Rajesh Khanna
Professor, Anesthesiology
Professor, BIO5 Institute
Professor, Neuroscience - GIDP
Professor, Pharmacology
Primary Department
Department Affiliations
(520) 626-4281
Work Summary
The focus of my laboratory’s’ research is to understand how ion channels, specifically, voltage-gated calcium and sodium channels, are regulated by novel protein interactions. Recent studies in my laboratory have focused on targeting protein-protein interactions with biologics (peptide aptamers) and small molecules; testing the activity of these novel chemical entities in biochemical and immunofluorescent-based assays of trafficking; examining their protein interaction signatures; testing them with whole cell voltage-clamp electrophysiology and voltage- and calcium sensitive fluorescence-based imaging. Regulating these protein networks to modulate the activity of ion channels in neurodegenerative diseases (Chronic Pain, Migraine, and Neurofibromatosis) is a key focus of the laboratory.
Research Interest
Regulation of Trafficking and Functions of Voltage-Gated Sodium and Calcium Channels; Identification of Novel Protein Regulators of Ion channels; Approaches to Targeting the Ion Channel Complexes in Neuropathic Pain and Neurodegenerative Diseases; Discovery of Novel Biologics and Small Molecules Targeting Pain and Neurodegenerative Diseases

Publications

Khanna, R., Wilson, S. M., Brittain, J. M., Weimer, J., Sultana, R., Butterfield, A., & Hensley, K. (2012). Opening Pandora's jar: a primer on the putative roles of CRMP2 in a panoply of neurodegenerative, sensory and motor neuron, and central disorders. Future neurology, 7(6), 749-771.

CRMP2, also known as DPYSL2/DRP2, Unc-33, Ulip or TUC2, is a cytosolic phosphoprotein that mediates axon/dendrite specification and axonal growth. Mapping the CRMP2 interactome has revealed previously unappreciated functions subserved by this protein. Together with its canonical roles in neurite growth and retraction and kinesin-dependent axonal transport, it is now known that CRMP2 interacts with numerous binding partners to affect microtubule dynamics; protein endocytosis and vesicular cycling, synaptic assembly, calcium channel regulation and neurotransmitter release. CRMP2 signaling is regulated by post-translational modifications, including glycosylation, oxidation, proteolysis and phosphorylation; the latter being a fulcrum of CRMP2 functions. Here, the putative roles of CRMP2 in a panoply of neurodegenerative, sensory and motor neuron, and central disorders are discussed and evidence is presented for therapeutic strategies targeting CRMP2 functions.

Khanna, R., Li, Q., Sun, L., Collins, T. J., & Stanley, E. F. (2006). N type Ca2+ channels and RIM scaffold protein covary at the presynaptic transmitter release face but are components of independent protein complexes. Neuroscience, 140(4), 1201-8.

Fast neurotransmitter release at presynaptic terminals occurs at specialized transmitter release sites where docked secretory vesicles are triggered to fuse with the membrane by the influx of Ca2+ ions that enter through local N type (CaV2.2) calcium channels. Thus, neurosecretion involves two key processes: the docking of vesicles at the transmitter release site, a process that involves the scaffold protein RIM (Rab3A interacting molecule) and its binding partner Munc-13, and the subsequent gating of vesicle fusion by activation of the Ca2+ channels. It is not known, however, whether the vesicle fusion complex with its attached Ca2+ channels and the vesicle docking complex are parts of a single multifunctional entity. The Ca2+ channel itself and RIM were used as markers for these two elements to address this question. We carried out immunostaining at the giant calyx-type synapse of the chick ciliary ganglion to localize the proteins at a native, undisturbed presynaptic nerve terminal. Quantitative immunostaining (intensity correlation analysis/intensity correlation quotient method) was used to test the relationship between these two proteins at the nerve terminal transmitter release face. The staining intensities for CaV2.2 and RIM covary strongly, consistent with the expectation that they are both components of the transmitter release sites. We then used immunoprecipitation to test if these proteins are also parts of a common molecular complex. However, precipitation of CaV2.2 failed to capture either RIM or Munc-13, a RIM binding partner. These findings indicate that although the vesicle fusion and the vesicle docking mechanisms coexist at the transmitter release face they are not parts of a common stable complex.

Quach, T. T., Wilson, S. M., Rogemond, V., Chounlamountri, N., Kolattukudy, P. E., Martinez, S., Khanna, M., Belin, M., Khanna, R., Honnorat, J., & Duchemin, A. (2013). Mapping CRMP3 domains involved in dendrite morphogenesis and voltage-gated calcium channel regulation. Journal of cell science, 126(Pt 18), 4262-73.

