Research in my lab focuses on two topics: 1) activity-dependent development of circuits in the central nervous system and 2) healthful compensatory responses of cells and organisms to stressful conditions. We use genetically manipulated mice, primary neuron tissue culture and C.elegans in our studies; our approach is cell and molecular biology.
During development synaptic activity refines and patterns connections among neurons and this is required for precise high-level behavior. We have found that glutamatergic synapses that include the GluA1 subunit have a privileged role in this process likely a function of specific electrophysiological properties and through the assembly of a large multi-protein complex in the sub-synaptic domain. A critical molecular component of this complex is SAP97, a scaffolding protein with >90 known binding partners.
We have taken a variety of approaches to identifying the critical binding partners of SAP97 that transduce activity of glutamate receptors assembled with GluA1 into dendrite growth, synapse specification and circuit function. Insight in the molecular logic of SAP97 function will have implications for childhood maladies such as intellectual disability and autism/autism-spectrum disorders.
Mutations in protein such as Cu++/Zn++ SOD and TDP43 cause adult onset neurodegenerative diseases such as Amyotrophic Lateral Sclerosis and Frontotemporal Dementia. We have found that these mutant proteins evoke maladaptive changes in cellular and organismal intermediary metabolism – re-wiring metabolism can blunt the adverse effects on neuronal survival. We have made parallel observations in an infantile/childhood motor neuron disease called Spinomuscular atrophy. In addition, mutant protein misfolding can be injurious to neurons by disrupting cellular protein homeostasis and we have identified suppressors of this toxicity. Targeting proximal events in neurodegenerative diseases will lead to novel therapeutic approaches.
These are some of the resources in the lab:
These are some of the techniques we use:
Robert G. Kalb, MD, is a research scientist at The Children’s Hospital of Philadelphia and a professor of Neurology at the Perelman School of Medicine at the University of Pennsylvania.
Left to Right: Kelly Gao, Matt Lan, Lisa Romero, Ogul Uner
SAP97 – The AMPA receptor subunit GluA1 forms a physical complex with the SAP97 protein in the post-synaptic density. There, GluA1/SAP97 translates activity of glutamatergic synapses into dendritic growth and specification of connectivity within a network. We are currently studying the role of this complex in the forebrain using a conditional knockdown mouse. The approaches we are taking include mouse behavior, anatomy and molecular.
CRIPT – One SAP97 binding partner of interest that we have identified is the cysteine rich interactor of PDZ3 (CRIPT). We are studying the mechanism by which CRIPT participates in GluA1/SAP97 dependent developmental events. CRIPT is a fascinating protein and loss of function mutations lead to a devastating developmental neurological disorder.
Zhou, Weiguo. Zhang, Lei. Guoxiang, Xiong. Mojsilovic-Petrovic, Jelena. Takamaya, Kogo. Sattler, Rita. Huganir, Richard. Kalb, Robert.: GluR1 controls dendrite growth through its binding partner, SAP97. Journal of Neuroscience 28(41): 10220-33, Oct 8 2008
White, S., Ortinski, P., Shayna H., Friedman, S.H., Neve,R. L., Kalb, R. G., Schmidt, H.D., and Pierce, R. C. A Critical Role for the GluA1 Accessory Protein, SAP97, in Cocaine Seeking. Neuropsychopharmacology doi: 10.1038/npp.2015.199, (2015)
Zhang, L., Hsu,F.-C., Mojsilovic-Petrovic, J., Jablonski, A.M., Zhai, J., Coulter, D.A. and Kalb, R.G. Structure-Function Analysis Of SAP97, A Modular Scaffolding Protein That Drives Dendrite Growth. Mol. Cell. Neurosci 65:31-44, (2015).
Boccitto, M., Doshi, D. , Newton, I.P., Nathke, I., Neve. R., Mao, Y., Zhai, J., Zhang, L., and Kalb, R.G. Opposing Actions of the Synapse Associated Protein of 97 kDa Molecular Weight (SAP97) and Disrupted in Schizophrenia 1 (DISC1) on Wnt/b-catenin Signaling. Neuroscience 2016 (in press).
Loss of protein homeostasis (proteostasis) is a common underlying pathological event in all neurodegenerative diseases. In a screen for proteotoxicity suppressors undertaken in C.elegans, we have identified rad23 as a gene of interest. We find that loss of rad23, both in worms and in mammalian neurons is neuroprotective and this is associated with accelerated degradation of misfolded proteins. We are interested in understanding the mechanism by which rad23 acts as an “anti-chaperone”.
