All multicellular organisms use signaling molecules to convey information between cells. Neurons and endocrine tissues- such as the brain, pituitary, pancreas and adrenal gland- make especially important signaling molecules: peptidergic neurotransmitters and peptide hormones.
Our research questions center on the regulated secretory pathway in which signaling molecules are made. We are especially interested in the synthesis of these signaling molecules by the proprotein convertases, as well as the chaperone mechanisms used to maintain the pathway and the synaptic environment free of misfolded protein aggregates. We would like to better understand the physiological mechanisms used by secretory tissues (neurons and endocrine cells) to control aberrant protein assembly and aggregation in the later stages of the secretory pathway -as well as in the extracellular milieu.
Many different disease processes are influenced by genetic variations in convertase sequences. The important prohormone convertase PC1/3, which controls the initial biosynthetic step of neuropeptide and peptide hormone production, is produced in a variety of human populations as two variants which are strongly associated with risk of obesity and diabetes. Our studies on convertase-mediated opioid peptide synthesis are also relevant to the control of pain pathways and opioid addiction, while our work on two secretory chaperones is of potential interest to patients suffering from Alzheimer’s as well as many other neurodegenerative diseases involving protein aggregation.
Alzheimer’s and Parkinson’s Diseases
Alzheimer’s disease is a devastating neurodegenerative disease presently affecting as many as 5.1 million Americans; the prevalence of the disease increases radically after age 65. The Census Bureau has estimated that the number of people over 65 will increase by 2050 to 88.5 million; thus, Alzheimer’s disease presents an enormous future public health problem which has been recognized by Congress with the allocation of 300 million in additional NIH research funding each of the last two years.
Alzheimer’s disease involves the aberrant aggregation of certain peptides and proteins such as Abeta and tau into insoluble formations within brain tissues: plaques and tangles respectively. Increasing evidence suggests that protein chaperones are involved in the formation and disposition of these insoluble aggregates. We are interested in the role of secreted brain chaperones, such as clusterin, 7B2, and proSAAS, in protein aggregation and segregation in neurodegenerative disease. The approaches used in this work range from immunohistochemistry of brain tissue from mouse models of Alzheimer’s, to primary neuron and cell line culture, to in vitro biochemistry, to behavioral assays of memory.
Parkinson’s disease. We are also interested in the effect of 7B2 and proSAAS on the formation of Parkinson’s disease protein aggregates, known as Lewy bodies, which arise from misfolded synuclein protein within specific brain stem areas that control movement. We have recently shown that proSAAS expression reduces the extent of cell death caused by synuclein overexpression in primary neuron cell cultures. Exciting preliminary data obtained by our collaborator Dr. Nigel Maidment (UCLA) indicates that virally-mediated proSAAS expression can reduce motor damage in a rat model of Parkinson’s disease.
Diabetes and Obesity
Diabetes, a disease of glucose misregulation, is increasingly prevalent both in the world population and in the US. The American Diabetes Association has estimated that in 2015 over 30 million Americans, or 9.4% of the population, live with this chronic disease, and up tp three times as many individuals are prediabetic. Certain forms of diabetes involve impaired synthesis of peptide hormones such as insulin and glucagon. These important signaling molecules are synthesized through the action of the proprotein convertsaes PC1/3 and PC2. We study the cell biology, the structure, and the regulation of these important enzymes, using Crispr-edited neuroendocrine cell lines as model systems. We have generated the naturally-occurring mutations in prohormone convertases which are associated with obesity, and have shown that inactivating mutations can lead to dominant-negative effects on peptide hormone biology in mice bearing only one mutant allele. We are now developing animal models that recapitulate human obesity mutations in an effort to better understand the cellular factors that underlie PC1/3-mediated obesity.
Biochemistry of Prohormone Convertases
Establishing the three-dimensional structure of the prohormone convertases. Using recombinant protein expression we can produce milligram quantities of recombinant convertases, as well as of their two endogenous binding proteins. Our work on mouse furin resulted in the publication of the structure of the first mammalian convertase in mid-2003 (Henrich et al, Nature Structural Biology 10,520-526). We have recently made substantial progress in obtaining recombinant convertases and would now like to obtain the structure of a convertase-inhibitor complex (PC2 and 7B2). This structural work is vital to understanding the control of peptide hormone production, and could eventually lead to the design of new therapeutics.
Model of the Furin Substrate Binding Site, Courtesy of Stefan Henrich and Manuel Than
Bone diseases, either genetic (X-linked hypophosphatemia) or dietary (rickets), represent an essential failure of the bone cell secretory system to maintain a stable calcium phosphate-mineralized collagen scaffold. Bone maintenance is a highly complex and dynamic process which is under the control of various hormones, growth factors, and vitamins. Our laboratory has studied the role of various proprotein convertases in the degradation and cell biology of FGF-23, a peptide hormone secreted by bone cells which controls phosphate metabolism via action in the kidney.
Cancer, the uncontrolled growth and migration of a small population of cells within a given tissue, is one of the leading causes of death in the United States in older adults. The expression of the proprotein convertase furin is strongly associated with increased metastasis (migration) of cancer cells; this is thought to be due to its ability to activate the cell surface enzymes responsible for extracellular matrix breakdown. In collaboration with several drug companies and academic laboratories, we developed furin inhibitors active both in the test tube and in cell culture. We have used a variety of cell models to test toxicity, cell penetration, and efficacy of furin inhibitors, and have identified small molecule inhibitors selective for cell surface furin action as well as inhibitors which also work intracellularly.
Optimization of convertase inhibitors and activators.
We discovered a potent small molecule inhibitor of furin, D6R, which has proven useful both in bacterial diseases where furin activation is critical to toxin activation as well as in cancer pathogenesis. We have screened a variety of different libraries to obtain new inhibitors for PC1/3, PC2 and furin, and have optimized our current leads through chemical modification. We are also interested in therapeutic application of convertase inhibitors, which we test in cell-based assays (see recent publications).
Diseases potentially amenable to convertase inhibitor therapy include diseases of excess hormone production such as ectopic peptide production in small cell carcinoma; furin inhibition would be beneficial in blocking cancer pathogenesis. Blocking the production of glucagon- largely a PC2-mediated process- could also be of benefit in diabetes, as glucagon acts in opposition to insulin.
To connect with Dr. Iris Lindberg and her team, please see the Contact page.
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