Anyonya Guntur, PhD
Faculty Scientist II
Center for Molecular Medicine
Guntur Lab
Understanding bioenergetics and mitochondrial biology in bone development and regeneration
Dr. Guntur is a bone biologist and is interested in identifying factors and mechanisms related to energy metabolism, bioenergetics, and mitochondria that can regulate skeletal cell activity and functions. His laboratory uses both in vitro and in vivo approaches to study bone. The Guntur Lab has generated multiple mouse models with both global and targeted deletion of signaling and mitochondrial-related factors in skeletal cells. These models are currently being utilized in the lab and through collaborations to study the role of mitophagy and mitochondrial dysfunction in Osteoporosis, skeletal fracture, Digit regeneration, IGF1/Insulin signaling in bone, mineralization, intervertebral disc development and polytrauma (burn and fracture repair). Mouse models are coupled with metabolomics, proteomics, lipidomics, and bioenergetic measurements using isolated mitochondria, permeabilized cells, and in vitro cell cultures to identify targets and pathways that can be manipulated for therapeutic purposes.
The major projects underway are described below:
A) Mitophagy and mitochondrial dysfunction in osteoporosis and skeletal fracture: The lab has identified BNIP3 and NIX, members of the atypical BCL2 family, as crucial players in mitochondrial regulation impacting bone mass. Originally thought to be involved only in removing damaged mitochondria, recent evidence suggests that NIX may also act as a pexophagy receptor, influencing peroxisome turnover. The Guntur lab’s investigations have unveiled the regulatory roles of BNIP3 and NIX in cellular bioenergetics, and mitochondrial stress signaling. By generating conditional alleles, including BNIP3flox/flox and NIXflox/flox, we have performed fracture healing in our double mesenchymal knockout mice and observed decreased bone mineral density.
BNIP3/NIX are required for proper bone formation. A) Representative µCT images of femora from control or mice with deletion of BNIP3/NIX in osteoprogenitor cells using Prrx1Cre.
B) Mitochondria and skeletal regeneration: This project was developed collaboratively with Dr. Mimi Sammarco at the Mayo Clinic and Dr. Robert Tower at UTSW and dissects the roles of BNIP3 and NIX during digit regeneration using spatial transcriptomics. The lab aims to unravel the intricacies of BNIP3 in stem cells within the nail bed, utilizing novel mitophagy-related transgenic mouse models generated in my lab. The project explores how BNIP3 signals through ROS and BMP ligands to NIX in the blastema, coordinating regeneration by modulating mitochondrial dynamics.This initiative aims to deepen the understanding of mitochondrial involvement in skeletal regeneration by leveraging reagents and modulators identified during the metabolic COBRE project (P20GM121301 “Essential role for mitophagy in osteoblast differentiation”). This project also leverages the expertise of Dr. Sammarco a digit regeneration biologist (Mayo Clinic) and Dr. Tower (UTSW) who has developed and successfully used spatial transcriptomics on skeletal tissue.
Representative 3D microCT images (Dr. Mimi Sammarco, Mayo) of regenerating digits from mice treated with the ROS-inducing menadione or vehicle control (corn oil).
C) IGF1/Insulin signaling in bone: Focusing on the crucial role of PI3K signaling in osteoprogenitor function, the Guntur Lab deleted IRS1 and IRS2 downstream of PI3K signaling in osteoprogenitors using Prrx1cre targeting. The absence of insulin and IGF-1-mediated signaling in osteoprogenitors has led to a significant decrease in cortical bone parameters, while no differences were observed in cancellous bone. The lab’s studies extend to downstream transcriptional factors responding to Insulin and IGF-1 signaling, particularly the conditional deletion of FoxK1,2 in mesenchymal stem cells using Prrx1Cre. The lab’s recent identification of FoxK1,2, transcription factors involved in metabolic rewiring and regulation of mitochondrial biogenesis, has opened new avenues of research. Collaborating with Dr. Sven Enerback at the University of Gothenburg, Sweden, and with a pilot project funding from MHIR and Roux institute (Kiran Vanaja PhD) the team has generated mouse models with floxed alleles for these factors crossed to bone-specific CRE mouse lines at MHIR. The significant bone phenotype observed in global knockout of FoxK2 underscores their potential importance downstream of Insulin and IGF-1 and their role in regulating mitochondrial and glycolytic metabolism. The research team have generated FoxK1, FoxK2, and FoxK1/K2 conditional knockouts and observed significant changes in bone length and size. These mouse models will be critical in identifying the roles of these transcriptional factors in skeletal biology.
Whole mount skeletal preparation stained with Alcian Blue and Alizarin red. To assess gross anatomical skeletal morphology, skeletal whole mounts were prepared from 12 week old A) Irs1cko, B) Irs2cko, C) Irs1/2cko and WT controls.
d) Parathyroid hormone, osteoblast bioenergetics and mitochondrial derived vesicles; The Guntur Lab has recently uncovered the effects of parathyroid hormone (PTH) on osteoblast bioenergetics. Acute treatment with PTH led to an increase in glycolytic metabolism in osteoblasts. However, the consequences of this on mitochondrial mitophagy and metabolism remain unknown. Notably, the lab observed a significant increase in mitophagy and mitochondrial-derived vesicles (MDVs) following PTH treatment. While the current understanding suggests that MDVs are formed in response to cellular stress for mitochondria to discard damaged parts, emerging evidence indicates potential physiological functions. Our ongoing research involves manipulating MDVs through chemical treatment, identifying and sizing them using flow cytometry. The focus is on understanding whether these particles serve solely as a quality control mechanism or if, particularly in bone cells, they play a distinct and more physiological role.
Calvarial osteoblasts (COB) after 21 days of differentiation (in osteogenic media). Calvarial osteoblasts were isolated form MitoQC mice (mitophagy reporter mice). The red punctae indicate mitophagy. Mitochondria in this model are visualized using GFP and mCherry overlay.