Jablonski, A.M., Lamitina, T., Liachko, N.F., Sabatella, M., Liu, J., Zhang, L., Ostrow, L.W., Gupta, P., Wu, C.-Y., Doshi, S., Mojsilovic-Petrovic, J., Lans, H., Wang, J., Brian C Kraemer, B.C., and Kalb, R.G.. Loss of RAD-23 Protects Against Models of Motor Neuron Disease by Enhancing Mutant Protein Clearance. J Neurosci 34:14,286-14,306 (2015).
Periz, G., Jiayin Lu, J.,Zhang, T., Mark W. Kankel, M.W., Jablonski, A.M. Kalb, R. G., McCampbell, A., Wang. J. Regulation of protein quality control by UBE4B and LSD1 through p53-mediated transcription PloS Biol DOI: 10.1371/journal.pbio.1002114 (2015)
Hypoxic insult at the time of birth (asphyxia) is a major cause of morbidity and mortality worldwide. Using C.elegans, we have defined a new pathway that confers resistance to hypoxic insult during development.
Flibotte, J.J., Jablonski, A.M. and Kalb, R.G. Oxygen sensing neurons and neuropeptides regulate survival after anoxia in developing C. elegans. PloS One 9;e101102 (2014)
Spinomuscular Atrophy (SMA) is a major motor neuron disease of infants and children. It is caused by loss of function mutations in the Survival of Motor Neuron (SMN) protein. In a C.elegans model we have identified suppressors of the loss of SMN phenotype and the resulting animals have a normal life span. We are interrogating the molecular pathways underlying this astounding phenotype.
Mitochondrial dysfunction is a universal feature of neurodegenerative disease and the impairment in ATP production and enhanced elaboration of reactive oxygen species leads to the activation of AMP-dependent protein kinase (AMPK). Active AMPK turns off energy consuming processes and activated energy producing processes. While a priori this rewiring of intermediary metabolism should be a benefit, it in fact is injurious to neurons. We are exploring why rewiring of metabolism damages neurons and the extent to which abrogating specific AMPK actions can be leveraged into a therapy
Lim, M., Selak, M., Xiang, Z., Krainc, D., Neve, R., Kraemer, B., Watts, J. and Kalb, R. Reduced activity of AMP-activated protein kinase protects against genetic models of motor neuron disease J. Neuroscience 32(3):1123-1141, 2012
Boccitto, M, Lamitina, T and Kalb, R. Daf-2 signaling modifies mutant SOD1 toxicity in C. elegans. PloS One 7(3) e33494 (2012)
Lim,M.A, Bence,K.K., Sandesara, I., Andreux, P. Auwerx, J., Ishibashi, J., Seale, P. and Robert G. Kalb, R. G. Genetically altering organismal metabolism by leptin-deficiency benefits a mouse model of amyotrophic lateral sclerosis Hum. Mol. Genet. doi:10.1093/hmg/ddu214 (2014)
Hexanucleotide repepat expansion (HRE) in an intron of the C9ORF72 gene is a major cause of ALS. One mechanism of toxicity originated in non-ATG, repeat associated translation of the HRE leading to the generation of toxic diamino acid peptide. We are modeling this in vitro and have identified a new cellular mechanism of toxicity that may be amenable to therapeutic intervention
Gupta, R, Lan,M., Mojsilovic-Petrovic,J. Choi,W. C., Safren,N., Barmada,S., Lee,M. J. and Kalb, R. The Proline/Arginine Dipeptide from Hexanucleotide Repeat Expanded C9ORF72 Inhibits the Proteasome. eNeuro 4(1) e0249-16.2017 1–18 (2017)
ARF GTP’ases are molecular switches that are involved in a variety of cell biological processes such as membrane traffic, lipid droplet formation and actin remodeling. We have found that inhibiting ARF action is neuroprotective in a variety of model systems. We are exploring the specific cell biological process that ARF inhibition impacts to promote the clearance of misfolded proteins
Zhai, J.,Zhang, L., Mojsilovic-Petrovic, J., Jian, X., Thomas, J.,Homma, K., Schmitz, A., Famulok, M., Ichijo, H., Argon, Y., Randazzo, P.A. and Kalb, R. G. Inhibition of cytohesins protects against genetic models of motor neuron disease. J. Neuroscience 35:9088-9105 (2015)