Below are the major research projects in the lab listed in no particular order. We seek funding from the NIH and USDA, which shapes our future directions.
Steroid hormone biosynthesis
Steroid hormones, indispensable for mammalian life, are made from cholesterol via biosynthetic pathways that originate in mitochondria. The first enzymatic step in steroidogenesis is the conversion of cholesterol to pregnenolone, a reaction that is carried out by CYP11A1 (P450 side chain cleavage) at the matrix side of the inner mitochondrial membrane (IMM). The transport of cholesterol from the outer mitochondrial membrane (OMM), across the intermembrane space (IMS), to the IMM occurs prior to this enzymatic conversion and forms the first and rate-limiting step in steroid hormone biosynthesis. Starting in the early 1990s, a mechanism began to take shape for this cholesterol transport process that involved two key players: the translocator protein (TSPO, previously known as the peripheral benzodiazepine receptor/PBR), and the steroidogenic acute regulatory protein (STAR). According to this model, TSPO in the OMM was considered the channel that receives cholesterol from STAR and mediates its transport to the IMM.
Recent research emanating from our laboratory using both TSPO knockout (Tspo-/-) mice (independently confirmed by others) and CRISPR/Cas9-mediated TSPO deletion in cultured steroidogenic cells has refuted this model and seriously challenged the requirement for TSPO in cholesterol transport and/or steroidogenesis. As a result, the function of TSPO remains unclear, and its abundant expression in steroidogenic cells is mechanistically unexplained. Current research in our lab is focussed on: (1) Describing the precise function of TSPO in steroidogenic cells. (2) Describing the mechanism of mitochondrial cholesterol import.
Figure 1. Evolution of Mitochondrial Cholesterol Import Models. (Mol Endocrinol, 2015)
Signaling in lipid metabolism and fatty liver disease
Nonalcoholic fatty liver disease (NAFLD) is the most common condition leading to chronic liver diseases, representing approximately 75% of cases in the US. NAFLD first manifests as simple steatosis, or abnormal lipid accumulations in the liver. Some patients with NAFLD progress to nonalcoholic steatohepatitis (NASH), a condition characterized by hepatocyte injury, hepatic inflammation in addition to the steatosis. Advanced NASH contributes to fibrosis and may progress to cirrhosis in extreme cases. NAFLD naturally develops in the absence of alcohol abuse and the exact pathogenesis remains unknown. Moreover, NAFLD progressing to NASH currently has no effective treatment and therefore is one of the most common indications that necessitate liver transplantation. Our lab is interested in identifying the mechanisms underlying shifts in lipid metabolism and the role of cholesterol in the etiology of fatty liver disease.
Figure 2. Metabolic changes as observed in high cholesterol diet induced NAFLD/NASH (Sci Rep, 2015)
Pluripotency regulation and livestock stem cells and applications
Although several studies using bovine cells have claimed successful derivation of induced pluripotent stem cells from cattle and other ruminants, measures of quality have remained quite arbitrary. Via systems biology studies on pluripotency signaling in the early bovine embryo, we have discovered paths to improve both the reprogramming approach and conditions to sustain self-renewal in bovine induced pluripotent stem cells (iPSCs). In this work, we have established the molecular signature of an authentic ground state of pluripotency in cattle. We are currently exploring paths towards applications from these cells in both assisted reproduction and banking genetic diversity of extant livestock breeds.
Figure 3. The extended transcriptional network sustaining bovine pluripotency. (Biology Open, 2021)
Preimplantation embryo development and placentation
Trophectoderm of blastocysts mediate early events in fetal-maternal communication enabling implantation and establishment of a functional placenta. Inadequate or impaired developmental events linked to trophoblasts directly impact early embryo survival and successful implantation during a crucial period that corresponds high incidence of pregnancy losses in dairy cows. The placental interface in cattle is the least invasive epitheliochorial type, with villous digitations between fetal and maternal tissues restricted to regions of the cotyledons. As yet, the molecular basis of bovine trophectoderm development and signaling towards initiation of implantation remains poorly understood. Our lab is interested in unravelling the mechanisms that regulate trophectoderm development leading to the initiation of implantation.
Video 1. Bovine trophoblast stem cells in culture.(Biol Open, 2019)
Larvameal as a protein source for animal feed
In the United States alone, the beef and dairy industries produce approximately 330 million tons of manure waste per year, presenting a significant global waste challenge which often impacts food security and health. The common housefly, Musca domestica, forms a considerable component of the natural biodegradation system as it completes the larval stage of its life cycle thriving largely in semi solid organic waste material like manure. In the ecosystem, birds and fish naturally consume insects and their larvae. Our lab is interested in evaluating the nutritional value of housefly larvae, and examining its value as a natural alternative protein-rich feed ingredient for livestock and aquaculture operations.
Video 1. Farming housefly larva meal into animal or fish feed.
Figure 4. What is larvameal? (PLoS ONE, 2017)