparate functions. Osteocytes regulate bone metabolism (remodeling) and bone homeostasis, while adipocytes regulate energy metabolism and energy storage. Here, we demonstrate that osteocyte phenotype consists of adipocytic features which are under control of peroxisome proliferator-activated receptor gamma (PPARG), a master regulator of adipocyte differentiation and function. Using a mouse model with osteocyte-specific deletion of PPARG (OT{gamma}KO) and osteocyte cellular model of MLO-Y4 cells edited with CRISPR/Cas9 for PPARG deficiency, we are demonstrating that under PPARG control osteocytes produce and secrete adiponectin (ADIPOQ), and they are equipped in adipocyte-specific mechanisms for lipid-storage and their metabolism. Under PPARG, osteocytes accumulate lipid droplets which correlate with their capability to cover up to 20% of energy requirements from fatty acids metabolism. Although osteocytes like osteoblasts mainly express perilipin 2 (Plin2), however similarly to adipocytes, lipid droplets accumulation is associated with expression of perilipin 1 (Plin1) under PPARG control. Similarly, lipids accumulation and metabolism involve adipocyte-specific activities including fatty acids binding protein 4 (Fabp4), hormone-specific lipase (Hsl) and adipocyte-specific triglyceride lipase (Atgl), which expression are under PPARG control. These studies provide a new understanding of osteocyte biology which include adipocyte-like endocrine and lipid metabolism features probably reflecting an adaptation to their unique localization and a need for a maintenance of functional fitness in these conditions. They deepen our comprehension of the crossroads of osteocyte and adipocyte function and underscore the therapeutic potential of targeting common molecular pathways in both cell types for managing metabolic disorders and skeletal diseases.

cell biology↗

bioRxiv2024

PPARG in osteocytes controls cell bioenergetics and systemic energy metabolism independently of sclerostin levels in circulation

ObjectiveThe skeleton is one of the largest organs in the body, wherein metabolism is integrated with systemic energy metabolism. However, the bioenergetic programming of osteocytes, the most abundant bone cells coordinating bone metabolism, is not well defined. Here, using a mouse model with partial penetration of an osteocyte-specific PPARG deletion, we demonstrate that PPARG controls osteocyte bioenergetics and their contribution to systemic energy metabolism independently of circulating sclerostin levels. MethodsIn vivo and in vitro models of osteocyte-specific PPARG deletion, i.e. Dmp1CrePpar{gamma}flfl male and female mice ({gamma}OTKO) and MLO-Y4 osteocyte-like cells with either siRNA-silenced or CRISPR/Cas9-edited Ppar{gamma}. As applicable, the models were analyzed for levels of energy metabolism, glucose metabolism, and metabolic profile of extramedullary adipose tissue, as well as the osteocyte transcriptome, mitochondrial function, bioenergetics, insulin signaling, and oxidative stress. ResultsCirculating sclerostin levels of {gamma}OTKO male and female mice were not different from control mice. Male {gamma}OTKO mice exhibited a high energy phenotype characterized by increased respiration, heat production, locomotion and food intake. This high energy phenotype in males did not correlate with "beiging" of peripheral adipose depots. However, both sexes showed a trend for reduced fat mass and apparent insulin resistance without changes in glucose tolerance, which correlated with decreased osteocytic responsiveness to insulin measured by AKT activation. The transcriptome of osteocytes isolated from {gamma}OTKO males suggested profound changes in cellular metabolism, fuel transport and usage, mitochondria dysfunction, insulin signaling and increased oxidative stress. In MLO-Y4 osteocytes, PPARG deficiency correlated with highly active mitochondria, increased ATP production, shifts in fuel utilization, and accumulation of reactive oxygen species (ROS). ConclusionsPPARG in male osteocytes acts as a molecular break on mitochondrial function, and protection against oxidative stress and ROS accumulation. It also regulates osteocyte insulin signaling and fuel usage to produce energy. These data provide insight into the connection between osteocyte bioenergetics and their sex-specific contribution to the balance of systemic energy metabolism. These findings support the concept that the skeleton controls systemic energy expenditure via osteocyte metabolism. HighlightsO_LIOsteocytes function as a body energostat via their bioenergetics C_LIO_LIPPARG protein acts as a "molecular break" of osteocyte mitochondrial activity C_LIO_LIPPARG deficiency activates TCA cycle, oxidative stress and ROS accumulation C_LIO_LIPPARG controls osteocyte insulin signaling and fuel utilization C_LI

physiology↗

bioRxiv2020

PPARG in osteocytes is essential for sclerostin expression, bone mass, marrow adiposity and TZD-induced bone loss

PPARG role in regulation of osteocyte function is largely unknown. We report that PPARG is essential for sclerostin production, a recently approved target to treat osteoporosis. There is an excellent correlation in osteocytes between Sost/sclerostin and PPARG at the transcript and protein levels, and increased bone mass in mice with osteocyte-specific deletion of PPARG ({gamma}OTKO) correlated with increased WNT signaling and bone forming activity of endosteal osteoblasts and decreased marrow fat. The 8 kb sequence upstream of Sost gene transcription start site possesses multiple PPARG binding elements (PPREs) with at least two of them binding PPARG with dynamics reflecting its activation and the levels of Sost transcript and sclerostin protein expression. Older {gamma}OTKO female mice are largely protected from TZD-induced bone loss providing proof of concept that PPARG in osteocytes can be pharmacologically targeted. Our study opens the possibility to consider repurposing PPARG as a target for treatment of osteoporosis.

physiology↗