This
prompted us to further examine whether PKCβ deficiency can suppress
diet-induced obesity and the associated metabolic complications.
PKCβ−/− mice exhibited resistance to HFD-induced obesity and maintained
insulin sensitivity [27]. Moreover, PKCβ levels are elevated in
adipose tissue of diet- or genetically-induced obese mouse models,
and deletion of PKCβ in ob/ob mice attenuates the obesity syndrome of
these mice [38]. White adipose tissue (WAT) in ob/obxPKCβ−/− mice
expresses genes characteristic of brown adipose tissue (BAT), including
peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α)
and uncoupling protein-1 (UCP-1). This is consistent with earlier studies
in mice showing that targeted disruption of several genes directly
involved in energy metabolism and fat accumulation leads to a lean
phenotype with a marked increase in UCP-1 expression in adipocytes,
particularly in white fat depots [39,40]. It is likely that total energy
consumption is increased in PKCβ−/− mice, presumably due to energy
dissipation in WAT resulting from expression of UCP-1 and increased
mitochondrial activity. The ability of white and brown adipocytes in
each depot to reversibly switch types had been reported earlier, but
the extent to which this occurred and the precise mechanisms involved
were not fully understood. The search for regulators that could mediate
conversion of white adipocytes (energy storing) into brown adipocytes
(energy consuming) led to the identification of PGC-1α, forkhead
box protein C2, and PR-domain-containing protein 16 as proteins that
promote a brown fat genetic program, whereas retinoblastoma protein
and RIP140 have been reported to favor a white adipose phenotype