Although hippocampal neurons are well-distinguished by the morphological characteristics of their dendrites and their structural plasticity, the mechanisms involved in regulating their neurite initiation, dendrite growth, network formation and remodeling are still largely unknown, in part because the key molecules involved remain elusive. Identifying new dendrite-active cues could uncover unknown molecular mechanisms that would add significant understanding to the field and possibly lead to the development of novel neuroprotective therapy because these neurons are impaired in many neuropsychiatric disorders. In our previous studies, we deleted the gene encoding CRMP3 in mice and identified the protein as a new endogenous signaling molecule that shapes diverse features of the hippocampal pyramidal dendrites without affecting axon morphology. We also found that CRMP3 protects dendrites against dystrophy induced by prion peptide PrP(106-126). Here, we report that CRMP3 has a profound influence on neurite initiation and dendrite growth of hippocampal neurons in vitro. Our deletional mapping revealed that the C-terminus of CRMP3 probably harbors its dendritogenic capacity and supports an active transport mechanism. By contrast, overexpression of the C-terminal truncated CRMP3 phenocopied the effect of CRMP3 gene deletion with inhibition of neurite initiation or decrease in dendrite complexity, depending on the stage of cell development. In addition, this mutant inhibited the activity of CRMP3, in a similar manner to siRNA. Voltage-gated calcium channel inhibitors prevented CRMP3-induced dendritic growth and somatic Ca(2+) influx in CRMP3-overexpressing neurons was augmented largely via L-type channels. These results support a link between CRMP3-mediated Ca(2+) influx and CRMP3-mediated dendritic growth in hippocampal neurons.

Moutal, A., Wang, Y., Yang, X., Ji, Y., Luo, S., Dorame, A., Bellampalli, S. S., Chew, L. A., Cai, S., Dustrude, E. T., Keener, J. E., Marty, M. T., Vanderah, T. W., & Khanna, R. (2017). Dissecting the role of the CRMP2-neurofibromin complex on pain behaviors. Pain, 158(11), 2203-2221.
BIO5 Collaborators
Rajesh Khanna, Michael T Marty

Neurofibromatosis type 1 (NF1), a genetic disorder linked to inactivating mutations or a homozygous deletion of the Nf1 gene, is characterized by tumorigenesis, cognitive dysfunction, seizures, migraine, and pain. Omic studies on human NF1 tissues identified an increase in the expression of collapsin response mediator protein 2 (CRMP2), a cytosolic protein reported to regulate the trafficking and activity of presynaptic N-type voltage-gated calcium (Cav2.2) channels. Because neurofibromin, the protein product of the Nf1 gene, binds to and inhibits CRMP2, the neurofibromin-CRMP2 signaling cascade will likely affect Ca channel activity and regulate nociceptive neurotransmission and in vivo responses to noxious stimulation. Here, we investigated the function of neurofibromin-CRMP2 interaction on Cav2.2. Mapping of >275 peptides between neurofibromin and CRMP2 identified a 15-amino acid CRMP2-derived peptide that, when fused to the tat transduction domain of HIV-1, inhibited Ca influx in dorsal root ganglion neurons. This peptide mimics the negative regulation of CRMP2 activity by neurofibromin. Neurons treated with tat-CRMP2/neurofibromin regulating peptide 1 (t-CNRP1) exhibited a decreased Cav2.2 membrane localization, and uncoupling of neurofibromin-CRMP2 and CRMP2-Cav2.2 interactions. Proteomic analysis of a nanodisc-solubilized membrane protein library identified syntaxin 1A as a novel CRMP2-binding protein whose interaction with CRMP2 was strengthened in neurofibromin-depleted cells and reduced by t-CNRP1. Stimulus-evoked release of calcitonin gene-related peptide from lumbar spinal cord slices was inhibited by t-CNRP1. Intrathecal administration of t-CNRP1 was antinociceptive in experimental models of inflammatory, postsurgical, and neuropathic pain. Our results demonstrate the utility of t-CNRP1 to inhibit CRMP2 protein-protein interactions for the potential treatment of pain.

Feldman, P., & Khanna, R. (2013). Challenging the catechism of therapeutics for chronic neuropathic pain: Targeting CaV2.2 interactions with CRMP2 peptides. Neuroscience letters, 557 Pt A, 27-36.

Chronic neuropathic pain management is a worldwide concern. Pharmaceutical companies globally have historically targeted ion channels as the therapeutic catechism with many blockbuster successes. Remarkably, no new pain therapeutic has been approved by European or American regulatory agencies over the last decade. This article will provide an overview of an alternative approach to ion channel drug discovery: targeting regulators of ion channels, specifically focusing on voltage-gated calcium channels. We will highlight the discovery of an anti-nociceptive peptide derived from a novel calcium channel interacting partner - the collapsin response mediator protein 2 (CRMP2). In vivo administration of this peptide reduces pain behavior in a number of models of neuropathic pain without affecting sympathetic-associated cardiovascular activity, memory retrieval, sensorimotor function, or depression. A CRMP2-derived peptide analgesic, with restricted access to the CNS, represents a completely novel approach to the treatment of severe pain with an improved safety profile. As peptides now represent one of the fastest growing classes of new drugs, it is expected that peptide targeting of protein interactions within the calcium channel complex may be a paradigm shift in ion channel drug discovery.